Myocyte enhancer factor 2C as a neurogenic and antiapoptotic transcription factor in murine embryonic stem cells

Calcium and Neural Stem Cell Proliferation

Intracellular calcium plays a pivotal role in central nervous system (CNS) development by regulating various processes such as cell proliferation, migration, differentiation, and maturation. However, understanding the involvement of calcium (Ca2+) in these processes during CNS development is challenging due to the dynamic nature of this cation and the evolving cell populations during development. While Ca2+ transient patterns have been observed in specific cell processes and molecules responsible for Ca2+ homeostasis have been identified in excitable and non-excitable cells, further research into Ca2+ dynamics and the underlying mechanisms in neural stem cells (NSCs) is required. This review focuses on molecules involved in Ca2+ entrance expressed in NSCs in vivo and in vitro, which are crucial for Ca2+ dynamics and signaling. It also discusses how these molecules might play a key role in balancing cell proliferation for self-renewal or promoting differentiation. These processes are finely regulated in a time-dependent manner throughout brain development, influenced by extrinsic and intrinsic factors that directly or indirectly modulate Ca2+ dynamics. Furthermore, this review addresses the potential implications of understanding Ca2+ dynamics in NSCs for treating neurological disorders. Despite significant progress in this field, unraveling the elements contributing to Ca2+ intracellular dynamics in cell proliferation remains a challenging puzzle that requires further investigation.

Genomic patterns linked to gray matter alterations underlying working memory deficits in adults and adolescents with attention-deficit/hyperactivity disorder

Attention-deficit/hyperactivity disorder (ADHD) is a highly heritable neurodevelopmental disorder, with onset in childhood and a considerable likelihood to persist into adulthood. Our previous work has identified that across adults and adolescents with ADHD, gray matter volume (GMV) alteration in the frontal cortex was consistently associated with working memory underperformance, and GMV alteration in the cerebellum was associated with inattention. Recent knowledge regarding ADHD genetic risk loci makes it feasible to investigate genomic factors underlying these persistent GMV alterations, potentially illuminating the pathology of ADHD persistence. Based on this, we applied a sparsity-constrained multivariate data fusion approach, sparse parallel independent component analysis, to GMV variations in the frontal and cerebellum regions and candidate risk single nucleotide polymorphisms (SNPs) data from 341 unrelated adult participants, including 167 individuals with ADHD, 47 unaffected siblings, and 127 healthy controls. We identified one SNP component significantly associated with one GMV component in superior/middle frontal regions and replicated this association in 317 adolescents from ADHD families. The association was stronger in individuals with ADHD than in controls, and stronger in adults and older adolescents than in younger ones. The SNP component highlights 93 SNPs in long non-coding RNAs mainly in chromosome 5 and 21 protein-coding genes that are significantly enriched in human neuron cells. Eighteen identified SNPs have regulation effects on gene expression, transcript expression, isoform percentage, or methylation level in frontal regions. Identified genes highlight MEF2C, CADM2, and CADPS2, which are relevant for modulating neuronal substrates underlying high-level cognition in ADHD, and their causality effects on ADHD persistence await further investigations. Overall, through a multivariate analysis, we have revealed a genomic pattern underpinning the frontal gray matter variation related to working memory deficit in ADHD.

The Role of MEF2 Transcription Factor Family in Neuronal Survival and Degeneration

The family of myocyte enhancer factor 2 (MEF2) transcription factors comprises four highly conserved members that play an important role in the nervous system. They appear in precisely defined time frames in the developing brain to turn on and turn off genes affecting growth, pruning and survival of neurons. MEF2s are known to dictate neuronal development, synaptic plasticity and restrict the number of synapses in the hippocampus, thus affecting learning and memory formation. In primary neurons, negative regulation of MEF2 activity by external stimuli or stress conditions is known to induce apoptosis, albeit the pro or antiapoptotic action of MEF2 depends on the neuronal maturation stage. By contrast, enhancement of MEF2 transcriptional activity protects neurons from apoptotic death both in vitro and in preclinical models of neurodegenerative diseases. A growing body of evidence places this transcription factor in the center of many neuropathologies associated with age-dependent neuronal dysfunctions or gradual but irreversible neuron loss. In this work, we discuss how the altered function of MEF2s during development and in adulthood affecting neuronal survival may be linked to neuropsychiatric disorders.

