Epigenetic mechanisms are implicated in the processes through which social stressors erode health in humans and other animals. Here I review progress in elucidating the biological pathways underlying the social gradient in health, with particular emphasis on how behavioral stresses influence epigenomic variation linked to health. The evidence that epigenetic changes are involved in embedding of social status-linked chronic stress is reviewed in the context of current knowledge about behavior within animal dominance hierarchies and the impacts of social position on behaviors that affect health. The roles of epigenetic mechanisms in responses to trauma and the evidence for their involvement in intergenerational transmission of the biological impacts of traumatic stress are also considered. Taken together, the emerging insights have important implications for development of strategies to improve societal health and well-being. Psychosocial stress involves neurophysiological changes resulting from the anticipation or perception of challenges to well-being that are located within the social environment. Recent research to understand the sources and impacts of psychosocial stress reveals that epigenetic mechanisms are an important interface through which the body interprets and responds to stressful experiences. Psychosocial stressors with epigenetic impacts are encountered in a variety of different circumstances and over a wide range of timescales, ranging from the early-life adversity caused by deficiencies of parental care during infancy and childhood, to the long-term, chronic stress of socio-economic deprivation and the intense traumas of warfare, famine and genocide. The adaptive physiological response to an acute and temporary exposure to a stressor is known as allostasis, which mitigates the impacts of the stressor and restores physiological equilibrium once the exposure to stressor has subsided . EffectiThe specific focus of this review is on the growing body of research into how behavioral stressors affect health across the life course and elicit long-term changes to the epigenome. The insights emerging from these studies are helping to explain how important aspects of the social become biological, and raise questions that have significant policy implications for improving public health and promoting social justice. For health inequalities that have socioeconomic causes, how might this new knowledge be harnessed to monitor and mitigate health risks? Moreover, if avoidable environmental exposures in one generation have the potential to influence the health, capabilities and life chances of the next, how should the freedoms and responsibilities of the present generation be balanced against the rights of future generations to live healthy lives? Improved understanding of the roles of epigenetic mechanisms in biological embedding of psychosocial stress will help to address these questions, and could enable the development of interventions to reduce or reverse the impacts of social stressors on health.Nr3c1 gene, encoding the glucocorticoid receptor (GR), in the hippocampus, along with increased methylation of CpG dinucleotides in the Nr3c1 promoter, and correspondingly high levels of hypothalamo–pituitary–adrenal (HPA) axis activity and serum glucocorticoids [A wide range of animal models of early-life adversity have been established in multiple species, revealing a consistent and enduring impact of pre- and post-natal stress, as well as reduced maternal care, on offspring development and behavior, including risk of psychopathology . Classicrticoids . Experimrticoids . Deprivirticoids .Bdnf locus, in the amygdala, hippocampus and medial prefrontal cortex of exposed offspring, both during adolescence and adulthood [Avp and Pomc and reduced DNA methylation at these loci [Nr3c1 in the paraventricular nucleus, and rendered Crh transcription refractory to adult chronic stress experienced after early-life stress [Crh in the hypothalamus to later chronic stressors, possibly via a GR-dependent mechanism.In rodents, the principal neural substrates targeted for epigenetic modification by the early-life stresses caused by reduced maternal care are the amygdala, HPA axis, hippocampus and medial prefrontal cortex . Maltreadulthood . In the ese loci ,24. Earle stress , indicatBdnf and increased DNA methylation of Bdnf promoter sequences in the hippocampus, as well as by increased expression of Crhr1 in the amygdala [The long-term impacts of prenatal maternal stress on offspring behavior and neural gene expression were illustrated further by a study examining the effects on adult offspring of prenatal exposure to predator odor during fetal gestation . Odor avamygdala . These aNR3C1 methylation changes in response to early-life adversity, parental stress and psychopathology, of which 27 were studies in humans [NR3C1 sequences are implicated as regulatory targets in these articles, the most consistent observation is a closely correlated increase in methylation at exon 1F in the human NR3C1 gene  and experience of early-life adversity. Exon 1F/17 contains a DNA sequence element that encodes a methylation-sensitive binding site for the neural activity-regulated transcription activator NGF1A/EGR1 [NR3C1 that is caused by increased methylation of this binding site thus diminishes the means of providing glucocorticoid-mediated negative feedback to the hypothalamus and pituitary, leading to the persistent activation of the HPA axis, and the resulting disorders. A range of experiences highly likely to induce prenatal stress, such as intimate partner violence [NR3C1 promoter methylation. Moreover, childhood abuse, neglect and deprivation were also found to be associated with increased NR3C1 promoter methylation [NR3C1 [NR3C1 expression is a component of the process leading to elevation of HPA axis activity, as a consequence of allostatic overload induced by a variety of stressful experiences. Despite such insights, it remains unclear how NR3C1 is specifically targeted for epigenetic silencing, and whether methylation of the NGF1A/EGR1 binding site, which prevents NGF1A/EGR1 recruitment to NR3C1 [NR3C1 expression in the brain. Noncoding RNAs such as the lncRNA GAS5 have been implicated as inhibitors of NR3C1 protein function [NR3C1 transcripts [MAOA, CRH, CRHBP, FKBP5, LGI1/LGI2, MORC1, BDNF, SLC6A4, KITLG, PM20D1 and SLC17A3 [NR3C1, together with a better understanding of how these genes are regulated, will help to reveal how experiences of prenatal stress, childhood maltreatment and deprivation of parental care become biologically embedded and exert long-term impacts that persist across the life course. Moreover, in-depth analysis of these processes could elucidate the biological basis of stress resilience and provide an evidence base with which to develop effective interventions.Research in humans has confirmed and extended the findings of animal experiments on the effects of early-life stress . Overalln humans . While sF1A/EGR1 . The redviolence , or mateviolence  were asshylation ,32–34. Mn [NR3C1 ,35–39. Tto NR3C1 , is accofunction ,41, and nscripts ,43. Howe SLC17A3 . FurtherStudies of early-life adversity have provided insights into the relationships between specific forms of social stress, their impacts on fetal and juvenile development and their long-term consequences for health and well-being. However, social adversity may be encountered at other stages of life, and indeed throughout the life course, as chronic exposure to a range of distinct behavioral stressors. Identifying the sources of social behavioral stress and determining their impacts on health requires a sound understanding of the costs and benefits of living in social groups, which is beginning to emerge through experimental studies with a wide range of group-living animals. Social behaviors between conspecifics provide many benefits that improve individual fitness, such as opportunities for co-operation and reciprocal interactions that facilitate divisions of labor and sharing of limited resources. Reciprocity and co-operation are nevertheless tempered by conflicts of interest over access to resources. Such conflicts can be resolved through competitive interactions to test individual capabilities, leading to the establishment of communities of conspecifics known as dominance hierarchies . DominanWhile dominance and subordinacy within a social group can be maintained as a stable equilibrium, primarily through reinforcement by dominant individuals, individual status can also reappraised, challenged and reassigned. Thus, in nonhuman primates such as baboons, chimpanzees, macaques and squirrel monkeys, social status is a relatively plastic phenotype, and maintaining position requires physical and/or political capabilities to resist challenge . In thesAlthough the behavioral and physiological consequences of subordinacy can be mitigated by affiliative interactions with kin and other subordinates ,55, the PTGS2, ILR8B and NFATC1 [Like baboons, rhesus macaques live in multifamily groups, and females typically adopt a dominance rank below that of their mothers . Female d NFATC1 . Moreoved NFATC1 . Studiesd NFATC1 . Moreoved NFATC1 . Interesd NFATC1 . The lind NFATC1 ,71.Astatotilapia burtoni can infer social rank by observing social interactions between conspecifics [GnRH1-expressing neurons within the hypothalamus, which act on pituitary gonadotrope cells, causing them to release leuteinising hormone (LH) and follicle-stimulating hormone (FSH) into the bloodstream, thus affecting reproductive physiology and behavior [GnRH1, LH and FSH transcription were accompanied by attenuation of CRF and CRFR expression in the hypothalamus and pituitary [egr-1 and c-fos immediate early gene transcription at multiple sites within the brain, and appreciable increases in FSH, glucocorticoid and androgen receptor expression in the testis [c-fos and egr-1 within the SBN, but this pattern of changes was quite distinct to that elicited by social ascent [A. burtoni subordinate males before exposing them to a control subordinate in a dominance contest. Administration of the DNA methylation inhibitor zebularine by injection increased the likelihood of the injected fish remaining as a subordinate from 50 to 82%, whereas injection of the DNA methylation enhancer l-methionine increased the likelihood of the injected fish becoming dominant from 50 to 83% [GnRH gene, in genomic DNA samples extracted from the preoptic area of the brain of control and zebularine-injected subordinate fish, revealed that zebularine treatment actually increased methylation of sequences associated with the GnRH gene, consistent with increased inhibition of both GnRH transcription and ascent to dominant status [GnRH regulatory elements, and so promotes transcriptional repression of this gene.The biological impacts of social position within dominance hierarchies on behavior and physiology have been elucidated further by studies of group-living teleost fish such as cichlids and zebrafish. Males of the cichlid fish species pecifics  and theypecifics . Social behavior . Increasituitary . Large ie testis ,77. The e testis , which il ascent . Thus, t0 to 83% . The molt status . These rDanio rerio, provide further evidence for a social status-driven, neural transcriptional response that underlies behavioral adaptations to social encounters [cfos and egr1, as well as additional genes such as npas4a, btg2 and nr4a1 [A. burtoni, a number of the observed gene transcription changes occurred in both dominant and subordinate fish [Experiments with another social teleost, the zebrafish counters ,82. Zebrcounters . Subordicounters . When pand nr4a1 ,82. Thesnd nr4a1 . As was ate fish ,87. Thusate fish  may be pA characteristic feature of unequal societies is that chronic health and social problems are more prevalent in neighborhoods and communities with lower socio-economic status (SES) ,92. The Income inequalities can be viewed as sensitive, quantitative indicators of relative position within a broader social status hierarchy that reflects differences in access to a variety of forms of social, educational and cultural capital, in addition to economic capital . It has The pervasive experiences of status competitions, through which rank is determined and monitored by the self and others, have been identified as potent sources of chronic behavioral stress and allostatic load, causing hypercortisolemia and increased levels of inflammatory biomarkers in blood ,102–103.An emerging literature identifies social networks as important health protective factors , and supcis-regulatory elements, intergenic regions and/or repetitive DNA sequences, remains to be elucidated. Recent reports have confirmed that genes whose transcription is involved in inflammatory and neuroendocrine responses to low SES also exhibit SES-responsive epigenetic changes [Long-term exposures to the social stressors associated with low SES across the life course are known to affect chronic disease risk, through their impacts on a wide range of physiological mechanisms involving the nervous, cardiovascular, hemopoietic and endocrine systems. The majority of published studies of the impacts of SES on the epigenome have reported altered patterns of DNA methylation in samples extracted from readily available tissues such as whole blood, fractionated white blood cells or buccal swabs. Several studies have shown that SES is associated with variation in genomic DNA methylation patterns . In one  changes ,126, whiSLC6A4 serotonin transporter gene promoter, elevated amygdala function and symptoms of depression [SLC6A4 was previously shown to be independently associated with child abuse [SLC6A4 at age 13–18 years, which was predictive of increased amygdala reactivity to a fearful stimulus (detected by fMRI) over the same period, and which in turn was associated with increased risk of depression at age 14–19 years for adolescents with a positive family history of depression. These results thus suggest a plausible biological pathway through which low SES, by methylation of SLC6A4, could attenuate expression of the serotonin transporter encoded by this gene, leading to increases in both amygdala reactivity and risk of depression. Moreover, these findings identify potential biomarkers for developing and evaluating preventive or treatment-based interventions that could buffer the impacts of low SES on lifetime risk of depression.Mental health problems such as depression, anxiety and addiction are worse in more unequal societies ,92, and pression . Differeld abuse , low SESld abuse , stress-ld abuse  and incrld abuse . Moreoveld abuse ,134. Theld abuse . Using sNR3C1 gene promoter, which facilitates GR-mediated feedback inhibition. A similar effect of maternal stroking of newborn offspring, on methylation of NR3C1 promoter sequences, has recently been confirmed in studies of human new mother–child pairs [As mentioned previously, the impacts of psychosocial adversity caused by low SES can be buffered by behavioral adaptations. Low maternal stress during fetal gestation and abundant parental support after birth are potent sources of protection against short- and long-term psychosocial stress in humans and other animals, by limiting HPA axis activity and stimulating oxytocin effector pathways . Animal ld pairs .Social interventions that increase levels of parental support during childhood and adolescence further buffer offspring against the long-term adverse impacts of low SES, reducing transcription of pro-inflammatory genes in blood cells as well as circulating levels of inflammatory biomarkers ,119. ChaNR3C1 hypermethylation in postmortem brain samples of suicide completers with a history of child abuse [NR3C1 promoter elements was found to be associated with increased risk for PTSD in survivors of the Rwandan genocide [NR3C1 promoter 1F regulatory element and reduced HPA axis activity [NR3C1 is a common target for epigenetic changes in response to these different types of trauma, the distinct differences in the patterns of NR3C1 methylation may reflect differences in the timings and periods of exposure to trauma as well as qualitative differences in the nature and context of the traumatic experiences themselves. Recent studies of epigenetic changes in combat veterans with severe PTSD have identified traumatic stress- and PTSD-associated variation in DNA methylation at the SKA2 locus [SKA2 encodes a protein that likely functions as a chaperone or regulator of GR activity, enabling cortisol-dependent GR-mediated negative feedback to the HPA axis. SKA2 was identified as a hypermethylated, underexpressed locus in postmortem cortical tissue of suicide completers, and variation in SKA methylation was also associated with suicidal behaviors in people with PTSD [SKA2 in the regulation of responses to traumatic stress, it currently remains unclear as to whether these changes are related in the different psychopathological behaviors under investigation.The intense stress resulting from exposure to traumatic experiences such as war, famine or genocide, increases the risk of mental health disorders, including post-traumatic stress disorder (PTSD), depression, schizophrenia and suicide. Trauma can exert long-term psychosocial and epigenetic impacts when experienced during early life, as was first demonstrated by the specific association between ld abuse ,32. In cgenocide , and in genocide ,39. US cactivity . Thus, wA2 locus ,150. SKAith PTSD ,152. WhiNR3C1 promoter elements [Research on the impacts of PTSD experienced by Holocaust survivors on their offspring implicates altered HPA axis activity, and more specifically dysregulation of the GR and its auxiliary factors, in intergenerational epigenetic responses to trauma . Offsprielements  and in aelements . These rNr3c1, which exhibited decreased promoter methylation and increased transcription in the hippocampi of the progeny of MSUS-treated mice. In addition, sperm from traumatized males contained trauma-induced miRNAs, and microinjection of purified RNA extracted from the sperm of these traumatized adult males recapitulated aspects of MSUS-induced behavioral abnormalities, indicating roles for these short noncoding RNAs in the intergenerational transmission of trauma-induced phenotypes [Nr3c1 methylation and decreased transcription of this gene in the hippocampus [Further evidence of intergenerational transmission of behaviors that are epigenetically mediated has emerged from experimental studies with rodents subjected to handling stress and deprived of maternal care. The Maternal Separation combined with Unpredictable Stress (MSUS) paradigm has demonstrated that postnatal trauma caused by reduced quality and quantity of maternal care causes mice to develop into adulthood with elevated depressive behaviors and reduced behavioral control in response to stressful stimuli, phenotypes which can be transmitted to two subsequent generations without further exposure of newborn pups to reduced maternal care . Reducedenotypes . Interespocampus . In a repocampus . Moreovepocampus . Taken tAn extensive literature documents the pervasive impacts of social stressors on health and wellbeing. Emerging evidence indicates that epigenetic processes are involved in the biological embedding of psychosocial signals within the body, affecting physiological functions that can influence health risks across the life course. Many vertebrates, including humans, non-human primates and teleost fish, exhibit social behaviours that reflect similar operating principles of hierarchical dominance, and engender stress responses that are accompanied by impacts on the epigenome. Social inequalities within hierarchies can function as chronic behavioural stressors and restrict access to resources, giving rise in humans to a social gradient in health and life expectancy. A wide range of behavioural stressors, including traumatic experiences, elicit epigenetic changes that show promise as biomarkers of disease risk, which might potentially be reversed by interventions to reduce the health impacts of adversity.This review documents the development of a growing area of research to identify epigenetic variants that are associated with social stressors, examples of which are summarized in Nr3c1, Avp, Bdnf loci in offspring CNS, while increasing anxiety, depressive symptoms and stress reactivity.Low levels of postnatal maternal care in a range of experimental animal species increase DNA methylation and attenuate transcription at Exposure of human offspring to distinct forms of social adversity during fetal gestation, infancy and childhood can induce behavioral, psychological and DNA methylation changes.Many vertebrates, including primates, rodents and fish, live within dominance hierarchies of conspecifics.Social position within a dominance hierarchy influences allostatic load, high levels of which can engender chronic stress.Low-ranking individuals within primate social hierarchies exhibit hypercortisolemia, rank-associated differential DNA methylation patterns and increased risks of chronic diseases.Social position within fish social hierarchies is linked to variation in HPA axis activity, levels of inflammatory biomarkers and expression of immediate early genes in a network of evolutionarily conserved brain nuclei.Risks of chronic illness and reduced life expectancy are greater in human communities with lower socioeconomic status.Perception of social rank develops early in humans and competitive interactions for access to resources are psychosocial stressors that can engender status anxiety.Low socio-economic status is associated with increased allostatic load, elevated inflammatory biomarkers and altered patterns of DNA methylation, which can be buffered by targeted social interventions.Variation in socioeconomic status has been linked to variation in patterns of blood cell DNA methylation in several cohort studies.SLC6A4 may provide a mechanistic link between low socio-economic status (SES), elevated amygdala function and depression.Differential methylation of Interventions that improve levels of parental support during childhood improve health in low SES communities and are accompanied by specific changes in patterns of DNA methylation in blood cells.Higher levels of cumulative lifetime stress are linked to more rapid epigenetic aging.NR3C1, SKA2 and FKBP5.Trauma, post-traumatic stress disorder and suicide are associated with variable DNA methylation at loci such as Animal models of postnatal trauma exhibit behavioral abnormalities that are accompanied by specific variation in DNA methylation patterns within the brain.Intergenerational transmission of trauma-induced behavioral abnormalities is linked to variation in sperm DNA methylation patterns and miRNA content.Epigenetic studies will help to improve understanding of the biological processes underlying the social gradient in health.Combining epidemiological studies of human populations with experimental studies in animal models will help to elucidate the roles of epigenetic mechanisms in the pathobiology of social stress related health risks.Public health and social interventions that buffer low SES communities against social adversity can reduce epigenetic aging and improve long-term health.


