Neuropsychiatric diseases such as schizophrenia and bipolar illness alter the structure and function of distributed neural networks. Functional neuroimaging tools have evolved sufficiently to reliably detect system-level disturbances in neural networks. This review focuses on recent findings in schizophrenia and bipolar illness using resting-state neuroimaging, an advantageous approach for biomarker development given its ease of data collection and lack of task-based confounds. These benefits notwithstanding, neuroimaging does not yet allow the evaluation of individual neurons within local circuits, where pharmacological treatments ultimately exert their effects. This limitation constitutes an important obstacle in translating findings from animal research to humans and from healthy humans to patient populations. Integrating new neuroscientific tools may help to bridge some of these gaps. We specifically discuss two complementary approaches. The first is pharmacological manipulations in healthy volunteers, which transiently mimic some cardinal features of psychiatric conditions. We specifically focus on recent neuroimaging studies using the NMDA receptor antagonist, ketamine, to probe glutamate synaptic dysfunction associated with schizophrenia. Second, we discuss the combination of human pharmacological imaging with biophysically informed computational models developed to guide the interpretation of functional imaging studies and to inform the development of pathophysiologic hypotheses. To illustrate this approach, we review clinical investigations in addition to recent findings of how computational modeling has guided inferences drawn from our studies involving ketamine administration to healthy subjects. Thus, this review asserts that linking experimental studies in humans with computational models will advance to effort to bridge cellular, systems, and clinical neuroscience approaches to psychiatric disorders. The human brain is a complex, dynamic system with computations occurring at several levels of organization, from individual synapses to networks that span multiple brain regions. These large-scale neural systems ultimately produce complex behaviors that are profoundly altered in the context of psychotropic drug administration or neuropsychiatric disease.One example is schizophrenia – a common, multi-faceted, and heterogeneous neuropsychiatric syndrome  associatN-methyl-d-aspartate glutamate receptor (NMDAR)  , disturb (NMDAR) . This in (NMDAR) . There i (NMDAR) , post-mo (NMDAR) , neuroim (NMDAR) , and pha (NMDAR)  illustra (NMDAR) , 20 and  (NMDAR)  have als (NMDAR) . Collect (NMDAR) . NeverthFunctional neuroimaging has consistently revealed both region-specific and network alterations in schizophrenia across a number of cognitive measures . For insThis review first focuses on resting-state functional connectivity MRI (rs-fcMRI) studies of schizophrenia that are providing distinct insights into cortical dysfunction associated with this disorder , 38. We The encouraging progress in understanding functional connectivity alterations in schizophrenia creates new opportunity to reconcile system-level findings with hypotheses emerging from molecular and cellular studies of this disorder. Failure to integrate these multiple levels of research undermines our understanding of the pathophysiology of this disorder and it will impede medications development. To this end, we next turn to studies using pharmacological models , such asFinally, we briefly articulate the utility of neuroscience theory and computational models for iteratively guiding our pharmacological and clinical experiments , 56. We Building on these insights, we emphasize the need for efforts to translate our basic discoveries in neuroscience and cellular-level hypotheses in schizophrenia with system-level observations that may directly relate to the complex behavioral abnormalities observed in this illness. We highlight multiple complementary neuroscientific approaches, including recent clinical studies , pharmacNearly two decades ago Biswal and colleagues  demonstrResting-state functional connectivity MRI approaches have been increasingly applied to neuropsychiatric illness . Use of Specific advantages of rs-fcMRI include: (i) speed, as the functional network architecture can be reliably assayed within 10 min of data acquisition , and perThe approach itself, however, is not without limitations. For instance, the size of the correlation coefficient is often used to examine the strength of coupling between different network nodes . While tAnother methodological issue pertains to how networks are identified. Many early functional connectivity studies both in healthy adults and in clinical populations used a seed-based approach, whereby the correlation from a given region of interest is examined with all other voxels in the brain. This approach has also been complemented by more complex graph theoretical and network-based methods . Seed-baNew methods are needed to detect more complex patterns of disorder-related disturbances in connectivity , illustrAnother data-driven method that has increasing applications in psychiatric neuroimaging involves ICA of BOLD signal fluctuations at rest. Here ICA provides a tool to identify spatially , 83 or tCollectively, the continued success of these methods suggests that ongoing refinement of tools to examine functional connectivity remains vital for development of biomarkers for psychiatric illness. Next, we turn to specific findings in the field of schizophrenia and bipolar research. We detail recent methodological advances in connectivity work that have been directly applied to better understand network disruption in these psychiatric conditions.There are now a number of influential hypotheses suggesting that, at its core, schizophrenia may be a disorder of large-scale neural connectivity , 85, i.eDespite its promise, a major obstacle in delineating successful neural markers for schizophrenia (or any other severe neuropsychiatric disease) using connectivity (or any other approach for that matter) has been the complexity of this illness and the vast range of behaviors it affects , as wellCertain studies using rs-fcMRI have, however, attempted to deal with clinical heterogeneity by focusing on the relationship between altered functional connectivity in specific pathways and linking those pathways to particular features of schizophrenia. For instance, studies by Hoffmann and colleagues have focused on better understanding alterations in connectivity specifically associated with auditory hallucinations , which ma priori predictions, Moran and colleagues found strong support for the disrupted relationship between the anterior insula and the control-executive and default-mode networks in schizophrenia, which again was predictive of cognitive performance. Most recently, a study by Palaniyappan and colleagues , as well as disturbances in dopaminergic neurotransmission along striatal-thalamic-cortical pathways , 109. AdHere it is important to consider some key differences between the dopamine and glutamate hypotheses in schizophrenia in relation to pharmacological findings and their therapeutic effects: (i) dopaminergic medication has not proved successful at ameliorating the full range of impairing symptoms in schizophrenia, particularly cognitive deficits ; (ii) phAs articulated above, the GBC functional connectivity approach is specifically designed to test the hypothesis that a given functional brain region has altered coupling with the rest of the brain . To test the efficacy of this approach, Cole and colleagues  used a rSimilar data-driven efforts have been applied to study global connectivity alterations in other psychiatric conditions. Specifically, Anticevic and colleagues extended the approach to study bipolar patients with and without a history of psychotic symptoms . While eFocusing on bipolar illness, Anticevic and colleagues examined the possibility that there are similar abnormalities in bipolar illness with a history of psychosis to those found in schizophrenia. Consistent with this hypothesis, Anticevic and colleagues found that bipolar illness is indeed associated with altered PFC rGBC specifically in a medial prefrontal/ventral cingulate region implicated in regulation of emotion . ImportaWhile promising, a key challenge facing data-driven approaches will be to establish whether identified effects consistently replicate across sites and samples. It may be possible that illness sample heterogeneity, illness stage, symptom severity, anatomical heterogeneity, or other factors will critically impact the patterns of data-driven effects across studies and samples. That is, it may be possible that different foci are detected as showing disruptions in different samples. Therefore, it will be critical to determine which of the identified data-driven global connectivity alterations are stable and replicable (perhaps capturing some core disturbances) and which alter as a function of other variables (perhaps capturing state effects). Such ongoing data-driven efforts should also continue to capitalize on recent advances in graph theory  as well As described above, the PFC has been repeatedly implicated in schizophrenia neuropathology. However, despite data-driven efforts to map PFC dysfunction, the PFC remains a challenge in the study of schizophrenia, owing largely to the complex individual differences in function and anatomy of the PFC. Therefore, to ultimately establish a viable large-scale, brain-wide marker of neural alterations in schizophrenia, an alternative approach can be taken. One possible path is to start from the thalamus as a key region of interest . That isConsistent with this view, a large body of evidence implicates significant thalamo-cortical communication disturbances in schizophrenia neuropathology , 131–134N = 62) and extended the approach to other thalamic nuclei  – indicating that the observed pattern explains only a small portion of the variance in symptom variation across subjects. An alternative possibility, given that the majority of patients were quite symptomatic, is that the small magnitude reflects a restricted range in symptoms whereby there was little variability in symptom severity across the patient sample.A subsequent report by Anticevic and colleagues examined thalamo-cortical dysconnectivity in 90 patients diagnosed with schizophrenia relative to 90 matched healthy comparison subjects . The keyThe identified thalamic dysconnectivity was successfully used for diagnostic classification via multivariate pattern analysis (MVPA)  with higLastly, the authors found that the bipolar illness sample exhibited an “intermediate” pattern of disturbance such that the patterns of thalamo-cortical connectivity were “shifted” relative to healthy comparison subjects but not as severely altered as those identified in schizophrenia. This finding in particular offers promise for using neuroimaging markers to inform our understanding of shared disturbances in the underlying biology that cut across diagnostic categories . The nexMost recently, Klingner and colleagues provided convergent results from a sample of 22 patients diagnosed with schizophrenia and 22 matched comparison subjects . In theiWhile this initial progress in mapping thalamo-cortical disturbances in schizophrenia represents a promising advance in psychiatric neuroimaging research, there are still fundamental gaps in our understanding of how such findings relate to neuropathological mechanisms of this illness. There are a number of future directions that the field should pursue to better