Transcriptional and functional consequences of alterations to MEF2C and its topological organization in neuronal models

Point mutations and structural variants that directly disrupt the coding sequence of MEF2C have been associated with a spectrum of neurodevelopmental disorders (NDDs). However, the impact of MEF2C haploinsufficiency on neurodevelopmental pathways and synaptic processes is not well understood, nor are the complex mechanisms that govern its regulation. To explore the functional changes associated with structural variants that alter MEF2C expression and/or regulation, we generated an allelic series of 204 isogenic human induced pluripotent stem cell (hiPSC)-derived neural stem cells and glutamatergic induced neurons. These neuronal models harbored CRISPR-engineered mutations that involved direct deletion of MEF2C or deletion of the boundary points for topologically associating domains (TADs) and chromatin loops encompassing MEF2C. Systematic profiling of mutation-specific alterations, contrasted to unedited controls that were exposed to the same guide RNAs for each edit, revealed that deletion of MEF2C caused differential expression of genes associated with neurodevelopmental pathways and synaptic function. We also discovered significant reduction in synaptic activity measured by multielectrode arrays (MEAs) in neuronal cells. By contrast, we observed robust buffering against MEF2C regulatory disruption following deletion of a distal 5q14.3 TAD and loop boundary, whereas homozygous loss of a proximal loop boundary resulted in down-regulation of MEF2C expression and reduced electrophysiological activity on MEA that was comparable to direct gene disruption. Collectively, these studies highlight the considerable functional impact of MEF2C deletion in neuronal cells and systematically characterize the complex interactions that challenge a priori predictions of regulatory consequences from structural variants that disrupt three-dimensional genome organization.

Progress on the roles of MEF2C in neuropsychiatric diseases

Myocyte Enhancer Factor 2 C (MEF2C), one of the transcription factors of the MADS-BOX family, is involved in embryonic brain development, neuronal formation and differentiation, as well as in the growth and pruning of axons and dendrites. MEF2C is also involved in the development of various neuropsychiatric disorders, such as autism spectrum disorders (ASD), epilepsy, schizophrenia and Alzheimer’s disease (AD). Here, we review the relationship between MEF2C and neuropsychiatric disorders, and provide further insights into the mechanism of these diseases.

Transcriptome comparisons detect new genes associated with apoptosis of cattle and buffaloes preantral follicles

Background

To develop new breeding technology to improve the breeding ability of bovine, it is the development trend to find the main reason for the occurrence of atresia in these organisms. Transcriptomes of small (100–120 μm) and large (200–220 μm) preantral follicles from cattle and buffalo ovaries were evaluated in vivo and in vitro to understand the transcriptional modulation in preantral follicles that leads to the phenomenon of atresia.

Methods

The preantral follicles were checked as dead, damage, or live follicles in vivo and in vitro by using trypan blue then bisbenzimide and propidium iodine. Transcriptomes of small (100–120 μm) and large (200–220 μm) preantral follicles of cattle and buffalo were evaluated in vivo and in vitro by microarray and RT-PCR. Healthy preantral follicles were selected based on staining results, and then RNA was extracted from them.

Results

The viability percentage of preantral follicles in cattle was higher (26.7% and 20%) than buffalo (10%) in vivo and in vitro, respectively. According to the microarray data analysis for cattle preantral follicles, only eleven genes were detected corresponding to five upregulated and six downregulated in large size (200–220 μm) compared to small (100–120 μm) size preantral follicles, while in buffalo, 171 genes were detected (92 upregulated and 79 downregulated) in large size compared to small preantral follicle size. The results of RT-PCR of the selected genes (FASTKD1, BAG2, RHOB, AGTR2, MEF2C, BCL10, G2E3, TM2D1, IGF-I, IGFBP3, PRDX3, and TRIAP1) validated the microarray results. In conclusion, the data of gene expression showed significant differences between small and large sizes in both buffalo and cattle preantral follicles.