PLP1 gene, which encodes a major myelin membrane protein. Severe clinical PMD phenotypes appear to be the result of cell toxicity, due to the accumulation of PLP1 mutant proteins and not due to the lack of functional PLP1. Therefore, it is important to clarify the pathological mechanisms by which the PLP1 mutants negatively impact the myelin-generating cells, called oligodendrocytes, to overcome this devastating disease. This review discusses how PLP1 mutant proteins change protein homeostasis in the ER of oligodendrocytes, especially focusing on the reaction of ER chaperones against the accumulation of PLP1 mutant proteins that cause PMD.Disease-causing mutations in genes encoding membrane proteins may lead to the production of aberrant polypeptides that accumulate in the endoplasmic reticulum (ER). These mutant proteins have detrimental conformational changes or misfolding events, which result in the triggering of the unfolded protein response (UPR). UPR is a cellular pathway that reduces ER stress by generally inhibiting translation, increasing ER chaperones levels, or inducing cell apoptosis in severe ER stress. This process has been implicated in the cellular pathology of many neurological disorders, including Pelizaeus-Merzbacher disease (PMD). PMD is a rare pediatric disorder characterized by the failure in the myelination process of the central nervous system (CNS). PMD is caused by mutations in the  PLP1 mutations was estimated to be 1.45 and 1.9 per 100,000 male live births in Japan and USA, respectively  is a pediatric inherited disorder of the central nervous system (CNS), mainly affecting oligodendrocytes, cells specialized in generating and maintaining myelin sheaths. Myelin is a membranous structure that wraps around the neuronal axons, enhancing the electronic conduction of neuronal circuits in the brain. Myelin also enables rapid and efficient movement of the body and cognitive function of the brain. Children with PMD thus show deficiencies in motor and intellectual development at an early stage of life, which usually continue thereafter. In addition, they present other neurological symptoms including nystagmus (involuntary rapid eye movement), spastic paraplegia (increased muscle tone and stiffness), ataxia , and dystonia (involuntary muscle contractions). PMD shows a wide range of clinical severity Figure . The mosPLP1 is located at Xq22.1 on the long arm of the X chromosome and encodes tetra-span myelin membrane lipoprotein; hence PMD shows X-linked recessive pattern of inheritance. Two alternative splicing variants differ in the inclusion or exclusion of the latter half of exon 3, to produce either PLP1 or DM20 protein; the former composes the major portion in the mature myelin. , which is the most abundant myelin membrane lipid protein in the CNS Inoue, . PLP1 isPLP1 mutations cause PMD through distinct molecular mechanisms  leading to no PLP1 production can cause a mild but slowly progressive PMD phenotype  , which is considered to be milder disease than PMD, while the most severe end is the connatal form PMD, which can cause premature mortality  mice carry an A243V mutation, which results in a very severe phenotype in both humans and mice. The rumpshaker (rsh) mice with an I187T mutation serve as a model for the mildest end of the PLP1-associated severity spectrum, SPG2. These mutants, along with the classic PMD mouse model jimpy (jp), have largely contributed to the understanding of the molecular pathogenesis of PMD. The mutant PLP1 protein associated with mild PMD phenotypes appear to be cleared quickly from the ER, via the proteasomal degradation pathway and/or ER exit, while the mutant PLP1 protein associated with severe PMD phenotypes is resistant to protein degradation and/or exclusion from the ER, triggering UPR activation , which is caused by mutations in the MPZ gene. The genetic removal of CHOP from the CMT model mice carrying S63del MPZ mutation ameliorated the demyelination and apoptotic cell death of Schwann cells  are maladaptive and CHOP induction leads to cell death and demyelination; however, CHOP may regulate a different set of downstream genes in oligodendrocytes, which presumably function as adaptive, or protective against cell death  in mice , Charcot-Marie-Tooth disease (targeting PMP22 and MPZ), retinitis pigmentosa (targeting RHO), and PMD  for clinical application, considering its side effects.Chloroquine, an anti-malarial drug, was found to reduce the accumulation of the mutant PLP1 and attenuate ER stress by enhancing the phosphorylation of eIF2α  and Grant-in-Aid for Scientific Research (Kiban-B: 16H05361).The author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


Smallpox (variola) virus is considered a Category A bioterrorism agent due to its ability to spread rapidly and the high morbidity and mortality rates associated with infection. Current recommendations recognize the importance of oral antivirals and call for having at least two smallpox antivirals with different mechanisms of action available in the event of a smallpox outbreak. Multiple antivirals are recommended due in large part to the propensity of viruses to become resistant to antiviral therapy, especially monotherapy. Advances in synthetic biology heighten concerns that a bioterror attack with variola would utilize engineered resistance to antivirals and potentially vaccines. Brincidofovir, an oral antiviral in late stage development, has proven effective against orthopoxviruses in vitro and in vivo, has a different mechanism of action from tecovirimat , and has a resistance profile that reduces concerns in the scenario of a bioterror attack using genetically engineered smallpox. Given the devastating potential of smallpox as a bioweapon, preparation of a multi-pronged defense that accounts for the most obvious bioengineering possibilities is strategically imperative. Despite official eradication in 1980, smallpox is still viewed as a significant threat due to its potential as a biological weapon . AccordiThe US Institute of Medicine concluded that antiviral agents with oral bioavailability would be important for containing the spread of smallpox in an immunologically naive population and that at least two therapeutics with different mechanisms of action should be available due to the potential for development of viral resistance . CurrentBrincidofovir  is comprised of a lipid moiety, 3-hexadecyloxy-1-propanol (HDP), conjugated to the phosphonate of cidofovir (CDV), an acyclic nucleotide analog of deoxycytidine monophosphate. BCV retains the broad-spectrum activity of CDV against dsDNA viruses, while lipid conjugation counters two major limitations of CDV, namely nephrotoxicity and the lack of oral bioavailability ,7. Impro50) for BCV against variola virus was estimated to be in the range of 0.05–0.21 μM, with an average of 0.11 μM across five strains chosen to represent distinct DNA polymerase genotypes [50 of BCV against rabbitpox and mousepox (ectromelia) viruses is approximately 0.5 μM; the EC50 against other orthopoxviruses has been reported to be in the range of 0.2–1.2 μM [In vitro studies have demonstrated that BCV inhibits orthopoxvirus replication, including variola virus, with enhanced potency compared to CDV ,9. The 52–1.2 μM ,10,11.Initial studies of BCV efficacy in the rabbitpox model of orthopoxvirus infection were performed in the laboratory of Richard Moyer at the University of Florida ,13. RabbA predicted effective dose for the treatment of smallpox in humans was established by comparing the pharmacokinetic (PK) exposure of BCV in rabbit plasma to the PK of BCV in human plasma. At a dose of 200 mg of BCV once weekly for 3 weeks, the mean exposure in humans exceeds that observed at the efficacious dose in rabbits ,16. FurtEfficacy of BCV in a second animal model, the mousepox (ectromelia virus) model of orthopoxvirus infection, has been established across numerous studies in the laboratory of Mark Buller at Saint Louis University exploring different mouse strains, viral inoculums, and BCV dosing regimens ,18,19. AData from over 1400 human subjects have contributed to the BCV safety database, which includes over 1000 complex immunocompromised adult and pediatric patients, many of whom participated in studies with a nominal 12-week treatment period. Over 500 of these immunocompromised individuals received a minimum of 3 weeks of BCV at the anticipated treatment regimen for smallpox, i.e., a total weekly dose of 200 mg administered orally for 3 consecutive weeks  [Recognizing the available data that indicate efficacy against orthopoxviruses, BCV has been made available for use under emergency investigational new drug applications in the US and under equivalent regulations outside of the US for the treatment of progressive vaccinia  and cowpBecause BCV has activity against other DNA viruses, it has multiple potential uses ,7 and haWhen considering the potential clinical impact of resistance on antiviral efficacy and durability, it is important to recognize the concept of “barrier to resistance”. Barrier to resistance relates to the relative ease with which viruses can become resistant to an active antiviral and encompasses numerous factors, including the genetic barrier to resistance, PK coverage, and viral fitness . The genOrthopoxviruses resistant to antivirals  can be selected in cell culture experiments. Numerous studies with orthopoxviruses have been conducted with CDV to investigate the development of resistance, which are relevant to BCV due to the shared active metabolite, CDV-PP. BCV/CDV resistance-associated mutations occur in the viral DNA polymerase gene. Single amino acid substitutions generally result in resistance of <10-fold , whereas two or more substitutions can result in resistance of up to 30-fold . HoweverConsistent with its mechanism of action, tecovirimat resistance-associated mutations occur in the F13L gene, which is involved in the production of enveloped orthopoxvirus virions. A single mutation of G277C resulted in a cowpox virus with >800-fold phenotypic resistance . While tIn the context of smallpox and bioterrorism, resistance takes on additional importance. Since resistant viruses can be created in the lab, either by cell culture selection or by synthetic biology, bioweapons could be created that render an existing antiviral ineffective. Equally concerning is the potential creation of viruses with enhanced virulence and/or resistance to vaccines. Ectromelia virus expressing murine interleukin 4 (IL-4) displayed increased virulence, killing mouse strains that are normally resistant to the virus, as well as mice that had been previously vaccinated ,30. HaviAntiviral therapy using combinations of drugs is often more effective and durable than monotherapy. Properly designed combination therapy has the potential to improve antiviral response and reduce the risk of resistance development . In HIV Given the established ability to “weaponize” variola virus and the potential for synthesis of drug-resistant or enhanced virulence variants, it is imperative our medical countermeasure strategy encompasses multiple therapeutic options, including vaccination and antivirals with different mechanisms of action and no cross-resistance. BCV has demonstrated a significant survival benefit even after treatment initiation was delayed to the mid-point of disease progression in two relevant animal models of orthopoxvirus infection. In addition, BCV is progressing in clinical development as a treatment for life-threatening viral infection in patients with impaired immune response due to transplant or congenital immunodeficiency. BCV’s mechanism of action complements that of the currently stockpiled tecovirimat and could be a critical component in an effective response to a smallpox outbreak involving drug-resistant or enhanced virulence virus. In the face of an increasing threat posed by smallpox as a bioweapon, including BCV in our readiness planning is supported by its demonstrated survival benefit in animal models, relevant clinical experience in high-risk adult and pediatric populations, robust clinical safety database, synergy with tecovirimat, and high barrier to resistance.