understand these observations. For instance, it remains unknown why there are dissociable disturbances across thalamic nuclei in schizophrenia. Future studies focused more exclusively on the medio-dorsal nucleus versus, say, the pulvinar  could begin to explain mechanism behind these differences. Although the original study by Welsh and colleagues provides clues here, follow-up studies with more power that focus on the medio-dorsal nucleus could provide finer-grained information regarding its patterns of dysconnectivity with the PFC.Another complex issue that is not adequately resolved by any of the noted investigations relates to medication effects. For instance, there are considerations of medication dose, type of medications (given that patients are often treated with multiple drugs from different medication classes), and possible systematic differences in the medications received by patients carrying the diagnoses of schizophrenia, schizoaffective, and bipolar . While all studies address this issue statistically to a certain extent , future studies in un-medicated patients are needed. It is possible, however, that medication may not necessarily be a confound in this case – instead, antipsychotic medication could actually stabilize thalamo-cortical dysconnectivity. Studies explicitly aimed at testing medication effects on connectivity could provide more detailed insight into this issue. It also remains unknown if the identified patterns of large-scale thalamo-cortical dysconnectivity are characteristic only of chronic stages of schizophrenia or whether they already appear in the prodromal or early stages of the illness. Establishing the link between identified thalamo-cortical dysconnectivity and illness progression remains a vital effort to inform the viability of this marker for predicting and/or tracking risk and progression of the disease. While one of the studies noted above provides a functional link between sensory-motor-thalamic over-connectivity and PANSS symptoms, it remains unknown if these patterns relate to cognitive and executive functional deficits characteristic of the schizophrenia syndrome . It may Additional questions still exist pertaining to the cross-diagnostic relevance of these observations. As noted above, it was shown by Anticevic and colleagues that qualitatively similar patterns of thalamic dysconnectivity are apparent in bipolar illness . It remains to be determined if those bipolar patients with a history of co-occurring psychosis are quantitatively more similar to alterations identified in schizophrenia . Such fiA longer-term goal will entail bridging this neural system-level marker of schizophrenia with evolving cellular-level hypotheses of schizophrenia neuropathology. It remains unknown how the identified neural system-level markers relate to hypotheses that propose disruptions at the cellular level in schizophrenia. For instance, Anticevic and colleagues articulate a possible role of the disruption in cortical excitation (E) and inhibition (I) balance within the cortical microcircuit in producing system-wide disruptions, which may occur in schizophrenia (see next section) and in turn affect cognition . It remaWe presented evidence, supported by several emerging studies, for profound alterations in thalamo-cortical information flow in schizophrenia, as well as evidence for alterations in PFC connectivity. Yet, the mechanisms that could inform rationally guided pharmacotherapy for these disturbances in schizophrenia remain unknown. One leading mechanistic hypothesis proposes possible disruptions in the E/I balance in the cortical micro-circuitry resulting from hypo-function of the NMDAR , which mA powerful candidate approach is to use ketamine, a non-competitive NMDAR antagonist and a leading schizophrenia pharmacological model, which transiently, reversibly, and safely induces characteristic schizophrenia symptoms in healthy volunteers . Here phFor instance, a recent resting-state connectivity study by Driesen and colleagues investigated the effects of acute ketamine administration to healthy volunteers on large-scale global cortical connectivity Figure A. The auA complementary area of research has investigated the effects of ketamine on functional connectivity  in relatincreased functional connectivity of the DLPFC during rest using the exact same seed. This set of observations in particular sheds light on how a pharmacological manipulation such as NMDAR antagonism may have profoundly different effects in the context of a cognitive task  and during rest. The mechanisms behind this observed difference are beyond the scope of this review and will be discussed in forthcoming studies.As an example of such an approach, another study examining the effects of ketamine by Anticevic and colleagues focused on understanding the functional impact of NMDAR antagonism on the organization of the large-scale, anti-correlated neural systems Figure B. This pBriefly, it may be possible that large-scale, network-level synchrony during WM is critically dependent on appropriate content-specific signals between neural subpopulations . In contAbove we discussed recent clinical and pharmacological neuroimaging findings that shed light on the nature of large-scale neural system alterations in schizophrenia. In particular, the pharmacological experiments provide a causal method to explicitly manipulate specific neurotransmitter mechanisms that may be involved in schizophrenia. In that sense, these studies can begin to address given neurotransmitter contributions to neural system-level and behavioral alterations observed in schizophrenia. Still, these studies cannot measure synaptic and cellular-level phenomena alone. Therefore, one possible methodological integration involves a formal link between such pharmacological/clinical experiments and computational models that contain this level of functional detail. One branch of computational model that provides a particularly productive platform involves biophysically based models that contain the relevant synaptic mechanisms , 192 thoRecent computational models have been developed to explicitly capture how the global pattern of resting-state functional connectivity arises through cortico-cortical interactions . In partDeco and colleagues , 193 extThe models described above were explicitly constructed to simulate resting-state fluctuations, rather than to implement a particular function such as WM. Nevertheless, functional models can still make predictions that can be tested using functional connectivity, especially task-based functional connectivity . To thisCollectively, we articulated recent focused developments in three areas of clinical neuroscience of schizophrenia: (i) we reviewed methodological advances in resting-state functional connectivity that were directly translated to understand neural system-level disturbances in schizophrenia. We specifically focused on data-driven techniques that offer a promising way to detect disrupted connectivity while bypassing the likely complexity and regional heterogeneity of network alterations that are present in schizophrenia. We also discussed ongoing developments in studies of thalamo-cortical dysconnectivity in schizophrenia that are directly informed by influential theoretical models of the illness. (ii) We highlighted select pharmacological studies of the NMDARs that offer a causal way to understand neural system alterations in psychiatric illness. (iii) We articulated the developments in biophysically based computational modeling studies that provide a platform for testing specific synaptic alterations. In turn, we demonstrate that such models can potentially be scaled to the level of neural systems to make relevant predictions for both resting-state or task-based connectivity experiments. We argue that the ongoing blend of these three approaches can provide advances in the field of clinical neuroscience that create a final output that is much greater than the sum of its parts.John H. Krystal consults for several pharmaceutical and biotechnology companies with compensation less than $10,000 per year. All other authors declare that they have no conflict of interest.


Autism spectrum disorder (ASD) is a group of developmental disabilities characterized by impairments in social interaction and communication and restricted and repetitive interests/behaviors. Advances in human genomics have identified a large number of genetic variations associated with ASD. These associations are being rapidly verified by a growing number of studies using a variety of approaches, including mouse genetics. These studies have also identified key mechanisms underlying the pathogenesis of ASD, many of which involve synaptic dysfunctions, and have investigated novel, mechanism-based therapeutic strategies. This review will try to integrate these three key aspects of ASD research: human genetics, animal models, and potential treatments. Continued efforts in this direction should ultimately reveal core mechanisms that account for a larger fraction of ASD cases and identify neural mechanisms associated with specific ASD symptoms, providing important clues to efficient ASD treatment. Autism spectrum disorder (ASD) is a group of developmental disabilities characterized by abnormal social interaction and communication, and stereotyped behaviors with restricted interest. Autism was first reported by Kanner  with a cCurrently, ASD is included in the diagnostic category of a neurodevelopmental disorders in the Diagnostic and Statistical Manual of Mental Disorders V . These models should share analogous genetic or anatomical impairments with humans , and show similar responses to the medications used to treat ASD in humans .T-maze test for restricted interests, and home cage behavior or marble burying assay for repetitive behaviors. Through these assays, many genetic and non-genetic animal models of ASD have been characterized and used to identify the etiology of ASD and develop novel treatments  in cerebellar Purkinje cells is sufficient to cause all core autism-like behaviors in mice in association with reduced excitability in Purkinje cells , another autism model with an Nlgn3 deletion identified in autistic patients, show occluded metabotropic glutamatergic receptor (mGluR)-dependent long-term depression (LTD) at synapses between parallel fibers and Purkinje cells in association with motor coordination deficits  and functional MRI (fMRI), have suggested that ASD involves abrogation of white matter tracts in brain regions associated with social cognition, such as the prefrontal cortex, anterior cingulate cortex, and superior temporal regions  with tyrosine kinase activity, is associated with ASD. Genetic variations including rs1858830 in the promoter region that abrogate MET transcription are associated with ASD in Italian and American families and case/control studies, and the levels of MET mRNA and protein are reduced in the cortex of autistic patients  are associated with autism . WNT2 is a critical regulator of multiple biological functions, including embryonic development, cellular differentiation, and cell-polarity generation. It also regulates neuronal migration, axon guidance, and dendrite branching  is associated with ASD. BDNF is a member of the neurotrophin family of growth factors that supports neurogenesis, axodendritic growth, neuronal/synaptic differentiation, and brain dysfunctions Figure  Huang a. Elevatect Table   in the RELN gene have been associated with autism in a Caucasian population  is one of the best examples. It is a member of a large family of methyl-CpG binding domain (MBD) proteins that selectively binds to methylated DNA and represses gene transcription Figure  Bienven. Its dowty Table      , and GABA receptors with altered subunit composition were observed in autistic brains   have been associated with ASD, intellectual disability, and schizophrenia , a postsynaptic membrane specialization composed of multi-synaptic protein complexes  amplitude and basal synaptic transmission  that encodes a synaptic transmembrane protein  and synaptic regulations have been associated with ASD. One of them is interleukin 1 receptor accessory protein-like 1 (OLIGOPHRENIN-1 (OPHN1), which encodes a GTPase-activating protein that inhibits Rac, Cdc42, and RhoA small GTPases. Since the initial report of the association of a truncation mutation of OPHN1 with XLID  and schizophrenia  , another X-linked gene which encodes a membrane protein which belongs to transmembrane 4 superfamily (TM4SF), plays important roles in the cell proliferation, activation, growth, adhesion, and migration , tuberous sclerosis complex (TSC1/TSC2), and phosphatase and tensin homolog (PTEN) are genes associated with neurological diseases with common autistic symptoms including neurofibromatosis , which binds to target mRNAs and regulates their translation and transport of mRNA into dendrites and synapses  induced by poly(I:C), the synthetic doublestrand RNA polyriboinosinic-polyribocytidilic acid, in pregnant mice leads to the development of core ASD-like phenotypes in the offspring, including impaired sociability, decreased USV, and increased repetitive behaviors  and valproic acid (VPA) cause rat offspring to display brain morphological abnormalities observed in ASD, including altered cerebellar structures and reduced number of cranial motor neurons  and aripiprazole (Abilify®), which act as dopamine/5-HT receptor antagonists  of D-cycloserine have cognition-enhancing effects  exert anticonvulsant effects in tonic convulsion models  deficiency exhibit abnormally increased grooming behavior, and this behavioral anomaly is reversed by D-cycloserine treatment , an animal model for Dravet's syndrome, recapitulate most features of the disorder, including epilepsy, ataxia, sleep disorder, anxiety-like behaviors, hippocampus-dependent learning impairments, sociability deficits, and excessive repetitive grooming behaviors  is decreased in GABAergic interneurons, and GABAergic transmission onto postsynaptic neurons was reduced. This would cause a shift in the balance between excitation and inhibition in postsynaptic neurons toward excitation, which may be corrected by stimulating GABA receptors in these neurons. Indeed, it was shown that both behavioral abnormalities and aberrant GABAergic transmission are rescued by low-dose administration of clonazepam  mouse models of autism are significantly alleviated by MPEP treatment  of MeCP2 gene. MeCP2 is a transcriptional repressor and activator, which binds widely across the genome and influence a large number of genes  Figure , neuro- MeCP2-null mice are partially rescued by IGF-1 treatment in association with normalization of impaired spine density, synaptic transmission, and cortical plasticity , their gene products both regulate protein synthesis in neurons  and fragile X syndrome (Fmr1−/y mice) display abnormal protein synthesis in opposite directions . In addition, crossbreeding of these two mouse lines rescues behavioral impairments and synaptic dysfunctions. These results strongly suggest that mGluR5-mediated synaptic plasticity and protein synthesis in the normal range is important and that deviation in either direction from a normal range can cause brain dysfunctions that yield similar behavioral manifestations.Shank2−/− mouse lines lacking exons 6 and 7 . These publications, which use diverse genetic and genomic approaches and often large size samples, have identified overlapping genes and mutations, which are likely to have greater influences on the development of ASD. Characterization of transgenic mouse lines that carry these frequent genetic variations would help us efficiently obtain ASD mechanisms with a greater impact.The synaptic and circuit mechanisms derived from ASD mouse model researches would provide clues to the ways to rescue synaptic/circuit phenotypes and ASD-like behaviors in mice. Given that there is no FDA-approved treatment for social deficits in ASD as of now, these rescue results will only be useful in supporting that the candidate mechanisms are indeed causing the ASD-like phenotypes in mice. Importantly, however, some of these mechanism-based rescues may serve as the basis for clinical trials. Eventually, some of the clinically verified medications may return to basic ASD research and be used to identify additional ASD mouse models with similar or novel underlying mechanisms, which will help us understand a bigger picture, where many synaptic and circuit mechanisms act together and converge into more comprehensive mechanisms.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


Neural stem cells in the subventricular zone (SVZ) of the lateral ventricle of adult rodent brain generate oligodendrocyte progenitor cells (OPCs) that disperse throughout the corpus callosum and striatum where some of OPCs differentiate into mature oligodendrocytes. Studies in animal models of stroke demonstrate that cerebral ischemia induces oligodendrogenesis during brain repair processes. This article will review evidence of stroke-induced proliferation and differentiation of OPCs that are either resident in white matter or are derived from SVZ neural progenitor cells and of therapies that amplify endogenous oligodendrogenesis in ischemic brain. More than 80% of stroke is ischemic stroke triggered by blockage of blood flow within major cerebral arteries by clots, which leads to infarction in white and gray matter . StudiesNeurogenesis, oligodendrogenesis, angiogenesis, and astrogliosis are major brain repair processes during stroke recovery . CerebraIn vitro, tracking the lineage progression of primary adult SVZ neural stem cells, Oligodendrocyte progenitor cells identified by the chondroitin sulfate proteoglycan NG2 and platelet-derived growth factor receptor α (PDGFRα) comprise 3–9% of the total cell number in the adult CNS and are the majority of proliferating cells . These OStroke acutely induces mature oligodendrocyte damage, leading to loss of myelin, which is associated with loss of axons . HoweverIn addition to serving as a source to generate myelination oligodendrocytes, OPCs act as a surveillance network to detect brain injury . MoleculStroke increases OPC generation in the SVZ, yet endogenous oligodendrogenesis from SVZ neural stem and progenitor cells in response to stroke is limited. Emerging preclinical studies show that cell and pharmacological based therapies initiated at days after stroke enhance endogenous oligodendrogenesis and axonal outgrowth , 2012. ESonic hedgehog (Shh) is a member of the family of the hedgehog proteins and binds to the transmembrane receptor protein, patched (ptc), which, in the absence of Shh, exerts an inhibitory effect on the seven transmembrane receptor smoothened Smo; . In the Wnt signaling in adult neural progenitor cells regulates oligodendrogenesis . OverexpPhosphatidylinositol 3-kinase (PI3K) and its downstream target, Akt, affect multiple cellular functions such as cell survival,proliferation, and differentiation . MitogenMicroRNAs (miRNAs), small non-coding RNAs, regulate neural stem cell function and play a pivotal role in controlling processes of OPC generation and differentiation . Dicer iIn vitro and in vivo studies show that activation and suppression of the Shh signaling pathway down- and up- regulated, respectively, expression of the miR17-92 cluster in SVZ neural progenitor cells under non-ischemic and ischemic conditions  activity is required for oligodendrocyte differentiation during brain development ,b. PharmStroke induces oligodendrogenesis. OPCs resident in white matter and OPCs derived from neural progenitor cells contribute to generation of mature myelination oligodendrocytes that interact with axons and astrocytes during post stroke brain remodeling. Potential mechanisms underlying stroke-induced oligodendrogenesis are emerging. Recent studies show that in addition to facilitating salutatory conduction, myelination in adult brain contribute to maintaining axonal integrity, neural plasticity and circuitry function . It is eThe authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


With the expansion of public repositories such as the Gene Expression Omnibus (GEO), we are rapidly cataloging cellular transcriptional responses to diverse experimental conditions. Methods that query these repositories based on gene expression content, rather than textual annotations, may enable more effective experiment retrieval as well as the discovery of novel associations between drugs, diseases, and other perturbations.p-weighted Pearson correlation proves the most suitable for comparing differential expression profiles. We apply this method to index all GEO DataSets, and demonstrate the utility of our approach by identifying pathways and conditions relevant to transcription factors Nanog and FoxO3.We develop methods to retrieve gene expression experiments that differentially express the same transcriptional programs as a query experiment. Avoiding thresholds, we generate differential expression profiles that include a score for each gene measured in an experiment. We use existing and novel dimension reduction and correlation measures to rank relevant experiments in an entirely data-driven manner, allowing emergent features of the data to drive the results. A combination of matrix decomposition and Content-based gene expression search generates relevant hypotheses for biological inquiry. Experiments across platforms, tissue types, and protocols inform the analysis of new datasets. With the development of the DNA microarray and other technologies that probe gene expression on an "omic" scale, we are now able to discover associations between biological conditions based on their molecular underpinnings. Seminal work by Golub et al.  classifiHere we develop methods for content-based gene expression search using an entire experiment as a query. That is, given an input experiment comparing case to control, we aim to identify other experiments that show similar patterns of differential expression. This concept is exemplified by the Connectivity Map , which sCurrent methods for content-based search typically involve a two-step process: they identify a gene set of interest and then search for experiments in which this gene set is important. Several groups have introduced methods for identifying experiments that co-express  or diffeWhile previous approaches require designating a group of differentially expressed genes, we explore the possibility of using as a query a differential expression (DE) profile, consisting of a complete list of features and associated expression scores. By examining all genes shared between query and queried experiments, we aim to identify experimental conditions and perturbations that exhibit similar transcriptional responses. A successful strategy in this effort should reconcile differences between species, platform types, and normalization methods, as well as overcome the confounding effects of noise and technical replicability. To achieve this, we consider combinations of methods for three tasks: data representation, dimension reduction, and search algorithm.p-value of differential expression.First, we consider the problem of data representation. Typical