Conclusion

Apoptotic genes were upregulated in the large preantral follicle compared with the small preantral follicles. Moreover, the expression level of these apoptotic genes was significantly upregulated in buffalo than in the cattle. Most of these genes were significantly upregulated in the large buffalo preantral follicle compared with the small size. However, anti-apoptotic genes were upregulated in large cattle preantral follicle and downregulated in large buffalo preantral follicle.

Involvement of myocyte enhancer factor 2c in the pathogenesis of autism spectrum disorder

Myocyte enhancer factor 2 (MEF2), a family of transcription factor of MADS (minichromosome maintenance 1, agamous, deficiens and serum response factor)-box family needed in the growth and differentiation of a variety of human cells, such as neural, immune, endothelial, and muscles. As per existing literature, MEF2 transcription factors have also been associated with synaptic plasticity, the developmental mechanisms governing memory and learning, and several neurologic conditions, like autism spectrum disorders (ASDs). Recent genomic findings have ascertained a link between MEF2 defects, particularly in the MEF2C isoform and the ASD. In this review, we summarized a concise overview of the general regulation, structure and functional roles of the MEF2C transcription factor. We further outlined the potential role of MEF2C as a risk factor for various neurodevelopmental disorders, such as ASD, MEF2C Haploinsufficiency Syndrome and Fragile X syndrome.

Genotypes and Phenotypes of MEF2C Haploinsufficiency Syndrome: New Cases and Novel Point Mutations

Aim: MEF2C haploinsufficiency syndrome (MCHS) is a severe neurodevelopmental disorder. We describe the clinical phenotypes and genotypes of seven patients with MCHS to enhance the understanding of clinical manifestations and genetic alterations associated with MCHS. Method: Seven patients (6 females and 1 male, aged between 2 years 5 months and 6 years) who had MEF2C mutations, and their parents underwent trio-based whole-exome sequencing; subsequently, their clinical features were assessed. A literature review of patients with MCHS was performed by searching the PubMed and Online Mendelian Inheritance in Man databases. Results: Seven mutations were identified, of which six were unreported in the past; of the reported cases, five patients had de novo mutations but two had an undefined inheritance pattern. All patients presented delays in developmental milestones, severe intellectual disabilities and lack of speech. Six patients exhibited infantile hypotonia, five patients experienced stereotypic movements and were unable to walk, four patients exhibited poor eye contact indicative of autism and two showed poor performance. While six patients experienced seizure, five among them became seizure free after receiving anti-seizure medicine. Three patients showed a regression in their development, whereas the mothers of two patients exhibited mosaicism but were healthy without any abovementioned symptoms. Interpretation: Regression was not a common phenomenon but occurred in MCHS. The prognosis of MCHS patients with epilepsy was good, but most patients can achieve a seizure-free status. Healthy people may have low-level mosaicism and carry a pathogenic MEF2C mutation.

Critical regulation of a NDIME/MEF2C axis in embryonic stem cell neural differentiation and autism

A microdeletion within human chromosome 5q14.3 has been associated with the occurrence of neurodevelopmental disorders, such as autism and intellectual disability, and MEF2C haploinsufficiency was identified as main cause. Here, we report that a brain-enriched long non-coding RNA, NDIME, is located near the MEF2C locus and is required for normal neural differentiation of mouse embryonic stem cells (mESCs). NDIME interacts with EZH2, the major component of polycomb repressive complex 2 (PRC2), and blocks EZH2-mediated trimethylation of histone H3 lysine 27 (H3K27me3) at the Mef2c promoter, promoting MEF2C transcription. Moreover, the expression levels of both NDIME and MEF2C were strongly downregulated in the hippocampus of a mouse model of autism, and the adeno-associated virus (AAV)-mediated expression of NDIME in the hippocampus of these mice significantly increased MEF2C expression and ameliorated autism-like behaviors. The results of this study reveal an epigenetic mechanism by which NDIME regulates MEF2C transcription and neural differentiation and suggest potential effects and therapeutic approaches of the NDIME/MEF2C axis in autism.

