Problems with executive functioning were assessed using the Behavior Rating Inventory of Executive Function. Academic achievement was assessed using the Woodcock–Johnson Tests of Achievement or Wechsler Individual Achievement Test. Academic self-concept was assessed using the youth-report version of the Behavioral Assessment System for Children. Surprisingly, findings indicate that academic achievement is not significantly associated with problems with executive functioning or academic self-concept. However, greater problems with executive functioning are associated with decreased academic self-concept. The overall model included several covariates and accounted for 10% of the variance in academic self-concept. Findings suggest that executive skills may be essential for aligning academic achievement with classroom performance. Though various child characteristic covariates were included, the model accounted for a small amount of variance suggesting that future studies should examine contributing contextual factors.The current study evaluated a model of youth academic self-concept which incorporates practical executive functioning behaviors and academic achievement. Though greater academic achievement has been linked to both positive self-concept and better executive functioning, these constructs have not been examined simultaneously. It was hypothesized that academic achievement would mediate the association between problems with executive functioning and academic self-concept such that youth with more problems with executive functioning would have lower academic achievement and, in turn, lower academic self-concept. Clinical data was analyzed from a diagnostically heterogeneous sample of youth ( Low self-concept is associated with a number of unfavorable social and emotional outcomes. Previous research indicates that academic achievement is associated with youth self-concept. Academic achievement, in turn, is often influenced by executive dysfunction, a cognitive impairment observed in a number of pediatric populations. Despite well-established connections between these variables, little research has examined the associations between executive functioning, academic achievement, and self-concept concurrently, and no known studies have explored these relationships simultaneously in pediatric populations characterized by executive dysfunction. The examination of these constructs simultaneously may provide a foundation for research further clarifying contributing factors to the development of low self-concept and examining additional avenues for intervention.Self-concept, or the internal evaluation of one’s own strengths and weaknesses, is an important contributing factor to a wide range of important life outcomes. Low self-concept has been implicated in internalizing problems, such as depressed affect and feelings of hopelessness . There iSelf-concept is conceptualized as a multidimensional construct. Global self-concept is the culmination of interrelated dimensions, with perceived strengths and weaknesses in dimensions that are more important to the individual contributing more . In earlResearch has consistently found a positive relationship between academic achievement and self-concept, suggesting academic achievement is an important factor influencing self-concept. Specifically, self-concept has been correlated with academic achievement in a large sample of sixth graders, such that one standard deviation higher academic self-concept was associated with greater academic skill mastery equivalent to having received three extra months of academic instruction . This asResearch in children with specific learning disorders also suggests that socio-economic status (SES) may play a role in the relationship between academic skills and self-concept. For instance, a study by Smith et al. in 1997 found that children with learning disorders from higher SES homes reported lower self-concept than children from lower SES homes. As a possible explanation for this finding, the authors suggest that parents of higher SES may have greater expectations of their children’s academic performance than parents of lower SES .Unfortunately, the practice of retaining students who may not be ready to transition to new grade levels has a negative impact on students’ self-concept. Studies indicate that youth who are retained early in their academic careers exhibit lower self-concept than same grade peers years following their retention . Given tThere is also evidence that gender is an important factor to consider when assessing academic self-concept as it relates to academic skills. Previous research suggests that girls tend to attribute their academic accomplishments to external causes rather than their own competency . FurtherThough many operational definitions of executive functioning exist throughout the research literature and a prevailing definition has yet to be elucidated, the current study defines executive functions as a set of “self-directed actions needed to choose goals and to create, enact, and sustain actions toward those goals ,11,12,13Executive functioning delays and deficits are common across a wide range of pediatric clinical populations and typically associated with frontal network dysfunction. This dysfunction may occur either developmentally, such as in Attention-Deficit/Hyperactivity Disorder (ADHD) and other neurodevelopmental disorders, or may occur as the result of a neurological insult, such as a traumatic brain injury or the delivery of cancer-treating agents that affect the central nervous system ,16,17.Owing in part to its multidimensional nature, measurement of executive functioning has been approached in a variety of ways. Measurement falls into two broad categories: performance-based tests and informant ratings. Performance-based assessment of executive functioning often occurs in a one-on-one setting with fewer distractions than the typical environment. Questionnaires assessing “practical executive functioning behaviors” incorporate items capturing executive skills occurring in the context of everyday activities in a naturalistic environment. Ratings may be obtained directly from the youth in question, or from a caregiver  or teacher. Interestingly, research suggests that executive functioning correlates poorly across performance-based and rating scales such that these assessment methods may in fact be tapping into different aspects of this construct and have different utility . In theiPrevious research has consistently found significant positive associations between performance-based executive functioning and youth academic achievement . For exaHowever, far fewer studies have explored this relationship using informant reports of practical executive functioning behaviors in the context of everyday activities. Studies which have examined this association have largely focused on the children’s emotion regulation in their academic achievement. Previous research has indicated significant associations between emotion regulation in early elementary school and performance-based mathematics and literacy achievement . In middThe link between self-concept and academic achievement is well-established. As the preceding section highlights, executive functioning is positively associated with academic achievement. Thus, it stands to reason that executive functioning may also be positively associated (either directly or indirectly) with academic self-concept. At this time, only one known study has examined these variables simultaneously. Conducted by Roebers, Cimeli, Röthlisberger, and Neuenschwander , this stLogically, it stands to reason that if executive dysfunction is associated with poorer academic achievement, which is in turn associated with low academic self-concept, executive dysfunction would also be associated with lower academic self-concept. However, there is also reason to believe that poor executive functioning may be protective against low self-concept. For instance, inflated self-concept has been reported in youth diagnosed with ADHD compared to same aged-peers . One posPrevious research suggests there is a complex relationship between youth academic achievement, self-concept, and executive functioning that will be important to better understand before effective interventions can be implemented to produce desired outcomes. Despite evidence that executive dysfunction is common across a wide variety of pediatric clinical populations and research highlighting deleterious outcomes associated with poor self-concept, no studies have directly examined the relationship between these variables in youth who (1) have reached an age at which typically developing children can report their self-concept; and (2) exhibit high rates of executive dysfunction. Additionally, prior studies examining associations between executive functioning and academic achievement have primarily used performance-based measures of executive functioning, leaving the question of how measures of practical executive functioning behaviors may be related to academic achievement.The goal of the current study was to examine the associations between practical executive functioning behaviors, academic achievement, and academic self-concept in a clinical pediatric population. It was hypothesized that greater problems with executive functioning would be related to more problems with academic self-concept and that this relationship will be mediated by academic achievement.Participant data was extracted from an Institutional Review Board (IRB)-approved databank of patients referred for neuropsychological testing at a University-affiliated psychology clinic. Participants were included if they completed all of the necessary measures for the current study and were between the ages of 8 years, 0 months and 17 years, 11 months at the time of evaluation. Participants were excluded if they had received a diagnosis of Autism Spectrum Disorder (ASD), as it is currently unclear how deficits in social reciprocity may impact the development of self-concept.One hundred and twenty-two participants met the study’s inclusion criteria. The majority of participants were male (62.3%) and White (83.1%). Consistent with the population typically seen in these settings, participants exhibited a broad range of comorbid diagnoses. Thus, only primary diagnoses were included in analyses. The primary diagnosis was assigned under the supervision of the licensed assessing clinician and reflected the most impairing diagnosis assigned to the child in the context of the assessment, with the majority of participants receiving a primary diagnosis of ADHD (55%) and all participants receiving at least one diagnosis. Though the sample included a full range of SES, participants were on average middle class. Additional sample characteristics are depicted in Caregivers completed a demographic form which collected information regarding the caregiver’s relationship to the child, the child’s age, gender, race, and ethnicity, and whether there was a history of grade retentions. This form also included details about the caregiver’s educational attainment and current occupation which was used in an algorithm to calculate an index of SES as described by Hollingshead, with lower index scores reflecting higher levels of SES .Academic self-concept was assessed using the Sense of Inadequacy subscale of the Behavioral Assessment System for Children, Self-Report of Personality, Child and Adolescent versions, 2nd Edition (BASC-2), a measure which demonstrates strong psychometric properties and has been externally validated . The SenThe current study sought to identify difficulties that may relate to executive dysfunction in everyday life. Thus, the Behavioral Rating Inventory of Executive Functioning (BRIEF), a parent-report measure of youth executive functioning with strong psychometric properties, was selected . The BRIAcademic achievement was measured using core subtests from either the Woodcock–Johnson Tests of Achievement, Third Edition (WJ III)  or WechsThough data from two academic tests was used, the tasks from both academic test batteries are comparable in scope and item content. That is, both spelling subtests require participants to dictate orally presented words that increase gradually in difficulty, both mathematics subtests require participants to solve mathematical equations that increase gradually in difficulty, and both reading subtests require participants to smoothly, orally decode English words that also increase gradually in difficulty. Normative values for both tests were established using large reference groups that were representative of the United States population across a variety of variables. Additionally, test developers for both test batteries correlated these measures against each other when determining convergent validity, which were noted to be high ,33. ThusCovariates were selected a priori based on theoretical support for their relevance in associations of interest. Gender and SES were included as covariates due to literature suggesting that they may modify the relationship between academic self-concept and academic performance ,34. PrioDescriptive statistics were calculated and are reported in Analyses indicated a significant direct effect of practical executive functioning behaviors upon academic self-concept such that individuals who had more difficulty with executive functioning also had more problems with academic self-concept. However, this relationship was not significantly mediated by academic performance. In fact, academic skills were not significantly associated with problems with practical executive functioning behaviors or academic self-concept. In terms of covariates, significantly greater difficulty with academic self-concept was seen in girls. Overall, the final model accounted for 10% of the variance in academic self-concept see .Exploratory analyses were conducted to examine the moderating effect of gender on the association between difficulties with practical executive functioning behaviors and academic self-concept. However, while the association between executive dysfunction and academic self-concept was only significant in girls, the interaction between gender and problems with executive function was not significant See .The results indicate that parent-reported difficulties with practical executive functioning behaviors are significantly associated with lower youth academic self-concept. However, neither of these variables was significantly associated with academic achievement testing measures. Furthermore, the current findings did not support moderation of the association between difficulties with practical executive functioning behaviors and academic self-concept by gender.The findings suggest that difficulty with practical executive functioning behaviors may not significantly impact a young person’s ability to demonstrate academic achievement in a formal testing situation. However, there was an observed relationship between problems with executive functioning and self-perceived ability to accomplish goals and be academically successful . Additionally, the current results suggest that moderation of this association by gender is likely not strong enough to be of clinical utility.The lack of association between problems with executive functioning and academic achievement in this sample is inconsistent with previous literature, which suggested that more problems with executive functioning would be associated with lower academic achievement ,22,23,24Additionally, the specific academic subtests that were chosen for the current study were intended to assess mastery of concepts but did not require speeded performance nor integration of higher-order academic skills. Prior research in younger children suggests that this assessment of academic concepts, particularly in reading, may have tapped into a more crystallized or automatized process that did not require engagement of executive function for success . AcademiFurther, the current findings are inconsistent with prior literature suggesting a significant positive association between ratings of emotion regulation and aspects of academic achievement, such as early performance-based reading and math skills and middle school grade point average. There are several possible explanations for this difference of findings. The association between ratings of emotion regulation and grade point average was observed in a non-clinical sample, which may have impacted generalizability to samples with significant impairments . As noteOther theoretical conceptualizations of executive function may also explain differences between the current study’s findings and prior research indicating positive associations between ratings of emotion regulation and performance-based academic achievement. More specifically, it has been argued in the literature that emotion regulation, though related to executive functioning, should be considered a separate construct ,13. A coOverall, the model accounted for only 10% of the variance despite the inclusion of a number of child-specific covariates that have been previously demonstrated to correlate with academic self-concept. What this model did not include are contextual factors, such as academic environment and teacher behaviors, which have been found to play a role in academic self-concept . FurtherThis is the first known investigation into the association between academic self-concept and problems with executive functioning in a clinical sample. It is also one of few studies examining the association between practical executive functioning behaviors and academic achievement. The selected sample’s age range allows for examination of youth who have reached an age at which they likely have the capability to comment on their self-concept and their typically developing peers are rapidly acquiring executive skills. Additionally, use of assessment measures commonly utilized in clinical practice maximizes the applicability of the current findings.However, the current study is not without limitations. This study utilized a cross-sectional design. As a result, the current findings are useful for developing hypotheses for future research but do not provide evidence of a causal relationship. Thus, it is unclear to what extent the results of the current study reflect a causal or bidirectional relationship between mood and cognition. That is, participants may exhibit low self-concept associated with a depressive mood state that could also impact problems with executive functioning . Though Additionally, utilizing a parent-report measure as an indicator of youth problems with executive functioning may have falsely strengthened the identified association with academic self-concept. Parent-report measures assess parent perceptions of youth functioning. These perceptions, if conveyed to the child, may directly impact self-concept. Thus, current findings may reflect the impact that parent perception of problems with executive function has on youth self-concept rather than the association between self-concept and executive functioning itself. To circumvent this confound, studies seeking to replicate these findings may utilize alternative methods of assessing practical executive functioning behaviors, such as observational coding systems that do not require report from important adults in the youth’s life.Furthermore, as archival clinical data were utilized, this study was limited to the use of measures chosen for clinical, rather than research, purposes. Thus, academic achievement was assessed using both the WJ-III and the WIAT-III. Though the academic subtests from the two academic achievement tests used for the current study appear to be very similar, and correlations conducted for norming of the measures suggest that the two tests use the same methods to examine the same underlying constructs, it would have been ideal for academic achievement to have been assessed using a single standard measure. Additionally, inclusion of a performance-based measure of executive functioning would have strengthened this study. However, due to the varying ages and referral questions of our participants, a consistent performance-based measure of executive functioning was not utilized in their assessments and as such was not available for analysis.Should future studies address these limitations and replicate the current study’s finding that practical executive functioning behaviors are significantly associated with youth academic self-concept, further research examining other possible mediators that may be more closely related to ratings of problems with executive functioning (such as report card grades and academic achievement tasks that require more executive skills) as well as moderators would be indicated. Additionally, as executive dysfunction is a primary deficit in goal-oriented behavior, it stands to reason that functional impairments would span various contexts, affecting multiple domains of self-concept. For example, executive functioning has also been associated with peer relations . Therefo


Gut microbial communities participate in key aspects of host biology, including development, nutrient absorption, immunity and disease. During host ageing, intestinal microbes undergo dramatic changes in composition and function and can shift from commensal to pathogenic. However, whether they play a causal role in host ageing and life span has remained an open question for a long time. Recent work in model organisms has revealed for the first time that gut microbes can modulate ageing, opening new questions and opportunities to uncover novel ageing-modulating mechanisms and to design anti-ageing interventions by targeting the gut microbiota. On the other hand, ecological (species-species competitive interactions) and evolutionary (emergence of novel strains within a species) dynamics in the microbial communities of the gut could also trigger age-dependent host demise. Rather than being mutually exclusive, a combination of immunosenescence and microbiota-intrinsic population and evolutionary dynamics could lead to irreversible host dysfunctions, resulting in rapid deterioration of health and increased risk for age-related pathologies and ultimately death  significantly affect life expectancy and ageing5. Additionally, important gene variants  have been associated in humans with extreme longevity6. On the other hand, environmental interventions, such as dietary restriction, changes in nutrient sensing, stress and changes in temperature, can also modulate life span and ageing in experimental model organisms10.Biological ageing is a multi-factorial phenomenon, consisting of the loss of homeostasis at multiple scales of biological complexity, from the molecular  to the organelle, cell, tissue, organ and metabolic/system level. Both genetic and environmental factors determine ageing progression in different species. Research in laboratory model organisms has demonstrated that single gene mutations 32, showed that heterochronic gut microbiota transfer from young subjects to middle-aged individuals led to life span extension and delayed motor decline33. Turquoise