microarray analysis methods represent differential expression as a fold-change, comparing the expression in one set of samples to that in another . HoweverA second challenge is that gene expression profiles from high-throughput technologies consist of up to tens of thousands of measurements per sample. In addition to the computational complexity involved in handling these large datasets, high dimensionality often confounds data mining techniques ,18. In pGiven an appropriate data representation for differential expression, the final challenge is how best to calculate the similarity between two experiments. While Fujibuchi et al. use Spearman rank correlation to compare individual microarrays , it is np-value weighted correlation coefficient that performs the best in our test compendium. Using the most successful parameters, we exhaustively index GEO DataSets (GDS) totaling 31,453 arrays and 2,089 experiments. We demonstrate the utility of our method by querying our database of DE profiles with several experiments examining transcription factor knockdown in embryonic and neural stem cells. This work demonstrates the feasibility of content-based microarray search for the large-scale discovery of functional links between gene expression experiments.To begin to address these challenges, we test several search schema representing combinations of data representation, dimension reduction, and correlation measures in a curated collection of 32 disease-related GEO experiments. We create DE profiles to represent the changes in transcription between normal and disease samples Figure , and evaTo develop a differential-expression search utility for GEO, we first evaluated various data processing pipelines in a compendium of 32 microarray experiments comparing normal to diseased tissue. This collection included three diseases with differing genetic origin: Duchenne muscular dystrophy, Huntington's disease, and breast cancer. The studies originated from different laboratories and measured primary human disease samples as well as animal disease models. Although these experiments represented various combinations of species, platform, and normalization techniques, they clustered primarily by disease and tissue , highly-connected subnetworks consisting of multiple profiles from the same dataset emerged. Clusters of profiles from multiple experiments also were apparent, linking datasets that examined related biological processes and perturbations. Figure Our comparisons of data processing methods and similarity measures suggested that the This search method allowed us to simultaneously investigate a wide range of perturbations, conditions, and comparisons using the hypothesis that experiments that differentially express similar genes and pathways would also share functional phenotypic relationships. To assess the utility of this approach, we used data from GDS1824 to investigate the effects of Nanog knockdown in embryonic stem cells (ESCs) . We creaIn addition to mouse ESC datasets, this search produced interesting comparisons with different experimental systems. Result 14 supports a similarity between Nanog knockdown and the comparison of non-small cell lung carcinoma (NSCLC) to small cell lung cancer (SCLC). SCLC, the more aggressive disease, has been linked with expression of stem cell factor  and the Our method also identifies the genes that drive the correlation between two profiles. These genes have the most significant coordinated changes in the two experiments. When we examined the genes driving the correlation for Result 14, we found cytokeratin KRT18 overexpressed in both Nanog knockdown compared to control and in NSCLC compared to SCLC Figure , fitting-/- FoxO3adult mice using normalized data from GSE18326. A query of GEO DE profiles yielded numerous significant results, the most significant of which are shown in Figure α) and HIF-2α. Bakker et al. found that FoxO3 is activated in response to hypoxic stress in mouse embryonic broblasts (MEFs), and furthermore that this activation requires functional HIF-1α +fxyd6.Click here for fileFXYD6 Expression in GDS1688. GEO Gene profile for FXYD6 in GDS1688. See http://www.ncbi.nlm.nih.gov/sites/entrez?db=geo&term=GDS1688[ACCN]+fxyd6.Click here for fileHomolog mapping. Excel Spreadsheet describing the number of genes mapped through Homologene to human for each dataset discussed in the text.Click here for file


Autism and autism spectrum disorders (ASDs) are behaviorally defined, but the biochemical pathogenesis of the underlying disease process remains uncharacterized. Studies indicate that antioxidant status is diminished in autistic subjects, suggesting its pathology is associated with augmented production of oxidative species and/or compromised antioxidant metabolism. This suggests ASD may result from defects in the metabolism of cellular antioxidants which maintain intracellular redox status by quenching reactive oxygen species (ROS). Selenium-dependent enzymes (selenoenzymes) are important in maintaining intercellular reducing conditions, particularly in the brain. Selenoenzymes are a family of ~25 genetically unique proteins, several of which have roles in preventing and reversing oxidative damage in brain and endocrine tissues. Since the brain's high rate of oxygen consumption is accompanied by high ROS production, selenoenzyme activities are particularly important in this tissue. Because selenoenzymes can be irreversibly inhibited by many electrophiles, exposure to these organic and inorganic agents can diminish selenoenzyme-dependent antioxidant functions. This can impair brain development, particularly via the adverse influence of oxidative stress on epigenetic regulation. Here we review the physiological roles of selenoproteins in relation to potential biochemical mechanisms of ASD etiology and pathology. The causes of autism and autism spectrum disorder  remain unknown, in part because of complex behavioral phenotypes and the likelihood that multiple genetic and environmental factors contribute to its etiology –3. In thAlthough ASD was previously thought to be rare, the number of persons receiving treatment for ASD has increased substantially during the past several decades and continues to increase. A recent US government report estimated the prevalence of ASD increased by 78% from 2002 to 2008 . HoweverUntil reliably accurate differential diagnoses are achieved, it is difficult to attain the goal of defining the biochemical and physiological lesions that initiate and/or perpetuate the dysfunctions of autism. However, one pathological mechanism present in many children with ASD involves defects in the control of oxidative damage. Distinctions in the nature of these perturbations in redox control may provide insight for identifying biochemically defined patient subgroups that may respond to specific therapeutic interventions. This paper focuses on potential associations between genetic and acquired defects in control of oxidative damage, particularly those that impinge upon selenium- (Se-)dependent enzymes (selenoenzymes). Se physiology is a vital process in the brain and neuroendocrine system, , 26 and,∙O22−), hydrogen peroxide (H2O2), superoxide–anion (O2−), singlet oxygen (1O2), and hydroxyl radicals (∙OH), are products of ongoing aerobic metabolism via mitochondrial oxidative phosphorylation ) to its reduced  . The onl2O2, which appears to be its rate-limiting step [2O2 and lipid hydroperoxides, appropriate antioxidant defense systems are essential to control excess oxidative stress. Three of the five GPx are expressed in thyrocytes and thyroid tissue [2O2 is increased [2O2 production, GPx production is also stimulated, thus upregulating antioxidant protection. By virtue of its ability to increase basal metabolism, thyroid hormone increases oxygen utilization, thereby increasing the demand for antioxidant.GPx  are selenoenzymes involved in antioxidant defense and redox regulation and modulation. GPx provide protection against oxidative damage and aid in the maintenance of membrane integrity by using GSH as a cofactor to catalyze reduction of hydrogen peroxide, forming oxidized glutathione (GS-SG) in the process. Thyroid hormone synthesis requires a continuous production of high concentrations of Hing step –74. Therd tissue –77. Studd tissue –83. Whenncreased . FurtherGPx4 reduces hydroperoxides of membrane phospholipid fatty acids and has particular relevance for autism. Along with TRx1, TRx2, DIO2, DIO3, and selenoprotein P (SelP), GPx4 is considered an essential selenoprotein whose levels are preserved in brain and endocrine tissues during Se deficiency. Suppression of neuronal GPx4 expression resulted in a selective loss of parvalbumin-expressing GABAergic interneurons  that areIn addition to the TRx and GPx selenoenzyme families, further selenoproteins have recently been implicated in processes known to be involved in neurodegenerative diseases, including protein folding, degradation of misfolded membrane proteins, and control of cellular calcium homoeostasis . CerebraThe cerebral cortex, hippocampus, cerebellum, and olfactory bulb express the highest numbers of selenoproteins . The braNot only is SelP important for Sec transport, but it also appears to have a vital role in neurogenesis. A study of its brain distribution found a remarkably higher concentration in ependymal cells, which are found at the ventricle surface . EpendymAll brain selenoenzymes are affected by loss of Se in the absence of SelP, but the DIOs, TRxs, and GPxs are the selenoproteins considered to have the most critical roles in the brain and endocrine system. Therefore, loss or compromise of their functions  would haObservations from family studies suggest that ASD has a strong genetic component –105, altGenetic risk of autism may be related to a differential sensitivity to environmental factors. Using a strict definition of autism, a recent study found a 58% concordance rate for monozygotic male twins and 60% for females and 21% and 27% for male and female dizygotic twins, respectively . Using tPolymorphisms of genes involved in glutathione metabolism, including genes for GPx and glutathione S-transferase (GST), have been reportedly associated with ASD. GPx1 is the predominant and most abundant isoenzyme of GPx and plays an integral role in reducing oxidative stress by catalyzing the reduction of potentially harmful peroxides. Ming et al.  found siJames et al.  examinedDNA copy number variants (CNVs) represent a major category of genetic risk for ASD and are implicated in approximately 10% of cases , 124. SeEpigenetic regulation utilizes covalent modifications such as DNA methylation and the addition/removal of various chemical moieties to histone tails (collectively known as epigenetic marks) to provide stable, transgenerational changes in gene expression without alteration of the underlying nucleotide sequence , 127. EpAs noted above, MS exerts powerful control over all methylation reactions via its influence over the SAM/SAH ratio, and MS inhibition by oxidative stress will cause both a decrease in SAM and an increase in SAH, while reducing conditions will have the opposite effect. A twofold increase in MS activity induced by IGF-1 is associated with a twofold increase in global DNA methylation, while inhibition of MS activity by ethanol is associated with a large decrease . Thus, xBeyond its direct epigenetic regulation of gene transcription, DNA methylation also regulates the activity of repetitive transposable elements dispersed throughout the human genome. Transposable elements comprise about 45% of the genome, and their earlier