Fast-tracking regenerative medicine for traumatic brain injury

Traumatic brain injury remains a global health crisis that spans all demographics, yet there exist limited treatment options that may effectively curtail its lingering symptoms. Traumatic brain injury pathology entails a progression from primary injury to inflammation-mediated secondary cell death. Sequestering this inflammation as a means of ameliorating the greater symptomology of traumatic brain injury has emerged as an attractive treatment prospect. In this review, we recapitulate and evaluate the important developments relating to regulating traumatic brain injury-induced neuroinflammation, edema, and blood-brain barrier disintegration through pharmacotherapy and stem cell transplants. Although these studies of stand-alone treatments have yielded some positive results, more therapeutic outcomes have been documented from the promising area of combined drug and stem cell therapy. Harnessing the facilitatory properties of certain pharmaceuticals with the anti-inflammatory and regenerative effects of stem cell transplants creates a synergistic effect greater than the sum of its parts. The burgeoning evidence in favor of combined drug and stem cell therapies warrants more elaborate preclinical studies on this topic in order to pave the way for later clinical trials.

Sex-specific impact of prenatal androgens on social brain default mode subsystems

Early-onset neurodevelopmental conditions (e.g., autism) affect males more frequently than females. Androgens may play a role in this male-bias by sex-differentially impacting early prenatal brain development, particularly neural circuits that later develop specialized roles in social cognition. Here, we find that increasing prenatal testosterone in humans is associated with later reduction of functional connectivity between social brain default mode (DMN) subsystems in adolescent males, but has no effect in females. Since testosterone can work directly via the androgen receptor (AR) or indirectly via the estrogen receptor through aromatase conversion to estradiol, we further examined how a potent non-aromatizable androgen, dihydrotestosterone (DHT), acts via the AR to influence gene expression in human neural stem cells (hNSC)-particularly for genes of high-relevance for DMN circuitry. DHT dysregulates a number of genes enriched for syndromic causes of autism and intellectual disability and for genes that in later development are expressed in anatomical patterns that highly correspond to the cortical midline DMN subsystem. DMN-related and DHT-affected genes (e.g., MEF2C) are involved in a number of synaptic processes, many of which impact excitation-inhibition balance. Androgens have male-specific prenatal influence over social brain circuitry in humans and may be relevant towards explaining some component of male-bias in early-onset neurodevelopmental conditions.

Emerging roles for MEF2 in brain development and mental disorders

The MEF2 family of transcription factors regulate large programs of gene expression important for the development and maintenance of many tissues, including the brain. MEF2 proteins are regulated by neuronal synaptic activity, and they recruit several epigenetic enzymes to influence chromatin structure and gene expression during development and throughout adulthood. Here, we provide a brief review of the recent literature reporting important roles for MEF2 during early brain development and function, and we highlight emerging roles for MEF2 as a risk factor for multiple neurodevelopmental disorders and mental illnesses, such as autism, intellectual disability, and schizophrenia.

HDAC4 in ischemic stroke: mechanisms and therapeutic potential

Stroke is one of the leading causes of death and disability worldwide, and the majority of the cases are ischemic stroke. However, it still lacks effective treatment except for thrombolytic therapy in an extremely narrow time window. Increased evidence suggests that histone deacetylase 4 (HDAC4) was dysregulated in ischemic stroke, which plays a key role in the pathogenesis of ischemic stroke and post-stroke recovery by affecting neuronal death, angiogenesis, and neurogenesis. Therefore, we aim to review the dysregulation of HDAC4 in ischemic stroke and the role of dysregulated HDAC4 in the pathogenesis of ischemic stroke. Furthermore, the therapeutic potential of modulating HDAC4 in ischemic stroke is discussed.