killifish undergo a wide range of age-related transformations that resemble human ageing-related phenotypes, including cancer, loss of pigmentation, reduced fecundity, neurodegeneration, cognitive decline, and cellular senescence, offering a unique opportunity to study ageing in a short-lived vertebrate34. Notably, unlike invertebrate model organisms, such as worms and flies, captive killifish have a very complex gut microbial community, consisting of hundreds of bacterial taxa, similar in complexity to other vertebrates, including mammals33. Although young-derived gut microbiota can extend life span and delay ageing in this short-lived vertebrate model, several important questions still need to be answered. Is the life span modulatory role of the gut microbes amplified in short-lived species or is this a more general mechanism that applies broadly to other vertebrates, including mammals? Do gut microbes modulate host ageing in vertebrates via conserved ageing pathways or via novel mechanisms?A recent study conducted in a naturally short-lived vertebrate, the turquoise killifish 45. In gnotobiotic mice, single microbial taxa  play complementary roles in the gut and can lead to specific metabolic alterations in gut epithelial mucus production and in short-chain fatty acid synthesis and consumption, which could be importantly linked with the risk for ageing-related pathologies46. Colonising the gastrointestinal tract of laboratory mice with microbiota from wild mice, investigators were able to reduce inflammation, promoting host fitness and survival after lethal viral infections and against colitis-associated tumorigenesis47. These results raise the question of whether similar effects could be induced by maintaining a highly diverse, young-associated intestinal microbiota throughout mice ageing. A functioning inflammasome and B-cell compartment are key to shaping the gut microbiota composition, as shown in experiments conducted in mice lackingNlrp6 andRAG2, respectively45. Specifically, inflammasome and adaptive immune function were essential to shaping the microbiota in the presence of pro-inflammatory bacteria45. It is possible that, during ageing, immune function shifts towards inflammatory responses against commensal bacteria, leading to host-microbiota disbalance. Similarly, chronic inflammation is associated with a higher risk for age-associated diseases44. In the context of infection, immune tolerance for commensal bacteria indeed shifts towards inflammation, compromising this delicate host-microbiota balance48. Systemic translocation of the gut pathobiontEnterococcus gallinarum in a mouse model predisposed to autoimmunity has been causally associated with triggering of autoimmune responses, further providing a mechanistic connection between microbiota composition and host immune status49.Pioneering work in nematode worms showed that mitochondrial unfolded protein response is the target of a key microbial metabolite, colanic acid, whose production leads to extended worm longevityde novo mutations or introgression from bacteria resident in other hosts50. If this approach is extended to the study of bacteria throughout host life span, it could be possible to ask whether microbes evolve during host ageing and whether higher virulence—associated with pathogenicity in older subjects—is the consequence of the microbial evolution to evade immune surveillance.Immunosenescence may indeed lead to a failure in maintaining commensal microbiota structure and function; on the other hand, microbial-intrinsic population dynamics—which could lead to the emergence of more pathogenic bacteria—may trigger immune failure and eventually induce functional decline in the host. Longitudinal studies in human samples over a six-month period have shown that gut microbial communities are rather stable, and within-host bacterial evolution is the consequence of horizontal gene transfer among bacterial strains from the same microbiota rather than occurring fromOverall, the study of the host-microbiota dynamics throughout ageing can help reveal novel physiological and molecular mechanisms that contribute to the maintenance of homeostasis and ultimately help design powerful and personalised interventions that target the microbiota as a novel fundamental player implicated in the regulation of host ageing processes.The intimate connection between host physiology and commensal microbial function supports the implication of host-associated microbiota in the majority—if not the entirety—of biological processes of the host, including ageing. The study of the microbiota in the context of host ageing is a novel field of research and sets itself at the interface of several fields of investigation, including medical microbiology, immunology, ecology, evolutionary and population genetics, tissue and cell biology, physiology, nutrition, and metabolic research. Several confounders affect the microbiota changes occurring during human ageing, including age-dependent dietary changes, drug use, changes in mobility and housing conditions (community dwelling or elderly care facilities). Beyond descriptive connections between microbial composition and host health status, very few studies to date have dissected the causal role of the gut microbiota during ageing. To unweave the complex functional connection between host and microbiota in the context of ageing, it will be of paramount importance to study the role of not only bacteria but also archaea, viruses, fungi and microbial eukaryotes living between complex multi-cellular hosts and their environment. This holistic understanding of community dynamics can help reveal the intricate ecology of health, disease and ageing processes. To this end, it will be key to adopt novel experimental and analytical approaches to study the impact of different complex microbial communities on the host. Ultimately, by acting on microbial composition, nutrition and the immune system, it will be possible to test the efficacy of novel interventions to beneficially impact ageing and delay the onset of age-related pathologies.


Mentorship carries the potential to improve the placement, persistence, and success of those working in geriatric mental health. We sought to explore the career preferences and perceived barriers to obtaining desired jobs in the field of clinical geropsychology using an online survey of trainees and etablished professional geropsychologists. This cross-sectional observational cohort study recruited 96 respondents .Both trainees (n = 42) and professional geropsychologists (n = 54) completed an online survey. Trainees endorsed a variety of characteristics to describe their ideal jobs in geropsychology; particularly interdisciplinary teamwork and jobs in medical settings, palliative/hospice care facilities, long-term care, and geriatric outpatient care. The most commonly endorsed perceived barrier to trainees’ ideal jobs was the location of the position. Responses from professional geropsychologists elucidated factors that influenced their first job and resources that were helpful, or would have been helpful, during their job search process. The majority of respondents described the role of mentoring in career development, specifically with skill development, decision-making assistance, and personal support. Mentorship is instrumental throughout one’s training and career and offers instrumental and emotional support in job-searching and defining one’s career. Results should be considered with respect to training and retention of clinical geropsychologists given the workforce shortage, particularly in academia.


Stem cells give rise to all cells and build the tissue structures in our body, and heterogeneity and plasticity are the hallmarks of stem cells. Epigenetic modification, which is associated with niche signals, determines stem cell differentiation and somatic cell reprogramming. Stem cells play a critical role in the development of tumors and are capable of generating 3D organoids. Understanding the properties of stem cells will improve our capacity to maintain tissue homeostasis. Dissecting epigenetic regulation could be helpful for achieving efficient cell reprograming and for developing new drugs for cancer treatment. Stem cell-derived organoids open up new avenues for modeling human diseases and for regenerative medicine. Nevertheless, in addition to the achievements in stem cell research, many challenges still need to be overcome for stem cells to have versatile application in clinics. The term stem cell (SC) appears in the scientific literature as early as 1868 in a publication written by Ernst Haeckel. However, it was only in the 1960s that definitive evidence of the existence of SCs in the hematopoietic system was provided, in which Till and McCulloch described the existence of clonogenic bone marrow (BM) precursors that generate macroscopic spleen colonies after being injected into irradiated recipient mice. Based on this eminent work, the two gold standard features of SCs were proposed: an SC is capable of long-term self-renewal and multilineage differentiation . MoreoveSeveral SCs and their niches in mammalian tissues have been identified, including hematopoietic SCs (HSCs) in the BM , germlinHSCs are probably the best-characterized SC population and have been shown to give rise to both myeloid and lymphoid lineages of blood cells Fig. a. Mice hThe most frequently self-renewing tissue in mammals is probably the intestinal epithelium, which is replaced every 4–5 days. This homeostasis is maintained by the intestinal SCs (ISCs) that are retained in the bottom of crypt-like invaginations and divide every 24 h . Lgr5 waThe hair follicles provide excellent models for the study of SC biology. Hair follicles consist of a permanent bulge region and a cycling portion that cycles through anagen (growth phase), catagen (retraction phase), and telogen (resting phase). Hair follicle SCs (HFSCs) were first described as label-retaining cells (LRCs) in the bulge region. Elaine Fuchs and colleagues found that the majority of LRCs expressed the SC marker CD34 Fig. c. The soOrganoids are SCs that form 3D structures which consist of organ-specific cell types and self-organize through spatially restricted lineage commitment. Both pluripotent SCs (PSCs) and restricted adult SCs (aSCs) can initiate organoids. Organoids can start, but are not essential, from a single aSCs, while cell aggregation is typical starting material for PSC-derived organoids. As a receptor for the secreted R-spondins and Wnt target gene, Lgr5 marks active aSC in many epithelia, and Lgr5+ aSCs exhibit a high capacity to form organoids. Lgr5+ crypt SCs were first established to grow epithelial organoids in culture as ‘‘mini-guts’’ Fig. d. Organo+CD38− fractions. Thus, a CSC was identified in AML. Moreover, the xenograft assay measured the frequency of the initiating cell to be one per million (~ 1/106) tumor cells [The cancer SC (CSC) concept was born from the observation of explicit histological heterogeneity in tumors and the observation that a new tumor could initiate from a single mouse tumor cell . In the or cells . Howeveror cells , 37. Solor cells –41. Consor cells , 43  and endothelial cells contribute to HSC maintenance , 49 Figa. AlthouHFSCs maintain a quiescent state that is synchronous with the rest phase of the hair cycle and only activate in the anagen of hair follicles. At the telogen phase, dermal fibroblasts secrete BMP4, subcutaneous fat produces BMP2, and the BMPs contribute mainly to the quiescence state of HFSCs . In addiMammalian