description as “junk DNA” has recently been revised in recognition of their ability to modulate gene transcription, mRNA splicing, micro-RNA formation, and other processes . ReflectOxidative stress and decreased methylation capacity are common in autism and abnormal epigenetic regulation may link the metabolic abnormalities to disruptions in brain development. Other comorbid features of autism, such as autoimmunity and gastrointestinal (GI) dysfunction , 134, maFrom conception to maturation, human development is a highly orchestrated expression of epigenetic regulation, so it is not surprising that genetic and environmental factors adversely affecting oxidative tone and methylation status can contribute to developmental disorders. The exceptionally dynamic redox-dependent epigenetic regulation in the brain increases its vulnerability to neurodevelopmental disorders. Autism is a prominent feature of Rett, Angelman, Prader-Willi, and Fragile-X syndromes, each of which has been linked to interruption of methylation-dependent regulation –138. TheCertain soft electrophiles are known to be neurotoxic at high exposures, presumably due to their effects on sulfur metabolism. Although these electrophilic species are highly interactive with cellular nucleophiles such as thiols, the Se of Sec is by far the strongest intracellular nucleophile. Therefore, selenoproteins are very vulnerable to enzyme inhibition by binding to neurotoxic electrophiles. Their toxic concentrations are generally miniscule in relation to sulfur, toxic levels generally equal or exceed the normal tissue concentrations of Se. Therefore, because of their high reactivity and low molar abundance, selenoenzymes are highly vulnerable to selective inhibition by high concentrations of electrophiles such as Hg. Soft electrophiles such as Hg have larger ionic radii and a more dispersed surface charge, making them more reactive with soft nucleophiles such as the Se of Sec at the active sites of enzymes.Only certain electrophiles are notably neurotoxic. Those that bind and potentially sequester Se would cooperatively diminish the biological availability of Se for performance of its necessary physiological roles . For exaLikewise, additional exposures to electrophiles are encountered in the form of environmental contaminants, such as toxic metals, pesticides, herbicides, and others. In addition, soft electrophiles are present as the active ingredients in many pharmaceuticals and food preservatives, while still others are produced during the degradation of these products. Therefore, instead of examining relationships between ASD incidence and exposures to individual agents, it may be more informative to examine ASD incidence in relation to aggregate exposures to these soft electrophiles and/or their effect on selenoenzyme activity in vulnerable individuals.High exposures to soft electrophiles have the potential to incapacitate various sulfur- and Se-dependent metabolic processes, thus disrupting many redox regulatory mechanisms that are required for healthy cell growth and function, particularly in brain and endocrine tissues. Increased selenium status is known to counteract the adverse effects of elevated exposures to neurotoxic electrophiles such as Hg, cadmium (Cd), lead (Pb), and vanadium (V) . These eTo prevent bacterial contamination in multiple-dose vials, thimerosal, the ethylmercury derivative of thiosalicylic acid, has been used as a preservative in various medical products, including vaccines. As autism rates increased, Bernard et al.  suggesteOrganic molecules such as acrylamide, acrolein, and diethyldithiocarbamate are structurally diverse, but these electrophilic species all share the potential to chemically react with strong nucleophiles . Just asInterestingly, the major acetaminophen-binding protein in the liver is Se binding protein-2 (SeBP2) , 172. BoN-acetyl-p-benzoquinone imine (NAPQI), a metabolic product of acetaminophen breakdown that is thought to be the proximal cause of hepatotoxicity following acetaminophen overdoses. When excessive quantities of NAPQI are formed, the primary metabolic (glucuronide and sulfate conjugation) pathways apparently become saturated. N-acetylcysteine is thought to counteract toxicity by either reducing NAPQI to the parent compound or providing sulfhydryl for conjugation of this metabolite [N-acetylcysteine protects against acetaminophen-induced hepatotoxicity by maintaining or restoring hepatic concentrations of GSH . Glutathtabolite . If suppThe nosology of ASD is complicated by the difficulties to differentiate the syndrome into subsets with similar symptoms and distinct etiologies. Children that share the diagnosis of ASD represent more than one distinct pathophysiological condition. Recognizing and distinguishing between groups with separate etiologies require identification of objective laboratory indices that clinicians can use for diagnosis and to monitor progression and treatment effects. The objective of this review is to discuss metabolic defects that may contribute to the onset and pathology of ASD, particularly in relation to Se physiology.Existing evidence indicates children with ASD have disruptions in GSH metabolism, and that impaired selenoenzyme and thiol metabolic pathways may be involved. These disruptions could occur as the result of multiple exposures to elemental and organic electrophiles  with exaBased upon the mechanisms outlined above, interventions designed to diminish oxidative damage and support methylation capacity could improve the health of individuals afflicted with ASD, particularly those with inadequate antioxidant defenses. In such individuals, dietary interventions may offer low-risk approaches with potential for significant improvements in neurodevelopmental outcomes. Although the etiology and pathology of ASD remain poorly resolved, research suggests that afflicted children may benefit from treatments designed to improve their antioxidant capacity.


Extracellular vesicles (EVs), including exosomes, have been widely recognized for their role in intercellular communication of the immune response system. In the past few years, significance has been given to exosomes in the induction and modulation of cell-fate-inducing signalling pathways, such as the Hedgehog (Hh), Wnts, Notch, transforming growth factor (TGF-β), epidermal growth factor (EGF) and fibroblast growth factor (FGF) pathways, placing them in the wider context of development and also of cancer. These protein families induce signalling cascades responsible for tissue specification, homeostasis and maintenance. Exosomes contribute to cell-fate signal secretion, and vice versa exosome secretion can be induced by these proteins. Interestingly, exosomes can also transfer their mRNA to host cells or modulate the signalling pathways directly by the removal of downstream effector molecules from the cell. Surprisingly, much of what we know about the function of exosomes in cell determination is gathered from pathological transformed cancer cells and wound healing while data about their biogenesis and biology in normal developing and adult tissue lag behind. In this report, we will summarize some of the published literature and point to current advances and questions in this fast-developing topic. In a brief foray, we will also update and shortly discuss their potential in diagnosis and targeted cancer treatment. Most of us have to declutter sometimes, pack things into bags before giving them away, but sometimes we do not get rid of those things. Cells also dispose of unwanted proteins in bags (vesicles) and also under some conditions reuse them to communicate with their environment. Small vesicles called exosomes can carry out both of these functions. They are generated within specific compartments of the cell called multivesicular bodies (MVBs) or endosome-like plasma membrane microdomains and then released from the cell. Exosomes carry a broad number of cargo, including cell-fate-promoting signalling molecules. Such molecules take part in determining cell identity, and deregulation of the induced signalling pathways is related to many forms of cancers. Interestingly, it has been shown that exosome-bound cell signals can shape the microenvironment of cancer cells or induce wound-healing processes. For that reason and due to their cell-type-specific composition, stability and easy accessibility from body fluids, exosomes have great potential to become valuable determinants in the diagnosis and targeted treatment of diseases such as cancer. This review will summarize and discuss some of the recently published data.www.isev.org; www.facebook.com/groups/exovesicles/; . Research into extracellular vesicles (EVs) underwent 2 major breakthroughs in the last 3 decades. Originally, exosomes were considered as garbage bags used to discard obsolete cytosolic and membranous molecular remnants, however in the mid-1990s with the discovery of antigen-presenting EVs from B-lymphocytes, they have been associated with immune system functions (Multivesicular bodies (MVBs) form an endosomal-intermediate compartment directing endocytosed cargo for lysosomal degradation. Surprisingly, pulse-chase and electron microscopy studies of transferrin receptor trafficking in reticulocytes in the 1980s, demonstrated that MVBs are also able to fuse back to the plasma membrane, releasing small vesicles that were later named “exosomes” . Exosomesicles/; ]. While unctions . Since tunctions –11]. Theunctions . In receunctions .Many cell-fate-determining ligands are evolutionary conserved, mostly secreted proteins that induce target gene expression according to their local concentration by binding to their respective receptors localized on responding cells [reviewed recently in ]. Once rDeregulation of any of the secretory pathways may alter signalling activities, leading to severe pathogenesis, including neurological diseases and cancer. This review will focus on the effects of secreted cell-fate proteins using the exosomal pathway. However, caution should be taken as the term “exosome” in some reports might refer to an operational use (e.g. vesicles obtained by high-speed ultracentrifugation) rather than to the cell-biological origin . In addihttp://www.microvesicles.org/; Once generated, MVBs can either fuse with the lysosome or the plasma membrane, thus releasing vesicles. What distinguishes secretory from degradative MVBs is still a conundrum. Proteomic cataloguing however, show some overlapping similarities in the profiles of secretory and degradative exosomes including membrane and cytosolic proteins (Drosophila S2 cells and is involved in the release of Wg/Evi complex from synaptic boutons of the neuro-muscular junctions (NMJs) in developing Drosophila larvae (+-ATPase (V-ATPase) as evidence suggested that it possibly participates in exosomal secretion of Hh-related proteins  and myosin 5  has been shown to enhance Wnt-exosome secretion in a larvae , 30. Thea larvae ; oligodea larvae ; and a sa larvae . Fusion a larvae . Anotherproteins . The samosophila. FinallyDifferent proteins are transported through exosomes but sorting signals for cargo are poorly understood. It has been shown that tetraspanin family members might play a role in cargo sorting. Tetraspanin are membrane proteins that cluster with themselves and with other membrane and cytosolic proteins into tetraspanin-enriched microdomains (TEMs). Such TEMs may function in signalling and also intracellular trafficking processes . For insUpon loading and release, exosomes travel through the extracellular space and are eventually internalized by cells. How target