Other potentially N2-fixing bacteria and archaea have also been detected in the pelagic water column, however, the activity and importance of these non-cyanobacterial diazotrophs (NCDs) remain poorly constrained. In this perspective we summarize the N2 fixation rates from recently published studies on photic and aphotic layers that have been attributed to NCD activity via parallel molecular measurements, and discuss the status, challenges, and data gaps in estimating non-cyanobacterial N2 fixation NCNF in the ocean. Rates attributed to NCNF have generally been near the detection limit thus far (<1 nmol N L−1 d−1). Yet, if considering the large volume of the dark ocean, even low rates of NCNF could make a significant contribution to the new nitrogen input to the ocean. The synthesis here shows that nifH transcription data for NCDs have been reported in only a few studies where N2 fixation rates were detected in the absence of diazotrophic cyanobacteria. In addition, high apparent diversity and regional variability in the NCDs complicate investigations of these communities. Future studies should focus on further investigating impacts of environmental drivers including oxygen, dissolved organic matter, and dissolved inorganic nitrogen on NCNF. Describing the ecology of NCDs and accurately measuring NCNF rates, are critical for a future evaluation of the contribution of NCNF to the marine nitrogen budget.Traditionally, cyanobacterial activity in oceanic photic layers was considered responsible for the marine pelagic dinitrogen (N Extensive research on free-living and symbiotic NCDs in soils has provided evidence of the activity, regulation, and the significance of these processes in terrestrial ecosystems . Here we summarize data from studies where N2 fixation rates were reported in parallel to molecular characterization of NCDs when cyanobacterial diazotrophs were not detected  supplies the high energetic demands of the N2 fixation process, while dissolved inorganic nitrogen (DIN) limits non-diazotrophic autotrophs. Yet, since the first molecular studies   and cyanobacterial diazotroph abundances in the North Atlantic  data as proof for NCNF. Despite the common detection of cyanobacterial and NCD nifH in DNA sequence libraries and, at times, in transcripts, only a few studies from surface layers reported the absence of cyanobacterial diazotrophs when N2 fixation rates were detected , which at typical concentrations requires large volumes in incubations  to constrain rates in deep waters. While N2 fixation rates per volume are most informative for budgetary calculations, rates normalized to PON concentration would provide an additional measure for comparing rates across studies. Further, variability of the natural δ15N background of PON, changes in the δ15N of PON that may occur over the incubation period or due to substrate additions, and δ15N of the N2 pool, should be considered  has recently advanced quantification of single-cell N2 fixation rates in UCYN-A , which could potentially result in false negatives for cyanobacterial diazotrophs, and subsequently, lead to false positive NCNF rates. Using small water volumes when abundance of cyanobacterial diazotrophs is low would increase the chances of reporting false negatives for these organisms. On the other hand, metabolic rate measurements of microbial samples brought to the surface from aphotic depths may be underestimated (Tamburini et al., In describing the communities, sequencing depth and primer specificity influence what portion of the NCD community is detected. In addition, the detection limit for diazotroph transcripts or genes and the detection limit for N2 fixation rates were reported from marine environments where NCD abundance was high and cyanobacterial diazotrophs were low or undetected. NCD nifH sequences show a wider geographical and depth distribution in pelagic environments overall than their cyanobacterial counterparts. The emerging data suggest that the NCD communities are diverse but only a few groups have been identified that appear in several studies (Farnelid et al., nifH transcripts in aphotic layers are scarce or missing for many areas of the oceans.Our compiled analysis of data illustrates that low N2 fixation rate data. Modeling the significance of NCNF in marine N2 fixation remains a challenge due to these various constraints. If these rates are confirmed, however, NCNF could contribute significantly to new N inputs to the ocean. How factors such as temperature, DIN, oxygen, trace elements, and hydrostatic pressure drive the metabolic capacities and adaptations of NCNF are currently only partially revealed. The actual activities and taxon specific roles of marine NCDs remain enigmatic at present, as do their contributions to regional and global N2 fixation.We currently lack a fundamental understanding of the key players and environmental regulation of NCNF in the ocean. Ecophysiological data of the organisms contributing to these rates are still preliminary and incomplete. Moreover, the measured rates in most environments are generally “snap-shots” determined during a cruise/sampling foray and have not been examined over seasonal and annual cycles. In addition, several methodological concerns complicate interpretation of NPM and LR designed the study, wrote the initial drafts, and compiled the majority of Table 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.


Through isoform-specific interactions with the intracellular C-terminal tail of neuronal Nav channels , FGF14 controls channel gating, axonal targeting and phosphorylation in neurons effecting excitability. FGF14 has been also involved in synaptic transmission, plasticity and neurogenesis in the cortico-mesolimbic circuit with cognitive and affective behavioral outcomes. In translational studies, interest in FGF14 continues to rise with a growing list of associative links to diseases of the cognitive and affective domains such as neurodegeneration, depression, anxiety, addictive behaviors and recently schizophrenia, suggesting its role as a converging node in the etiology of complex brain disorders. Yet, a full understanding of FGF14 function in neurons is far from being complete and likely to involve other functions unrelated to the direct regulation of Nav channels. The goal of this Mini Review article is to provide a summary of studies on the emerging role of FGF14 in complex brain disorders.The finely tuned regulation of neuronal firing relies on the integrity of ion channel macromolecular complexes. Minimal disturbances of these tightly regulated networks can lead to persistent maladaptive plasticity of brain circuitry. The intracellular fibroblast growth factor 14 (FGF14) belongs to the nexus of proteins interacting with voltage-gated Na+ (Na In 2014, nearly one in four adults in the United States was diagnosed with a mental illness  channels and promotes their localization to the proximal region of the axon, providing the fine-tuned regulation necessary for normal functioning , which serves as the action potential initiation site , a naturally occurring complex neurodegenerative disorder characterized by onset of ataxia in early adulthood and deficits in cognition, memory and behavior  to be a putative risk factor for other neuropsychiatric diseases including depression, addiction and schizophrenia, as well as neurodegenerative diseases, such as Alzheimer’s Disease .Recent studies have added a new dimension to FGF14, showing that its interaction with the Nav1.6 interactions , a phenotype that is accompanied by reduced AMPA receptor-mediated excitatory postsynaptic currents and decreased expression of vesicular glutamate transporter 1, a specific presynaptic marker at PF-Purkinje neuron synapses  and vesicular GABA transporter (vGAT), presumably deriving from fast-spiking parvalbumin (PV) interneurons synapses  at the Schaffer’s collaterals to CA1 synapses, which is accompanied by decreased expression of synaptic vesicles docked at the active zone, and fewer miniature excitatory postsynaptic currents in primary hippocampal neurons (Xiao et al., Fgf14−/− terminals, at which repetitive stimuli causes significant synaptic fatigue, consistent with impaired presynaptic function (Xiao et al., Studies have also supported a role of FGF14 in synaptic plasticity in the hippocampus. Fgf14−/− mice show impaired transition from late immature neuronal progenitor cells to mature neurons, which is accompanied by reduced paired-pulse facilitation at the perforant path to granule neurons in the dentate gyrus (Alshammari >M. A. et al., Adult neurogenesis, or the proliferation, differentiation and integration of new neurons into existing brain circuitry has become an area of research interest in part due to its implication in the cognitive pathophysiology of several neuropsychiatric disorders, including Alzheimer’s disease, depression and schizophrenia (Ming and Song, FGF14 in the context of neuropsychiatric disorders (Table FGF14 intronic region and thus their role on the protein expression and function are unclear, they might provide guidance for future investigations. A Brazilian pilot study on early onset/familial schizophrenia found a link between early-onset schizophrenia and FGF14 (Gadelha et al., FGF14 and schizophrenia, which is corroborated by a linkage study of familial schizophrenia in Canadian families of Celtic or German descent (Brzustowicz et al., FGF14 have been associated with dependence on alcohol and illegal substances in humans, and a fine-mapping study found several SNPs to be associated with major depressive disorder in a study of Dutch twins (Drgon et al., FGF14 SNP is associated with volumetric changes in the entorhinal cortex in AD patients (Yang et al., FGF14 are linked to the pathophysiology of several neuropsychiatric disorders, a promising area for further research that is supported by studies in Fgf14−/− preclinical models (Alshammari T. K. et al., As many neuropsychiatric disorders are heterogeneous and complex, GWAS have become an important tool for sorting relevant genetic information from large patient populations. Numerous GWAS have reported SNPs in rs Table . AlthougFGF14 plays a role in all fundamental properties of neurons: intrinsic firing, synaptic transmission of excitatory and inhibitory neurons and plasticity, while deletion of the gene leads to disruptive motor and cognitive behaviors. The role of FGF14 in humans is yet to be fully understood, but the emerging technologies for genome sequencing and protein characterization will provide potential opportunities for identifying new disease signatures associated with FGF14.All of the authors have contributed substantially to the work. JDR and FL contributed to writing and editing the manuscript. PAW created the image and legend for Figure This research was funded by National Institute of Mental Health: grant no. 1R01MH111107-01A1, R01 MH095995-A1 and the National Institutes of Health: grant no 5T32AG051131-02.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.