skin is covered with a stratified epidermis, and the basal epidermal layer of interfollicular epidermis (IFE) contains epidermal SCs that express keratin5 and keratin14 (K5/K14). These epidermal SCs undergo self-renewal and differentiate into nonproliferative, K1/K10 and involucrin-positive outer epidermal layers . EpidermSCs can generate organoids in conditions that mimic the SC niche of physiological SC self-renewal or tissue repair. Thus, organoids could be used as a powerful tool to dissect the niche of SCs. Early studies found that in vivo niche signals, such as Wnt/R-spondin that regulates ISCs and crypt homeostasis, are also indispensable for the in vitro maintenance of ISCs in organoid cultures –91. MoreAccumulating data suggest that the growth of at least some cancers is driven by CSCs . TumorigThe study of cellular plasticity initiated at the beginning of the new century and found that cellular identity could cross developmental germ layers and undergo extreme changes . HoweverSomatic cells within a multicellular organism are progressively committed to phenotypically and functionally distinct fates during development. Somatic cells are considered to be stably restricted in differentiated status throughout the lifespan of the organism. In the 1960s, Gurdon transferred the nuclei from highly differentiated tadpole intestinal cells into ultraviolet-light-irradiated oocytes and successfully generated normal adult frogs , 110. GuYamanaka’s induced reprogramming also highlights a new type of trans-differentiation approach known as direct reprogramming, whereby terminally differentiated cells could convert to other cell types. Transdifferentiation of pancreatic exocrine cells into insulin-producing β-cells has been described and was accomplished via forced expression of a series of transcription factors . In addiTissue regeneration in mammals is more limited than in amphibians and invertebrates. Nevertheless, recent studies found that mammalian aSCs could display remarkable plasticity and reversibility, such as SCs in hair follicles, intestines, and the lung airway. The bulge of telogen hair follicles maintains heterogeneous and hierarchical SC compartments. The SCs located at the upper and lower bulges express CD34, whereas Lgr5-expressing SCs are restricted to the lower bulge and the hair germ . During The intestinal epithelium’s rapid self-renewing and turnover tissue in mammals is fueled by daily symmetric division of SCs in crypt bottoms to produce rapidly dividing daughter cells. These cells will further differentiate into secretory cells or absorptive enterocytes . Animal In the mouse trachea, keratin 5 (K5)-expressing epithelial basal SCs are responsible for cellular replenishment. Basal cells have the potential to self-renew and give rise to Clara cells and ciliated cells during homeostasis and after injury, rendering basal SCs at the top of the cellular hierarchy in the tracheal epithelium . IntriguThe plastic transition between the epithelium and mesenchyme is called epithelial–mesenchymal transition (EMT) and is integral to normal development and cancer progression, in which epithelial cells acquire mesenchymal properties and exhibit decreased intercellular adhesion, enhanced motility and resistance to apoptosis . EMT andThus, EMT confers SC traits to carcinoma cells that are associated with high-grade self-renewal, malignancy and resistance to apoptosis, which are dangerous for cancer patients. Conclusively, EMT programs are associated with the acquisition of SC characteristics in both normal and neoplastic cells Fig. h. HoweveIn addition to cellular plasticity in homeostasis and repair, studies in cancer biology found that CSCs and non-CSCs could undergo phenotypic transitions with certain stimuli. Breast cancer cell lines consist of cell populations that display SC-, basal-, or luminal-like phenotypes. All three subpopulations were capable of generating cells of the other two phenotypes . Thus, CThe embryonic development of mammals is a tightly regulated process in which distinct cell types are generated in a highly ordered manner, and this process is established by tight transcriptional and epigenetic manipulation. Epigenetics is a stably heritable yet reversible phenotype of alteration in a chromosome without changes in the DNA sequence . DNA metEpigenetic regulation is highly dynamic during the differentiation of mouse PSCs and human PSCs (hPSCs), especially at the initial transition from the pluripotency state to a lineage-committed cell . In PSCscis-regulatory sequences that lack DNA methylation but are nucleosomal [Transcription factors tend to bind within open chromatin. However, pioneering factors can directly bind to related DNA motifs, evict nucleosomes and initiate enhancer activation, even in compact chromatin . Thus, tleosomal . The binleosomal , 177. Thleosomal .Together, these chromatin dynamics are likely crucial for the turn-off of the somatic expression program and the transition to pluripotency. The exact nature of the interactions among these coregulators is still unclear, although current studies have highlighted a number of crucial players that direct the reprogramming process. However, with manipulation of several pioneer factors, we could generate iPSCs from somatic cells.HSCs give rise to the highly specialized cell types in the mammalian blood system . AccordiHistone acetylation favors transcriptional activation by leading to the loosening of chromatin. The histone acetyltransferase cofactor TRRAP promotes HSC self-renewal, and its ablation leads to BM failure . HistoneThe cell fate of ISCs and non-SCs in the intestinal epithelium SC pool showed extensive plasticity . AccumulTet1−/− adult mice exhibit a decreased number of NPCs in the SGZ and specific impairments in extinction learning and short-term memory [Neurogenesis is the process in which NSCs or neuronal progenitor cells (NPCs) generate new neurons . In mousm memory , 211. Tem memory .Histone methylation/demethylation is precisely orchestrated to ensure expression of the correct set of genes at different neurogenic stages . During S-adenosylmethionine, which in turn promotes hypermethylation in specific retrotransposon elements and associated with transcriptional silencing [Pancreatic Cancer (PDA) is an aggressive malignancy characterized by early metastasis and a high mortality. using lineage tracing markers or by assessment of tumorigenesis in xenograft, CSCs in PDA were empirically defined , 218. Thilencing . In the SCs, which build all the structural and functional units in the human body, are promising treatments for many incurable diseases, such as hematological disorders, cardiac disease and Alzheimer’s disease. Among the SCs that present at various stages of life , aSCs exhibit great potential and are the safest for clinical application.BM transplantation is widely applied in SC-based therapy for the treatment of malignant and nonmalignant hematological disease. Edward Donnall Thomas performed the first human BM transplant in the 1950s . HSCs, dMesenchymal stem cells (MSCs) are characterized by their regenerative properties and capacity for differentiation of multiple cell lineages and hold extensive promise in cell-based therapies for various diseases. MSCs were initially identified in 1967 by Friedenstein as fibroblast-like clonogenic cells from mouse BM and named colony-forming unit-fibroblasts (CFU-F); later, these cells were referred to as MSCs . HoweverIn addition to the potential of ISCs in regenerative medicine, SCs can give rise to organ-like structures known as organoids, which hold great promise for studying normal development and disease processes and open up new avenues for medical research and drug discovery. Disease research commonly involves animal models and experiments. However, profound differences in genetics, metabolism, size and life span all contribute to the fact that most pharmaceuticals developed in animals ultimately fail in human clinical trials. Organoids provide an alternative to animal-associated research strategies and exhibit human cell metabolism and homeostasis, and organoids have already been used successfully for the establishment of personalized human cancer models and for the assessment of patient-specific therapeutic efficacies of cystic fibrosis drugs Fig. c 236, 2. TransplCSCs are characterized by their capacity to fuel tumor propagation and may contribute to tumor relapse and metastasis, and CSCs that are intrinsically or extrinsically instructed by the tumor microenvironment are more resistant to medical therapy than are ‘differentiated’ tumor cells . An incrIf CSCs fuel tumor propagation, killing CSCs, targeting CSC proliferation or forcing CSCs to differentiate are alternative and independent approaches that potentially inhibit tumor growth Fig. d. PractiApodemus sylvaticus into Mus musculus blastocysts. Notably, viable chimaeras contained a wide variety of donor cells in all major organs, including germ cells, of the host [Recent progress with various organoids has demonstrated the enormous self-organizing capacity for PSCs to form whole tissues. However, it remains particularly challenging to build real organs in vitro. Xenograft chimeras provide a possible solution for generating real organs. Typically, a chimaera is defined as an organism composed of cells that derive from more than one zygote. Based on whether cell derivatives from two zygotes are from different or the same species, chimaeras can be categorized as interspecies or intraspecies, respectively. In SC research, an interspecies chimaera is generated by transplanting SCs from the donor into an animal recipient at different stages of development . Currentthe host . Furtherthe host .Similar to chimera generation via interspecies blastocyst complementation with naive rodent PSCs, naive hPSCs have the potential to generate interspecies chimeras for studying human development and producing functional human tissue. To date, many studies have investigated the generation of hPSC-derived interspecies chimeras; however, the human–mouse chimera is rather inefficient because only a few human cells were detected in few chimeric embryos , 259. CoHeterogeneity is the hallmark of SCs in normal and early neoplastic tissues, and the hierarchy that is established among heterogeneous SCs seems to be strictly regulated by the niche environments. However, cellular plasticity renders the SC hierarchy reversable and provides an alternative cellular mechanism through which tissues can regenerate when SCs are damaged. In addition, the robust plasticity of nontargeted cancer cells observed in CRC cells challenges the strategy of CSC-targeting cancer therapy. Epigenetic modifications play a crucial role in the underlying mechanism of cellular plasticity, and relevant epigenetic patterns have been well dissected in the context of cell reprogramming and differentiation. However, a more comprehensive picture of in vivo epigenetic modification in normal and disease cells requires further investigation. Organoids open new avenues for human cancer models and are promising for drug discovery. In addition to the potential of patient-derived organoids in basic biological research and regenerative medicine, these organoids can be used as a relevant model for personalized cancer treatments. While SCs are used to generate differentiated functional cells and 3D organoids, they are also used to generate interspecies chimaeras and have carved out new paths for fundamental biology studies as well as potential applications in regenerative medicine.