cells are chosen is not well understood. Macropinocytosis, clathrin-dependent endocytosis and phagocytic mechanisms have all been discussed , 46. DifMost cell-fate proteins (bicoid transcription factor being an exception) unfold their signalling capacity through binding to specific cell-surface receptors. Therefore, it will be of great interest to identify a possible role the respective receptors might play in exosome–cell interactions.Drosophila Wnt protein) can spread through wing imaginal disc epithelial tissue  as well as with overexpressed Rab4 GTPase outside the Wg expressing domain in the wing imaginal disc of Drosophila, however the functional data suggested are not available -exosomes -derived fibroblasts. For tumour suppression or progression, cross-talk between the different components of the microenvironment is needed. Such communication is executed by growth factors, including chemokines and cytokines and cell-fate-signalling molecules. Although the intrinsic variability of the microenvironment of tumours might produce different outputs, it seems clear that exosomes play an important role in this exchange of information.As mentioned earlier, vascularization provides a means of transport of nutrients to tumour growth sites ; in progFinally, autocrine-produced EVs might determine tumour cell-fate itself. For example, exosomes produced by human pancreatic tumour cell lines can hamper their own Notch survival pathway leading to apoptosis .It has recently been shown that exosomes can also modulate the strength of signalling through the cellular export of downstream effector molecules. In this way, cells can attenuate canonical Wnt activity through the removal of the downstream effector β-catenin . In thisIn summary, the examples described above show just how important and versatile exosomes are in all stages of cancer generation. Associated with cell-fate-determining proteins, they can cause profound cell changes and therefore shape the pathological transformed microenvironment. As exosome composition seems to be cell and tissue specific, they are highly suitable to serve as diagnostic markers.During cancer progression to more aggressive phenotypes, cancer cells alter their molecular signature causing quali- and quantitative changes of exosomes that in turn affect their (micro-) environment. These properties, together with exosomes’ stability and easy accessibility from body fluids such as blood, urine, cerebrospinal liquid, saliva or breast milk amongst others, label them as ideal biomarkers. For instance, as tumours become more aggressive, heparanase activity is enhanced in myeloma, lymphomas or breast cancer, increasing both the number of exosomes released and the amount of syndecan-1, VEGF and HGF molecules exposed on their surface , making Exosomes could be considered as naturally occurring liposomes  carrying proteins, such as antigens, mRNA and microRNA. Liposomes have long been thought of as a delivery system for therapeutics . One feaHow can exosomes be considered as cancer therapeutics? Since exosome identity depends on the cell type, one way would be to load the inner vesicular space of signalling exosomes with biological or chemical agents. That could be done, for instance, by semi-synthetic exosomes produced by genetically designed cells and subsequent re-injection into the organism. A similar approach could be used to re-supply tissues with signalling molecules to overcome signalling deficits (regeneration after stroke or heart attack) or to help cell differentiation in vivo. In addition, the effects of chemical compounds on cancer exosome cell mixtures could be directly studied in high-throughput formats. These approaches will need a good understanding of the fundamental cell biology of exosome biogenesis.Thus, do we talk about garbage bags after all when we talk about exosomes? Much of the evidence presented here concerning their role in signalling seems to support this idea in a very particular way. For instance, cancer cells produce an abundance of upregulated miRNA, mRNA and proteins, with signalling ligands amongst them. Consequently, cells might use exosomal export as one route to get rid of this excess material. Cancer cells present a special physiological state, constantly modulating and adjusting their composition, competing with their neighbouring cells for a niche to settle in. All too convenient in this struggle might be the export of signalling ligands, which help to set and shape the microenvironment. We hypothesize that exosome-bound signals might be more stable in the extracellular space than free-accessible ones, bringing along additional factors and increasing local concentrations, all in all prerequisites to increase their chance to impact on distant cells. These properties and their easy access in body fluids are working in our favour as the quali- and quantitative composition of exosomes might report on the kind, progression and aggressiveness of a particular cancer, as has been reported in selected cases. Concluding from the presented data, exosomes could be utilized in at least 2 ways in cancer therapy: re-applying naturally or synthetically altered exosomes to the organism to target signalling, or by interception of any of the steps during the “life” of an exosome through specific drug intervention. Both ways will need intensive research into the fundamental cell biology of exosome biogenesis. Highly interesting for the biomedical community will be the question whether signalling exosomes hold systemic information for cancer cells to metastasize. Not least, investigating the functional role of exosomes as a carrier of signalling ligands in the developing and adult organism will remain as another major challenge for the future. The enticement to follow these threads lies just in front of us.


We demonstrate a new hyperpigmentation on the tongue of a 68-year-old female patient who was diagnosed with stage IIA infiltrating ductal carcinoma of the left breast who underwent modified radical mastectomy followed by a triple chemotherapy regimen which consisted of doxorubicin, docetaxel, and cyclophosphamide.The patient developed the tongue hyperpigmentation a few weeks after the initiation of chemotherapy. She never had similar lesions in the past, nor had any involvement of other parts of the body, including palms, soles, trunk, nails, or scalp. A few months after stopping the chemotherapy, the patient had a remarkable improvement in her tongue discoloration.Hyperpigmenation of the tongue following a treatment with chemotherapy has been previously reported –3. Both The exact pathophysiology is still not well understood; it has been suggested that melanocyte-stimulating hormone (MSH) may be boosted by certain chemotherapy agents like doxorubicin , and thaIt is usually self-limited and disappears a few weeks after treatment is completed.


Although current theories all point to distinct neural systems for sequencelearning, no consensus has been reached on which factors crucially define thisdistinction. Dissociable judgment-linked versus motor-linked and implicit versusexplicit neural systems have been proposed. This paper reviews these twodistinctions, yet concludes that these traditional dichotomies proveinsufficient to account for all data on sequence learning and its neuralorganization. Instead, a broader theoretical framework is necessary providing amore continuous means of dissociating sequence learning systems. We argue that amore recent theory, dissociating multidimensional versus unidimensional neuralsystems, might provide such framework, and we discuss this theory in relation tomore general principles of associative learning and recent imaging findings. A fundamental characteristic of human cognition is the ability to learn sequenceinformation and to adapt to the environment based on this newly acquired knowledge,reflecting the remarkable plasticity of the human brain. Sequence knowledge iscrucial for efficient daily functioning and therefore, omnipresent during life.For insIt should therefore come as no surprise that the neural basis of sequence learninghas interested researchers for many years. Numerous studies used imaging techniquessuch as positron emission tomography  learning task (VXVS) are presented that are constructedaccording to a finite-state grammar. This grammar represents a rule system definingthe serial order in which letters can follow each other. In the learning phase,participants have to observe and memorize these meaningless letter strings. In asubsequent test phase, they are asked to judge whether new strings conform to thegrammar or not. Successful, better-than-chance judgment suggests that participantshave acquired sequence knowledge (motor-linked tasks assess sequence knowledge via the reactiontime (RT) of motor responses, that is, the extent to which motor responses becomemore facilitated to sequenced stimuli compared to random stimuli. The most studiedtask that measures sequence learning via RT performance is the serial reaction time(SRT) task  task . Ina baRT) task .It has been suggested that tasks using judgment-linked versus motor-linked measuresinvolve independent learning mechanisms relying on different areas in the brain,with the basal ganglia supporting the latter but not the former type of learning, 1998. OHowever, results from other neuropsychological and imaging studies question such astrict dissociation. When modified versions of the judgment-linked AG and themotor-linked SRT task were used to more thoroughly investigate sequence learningabilities of patients with Parkinson’s disease, different results have beenobtained. Impaired AG learning has been reported in a group of PD patients whenusing an AG task in which grammaticality judgments were made already during thelearning phase and in which learning depended on trial-by-trial feedback learning. On theThese recent data from neuropsychological studies thus seem to indicate that a strictdissociation between sequence learning mechanisms assessed through judgment-linkedand motor-linked tasks is difficult to hold; sequence learning abilities of patientswith striatal dysfunctions are also dependent on numerous aspects of groupcharacteristics and methodology. Moreover, no clear double dissociations inneuropsychological research have been reported to date that supports ajudgment-linked versus motor-linked dichotomy. Additionally, results from recentfunctional imaging studies challenge the idea that only motor-linked measures ofsequence learning are reliant on the basal ganglia. Indeed, an important functionfor the caudate nucleus has been reported in imaging studies using AG  and otheThus, while functional dissociations between tasks using judgment and motor-linkeddependent measures have been demonstrated behaviorally , 1998,rThe process of sequence learning typically involves several successive stages,going from an early, fast learning phase with strong performance improvements toa later phase of automatization and consolidation, which rely on different areasin the brain . AssuchAG learning is generally considered to reflect higher-order perceptual learningwhile SRT learning is viewed as motor skill learning . Within In recent fMRI studies, we specifically focused on the question whether separateneural networks are specialized for perceptual (non-motor) related versus motorrelated implicit sequence learning or, alternatively, whether these differentmodalities share a common network , 2011. WLikewise, in the context of intentional motor skill learning, there is also ampleevidence indicating that the learning phase and modality of