Furthermore, we examine the crosstalk between autophagy and other cellular stresses implicated in ALS pathogenesis and the therapeutic implications of regulating autophagy in ALS.Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder that results from the loss of upper and lower motor neurons. One of the key pathological hallmarks in diseased neurons is the mislocalization of disease-associated proteins and the formation of cytoplasmic aggregates of these proteins and their interactors due to defective protein quality control. This apparent imbalance in the cellular protein homeostasis could be a crucial factor in causing motor neuron death in the later stages of the disease in patients. Autophagy is a major protein degradation pathway that is involved in the clearance of protein aggregates and damaged organelles. Abnormalities in autophagy have been observed in numerous neurodegenerative disorders, including ALS. In this review, we discuss the contribution of autophagy dysfunction in various  Amyotrophic Lateral Sclerosis (ALS) is a fatal, age-related neurodegenerative disorder characterized by progressive loss of both upper and lower motor neurons in the brain and spinal cord , sequestosome 1 (SQSTM1), ubiquilin 2 (UBQLN2), dynactin (DCTN1), MATR3 and valosin-containing protein  and sporadic ALS (sALS). SALS is more common, comprising 90%–95% of cases and does not have any known genetic inheritance. On the other hand, fALS affects 5%–10% of cases and is hereditary  and the autophagy-lysosome pathway. The UPS, the major proteolytic pathway in the cell, degrades short-lived, soluble proteins. Autophagy, on the other hand, is responsible for degrading relatively long-lived, cytoplasmic proteins, soluble and insoluble misfolded proteins, and also entire organelles. In this review, we discuss the importance of the autophagy pathway in the context of ALS. In addition, we discuss the interaction of autophagy with other biological pathways relevant to motor neuron degeneration and provide perspective on the role of autophagy in the overall pathogenesis of ALS.Proteins are dynamic molecules within a cell, undergoing synthesis, proper folding and assembly and timely degradation. The balance between these events is maintained by a network of pathways called the proteostatic network , characterized by a hexanucleotide repeat (HRE) expansion of GGGGCC in the first intron of the gene  is a well-characterized major regulator of autophagy initiation  with PE  complexes to endosomes and lysosomes  failure in autophagy initiation; (ii) failure in autophagosome formation and/or maturation; (iii) defects in the transport of cargo within autophagosomes; (iv) failure in the fusion between autophagosomes and lysosomes; or (v) defective lysosomal degradation. Thus, it is imperative to study the mechanism of autophagy in a variety of 2O2; Wang et al., SOD1 gene in individuals with fALS  and hydrogen peroxide  is a heterogeneous nuclear protein that is a prominent feature of ubiquitinated cytoplasmic inclusions observed in ALS and FTLD patients  ALS, whereas mutations such as R521C and R518K are associated with late-onset disease presentation  and UBA (ubiquitin-associated) domains facilitate their dual role in autophagy and ubiquitin-proteasome systems  either the pathways activate autophagy downstream and this crosstalk is perturbed in ALS; (ii) the downstream activation of autophagy in these pathways could overwhelm the autophagy pathway, resulting in toxic effect; or (iii) the other pathogenic mechanisms work in conjunction with a failed autophagy system, pushing the cells over the edge and thus causing neurodegeneration. Nevertheless, investigation of the crosstalk between the mechanisms may elucidate the role of autophagy itself by drawing attention to molecular links that could be further studied for determining early disease therapeutic interventions.In silico analyses of motor neurons from transgenic mutant SOD1 mice revealed ER stress to be an early pathological feature  is a crucial organelle in which both membrane proteins and secreted proteins are synthesized and modified for protein folding. In a cell, more than one-third of the proteins synthesized are misfolded , ATG7, ATG10, GABA Type A receptor-associated protein (GABARAP) and ATG5, thereby inducing autophagy  and DNA damage inducible transcript 3 (DDIT3), independently and together, promote transcription of several autophagy genes, including BECN1 expression  pathway, which induces autophagy through mammalian target of rapamycin (mTORC1) inhibition  promotes expression of Death-associated protein kinase 1 , reduced respiration and ATP synthesis, disrupted calcium homeostasis and increased ROS production  and expression of enzymes involved in base-excision repair Coppedè, . When DN+ reserves in the cell. This causes a decrease in ATP levels leading to downstream activation of AMPK pathway. An alternative pathway of AMPK activation occurs via dissociation of FOXO3 from DNA during DNA damage (Eliopoulos et al., LC3 and BNIP3 (Czarny et al., As the role of DNA damage in ALS and the potential to target DNA damage in early stages of the disease becomes increasingly prominent, it is interesting to note that DNA damage-repair acts as a cytoprotective mechanism by inducing DNA damage repair mechanisms, and also by inducing autophagy Figure . DNA damCytoplasmic mislocalization and formation of aggregates in either the cytoplasm and/or the nucleus by RNA-binding proteins is a hallmark of multiple neurodegenerative disorders (Ugras and Shorter, SOD1G93A mouse model of ALS found that lithium administration reduced motor neuron loss and increased survival (Pizzasegola et al., Autophagy-modulating drugs have been studied for treating various human neurodegenerative diseases as well as aging (Ballou and Lin, in silico library that consisted of over a million potent autophagy activators (Barmada et al., SOD1-ALS mice (Hsueh et al., The benefits of using high-specificity small molecule regulators of autophagy have been explored in several neurodegenerative diseases (Sarkar and Rubinsztein, Dysregulation in autophagy is emerging as a major pathogenic hallmark of ALS. Most evidence point to a reduction in autophagy in diseased neurons and the subsequent therapeutic effects of inducing autophagy. One potential mechanism through which autophagy dysregulation could be caused is by a direct dysfunction of proteins involved in protein degradation. This hypothesis was solidified by the discovery of ALS-causing mutations in these proteins. An alternative mechanism could be through a combined effect of autophagy defects along with other cellular stresses that depend on autophagy for their alleviation. Prominently, phase separation defects caused by mutations in RNA-binding proteins with a low complexity domain allow them to aggregate into stress granules in diseased neurons. These stress granules act as a seed for self-aggregation of these proteins as well as interacting proteins. Over the life of a neuron, these cellular insults accumulate to the point of motor neuron death. Development of therapeutics that specifically target upstream cellular events could aid in alleviating cellular stress. A combination therapy with drugs that upregulate autophagy could be a promising therapeutic strategy for ALS.NR wrote this review article. UBP edited and revised it.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.