NitroSynapsin therapy for a mouse MEF2C haploinsufficiency model of human autism

Transcription factor MEF2C regulates multiple genes linked to autism spectrum disorder (ASD), and human MEF2C haploinsufficiency results in ASD, intellectual disability, and epilepsy. However, molecular mechanisms underlying MEF2C haploinsufficiency syndrome remain poorly understood. Here we report that Mef2c +/-(Mef2c-het) mice exhibit behavioral deficits resembling those of human patients. Gene expression analyses on brains from these mice show changes in genes associated with neurogenesis, synapse formation, and neuronal cell death. Accordingly, Mef2c-het mice exhibit decreased neurogenesis, enhanced neuronal apoptosis, and an increased ratio of excitatory to inhibitory (E/I) neurotransmission. Importantly, neurobehavioral deficits, E/I imbalance, and histological damage are all ameliorated by treatment with NitroSynapsin, a new dual-action compound related to the FDA-approved drug memantine, representing an uncompetitive/fast off-rate antagonist of NMDA-type glutamate receptors. These results suggest that MEF2C haploinsufficiency leads to abnormal brain development, E/I imbalance, and neurobehavioral dysfunction, which may be mitigated by pharmacological intervention.

Getting Closer to an Effective Intervention of Ischemic Stroke: The Big Promise of Stem Cell

Stem cell therapy for ischemic stroke has widely been explored. Results from both preclinical and clinical studies have immensely supported the judicious use of stem cells as therapy. These provide an attractive means for preserving and replacing the damaged brain tissues following an ischemic attack. Since the past few years, researchers have used various types of stem cells to replenish insulted neuronal and glial cells in neurological disorders. In the present review, we discuss different types of stem cells employed for the treatment of ischemic stroke and mechanisms and challenges these cells face once introduced into the living system. Further, we also present different ways to maneuver and overcome challenges to translate the advances made at the preclinical level to clinics.

Molecular Pathway to Protection From Age-Dependent Photoreceptor Degeneration in Mef2 Deficiency

Purpose

Photoreceptor degeneration in the retina is a major cause of blindness in humans. Elucidating mechanisms of degenerative and neuroprotective pathways in photoreceptors should afford identification and development of therapeutic strategies.

Methods

We used mouse genetic models and improved methods for retinal explant cultures. Retinas were enucleated from Mef2d^+/+ and Mef2d^−/− mice, stained for MEF2 proteins and outer nuclear layer thickness, and assayed for apoptotic cells. Chromatin immunoprecipitation (ChIP) assays revealed MEF2 binding, and RT-qPCR showed levels of transcription factors. We used AAV2 and electroporation to express genes in retinal explants and electroretinograms to assess photoreceptor functionality.

Results

We identify a prosurvival MEF2D-PGC1α pathway that plays a neuroprotective role in photoreceptors. We demonstrate that Mef2d^−/− mouse retinas manifest decreased expression of PGC1α and increased photoreceptor cell loss, resulting in the absence of light responses. Molecular repletion of PGC1α protects Mef2d^−/− photoreceptors and preserves light responsivity.

Conclusions

These results suggest that the MEF2-PGC1α cascade may represent a new therapeutic target for drugs designed to protect photoreceptors from developmental- and age-dependent loss.

miR-124 and miR-9 mediated downregulation of HDAC5 promotes neurite development through activating MEF2C-GPM6A pathway