Moreover, they are diverse in structure, size, and charge, and their chemical functional groups can be easily modified to match the needs of the final application and mode of administration. This review focuses on polysaccharidic nanocarriers based on chitosan and hyaluronic acid for small interfering RNA (siRNA) delivery, which are highly positively and negatively charged, respectively. The key properties, strengths, and drawbacks of each polysaccharide are discussed. In addition, their use as efficient nanodelivery systems for gene silencing applications is put into context using the most recent examples from the literature. The latest advances in this field illustrate effectively how chitosan and hyaluronic acid can be modified or associated with other molecules in order to overcome their limitations to produce optimized siRNA delivery systems with promising  Caenorhabditis elegans . Hy. Hy52]. In addition to the beneficial attributes of natural polysaccharides , hyaluronic acid also exhibits great potential for targeted drug delivery due to the presence of hyaluronic acid receptors in many tissues, such as the liver, kidneys, and most cancer tissues ,128. Forin vitro with the optimized HA:siRNA ratio [Carbohydrates typically stabilize nucleic acids through hydrogen bonds and Van der Waals interactions . In a reNA ratio .in vitro model of acute inflammatory response in human hepatocytes. For covalent crosslinking, Lee and co-workers fabricated nanogels with thiol-conjugated hyaluronic acid using an inverse emulsion method followed by crosslinking through disulfide bonds. During the emulsification process, siRNA was physically entrapped with an encapsulation efficiency of ~50% and inhibited 60% of GFP expression in HCT-116 cells [Anionic nanocarriers made solely of siRNA and hyaluronic acid can be prepared by ionic or covalent crosslinking to form nanogels. Forti and co-workers used calcium ions to ionically crosslink the negatively charged siRNA and hyaluronic acid . Their n16 cells .Nevertheless, siRNA nanocarriers based solely on hyaluronic acid are not frequently designed because hyaluronic acid’s negative charge does not favor siRNA loading. Therefore, most hyaluronic acid-based nanocarriers for siRNA delivery incorporate chemical modifications or include a cationic component, usually another polymer, to enhance siRNA loading by electrostatic interactions. The nature of the included polycation or modification deeply influence the whole system’s gene silencing efficiency.Unlike cationic polymers such as chitosan, the main shortcoming of hyaluronic acid for siRNA delivery is its low binding capacity for nucleic acids due to electrostatic repulsion, what usually gives rise to poor siRNA loading efficiencies and stability issues. However, these limitations are being surpassed thanks to research into new methods to modify hyaluronic acid or use it as a coating of siRNA–polycation complexes. When hyaluronic acid is exposed on the outer shell, it endows the nanocarrier with its natural targeting ability, which can be further modulated depending on the therapeutic objective. This property is extensively described in the In contrast to the traditional siRNA polyplexes that are obtained by electrostatic interactions, an innovative approach to load siRNA into hyaluronic acid nanocarriers was recently developed by Choi and colleagues . They deHigher siRNA loadings are usually obtained with polyelectrolyte complexes. However, the electrostatic repulsion between siRNA and hyaluronic acid, both negatively charged, prevent the formation of polyelectrolyte complexes, unless a cationic additive is present. The cationic component allows the formation of electrostatic interactions with the siRNA, which usually improves the siRNA loading of the hyaluronic acid-based nanocarrier. On the other hand, hyaluronic acid has been used in association with cationic nanocarriers to enrich them with improved properties such as biocompatibility, reduced cytotoxicity, and specific targeting ,135.PEI is clearly one of the most successful cationic polymers used in combination with hyaluronic acid. In fact, nanocarriers combining these two polymers enjoy the advantages that each polymer supplies. The presence of hyaluronic acid reduces the cytotoxicity of PEI-containing nanomaterials . At the Multimerization of siRNAs into polysiRNA through disulfide bonds originates a long siRNA double strand formed by individual siRNA molecules covalently bonded. This has been reported to be an effective strategy to increase the encapsulation efficiency into bPEI/HA polyplexes as well as their stability in the vitreous humor (the extracellular matrix in the center of the eye) to treat retinal or choroidal disorders. Once in the cytosol, where there is a high concentration of glutathione, disulfide bonds are cleaved and lengthened siRNA splits back into single molecules, which makes it easier for siRNA to interact with RISC proteins .in vitro gene silencing efficiency compared to the complex formed with non-cleavable HA−siRNA conjugate and LPEI [siRNA can also be chemically conjugated to hyaluronic acid and further complexed with a polycation. Compared with physical encapsulation, covalent conjugation provides a longer circulation time in plasma and a reduced burst release of the cargo . Howeverand LPEI .in vitro and/or in vivo conditions of the studies, and if a combination therapy strategy has been used.The association of hyaluronic acid with cationic polymers to form the nanocarriers for siRNA delivery can be mediated by electrostatic interactions or by covalent interactions. Some properties of siRNA/polycation/hyaluronic acid nanocarriers formed by electrostatic interactions are influenced by the component mixing order during their preparation ,154. siRin vivo conditions if the polycation in the core become deprotonated [in vitro and in vivo [According to the literature, the mixing order most commonly used consists of the initial formation of the siRNA/polycation complex followed by a hyaluronic acid coating ,142,143.otonated . MoreoveWhile some researchers prefer to associate hyaluronic acid to polycations by electrostatic complexation on the argument that chemical modification could disturb the functionalities of native hyaluronic acid , others in vivo results. In fact, among an extensive screening of functionalized hyaluronic acid derivatives to form self-assembling nanosystems with siRNAs, HA-PEI/HA-PEG/siRNA was found to be the ideal system that could deliver the siRNA most efficiently and showed the highest target gene knockdown in subcutaneous A549 tumours [The combination of HA-PEI with HA-PEG conjugates to form siRNA nanocarriers is giving promising  tumours .in vitro or in vivo gene silencing, such as spermine  [Apart from PEI, other polycations have also been conjugated to hyaluronic acid to form nanosized siRNA delivery systems and have shown efficient raamine)  and polyraamine) , respectThe great potential of hyaluronic acid for targeted drug delivery derives from the presence of hyaluronic acid receptors in many tissues  ,158,159.in vivo fluorescence showed that HA-PEI/siRNA nanopolyplexes significantly accumulated in the liver, while PEI/siRNA mainly accumulated in the lung. This targeted siRNA delivery into cirrhotic liver sinusoidal endothelial cells (LSECs) resulted in highly effective downregulation of COX-1 (an enzyme overexpressed in cirrhosis) and therapeutic improvement, although liver fibrosis was not reversed [Consequently, hyaluronic acid-based nanocarriers are an excellent system for the specific delivery into the liver and they have been used to treat liver-related diseases ,161. In reversed .in vivo liver uptake and increase their circulation time in the blood [Nevertheless, when the liver is not the delivery target, the preferential accumulation of these carriers in the liver, after systemic administration, could be a problem. However, this issue can be solved by the incorporation of chemical modifications to the nanocarrier, such as PEG, which can reduce the he blood ,148,163.It has been shown that the degree of hyaluronic acid chemical modifications and hyaluronic acid molecular weight are critical factors that influence biodistribution, since they affect the binding affinity between the polysaccharide and its receptors . MizrahyCD44-overexpressing cancers are exceptional targets for the selective delivery of siRNA using hyaluronic acid-based nanocarriers. A preferential accumulation of fluorescently labeled siRNA loaded into fluorescently labeled HA nanoparticles was observed by Yin and co-workers in tumour site after 24 h. Moreover, when mice were pre-administered with a dose of free HA to saturate CD44 receptors, the fluorescence signal in the tumour significantly weakened compared to that of unsaturated receptors , demonstO-gallate (EGCG), that can directly interact with the siRNA, polycation, and hyaluronic acid, avoiding the need of a hydrophobic loading microenvironment in the nanocarrier [There are several examples of siRNA and drug co-delivery using hyaluronic acid/polycation/siRNA complexes, mainly