The generation of individual neurons (neurogenesis) during cortical development occurs in discrete steps that are subtly regulated and orchestrated to ensure normal histogenesis and function of the cortex. Notably, various gene expression programs are known to critically drive many facets of neurogenesis with a high level of specificity during brain development. Typically, precise regulation of gene expression patterns ensures that key events like proliferation and differentiation of neural progenitors, specification of neuronal subtypes, as well as migration and maturation of neurons in the developing cortex occur properly. ATP-dependent chromatin remodeling complexes regulate gene expression through utilization of energy from ATP hydrolysis to reorganize chromatin structure. These chromatin remodeling complexes are characteristically multimeric, with some capable of adopting functionally distinct conformations via subunit reconstitution to perform specific roles in major aspects of cortical neurogenesis. In this review, we highlight the functions of such chromatin remodelers during cortical development. We also bring together various proposed mechanisms by which ATP-dependent chromatin remodelers function individually or in concert, to specifically modulate vital steps in cortical neurogenesis. Development of the cortex (corticogenesis) is marked by coordination of many key molecular and cellular processes that afford proper brain structure and function. Neurogenesis, one of such cellular events, involves the generation of neurons from neural progenitor cells (NPCs). Embryonic cortical neurogenesis is thus the prenatal aspect of corticogenesis, at which stage the bulk of excitatory (neo)cortical neurons are generated by distinct types of NPCs. Different NPCs can be identified based on their molecular characteristics, morphology, cell lineage commitment, and their site of cell division  cells are resident in the SVZ or the oSVZ and afford another avenue for increasing neuron output in the developing cortex  complexes, imitation switch (ISWI) complexes, chromodomain helicase DNA-binding (CHD)/Nucleosome Remodeling Deacetylase (NuRD) complexes, and INO80/SWR complexes; based on differences and similarities in their catalytic ATPase domains Figure  and assoRemodeling factors within this category are responsible for the maturation of prenucleosomes (early histone-DNA complexes) into octameric mature nucleosomes, as well as the correct spacing of newly formed nucleosomes. This occurs immediately after replication and in association with the replication machinery  to produce mature nucleosomes with ~147 bp of DNA associated to them  subfamily. They make the DNA within the nucleosomes more accessible to other DNA-associated molecules—exposing sites for other proteins  to bind and affect gene expression. They can do so by sliding nucleosomes, evicting nucleosome components (like histone dimers) or completely ejecting full nucleosomes Figure .Through DNA translocation, this type of remodelers allow the release of longer stretches of linker DNA to be exposed to DNA-binding machinery. By doing so, nucleosomes can translocate near one another, invading the neighboring DNA territory and thus promoting the removal of histone dimers and eventually the expulsion of the complete histone octamer, resulting in nucleosome disassembly  are enriched in nucleosome-free regions of active promoters in the genome. H2AZ and H3.3 are associated with facilitated access to transcription factors and increased transcriptional activity  and drosophila , the mammalian (m)SWI/SNF complexes are also present in two variants, namely homologous BAF (Brg1/BRM associated factor) and PBAF (Polybromo-associated BAF) complexes. The BAF and PBAF complexes have BRG1/BRM or only BRG1 as their catalytic subunit, respectively  acts as the catalytic subunit for at least 7 complexes, amongst them are CHRAC, ACF, WICH, RSF, CERF, NoRC, and NURF Figure .in vitro in the presence of a histone chaperone (like NAP1 or CAF1). It can also modulate the spacing between nucleosomes, thus changing chromatin accessibility , a protein structurally similar to ACF1 Figure . ThroughThe complex termed NoRC (nucleolar remodeling complex) is formed by the interaction of the ISWI homolog SNF2H and the protein TIP5 Figure . It was The NURF complex has the ISWI homolog SNF2L as catalytic subunit, and is involved in transcriptional activation. Human NURF has been found in high levels in the brain, where it can regulate the transcription of genes like Engrailed, suggesting important roles during development , targeting these sites for nucleosomal remodeling  is highly expressed in the nervous system and has been associated with regulation of neural development  superfamily of proteins is a large class of DNA-binding proteins that can act as chromatin remodeling complexes, and thus regulate gene expression. The members of this class of ATP-dependent chromatin factors are diverse but share a few common characteristics, particularly in the presence of an N-terminal chromodomain, a central SNF2-like helicase motif and a C-terminal DNA-binding domain  can act as monomeric units to directly regulate chromatin and transcription  are core catalytic components (ATPases) of the nucleosome remodeling deacetylase NuRD complex Figure . They caSubfamily III (CHD5-9) contains recently discovered members that have few known interaction partners. But like the other CHD proteins, they seem to be associated with chromatin structure and remodeling . It has been commonly proposed that some chromatin remodel complexes, such as the BAF and NuRD complexes, can be functionally specified by reconstituting or reshuffling some of their subunits to configure the entire complex toward specific ontogenetic functions. The existence of polymorphic or paralogous forms of the subunits of these ATP-dependent chromatin remodeling factors thus allow for some plasticity of their related complexes to customize their overall functional activity.For example, as recently reviewed in Sokpor et al. , the BAFThe neural progenitor BAF (npBAF) complex formed in NPCs as ESCs acquire multipotent NPC fate, is distinctively composed of high amounts of BAF155, low levels of BAF170, BAF250a/b, and BRG1 or BRM ATPase. However, subunits like BAF45a/d, BAF53a, and BAF55a in the esBAF complex are maintained in the npBAF complex. On the other hand, the reconstitution of the npBAF complex to form the neuronal BAF (nBAF) complex during differentiation of NPCs into neurons entails substituting BAF45a, BAF53a, and BAF55a for BAF45b/c, BAF53b, and BAF55b, respectively, and alongside low levels of BAF155 and high amounts of BAF170. The combinatorial assembly of the BAF complex is also elegantly reviewed in Ho and Crabtree  and thatin vivo animal models and neural progenitor culture systems in vitro, these specific events have been investigated to elucidate various epigenetic mechanisms regulating them. In the following subsections, we put together various studies that implicate specific ATP-dependent chromatin remodeling factors in controlling the aforementioned aspects of cortical neurogenesis.As previously mentioned, neocortical development comprises specific developmental processes such as neural specification and patterning, establishment and subsequent transformation of NEs to RGs, proliferation and differentiation of neural progenitors, neuronal subtype specification and migration, neuronal maturation, and ultimate integration of neurons into maturating functional cortical circuits. By applying The induction and areal specification of neural tissue are fundamental processes responsible for the development of the nervous system. Through the orchestration of several morphogenetic elements, including signaling and transcriptional factors, specific aspects of the simple embryonic ectoderm receive instructions to progressively transform into more complex neural structures in the course of development /Foxg1 probe, it was observed that the forebrain neuroepithelium was abnormally located underneath the thalamus. Examination of the SRG3 mutant head structures at E16.5 revealed several anomalies, including gross morphological malformation of the cerebral cortex and other forebrain structures. An elevated expression level of SRG3 protein early in the development of the telencephalon, that is during neural tube closure (E8.5–E9.5), and the sustenance of its constitutive high expression level in the central nervous system seem to be critical for the proper specification and development of the cortex , a mouse homolog of the human BAF complex subunit BAF155, has been shown to be essential in the specification and spatial patterning of telencephalic regions of the developing brain. About 20% of mice heterozygous for SRG3 displayed abnormal location and formation of the forebrain, a condition called exencephaly , which is also a variant subunit of the BAF complex, is a powerful morphogen in sensorimotor area specification and patterning during neocortical neurogenesis  caused reduced proliferative capacity of the CHD4-deficient NPCs at late cortical neurogenesis stages. The decreased proliferation of such NPCs was linked to (i) their precocious exit from the cell cycle, (ii) failure to differentiate, and (iii) eventual cell death  resulted in blockage of proliferation  caused increase in NPC proliferation in the developing mouse cortex  of CHD8 resulted in premature reduction of neural progenitor pool  inhibitor p21  co-repressor complex also resulted in a reduction in Tbr2+ basal progenitors with attendant phenotype  quite reminiscent of BAF170 over-expression phenotype during embryonic corticogenesis. The MBD3/NuRD complex was however reported to be dispensable in the requirement of lineage commitment of Pax6+ apical progenitors such as aRGs , with striking reductive effects seen at later developmental stages  to exert later effects. If the latter is the case, at least as partly implicated in the recent work of Albert et al. , then itDuring cortical development, a great number of neurons are generated from different progenitor populations. The vast number of neurons generated during cortical neurogenesis obtain various subtype identities, making it possible to generate (by definition) the six cellularly distinct laminae that typify the mature cortical plate  that are born from progenitors in the germinative zones of the developing cortex are sorted out  through differential activation and deactivations of batteries of developmental cell programs, including transcriptional and epigenetic mechanisms. These afford acquisition of specific identities to yield the typical PNs diversification in the neocortex  have also been identified to play pivotal roles in neuronal subtype specification during corticogenesis. Whereas Ctip1 is distinctly expressed by post-mitotic cortical neurons that make callosal and corticothalamic connections, Ctip2 is strongly expressed by subcerebral cortical neurons that make corticofugal connections with brainstem nuclei and the spinal cord. In other words, Ctip1 finely regulates cortical neurogenesis through modulation of pathways that lead to deep layer neuron generation, whereas Ctip2 expression or presence in the BAF complex orchestrates the establishment of neurons that make, for example, corticospinal projections  suppression by Tbr1 is needed for the formation of cortical layer 6  out mainly radially from their birthplaces to their home layers in the cortical plate. Together with default dispositions such as specific time and place of birth, and type of parent progenitor involved, these newly born (immature) cortical neurons are able to collect many regulatory molecular cues in the microenvironment along their migratory trajectory , which cannot be nitrosylated at the said cysteine residues, could not migrate out of the IZ to reach the CP. Interestingly, by means of bead-array analysis of the developing cortex, it was observed that S-nitrosylation of HDAC2 activates the expression of the BRM component of the BAF (mSWI/SNF) complex  caused disruption of radial migration of Cux1+ neurons in the developing cortex, which was a phenocopy of mouse cortical neurons lacking nitric oxide synthase (nNOS−/−): the enzyme responsible for S-nitrosylation. Put together, NO signaling seem to cause HDAC2 nitrosylation which in turn regulates the levels of BRM to control radial migration of neurons in the developing cortex  of the NuRD complex subunit HDAC2 is known to control its association with chromatin  electroporated into the E13.5 cortex affected radial cortical neuron migration when visualized at E18.5. Particularly, CHD3 knockdown caused delay in radial neuronal migration, with significant cell retention in the lower CP as compared with fewer numbers reaching the upper CP. Similarly, knockdown of CHD5 impaired neuronal migration such that many multipolar neurons abnormally accumulated in the IZ, likely reflecting defective multipolar-bipolar state transition, and their overall failure in reaching the CP. Interestingly or perhaps expectedly, loss of CHD4 using either shRNA or Cre-recombinase in CHD4Following generation and migration of neurons, various differentiation and morphogenetic programs are turned on to ensure attainment of neuronal identity and maturity to permit correct functional neuronal circuitry in the cortex. The elaboration of dendrites (dendritogenesis) or extension of axons (axonogenesis) from neurites are major neuronal maturation events that ensure synapse formation needed for neuronal information processing.