sequencerepresentation must be taken into account to fully understand the neuralorganization of sequence learning  task paradigms contrasting the neural responsesbefore and after participants became aware of the presence of a sequence structure. As suchDestrebecqz et al.  used anoOther imaging studies, however, challenge the idea that independent brain networksare involved in implicit and explicit sequence learning and report no cleardissociation. For instance, Schendan and colleagues  contrastIn sum, we can conclude that previous results on the issue whether dissociable brainsystems are involved in implicit and explicit sequence learning are far fromunivocal: Some studies report non-overlapping brain activations while others reportconsiderably overlapping neural networks. The interpretation of these contradictoryresults is complicated by the fact that different sequences were used  with different amounts of prior sequenceknowledge in the explicit learning conditions. It is also questionable whether thedifferential activation between conditions is not related to differentialattentional requirements or to time-related factors . Moreover, as argued by Destrebecqz andcolleagues , anotherAlthough these previous frameworks have provided useful insights in how neuralnetworks of sequence learning might be dissociated, the literature overviewindicates that the judgment versus motor linked and the implicit versus explicitdichotomy prove insufficient. It appears that a broader theoretical framework isnecessary to explain the various findings on sequence learning and its neuralorganization. One such framework has been proposed by Keele, Ivry, Mayr, Hazeltine,and Heuer . Their tdimension refers to a specific type or modality of sequenceinformation. Our daily environment involves a continuous stream of various types ofsequential information coming from multiple sources. For instance, when riding homefrom work, we coordinate our limbs in a sequential pattern to move forward and,simultaneously, we process the succession of visual and auditory informationsurrounding us. As argued by Keele et al. . As such, the multidimensional system is proposed tobuild associations between events from these multiple dimensions  whereas the unidimensional system is restricted tothe association of information along a single dimension . Evidence for this theory stems largely from studies contrastingperformance during single and dual SRT task conditions. In the latter condition,successive stimuli typically alternate between two dimensions, that is, the spatialinformation from the primary SRT task and the auditory information from thesecondary tone-counting task ; forcombining detailed information from multiple cortical streams into a unifiedrepresentation rather than for processing simple, elemental information  are more sensitive to themultidimensional system than judgment-linked tasks. Sequence learning assessedthrough the SRT task naturally involves a mix of response, stimulus, andstimulus-response contingencies. On the other hand, judgment-linked sequencelearning with the AG task only involves stimulus contingencies in the form ofletter strings. The differential involvement of cross-dimensional sequenceinformation, and thus the differential sensitivity for an engagement of themultidimensional system, might explain previous imaging findings. That is, animportant function for the hippocampus has been reported in SRT sequencelearning  while AGInterestingly, the multidimensional-unidimensional framework also offers a newperspective on the distinction between implicit and explicit learning . Since tMoreover, the inconsistent results from neuropsychological studies on amnesicpatients with hippocampal damage might be understood within themultidimensional-unidimensional framework. Traditionally, it has been claimedthat the hippocampus subserves explicit learning but not implicit learning and indeResearch on the neural basis of sequence learning has led to the consensus thatsequence learning is not unitary in nature but is mediated by distinct neuralsystems. However, how exactly these learning systems are divided remains unclear. Adistinction has been proposed between sequence learning assessed throughjudgment-linked  and motor-linked  tasks , 1998. HAltogether, we feel a more coherent framework is necessary that crosses previousdichotomies; a framework that uses a more continuous approach to characterizedistinct learning systems. We have argued that another theory, dissociatingmultidimensional versus unidimensional sequence learning systems , might p


Spinal cord injury (SCI) is a serious disease of the center nervous system (CNS). It is a devastating injury with sudden loss of motor, sensory, and autonomic function distal to the level of trauma and produces great personal and societal costs. Currently, there are no remarkable effective therapies for the treatment of SCI. Compared to traditional treatment methods, stem cell transplantation therapy holds potential for repair and functional plasticity after SCI. However, the mechanism of stem cell therapy for SCI remains largely unknown and obscure partly due to the lack of efficient stem cell trafficking methods. Molecular imaging technology including positron emission tomography (PET), magnetic resonance imaging (MRI), optical imaging ) gives the hope to complete the knowledge concerning basic stem cell biology survival, migration, differentiation, and integration in real time when transplanted into damaged spinal cord. In this paper, we mainly review the molecular imaging technology in stem cell therapy for SCI. Spinal cord injury (SCI), which results from trauma or progressive neurodegeneration, is a devastating and life-altering injury. It often affects young and healthy individuals who are suffering from severe functional and sensory deficits. This debilitating condition not only creates enormous physical and emotional cost to individuals but also is a significant financial burden to the society. The annual incidence of SCI is 15–40 cases per million worldwidely [SCI is mainly divided into two types: traumatic SCI and nontraumatic SCI. A global-incident rate 2007) of traumatic SCI is estimated at 23 traumatic SCI cases per million [007 of trDespite the progress of medical and surgical management as well as rehabilitation approaches, many SCI patients still experience substantial neurological disabilities , 5. MorePrevious researches on SCI mainly focused on improving neurological manifestations of SCI while ignoring the pathological changes of spinal cord. According to the progress, SCI could be divided into primary injury phase which is the physical injury and secondary injury phase , 10. TheIncreasing interest has focused on the development of innovative therapeutic methods that aim to regenerate damaged CNS tissue by taking advantages of recent advances in stem cell and neuroscience research , 26. Prein vivo, including survival, migration, distribution, rejection, integration, and differentiation.Recent studies suggested that stem cell therapy could improve neural function in SCI by replacing damaged cells , 30. Thein vivo bioluminescence imaging (BLI) and fluorescence imaging (FLI). The label of stem cells requires labelling methods making grafted cells distinguishable from host cells to follow transplanted stem cells by the above methods.Fortunately, molecular imaging gives an effective way for such research. Well-established imaging modalities used by researchers for the purpose of molecular imaging are positron emission tomography (PET), magnetic resonance imaging (MRI), whereas others have employed newer modalities based on the transmission of light through tissues, such as in vivo. MRI can be used for noninvasive tracking of transplanted cells which are usually labeled with super-paramagnetic nanoparticles as contrast agents in longitudinal studies on living animals. Gadolinium and ferric oxide are two common contrast media used for cell labeling in MRI [in vivo using noninvasive MRI techniques. BLI is a newly developing technology for dynamically observing biological behavior. It is based on an enzymatic light production system. The enzyme in action is a luciferase which uses the substrate luciferin to produce light. Then the emitted light is subsequently captured by a highly sensitive CCD camera. Using this technology, cells should be transgenically modified to steadily express luciferase. Then, cells can be tracked in a long periods of time because luciferase expression is preserved during proliferation so that all cells and their descendants express luciferase without dilution. Thus, we can observe the stem cells' dynamic behavior in vivo through this method.PET is a nuclear imaging technique that produces a three-dimensional image or picture of functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide (tracer), which is introduced into the body on a biologically active molecule. It can provide metabolic changes and be used for tracing radioactively labeled stem cells g in MRI . Recentlg in MRI –34. TheiAccording to the pathophysiological targets of SCI, transplanted cells should satisfy the following requirements. Firstly, enable regenerating axons to cross any cysts or cavities; secondly, functionally replace dead cells; thirdly, create an environment to support axonal regeneration and myelination. Stem or progenitor cells are capable of modifying the lesion environment, providing structural support, myelination, increasing neurotrophic factors for neuroprotection, and endogenous activation –38. As aCharacteristics and purported mechanisms of action of stem cells will then be discussed, with specific attention paid to axonal regeneration and regrowth, growth factor release, guidance through inhibitory cues, remyelination, and induction of anatomical neuroplasticity.Transplantation of bone marrow-derived mesenchymal stem cells (BMSCs) for SCI has been previously reviewed –43. ManyThere are two types of adult bone marrow stem cells: hematopoietic stem cells (HSCs) and mesenchymal stem cells (MSCs). Zhu et al. compared various properties of human umbilical cord-derived MSCs (HUCMSCs) with human placenta-derived MSCs (HPDMSCs), including cell proliferation, apoptosis, cellular morphology, ultrastructure, and their ability to secrete various growth factors. Their findings indicate that different sources of MSCs have different properties and that care should be taken when choosing the appropriate sources of MSCs for stem cell transplantation . In rodeThe grafting of MSCs to treat SCI has shown promising results in animals; however, less is known about the effects of autologous MSCs in human SCI. Park et al. explored 10 SCI patients who underwent intramedullary direct MSCs transplantation into injured spinal cords. All patients did not experience any permanent complication associated with MSC transplantation. Three patients showed gradual improvement in activities of daily living, changes on magnetic resonance imaging such as decreases in cavity size and the appearance of fiber-like low signal intensity streaks, and electrophysiological improvement .Despite these potential benefits, there are reported adverse effects of MSCs, such as increased recurrence of hematological malignancies and enhanced tumor growth and metastases , 51, 52.Neural stem cells (NSCs) have been classified as a kind of neural lineage stem cell which is able to self-renew and to give rise to all types of mature neural cells including neurons, astrocytes, and oligodendrocytes , 54. TheNSCs and NPCs are found in both fetal and adult CNS . Adult Nα, and CXCL1, also increase remarkably