The class IIa histone deacetylases (HDACs) play important roles in the central nervous system during diverse biological processes such as synaptic plasticity, axon regeneration, cell apoptosis, and neural differentiation. Although it is known that HDAC5 regulates neuronal differentiation, neither the physiological function nor the regulation of HDAC5 in neuronal differentiation is clear. Here, we identify HDAC5 as an inhibitor of neurite elongation and show that HDAC5 is regulated by the brain enriched microRNA miR-124 and miR-9. We discover that HDAC5 inhibits neurite extension both in differentiated P19 cells and primary neurons. We also show that the neuronal membrane glycoprotein GPM6A (M6a) is a direct target gene of HDAC5 regulated transcriptional factor MEF2C. HDAC5 inhibits neurite elongation, acting at least partially via a MEF2C/M6a signaling pathway. We also confirmed the miR-124/miR-9 regulated HDAC5-MEF2C-M6a pathway regulates neurite development in primary neurons. Thus, HDAC5 emerges as a cellular conductor of MEF2C and M6a activity and is regulated by miR-124 and miR-9 to control neurite development.

Neuregulin1β Effects on Brain Tissue via ERK5-Dependent MAPK Pathway in a Rat Model of Cerebral Ischemia-Reperfusion Injury

Neuregulin1β (NRG1β), a member of the excitomotor of tyrosine kinase receptor (erbB) family, was recently shown to play a neuroprotective role in cerebral ischemia-reperfusion injury. The present study analyzed the effects and its possible signaling pathway of NRG1β on brain tissues after cerebral ischemia-reperfusion injury. A focal cerebral ischemic model was established by inserting a monofilament thread to achieve middle cerebral artery occlusion, followed by an NRG1β injection via the internal carotid artery. NRG1β injection resulted in significantly improved neurobehavioral activity according to the modified neurological severity score test. Tetrazolium chloridestaining revealed a smaller cerebral infarction volume; hematoxylin-eosin staining and transmission electron microscopy showed significantly alleviated neurodegeneration in the middle cerebral artery occlusion rats. Moreover, expression of phosphorylated MEK5, phosphorylated ERK5, and phosphorylated MEK2C increased after NRG1β treatment, and the neuroprotective effect of NRG1β was attenuated by an injection of the MEK5 inhibitor, BIX02189. Results from the present study demonstrate that NRG1β provides neuroprotection following cerebral ischemia-reperfusion injury via the ERK5-dependent MAPK pathway.

MEF2 transcription factors: developmental regulators and emerging cancer genes

The MEF2 transcription factors have roles in muscle, cardiac, skeletal, vascular, neural, blood and immune system cell development through their effects on cell differentiation, proliferation, apoptosis, migration, shape and metabolism. Altered MEF2 activity plays a role in human diseases and has recently been implicated in the development of several cancer types. In particular, MEF2B, the most divergent and least studied protein of the MEF2 family, has a role unique from its paralogs in non-Hodgkin lymphomas. The use of genome-scale technologies has enabled comprehensive MEF2 target gene sets to be identified, contributing to our understanding of MEF2 proteins as nodes in complex regulatory networks. This review surveys the molecular interactions of MEF2 proteins and their effects on cellular and organismal phenotypes. We include a discussion of the emerging roles of MEF2 proteins as oncogenes and tumor suppressors of cancer. Throughout this article we highlight similarities and differences between the MEF2 family proteins, including a focus on functions of MEF2B.

Recent Advances in Stem Cell-Based Therapeutics for Stroke

Regenerative medicine for central nervous system disorders, including stroke, has challenged the non-regenerative capacity of the brain. Among the many treatment strategies tailored towards repairing the injured brain, stem cell-based therapeutics have been demonstrated as safe and effective in animal models of stroke, and are being tested in limited clinical trials. We address here key lab-to-clinic translational research that relate to efficacy, safety, and mechanism of action underlying stem cell therapy. Recognizing the multi-pronged cell death processes associated with stroke that will likely require combination therapies, we next discuss potent drugs and novel technologies directed at improving the functional outcomes of stem cell-based therapeutics. We also examine discrepant transplant regimens between preclinical studies and clinical trials, as well as missing appropriate control arm (i.e., stroke subjects undergoing rehabilitation) on which to directly compare the therapeutic benefits of cell therapy. Finally, the bioethics of cell therapy is presented in order to assess its prevailing social status. With preliminary results now being reported from on-going clinical trials of stem cell therapy for stroke, a careful assessment of the true functional benefits of this novel treatment will further direct the future of regenerative medicine for neurological disorders.