−/−) cultured cortical neurons are unable to undergo activity-dependent dendritic outgrowth. Such BAF53b−/− mutant cortical neurons were however able to elaborate dendrites only in the presence of BAF53b functional restoration, but not its homolog BAF53a  or SS18-like protein 1 (SS18L1), has been shown to play an essential role in neuronal morphogenesis. CREST expression is detectable in the developing mouse cortex from E18.5, with peak expression level at P1 and minimal but constant levels from P10 onwards. Activation of CREST is suggested to be a mechanistic aspect of calcium signaling known to regulate development of dendrites during early cortical development -dependent gene expression pathways , is critically regulated by external and inherent cellular programs that are mainly stimulated by neurogenic transcription and signaling factors. Epigenetic factors are known to implicitly contribute to such regulatory developmental decisions during cortical neurogenesis. Among such epigenetic programs, chromatin modification constitutes a formidable global mechanism used by NPCs to fundamentally adapt their transcriptional response to varying environmental conditions during corticogenesis. More so, extensive remodeling of chromatin architecture permits the sequential transformation of multipotent apical NPCs through specific intermediate precursor cell species into fully differentiated cortical neurons.By using strategic regulatory mechanisms of action, ATP-dependent chromatin remodelers are able to modulate gene expression programs and other cofactors involved in specific aspects of neurogenic events leading to derivation of neurons from the simple neuroepithelium. The existence of diverse multi-subunit complexes that function as ATP-dependent chromatin remodeling factors may largely depict their unsubstituted requirement in regulating specific parts of cortical neurogenesis rather than providing compensatory functions in the absence or dysfunction of others. Classically, complete or partial inactivation of specific ATP-dependent chromatin remodelers in the developing brain elicit a range of abnormalities such as (i) compromise in neural specification, (ii) up or downregulation of proliferative capacity of apical and basal progenitors, (iii) precocious or delayed differentiation of apical/basal progenitor cells, and (iv) impaired migration and terminal differentiation of post-mitotic neurons. Such aberrant cortical developmental processes are known to culminate into various brain structure and function perturbations.de novo mutations in genes coding for chromatin remodeling proteins gives compelling biological significance of stepping up investigative efforts into knowing how ATP-dependent chromatin remodelers regulate cortical neurogenesis. In that direction, applying state-of-the-art tools that can allow us to target and identify associated cofactors and mechanisms involved will help consolidate our understanding of chromatin regulation during brain development in health or disease RNA-seq technique. Furthermore, the newly developed super-resolution nanoscopy coupled with new-labeling methods will provide an additional insight into how chromatin-remodeling factors control chromatin dynamics during neural development. Finally, the application of a robust epigenome-editing technology can afford accurate targeting of chromatin remodeling factors at relevant gene loci to determine their inter- and intra-species gene expression regulatory patterns in the brain.Altogether, these strategies can permit precise segregation of the heterogeneous cell populations in the developing cortex and identify their unique chromatin remodeling profiles and epigenetic landscapes that specifically contribute to cortical development and evolution.GS, RC-H, JR, JS, and TT all contributed to writing and editing the manuscript.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.


The omnipresence of MSC throughout vascularized organs equates to a reservoir of potentially therapeutic regenerative depots throughout the body. However, these reservoirs could be subjected to cellular senescence. In this review, we will discuss current progress and challenges in the understanding of different biological pathways leading to senescence. We set out to highlight the seemingly paradoxical property of cellular senescence: its beneficial role in the development and tissue repair and detrimental impact of this process on tissue homeostasis in aging and disease. Taking into account the lessons from the different cell systems, this review elucidates how autocrine and paracrine properties of senescent MSC might impose an additional layer of complexity on the regulation of the immune system in development and disease. New findings that have emerged in the last few years could shed light on sometimes seemingly controversial results obtained from MSC therapeutic applications.Mesenchymal stem/stromal cells (MSC) have been tested in a significant number of clinical trials, where they exhibit regenerative and repair properties directly through their differentiation into the cells of the mesenchymal origin or by modulation of the tissue/organ microenvironment. Despite various clinical effects upon transplantation, the functional properties of these cells in natural settings and their role in tissue regeneration  One of the drawbacks is a loss of tissue repair capacity due to diminishing self-renewal (pool preservation impact) and differentiation  caused by the cell cycle arrest. The other is a microenvironment modulation by senescent MSC due to secretion of pro-inflammatory and matrix-degrading molecules, which, if escalated, might have a significant local or systemic impact on overall organism homeostasis. The functional relevance of senescent cells has been reported in three seemingly diverse contexts: (1) in normal embryonic development and regeneration during organ and tissue turnover in adults , (2) upon aging and in age-related diseases (harmful chronic senescence), and (3) during therapeutic interventions that deploy potent genotoxic stressors that cause accelerated premature senescence—Unlike senescence during aging and in age-related disease . We will also discuss the ability of senescence cells to propagate or spread information about their status and build a parallel suggesting how this knowledge can be applied to understanding the functional role of MSC senescence in both non-pathological and pathological settings. Lastly, we will discuss how the senescence cells messaging secretome (SMS)  links together senescence, inflammation, and immunological responses. In this review, we will illustrate examples “when, where, and how” such senescence-orchestrated cascades can be both beneficial and detrimental.In this review, we will try to provide a synapse of exciting research developments in the field studying different models of senescence senescent” describing cells was introduced several decades ago defining a concept that helps to explain the process of maintaining cellular homeostasis with aging. The lessons learned since then indicate that senescence is perhaps not a single unique and unambiguous cell state   by transforming growth factor (TGF)-β/SMAD and PI3K/FOXO pathways  or chronic. Such distinction allows grasping the dualistic  impact of this process on normal developmental and regenerative events, as well as its role in the pathology of human disease and aging. A summary of the different senescence modes is shown in Figure While the molecular mechanism governing the different type of senescence in vitro , cells enlarge, become more granular with increased lysosomal content characterized by senescence-associated β-galactosidase , and slow down their proliferation rate. While resistant to apoptosis, the senescent cells will retain their metabolic activity and can be kept in the culturing media in this state for a prolonged time.All human somatic and adult stem cells that can be successfully expanded in culture will eventually undergo replicative senescence DNA damage response (DDR). DNA damage sensors ATM/ATR lead to activation and stabilization of p53-dependent checkpoints, which eventually results in the exit from cell cycle mediated by p53-p21Cip1 pathway and senescent phenotype  are inactivated in senescent cells by CDK inhibitors (CDKI) , which have a dual activity in cell cycle regulation. This family negatively regulates a cell cycle progression by binding to cyclin E, A, B/cdk2, and cyclin D/cdk1 complexes and inhibiting their enzymatic activity  that acts upon the cell cycle by blocking the activity of cdk4 and cdk6 and impedes their association with cyclin D  in the G1 phase due to lack of ability to sustain DNA replication. In many cases, this is because the set of cell Cip1 and p16Ink4a genes are drastically increased within the cells  are also involved in G2 cell cycle arrest  induces the accumulation of p16Ink4a, p53, and ARF and triggers cellular senescence  has a capacity to induce senescence in both human and mouse melanoma models. This induction, however, occurs through a seemingly different mechanism involving p16Ink4a and activation of pyruvate dehydrogenase (PDH), an essential component of the metabolic signaling axis   acts as a potent inducer of senescence via PI3K –> AKT–> mTOR pathway  pathway  by acquiring mutation in p53  uphold MSC senescence by activation of the PI3K/AKT pathway in patients with systemic lupus erythematosus , have outlined the seemingly similar signaling pathways among different stress-inducer stimuli, that confer to the common paracrine circuit that we will discuss later   cells undergo senescence Cip1-deficient animal models display minimal to no developmental defects  or senescence-associated secretory phenotype (SASP) is necessary for tissue or organ remodeling and regeneration , where senescent hepatocytes undergo immune-mediated clearance  specks that are efficiently phagocytosed by other cells in the neighborhood. The ASC nucleation, and the speck release in the extracellular medium act as the inflammasome-perpetuating signal when consumed by recipient cells  and maturation of the cytokines, the inflammasome activation also advances the release of ASC , hepatocyte growth factor (HGF), epithelial growth factor (EGF), fibroblast growth factor (FGF-2) and insulin-like growth factor-1 (IGF1). Systemically, all of these factors have shown to increase fibroblasts, epithelial and endothelial cell division or differentiation , IL-2, IL-12, tumor necrosis factor-alpha (TNF-α) and interferon-gamma (INF-γ) , which in turn mediate an effective antitumor response by clearing senescence cells and shrinking tumor size  and FasL-deficient (gld), have shown lymphoproliferative changes, thus suggesting that Fas/FasL system is required for suppression/regulation of activated effector T cells . Fas/FasL could moderate a development of tolerogenic DCs and Treg, therefore accelerating a suppression of the effective immune response  is a transmembrane protein belonging to the TNF/nerve growth factor receptor superfamily. Fas binds to its natural ligand FasL (CD178) , one of the three members of the selectin family, is expressed on granulocytes, monocytes and lymphocytes and performs a vital function in maintaining such immune surveillance, by directing naive lymphocytes to peripheral lymph nodes for subsequent activation upon antigen interaction  is expressed in non-inflamed skin endothelium and become present on endothelium cells of most organs upon activation , is among those overexpressed in the MSC's SMS. ICAM-1 is a member of the immunoglobulin superfamily   is a ligand for interleukin-1 (IL-1) receptor family with significant anti-inflammatory property   found in abundance in the MSC SMS (Table The significance of cellular senescence during normal development as well as in age-related pathologies and cancer, has attained a remarkable level of scrutiny in recent years. Remarkably, in the last ten years we gained deeper knowledge related to the multifaceted influences of the p53 and Rb pathways in mechanistic underpinnings of senescent phenotypes establishment and maintenance. Despite this steady progress in probing the roles of the p53-Rb axis, there is still plenty of uncharted territory remainingwhen it comes to other mechanisms that might contribute to the senescent phenotype of MSC and biological and pathophysiological consequences of the autocrine and paracrine influences of senescent MSC on the tissues and organs homeostasis.MSC mediate numerous therapeutic effects by promoting repair directly via differentiation into critical cell types or indirectly through the secretion of substances and the activation of endogenous mechanisms. The success of the MSC transplantation therapy may depend on a variety of factors, which importantly, might depend on the ability of these cells to undergo replicative, stress-induced and oncogene-induced cellular senescence in local micro-environment. SMS secreted by MSC might not only affect the ability of the transplanted material to migrate to specific organs, or interact with vascular endothelium and transmigrate across it, but also ultimately to communicate with the immune system to control for tissue and organ homeostasis. Additionally, many therapeutic approaches, particularly those that employ genotoxic stressors, such as irradiation and DNA damaging agents, might also influence the stromal environment within human pathologies. The role of MSC and their stress-induced senescence or TIS need to be better elucidated in the context of the broad spectrum of human malignancies. Since besides cell death, senescence can be induced in tumor cells and surrounding tissue during chemotherapy, radiotherapy and immunotherapy in autocrine and paracrine fashion, the bystander senescence effects of stromal or adult stem cells should be taken into account when developing drugs and therapeutic approaches to counteract with malignancies. In the light of their physiological functions, senescent MSC cells through their SMS may induce changes in the tissue microenvironment and, unless immunologically cleared, could both positively and negatively counteract with therapeutic approaches. A better understanding of senescence process itself will allow us to control and modulate the course of numerous MSC therapeutic treatments, thus ushering only beneficial effects of senescence rather than boosting its detrimental side, which in many ways, might evoke an adverse response to a broad spectrum of therapeutic end-points.VL and MG: Conceived and wrote the review; VL and MG: Generated figures; AA-O: Helped in preparation of the manuscript.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.