in the injured spinal cord [The extent of glial scar formation and the characteristics of inflammation are the most remarkable difference in the injured spinal cord microenvironment between the subacute and chronic phases. By contrast, the distribution of chronically grafted NSPCs was restricted compared to NSPCs grafted at the subacute phase because a more prominent glial scar located around the lesion epicenter enclosed the grafted cells. Therefore, glial scar formation and inflammatory phenotype should be considered in order to achieve functional recovery by NSPCs transplantation in cases at the chronic phase . Anothernal cord . These cnal cord , 62.in vitro [in vivo [When transplanted into mice in an animal model of SCI, human NSCs promoted locomotor recovery . The stuin vitro  and in v[in vivo , 68. Rec[in vivo .Simultaneously, the aims of axonal regeneration through the injury area have been replaced preclinically by more realistic objectives of remyelination and provision of trophic support for endogenous precursors and axons. It makes NPCs much more promising candidates of cell therapy for SCI and probably heralds their increased use in clinical trials.Embryonic stem cells (ESCs) are pluripotent cells derived from the inner cell mass of developing blastocyst embryos that can differentiate into nearly all cell types . NotablyThe discovery of induced pluripotent stem cells (iPSCs) has opened a new potential therapeutic approach for regenerative neuroscience, although iPSCs have not yet been used clinically in SCI cell therapy. iPSCs were developed in 2006 by Takahashi and Yamanaka, who showed that mouse somatic cells, such as fibroblasts, could be reprogrammed to pluripotency with retroviral expression of four transcription factors OCT4, SOX2, KLF4, and c-MYC and achieve similar morphology, pluripotency, self-renewal, and gene expression as ESCs, without the requirement for an embryo .The clinical use of ESCs is complicated; however, by ethical and immunological concerns, both of which might be overcome by using pluripotent stem cells which can be derived directly from a patient's own somatic cells . ExperimDifferent kinds of iPSCs have different performance in SCI treating. Transplantation of “unsafe” iPS-derived neurospheres may result in teratoma formation and sudden loss of locomotor function . Kramer'Undifferentiated IPSCs, like ESCs, have high tumourigenicity in pathological conditions . TherefoTransplantation of stem cells has a good prospect of clinical application. However, the challenges in the field of molecular imaging are to develop effective imaging strategies with reporter systems and probes which should firstly reveal cellular and molecular processes throughout an entire study period. Secondly, probes should be highly sensitive to small changes in cell function and distribution. Finally, they do not alter the labeled biological process itself significantly. Molecular imaging technologies will greatly facilitate the functional monitoring and evaluation of a wide range from genes to organs for their roles in health and disease. Herein, molecular imaging has served as a platform to test stem cell therapy for SCI.Cell labeling can be divided into two types: physical cell labeling and reporter gene imaging. Physical cell labeling is completed before cell administration and can be accomplished with superparamagnetic iron oxide (SPIO) particles for MRI , 84, rad18FDG PET imaging, has been used mainly in cancer [in vivo to monitor labeled stem cells and it also has been applied widely to detect and quantify subtle abnormalities in CNS diseases. PET has served as a platform to test stem cell therapy for neurological disease allowing more rapid progression in both preclinical and clinical studies. In order to explore the effect of in vivo PET in tracking the stem cells transplanted into spinal cord, Bai et al. transplanted human neural progenitor cells into rabbits' injured spinal cord; rabbits were injected with 11C-raclopride intravenously and then underwent PET imaging [11C-raclopride PET imaging of the live rabbits showed accumulation of radioactivity at the hNPC-TERT cell injection site with a standard uptake value significantly higher than that of control group (the HeLa cell transplantation group) (P < 0.01). 11C-raclopride PET imaging of the isolated spinal cords showed rounded focal image of increased radioactivity in the hNPC-TERT cell transplantation group and linear image of radioactivity without clear border in the HeLa cell transplantation group. Meanwhile, fluorescent microscopy showed the same results. These results suggested that PET with radioisotope labeled tracer is useful for functional studies in developing cell-based therapies.Positron emission tomography (PET) imaging, especially n cancer –90. PET  imaging . 11C-racin vitro and labeled NPCs were found migrating along white matter tracts as demonstrated by MRI [in vivo for tracking hUC-MSCs' fate with noninvasive MRI [In vivo MRI 1 and 3 weeks after injection showed a large reduction in signal intensity in the region transplanted with SPIO-labeled hUC-MSCs. The results showed that noninvasive imaging of transplanted SPIO-labeled hUC-MSCs is feasible. Recently, Amemori et al. used neural stem cell line derived from human fetal spinal cord tissue (SPC-01) to treat a balloon-induced SCI [Magnetic resonance imaging (MRI) is a widely used and powerful imaging technique which can provide high resolution and 3D anatomical imaging. It can be used to evaluate the reparation of the injured spinal cord . For mond by MRI . In addid by MRI . Such masive MRI . SPIO wauced SCI . SPC-01 in vivo by virtue of their reporter gene, which is expressed only when cells are alive [in vivo luminescence which is obtained from the North American firefly. This Luc gene encodes a 550 amino acid protein, Luc. Considering the near absence of endogenous light from mammalian cells and tissues, luciferases have a significant advantage as optical indicators in live mammalian cells and tissues, the inherently low background [in vivo as a marker of gene expression requires that the substrate is nontoxic and well distributed to the animals' tissues after exogenously adding . At present, no humoral immune responses, hepatic toxicity, or germ-line integration were observed in models of luciferase reaction. Studies have also suggested that luciferin could be distributed throughout the entire animal and even could not be restricted by the blood-brain or placental barriers [3 cells in the peritoneal cavity, 1 × 104 cells at subcutaneous sites, and 1 × 106 circulating cells immediately following injection [Bioluminescence imaging (BLI) uses luciferase-transduced transplanted cells that can be detected noninvasively re alive , 96. Lucckground . It is ackground . Using tbarriers . Previounjection , 100. Renjection . Okada enjection . The thiin vivo but lacks the ability of providing detailed anatomic structures. SPIO-labeled stem cells can be detected by means of MRI and get high resolution and 3D anatomical imaging; however, the low sensitivity limits its application on cell tracing. Furthermore, cell division may dilute intracellular markers and then the signals may fail to reflect cells' number and location due to shedding of iron particles [No single imaging modality can provide all the information required to track transplanted stem cells and monitor their functional effects. Every imaging modality for stem cell tracing has its own advantages and disadvantages , 82 Tab. PET hasarticles . Hence, in vivo within the same animal. In recent study, Kim et al. evaluated the therapeutic effects of transplanted human glial precursor cells (hGPs) together with the in vivo fate of these cells using MRI and BLI [Computed tomography (CT) scanners can overcome the lacks of anatomic structures. PET and CT scanners can be used in conjunction to get more detailed, fused images. In a research of Nandoe Tewarie RD, PET was used in combination with CT imaging techniques for longitudinal monitoring of the injured spinal cord. With PET-CT, combined with a simulation-based partial-volume compensation (PVC) method, they can serially measure standardized uptake values of the T9 and T6 spinal cord segments and reveal small, but significant, differences . Because and BLI . In ordeThere are also some problems of nonspecific signals obtained with the different imaging modalities as a result of grafted cells that have died. For example, grafted cells prelabeled with iron oxide nanoparticles that have died postgrafting may result in MRI signals representing macrophage phagocytosis of labeled cell debris. However, PET can use report gene system to avoid such disadvantage, and the high detection sensitivity of PET imaging techniques could offset nonspecific signals of MRI. Hybrid PET/MR imaging might present a formidable technical and suggest potential spinal cord applications exploiting unique properties of the combined instrumentation.The potential of stem cells to reconnect the injured spinal cord and repopulate the area of injury has fascinated SCI researchers. Although some authors believe that endogenous remyelination is effective albeit somewhat slower. The field has learned a great deal about evaluating the fate of stem cells once they are implanted into the cord. How many survive? Do they integrate and migrate? How do they influence the host microenvironment? More and more evidence suggest that the stem cells themselves may be the source of growth factors and have remarkable influence on the injured microenvironment.The interest in stem cell transplantation for SCI will remain high. This field will obviously continue to evolve, with hopes that further refinement, and understanding will increase the chances that cell transplantation will someday emerge as a fruitful treatment for patients. The complexities of attenuating the tissue damage and secondary complications due to trauma and reconstructing the cytoarchitecture of the injured spinal cord are very challenging. Hopefully, the rapid advances being made in stem cell biology will result in effective experimental and clinical trials of stem cell therapy for SCI.in vivo of cellular and molecular aspects of pathophysiological processes and therapeutic interventions. PET has high flexibility for the production of specific probes for the detection of different processes in the living subject. However, the production of PET needs advanced chemistry and tight quality control. MRI is also a contending and complementing modality in molecular imaging essential for stem cell studies. It can be used to evaluate the reparation of the injured spinal cord as well as tracing labeled stem cell in vivo. Optical imaging has a high molecularly sensitivity, but it provides lesser anatomical localization and is mainly used in small animals.Molecular imaging is a new discipline which makes it possible in vivo imaging allows the direct observation of dynamic regenerative events of individual stem cells after traumatic injury in the living subject [In summary, the usage of stem cell treatment might restore axonal continuity, connect the area for axonal regeneration, and promote axonal growth back to its distal targets. And the use of a noninvasive imaging method would have the advantage that stem cells transplanting in individual animals can be monitored longitudinally. The multimodality imaging technique allows for studying acute pathological events following a spinal cord lesion, and the development of implanted spinal chamber enables long-term imaging for chronic spinal cord preparations. Therefore,  subject . We pred