addressed to improve anticancer treatments. Conventional chemotherapy agents exhibit strong hydrophobicity. Therefore, in most cases the nanocarrier system has been modified to have a hydrophobic core where the hydrophobic drug is entrapped, either through inclusion of hydrophobic polymers as poly(lactic-co-glycolic acid) (PLGA) ,143,165 ocarrier .Although co-delivery of siRNA and drug together in the same nanocarrier may maximize their therapeutic efficacy, the sequential delivery of siRNA and drug has also demonstrated therapeutic benefits. A synergistic antitumour response in cisplatin resistant tumours was induced by the tandem delivery of siRNA loaded hyaluronic acid nanoparticles, which downregulated genes responsible for cisplatin resistance, followed by treatment with cisplatin loaded hyaluronic acid nanoparticles. Although the resistance was still not completely reversed (the inhibition of the tumour growth was increased from 30 to 60%), it may be due to the involvement of other genes in the resistance mechanism  148,149149. In asiRNA/chitosan binary complexes offer many advantages, such as high siRNA binding ability and rapid cellular internalization (further described in sections of this review related to chitosan-based nanocarriers). However, these complexes are prone to aggregation in the presence of serum proteins, are rapidly removed by the mononuclear phagocyte system, and can also induce systemic toxicity during intravenous administration ,142. On + tumor endothelial cells (by 2.1-fold) [The formation of chitosan matrices cross-linked with TPP by ionotropic gelation, inside which siRNA and hyaluronic acid molecules are condensed, has been reported. As depicted in this interesting study, using isothermal titration calorimetry, hyaluronic acid competed with siRNA for chitosan binding, lowering chitosan–siRNA binding strength by 25%. This suggests that besides improving cell biocompatibility of chitosan, hyaluronic acid might also promote siRNA release by loosening the chitosan–siRNA binding . In othe.1-fold)  and to i.1-fold) .in vitro analysis between two HA-based polyplex systems (one including poly(hexamethylene biguanide) and the other one chitosan as the cationic component) revealed that chitosan nanoparticles present the right compromise between polyplex stability and siRNA release. The stronger interactions between poly(hexamethylene biguanide) and siRNA (and HA) negatively affected the silencing efficacy of such nanoparticle, possibly due to the lower availability of the nucleic acid, although they provided a higher stability against nucleases [A comparative ucleases .in vivo. The development of siRNA delivery systems that are simultaneously safe and effective will be decisive for the successful application of siRNA-based therapies. Nanostructured delivery systems provide unique advantages, such as protection from premature degradation and improved interaction with the biological environment. They also offer the possibility to enhance tissue absorption, extend siRNA residence time, improve cellular internalization, and facilitate siRNA transport into the cytoplasm of target cells.The therapeutic success of siRNA-based formulations hinges on overcoming the many challenges involved with siRNA delivery In this review we focused on siRNA delivery systems based on two natural polysaccharides: chitosan and hyaluronic acid, which are widely studied since they are commonly considered to be highly biocompatible, biodegradable, and non-immunogenic mucoadhesive polymers. On the one hand, positively charged chitosan can interact with siRNA to form stable polyplexes. Such strong electrostatic interactions help protect the nucleic acid from degradation but may also limit its release. The main hurdles associated with the clinical use of chitosan-based delivery systems are their low stability at physiological pH, weak buffering capacity, and lack of cell specificity. However, understanding these limitations has encouraged the use of chitosan derivatives as alternative delivery systems to combat the aforementioned deficiencies. On the other hand, anionic polysaccharides, such as hyaluronic acid, often require the presence of cationic components to favor a more efficient interaction with siRNA. However, hyaluronic acid has displayed great potential for the specific delivery of siRNA to tissues such as the liver and tumours, which express its natural receptors. Furthermore, the association of siRNA with both chitosan and hyaluronic acid is an effective strategy whereby chitosan ensures a strengthened siRNA binding while hyaluronic acid provides stability, low protein adsorption, and targeting capacity.in vitro and in vivo with both biopolymers has shown their potential as siRNA delivery systems for gene silencing applications and the development of multifunctional co-delivery systems, especially those combining siRNA and chemotherapy drugs represent particularly promising synergistic anticancer treatments [The promising results obtained eatments ,142,149.


Rarres2, is a newly discovered adipokine involved in inflammation, adipogenesis, angiogenesis and energy metabolism. In humans, local and circulating levels of chemerin are positively correlated with BMI and obesity-related biomarkers. In this review, we discuss both peripheral and central roles of chemerin in regulating body metabolism. In general, chemerin is upregulated in obese and diabetic animals. Previous studies by gain or loss of function show an association of chemerin with adipogenesis, glucose homeostasis, food intake and body weight. In the brain, the hypothalamus integrates peripheral afferent signals including adipokines to regulate appetite and energy homeostasis. Chemerin increases food intake in seasonal animals by acting on hypothalamic stem cells, the tanycytes. In peripheral tissues, chemerin increases cell expansion, inflammation and angiogenesis in adipose tissue, collectively resulting in adiposity. While chemerin signalling enhances insulin secretion from pancreatic islets, contradictory results have been reported on how chemerin links to obesity and insulin resistance. Given the association of chemerin with obesity comorbidities in humans, advances in translational research targeting chemerin are expected to mitigate metabolic disorders. Together, the exciting findings gathered in the last decade clearly indicate a crucial multifaceted role for chemerin in the regulation of energy balance, making it a promising candidate for urgently needed pharmacological treatment strategies for obesity.Metabolic syndrome is a global public health problem and predisposes individuals to obesity, diabetes and cardiovascular disease. Although the underlying mechanisms remain to be elucidated, accumulating evidence has uncovered a critical role of adipokines. Chemerin, encoded by the gene  Rarres2), also known as tazarotene-induced gene 2 (TIG2), was recently identified as one of the adipokines with autocrine, paracrine and even endocrine roles in vivo (Rarres2). Retinoic acid responsiveness of chemerin was later confirmed in various tissues and cells , cerebrospinal fluid (chemerin-K158), ascites (chemerin-S157), hemofiltrate (chemerin-F154) and synovial fluid (chemerin-K158) under inflammatory conditions have been detected , extracellular signal-regulated kinases (ERK) and phosphatidylinositol 3 kinase (PI3K)-AKT pathways to regulate biological functions such as angiogenesis and inflammation  mRNA in the WAT was associated with a decrease of serum chemerin concentration. When these rats were re-fed after diet restriction, both chemerin expression in WAT and serum chemerin concentration were upregulated  mRNA is expressed in the hypothalamus  mRNA expression is increased in the hypothalamus, whereas CMKLR1 expression is simultaneously decreased in the cortex and hypothalamus  transcripts were localised in the ependymal cells and tanycytes, specialised glial cells lining the third ventricle and extending into the arcuate nucleus, hypothalamic areas closely associated with homeostatic appetite regulation. The third chemerin receptor CCRL2 was also found in the same hypothalamic loci, possibly increasing the local chemerin signal  and adipocyte number (hyperplastic obesity) . Inactivin vitro by promoting the proliferation, differentiation, capillary tube formation and migration of endothelial cells  . Beyond in vivo and in vitro studies. Given that the insulin signalling pathway is the hub to maintain glucose homeostasis by increasing the uptake of glucose into fat and muscle and reducing the production of glucose in the liver, here, we summarise the function of chemerin in regulating insulin secretion and sensitivity (Type 2 diabetes mellitus (T2DM) is a metabolic disorder featured by insulin resistance ensued by elevated blood glucose (hyperglycaemia). Increased serum chemerin that occurs with obesity is highly correlated with the development of T2DM in humans  promoter , National Natural Science Foundation of China (31771131) and Strategic Priority Research Program of the Chinese Academy of Sciences (XDA16020100) to Q F W.