The mechanistic target of rapamycin (mTOR), via its two distinct multiprotein complexes, mTORC1, and mTORC2, plays a central role in the regulation of cellular growth, metabolism, and migration. A dysregulation of the mTOR pathway has in turn been implicated in several pathological conditions including insulin resistance and cancer. Overactivation of mTORC1 and disruption of mTORC2 function have been reported to induce insulin resistance. On the other hand, aberrant mTORC1 and mTORC2 signaling via either genetic alterations or increased expression of proteins regulating mTOR and its downstream targets have contributed to cancer development. These underlined the attractiveness of mTOR as a therapeutic target to overcome both insulin resistance and cancer. This review summarizes the evidence supporting the notion of intermittent, low dose rapamycin for treating insulin resistance. It further highlights recent data on the continuous use of high dose rapamycin analogs and related second generation mTOR inhibitors for cancer eradication, for overcoming chemoresistance and for tumor stem cell suppression. Within these contexts, the potential challenges associated with the use of mTOR inhibitors are also discussed. The mechanistic target of rapamycin (mTOR) is an atypical 289-KDa cytoplasmic serine/threonine protein kinase that belongs to the phosphoinositide 3-kinase (PI3K)-related kinase family of molecules  formation. We also emphasized on the need for prudent mTOR targeting to ameliorate insulin resistance. Additionally, an overview on the present status of the use of mTOR inhibitors for cancer and CSCs eradication will be provided.mTOR plays a major role in nutrient sensing within the body. Under normal physiological state, increase in glucose and amino acid levels following a meal stimulates the secretion of insulin by the pancreatic β cells. Insulin begins its effect by binding to its cognate receptor, insulin receptor. Once activated, insulin receptor phosphorylate insulin receptor substrates 1 and 2 (IRS1 and IRS2) at its tyrosine residues, allowing them to associate with PI3K, thereby leading to the activation of downstream effectors such as AKT and protein kinase C , AKT, phosphatase, and tensin homolog (PTEN), PDK1, TSC1/2, RHEB, and EIF4B. Dysregulation of some of them have been reported to induce pathological changes which have been implicated in malignant transformation of cells. Indeed, a deranged PI3K pathway can be found in almost all cancers. Up to 70% of ovarian cancer showed an activated PI3K/AKT/mTORC1 signaling , and TSC1/2. In many cancers, the ability of PTEN, a negative regulator of AKT, to reduce the activity of mTORC1 via AKT is diminished when it is mutated, silenced, or deleted  resulted in increased insulin sensitivity through mTORC1 disruption while prolonged exposure (>24 h) render cells refractory to the actions of insulin via mTORC2 inhibition ]-propionic ester of rapamycin that demonstrated better water solubility and stability In vitro study of everolimus in 24 tumor cell lines demonstrated that everolimus exhibited potent antiproliferative activity with a median IC50 value of 8.8 nM  or 42-O-(2-hydroxyethyl)-rapamycin is another rapalog that has been developed. It is more polar and has improved oral bioavailability compared to rapamycin  has also been developed. Unlike temsirolimus, it is not a rapamycin prodrug and has greater stability compared to the other rapalogs  , indicating the lack of benefit of GDC-0980 over everolimus in this group of patient . To date, most data is available for combination therapy based on rapalogs. Outcomes of these trials again showed high variability . Results from an early phase Ib study of GDC-0980 in combination with carboplatin, paclitaxel with or without bevacizumab or GDC-0980 with cisplatin and pemetrexed in patients with advanced cancer or non-small cell lung cancer (NSCLC) is encouraging with preliminary activity of these combinations observed as in NSCLC (Calvo et al., Overall, current evidence indicates that modulation of mTOR activity with mTOR inhibitors in selected tumors is useful in preventing their progression and overcoming their chemoresistance to other anticancer agents.The notion that therapeutic targeting of mTOR may be useful in eradicating CSCs originates from the prevailing evidence that mTOR signaling is activated in CSCs while its tight regulation is required for maintenance of normal stem cell pool (Yilmaz et al., in vitro and in vivo studies have since identified more second generation mTOR inhibitors with CSCs inhibitory properties (Dubrovska et al., in vitro and in vivo (Fang et al., More importantly, available evidence suggests that the newly developed second generation mTOR inhibitors have stronger preferential inhibitory effect on CSCs compared to normal stem cells than rapamycin or rapalogs (Cai et al., in vitro tumorigenicity as well as in vivo growth of patient derived and BT474 CSCs than either agent alone (Zhu et al., in vitro (Wang W.-J. et al., Although monotherapy of second generation mTOR inhibitors showed promising activity against CSCs in preclinical studies, combinatorial use of rapamycin or these inhibitors with other signal transduction inhibitors or conventional chemotherapeutics/radiotherapy has been promulgated. This arises from the idea that stemness of CSCs can be caused by numerous pathways with mTOR signaling being only one of them (Fitzgerald et al., mTOR is a druggable target implicated in the development of IR and cancer. Careful manipulation of the activities of mTORC1 and mTORC2 complexes may aid in the management of these pathological conditions. For combating IR, care must be taken to avoid mTORC2 inhibition and prolonged reduction of mTORC1 activity. Low dose, intermittent rapamycin use to carefully manage overactivation of mTORC1 is a potential strategy to sensitize cells to the action of insulin. Currently, no human study has been done in this area. Clinical trials should be performed in the future to elucidate a suitable dosing schedule for low dose rapamycin therapy. Additionally, combinatorial use of low dose rapamycin with other agents capable of ameliorating IR should be explored in clinical studies. Two such combinations include concurrent use of low dose rapamycin with either metformin or resveratrol. For the former, the ability of metformin to inhibit hepatic gluconeogenesis may be beneficial for rapamycin therapy since rapamycin use has been known to induce gluconeogenesis. Such mechanism based rationale drug combination may make the use of low dose rapamycin safer. For the latter, combined use of resveratrol with rapamycin has already been shown in murine model to potentiate the action of rapamycin at preventing hyperinsulinemia (Leontieva et al., In cancer treatment, efficacy of mTOR inhibitors in clinical practice is limited to a subset of patient. This has been attributed to a lack of clinically useful predictive markers to guide the use of these agents in patients that are most likely going to benefit from them. Although several preclinical studies and analysis of archival tumor samples from patients who have participated in various trials have identified candidate genetic and non-genetic response markers, these markers may be tumor specific (Weigelt and Downward, Apart from predictive biomarkers identification, resistance to mTOR inhibitors have been increasingly reported (Czarnecka et al., In conclusion, mTOR signaling plays an important role in IR and tumorigenesis. Its careful modulation is crucial to the management of these pathological conditions. Studies to identify rational rapamycin containing regimens may provide an alternative strategy for ameliorating IR. In cancer treatment, data from ongoing trials of second generation mTOR inhibitors may offer opportunities for treating cancers with aberrant mTOR activities. Improvement to mTOR targeted therapy can be further achieved through careful stratification of patients based on predictive biomarkers identified and use of mechanistically synergistic combinations.PO, LW, and GS conceived and designed the manuscript. All authors contributed to the writing.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.