This article provides an overview of neuroimaging biomarkers in experimental epileptogenesis and refractory epilepsy. Neuroimaging represents a gold standard and clinically translatable technique to identify neuropathological changes in epileptogenesis and longitudinally monitor its progression after a precipitating injury. Neuroimaging studies, along with molecular studies from animal models, have greatly improved our understanding of the neuropathology of epilepsy, such as the hallmark hippocampus sclerosis. Animal models are effective for differentiating the different stages of epileptogenesis. Neuroimaging in experimental epilepsy provides unique information about anatomic, functional, and metabolic alterations linked to epileptogenesis. Recently, several in vivo biomarkers for epileptogenesis have been investigated for characterizing neuronal loss, inflammation, blood-brain barrier alterations, changes in neurotransmitter density, neurovascular coupling, cerebral blood flow and volume, network connectivity, and metabolic activity in the brain. Magnetic resonance imaging (MRI) is a sensitive method for detecting structural and functional changes in the brain, especially to identify region-specific neuronal damage patterns in epilepsy. Positron emission tomography (PET) and single-photon emission computerized tomography are helpful to elucidate key functional alterations, especially in areas of brain metabolism and molecular patterns, and can help monitor pathology of epileptic disorders. Multimodal procedures such as PET-MRI integrated systems are desired for refractory epilepsy. Validated biomarkers are warranted for early identification of people at risk for epilepsy and monitoring of the progression of medical interventions. Epilepsy is the most complex brain disorder characterized by spontaneous recurrent seizures, which are abnormal electrical discharges in the brain. Epilepsy affects 1.2% of the U.S. population and about 40% exhibits intractable seizures that do not respond to antiepileptic drugs. However, there currently is no treatment available that prevents epilepsy following an epileptogenic insult by genetic or acquired conditions. Epileptogenesis is a complex process through which a normal brain is converted into a brain debilitated by recurrent seizure activity. This process ensues after several plastic changes occur in the brain . Latent There are over two dozen antiepileptic drugs (AEDs) for the treatment for epileptic seizures. However, approximately 40% of patients with epilepsy have intractable seizures that are pharmacoresistant to currently available AEDs . MoreoveCuring epilepsy is identified as the top priority in the National Institutes of Health Benchmarks for Epilepsy Research. Many research efforts, therefore, are focused on investigating the pathophysiologic mechanisms underlying epileptogenesis. There are crucial gaps in knowledge of the neural network pathways that are responsible for the spatial and temporal events underlying the development of epilepsy . To addrExperimental neuroimaging systems are valuable to characterize early biomarkers in epilepsy. Animal models are also effective for characterizing the different stages of epileptogenesis, providing information about processes that cannot be studied in patients. Imaging biomarkers in preclinical models of epilepsy have tremendous value for non-invasive examination of structural, functional, and molecular changes in the brain. Several established neuroimaging modalities have aided in preclinical efforts for screening novel therapeutic interventions for epilepsy. Over the past decade, many biomarkers for epileptogenesis have been tested in characterizing neuronal cell loss (neurodegeneration), neuroinflammation, blood-brain barrier (BBB) alterations, changes in neurotransmitter density, neurovascular coupling, cerebral blood flow (CBF) and volume (CBV), network connectivity, and neuronal metabolic activity in the brain .Imaging of epileptogenic biomarkers with magnetic resonance (MR), positron emission tomography (PET), and single photon emission computer tomography (SPECT) has significantly contributed to our understanding of the pathophysiological mechanisms that underlie the development of epilepsy . PreclinIn this article, we describe various neuroimaging biomarkers in experimental epileptogenesis and refractory epilepsy. We highlight embracing these neuroimaging modalities as experimental biomarkers for in vivo monitoring of neuropathology and guide therapeutic response of interventions for modifying the development of epilepsy.An epilepsy biomarker is defined as an objectively measured characteristic of a normal or pathologic epileptogenic process ,14. IdenMRI is a widely used in vivo imaging modality for detecting structural and functional changes in the brain. MRI is primarily used to measure microstructural and functional changes in the brain at the network level. MRI is also effective in assessing hemodynamics with high spatial resolution ,18. By gNo radioactive material is required for MRI, making it a non-invasive imaging modality. The results from MRI have high translational value because the same imaging approaches can be used in both animal models and patients. In this report, we describe various MRI techniques and sequences, and their applications in various animal models of epilepsy. We provide a detailed review of the preclinical studies utilizing MRI imaging and their major findings. In the subsequent sections, the structural and functional alterations that can be imaged using MRI are summarized. These include pathophysiologic changes such as edema, microhemorrhages, CBF and CBV alterations, mossy fiber sprouting, BBB impairment, cell swelling, neurovascular coupling, and metabolic changes.Anatomical imaging with MRI is most commonly achieved by unique relaxation times (T1 and T2) which characterize various tissues and pathologies. Anatomic imaging is the basic form of MRI that is part of almost all imaging modalities with this technique. Achieving T1 or T2 relaxation times can be done by adjusting timing parameters in MRI pulse sequence generation. T1-weighting is typically used in human imaging to assess anatomical detail, whereas T2-weighting is primarily used in looking at pathological lesions.T1 and T2 relaxation times are largely based on the relaxation time of water in different tissue types. Tissue substances with the highest amount of water have longer relaxation time. For example, cerebral spinal fluid (CSF), which has a high water content, has a long relaxation time. Relaxation-based MRI contrast is particularly useful for imaging pathologic alterations such as edema, BBB impairment and microhemorrhage in animal models of epilepsy .In status epilepticus (SE) models, T1- and T2-weighted MRI relaxation times increased after the onset of SE and peaked at 24 h ,27. OnceIn epileptogenic models of stroke and TBI, pathological changes such as acute edema, reabsorption, and atrophy can be observed in a time-course fashion . HemorrhAs demonstrated by the studies summarized above, T2-weighted MRI represents a highly sensitive technique to characterize edema, microhemorrhages, lesion extent, and microstructural atrophy in animal models of epilepsy. However, there has been limited MRI study of neuronal injury progression in rodents, especially after organophosphate intoxication models . We inveContrast-enhanced MRI with gadolinium is utilized in epilepsy models to measure alterations in CBF, CBV, and BBB integrity . CBF andIn SE models, hemodynamic imaging shows increased CBF and CBV in the amygdala, characteristic of vascular reorganization following SE . These fDamage to the BBB resulting from epileptogenesis can be assessed on T1-weighted MRI after gadolinium injection. In kainic acid (KA)-induced SE, BBB damage in specific brain regions was reported for up to 6 weeks post-SE . SimilarThe findings described above demonstrate the multiple applications of contrast-enhanced MRI in animal models of epilepsy. They also expand on the role of hemodynamic changes and BBB impairment as potential biomarkers for epilepsy. These studies also demonstrate the potential of contrast-enhanced MRI for further characterization of the latent phase of epileptogenesis.Other less commonly used contrast agents such as iron oxide and manganese have also been used in MRI animal epileptic studies. Iron oxides are considered negative contrast agents because their superparamagnetic property shortens T2 relaxation times and darkens affected tissue . Studies2+), which shortens T1 relaxation times [2+ has the same radius and charge as calcium (Ca2+) and thus acts as a Ca2+ analog in the brain, entering cells through Ca2+ channels and transporters and binding to Ca2+ binding sites [Manganese-enhanced MRI (MEMRI) is based upon the paramagnetic property of manganese  permeability. In functional MEMRI studies, Mn2+ permeability is increased by co-administration of mannitol. The MEMRI approach has been well-reported in animal models of epilepsy demonstrating mossy fiber sprouting and BBB leakage [Several factors influence the rate of Mn leakage ,49,50,51A major drawback is that toxicity of manganese results in long-term structural and functional consequences. Furthermore, long-term exposure to manganese following systemic administration can lead to manganism, a neurodegenerative condition similar to Parkinson’s disease. This significantly limits its translation potential from animal models and restricts its clinical application . NonetheWater diffusion is restricted by cellular membranes and myelin sheaths in a normal brain. Altered water diffusion is observed in pathologic processes that underlie epilepsy such as cytotoxic edema and cell swelling .Apparent diffusion coefficient (ADC) is the most commonly used parameter in diffusion MRI. Following brain insults that precede epileptogenesis, the ADC is reported to decrease in the first hours after insult. This initial and rapid diffusion drop down to about 60–80% of normal has been observed in both SE and focal lesion models of stroke and TBI . CytotoxDiffusion tensor imaging (DTI) can be used to assess differences in white matter following chronic epilepsy . DTI canThese studies demonstrate that cytotoxic edema, cell swelling, and microstructural changes all occur early in the epileptic brain, marking them as possible biomarkers in the development of epilepsy development. More studies will help elucidate whether these changes are specific to epileptogenesis or are secondary artifacts from the initial precipitating event.Functional MRI (fMRI) measures hemodynamic changes in the blood oxygen level in different parts of the brain by means of blood oxygen level-dependent (BOLD) sequences, thus attempting to indirectly measure neuronal activity . fMRI wiIn LFPI models, fMRI revealed decreased connectivity between the ipsilateral and contralateral parietal cortex. A decrease in connectivity was also seen between the parietal cortex and hippocampus on the same side as the injury . Further+) MRS can be used for detection of high water and fat signal associated with epileptogenesis or epilepsy in several animal models (N-acetyl aspartate (NAA) can be detected in SE models as a marker of the chronic phase of the disease [Magnetic resonance spectroscopy (MRS) can be used to analyze different metabolites in the brain tissue. Proton  in PET imaging. Alterations in glucose metabolism is an important feature underlying epilepsy and has several applications to neuronal death and dysfunction  have also proven effective in imaging BBB impairment in animal models of epilepsy. One study demonstrated that PET, SPECT, and MRI are all equally capable of sensitively detecting BBB disturbances in epileptogenesis. The study found that increased BBB permeability occurs 48 h post-SE predominantly in brain regions associated with epileptogenesis such as the hippocampus, piriform cortex, thalamus, and amygdala . These rEpilepsy is a challenging disease to study because patients diagnosed with epilepsy present symptoms long after the pathologic process of epileptogenesis has ensued . In vivoNonetheless, in vivo imaging studies can be a reliable tool in various epilepsy research designs, especially for evaluating the effectiveness of AEDs in preclinical models. These imaging studies are valuable because of their high translational potential. Due to the non-invasive nature of these techniques, human testing faces fewer ethical and organizational obstacles. The broad spectrum of imaging modalities discussed in this review such as MRI, PET, and SPECT all represent highly specific and precise approaches for assessing and quantifying a host of underlying pathological changes in epileptogenesis. The ideal standard for determining in vivo imaging biomarkers is to combine imaging data with video-EEG monitoring. This concurrent analysis provides better correlation between the behavioral patterns of epileptogenesis and the anatomical and functional alterations observed through in vivo imaging.Although MRI is a sensitive method for obtaining information about structural and functional changes in the brain, future development of microstructural contrasts can improve specificity . This isOverall, considering the latent nature of epileptogenesis, reliable, non-invasive, and clinically-translational models of epilepsy are necessary to study the pathophysiological changes throughout the process. While most studies discussed in this review used common animal models of epilepsy such as pilocarpine or KA-induced SE, kindling-induced seizures, or LFPI model of TBI, in vivo imaging techniques can be applied to a host of other relevant epilepsy models. There are many areas of need for biomarkers including identification of people at risk for epilepsy and reversing its progression with therapeutic interventions. A pressing area of need for biomarkers is to identify patients with refractory or pharmacoresistant seizures. Further discoveries in imaging biomarkers will undoubtedly allow for better characterization of the epileptogenic process and offer valuable insight into preventing or reversing the course of epilepsy.


Decision-making impairments reflect tendencies towards risky or unwise choices as manifested by presence of psychiatric symptoms or cognitive impairment . Such impairments are suggested by the hallmark symptoms of substance and behavioral addictions, which include escalation over time (of substance intake or a given behavior), lack of control, neglect of other domains of life, and cognitive distortions (such as ‘chasing losses’ in gambling disorder). Amongst the putative behavioral addictions, most epidemiological data exist for gambling disorder, which is now included in DSM-5 as a substance-related and addictive disorder. However, other disorders share parallels and may also constitute behavioral addictions, such as compulsive stealing (kleptomania), compulsive shopping, and compulsive sexual behavior. The current paper presents a narrative review of evidence for cognitive decision-making impairments in addictions, as well as pharmacological treatments of these disorders that may have relevance for improving decision-making. We find that objective decision-making deficits have been widely reported in patients with substance use disorders and gambling disorder, compared to controls. Decision-making in the other behavioral addictions is under-studied. Evidence-based pharmacological treatments for some of these addictive disorders, for example, opioid antagonists and glutamatergic agents, modulate neural systems playing key roles in decision-making. But clinical trials have seldom examined effects of such treatments on objective decision-making measures. Future research directions are discussed, including the need to include standardized outcome measures of decision-making (tasks and imaging) alongside traditional clinical measures, to better understand and enhance underlying treatment mechanisms. Decision-making impairment can be defined, operationally, as a tendency towards risky or unwise choices as manifested by presence of psychiatric symptoms or cognitive impairment. Decision-making from a cognitive perspective is not a unitary domain but rather encompasses a number of relevant processes, including representation of value, inhibitory control, response selection, and learning  that substance and behavioral addictions, as defined as above, are characterized by objective decision-making deficits on cognitive tasks dependent on fronto-striatal circuitry, and (ii) that pharmacological treatments with efficacy in these disorders may act partly via modulation of fronto-striatal circuitry and neurochemical systems crucially involved in decision-making.Literature searches were conducted in PubMed for data papers and meta-analyses addressing (i) cognitive findings in substance use disorders and behavioral addictions compared to controls (scope of disorders defined per the introduction), (ii) pharmacological treatment studies in substance use disorders and behavioral addictions. Due to the thematic breadth of the paper and variability in the decision-making measures utilized across the literature, we opted pragmatically for a narrative selective review rather than a systematic review or meta-analysis.N = 500) compared to controls, with medium effect size , a total of 64 data papers were identified  versus controls, with large effect size (d = 1.034). Interestingly this impairment was statistically larger than that found in the alcohol use disorder literature. There was no evidence for publication bias based on funnel plots, but there was high heterogeneity. In the meta-analysis of MacKillop and colleagues  and Set-Shifting task performance . Here, we focus on treatment data for alcohol use disorder as an example, which is common and often treated in clinical practice, and for which a fair body of controlled trial data exist. Some data exist for the use of various medications in alcohol use disorder , which are discussed in excellent reviews elsewhere , opioid antagonists, glutamatergic agents, and the anti-dopaminergic medication olanzapine. One trial used the SRI sertraline, and found ~70% treatment response irrespective of whether patients received active treatment or placebo, that is, this was a robust negative result , showed significant symptomatic benefit over placebo for gambling disorder in two trials  is an amino acid prodrug that dampens glutamatergic transmission in preclinical models of addiction  after initial treatment with open-label escitalopram. Relapse rates did not differ significantly between the treatment arms indicating that escitalopram did not differentiate from placebo  in some cases of Parkinson’s Disease , acute methylphenidate led to more conservative decision-making on the Cambridge Gambling Task, compared to placebo  into intermediate biological markers  in compulsive shopping and kleptomania (Grant et al., It is seen from this selective overview of the existing addiction literature that while pharmacological treatments exist for the symptomatic treatment of addictions linked with decision-making impairments, it is not yet clearly established that objective improvements in decision-making on laboratory-based tasks are directly linked with symptomatic improvement. Because cognitive impairments germane to decision-making appear common in addictive disorders, it would be valuable for future clinical trials to include such measures alongside the more traditional symptom outcome measures (Goodie & Fortune,