Utilizing pharmacotherapy and mesenchymal stem cell therapy to reduce inflammation following traumatic brain injury

The pathologic process of chronic phase traumatic brain injury is associated with spreading inflammation, cell death, and neural dysfunction. It is thought that sequestration of inflammatory mediators can facilitate recovery and promote an environment that fosters cellular regeneration. Studies have targeted post-traumatic brain injury inflammation with the use of pharmacotherapy and cell therapy. These therapeutic options are aimed at reducing the edematous and neurodegenerative inflammation that have been associated with compromising the integrity of the blood-brain barrier. Although studies have yielded positive results from anti-inflammatory pharmacotherapy and cell therapy individually, emerging research has begun to target inflammation using combination therapy. The joint use of anti-inflammatory drugs alongside stem cell transplantation may provide better clinical outcomes for traumatic brain injury patients. Despite the promising results in this field of research, it is important to note that most of the studies mentioned in this review have completed their studies using animal models. Translation of this research into a clinical setting will require additional laboratory experiments and larger preclinical trials.

Inducible knockout of Mef2a, -c, and -d from nestin-expressing stem/progenitor cells and their progeny unexpectedly uncouples neurogenesis and dendritogenesis in vivo

Myocyte enhancer factor (Mef)-2 transcription factors are implicated in activity-dependent neuronal processes during development, but the role of MEF2 in neural stem/progenitor cells (NSPCs) in the adult brain is unknown. We used a transgenic mouse in which Mef2a, -c, and -d were inducibly deleted in adult nestin-expressing NSPCs and their progeny. Recombined cells in the hippocampal granule cell layer were visualized and quantified by yellow fluorescent protein (YFP) expression. In control mice, postmitotic neurons expressed Mef2a, -c, and -d, whereas type 1 stem cells and proliferating progenitors did not. Based on this expression, we hypothesized that Mef2a, -c, and -d deletion in adult nestin-expressing NSPCs and their progeny would result in fewer mature neurons. Control mice revealed an increase in YFP(+) neurons and dendrite formation over time. Contrary to our hypothesis, inducible Mef2 KO mice also displayed an increase in YFP(+) neurons over time-but with significantly stunted dendrites-suggesting an uncoupling of neuron survival and dendritogenesis. We also found non-cell-autonomous effects after Mef2a, -c, and -d deletion. These in vivo findings indicate a surprising functional role for Mef2a, -c, and -d in cell- and non-cell-autonomous control of adult hippocampal neurogenesis that is distinct from its role during development.

Optogenetic Stimulation of Neural Grafts Enhances Neurotransmission and Downregulates the Inflammatory Response in Experimental Stroke Model

Compelling evidence suggests that transplantation of neural stem cells (NSCs) from multiple sources ameliorates motor deficits after stroke. However, it is currently unknown to what extent the electrophysiological activity of grafted NSC progeny participates in the improvement of motor deficits and whether excitatory phenotypes of the grafted cells are beneficial or deleterious to sensorimotor performances. To address this question, we used optogenetic tools to drive the excitatory outputs of the grafted NSCs and assess the impact on local circuitry and sensorimotor performance. We genetically engineered NSCs to express the Channelrhodopsin-2 (ChR2), a light-gated cation channel that evokes neuronal depolarization and initiation of action potentials with precise temporal control to light stimulation. To test the function of these cells in a stroke model, rats were subjected to an ischemic stroke and grafted with ChR2-NSCs. The grafted NSCs identified with a human-specific nuclear marker survived in the peri-infarct tissue and coexpressed the ChR2 transgene with the neuronal markers TuJ1 and NeuN. Gene expression analysis in stimulated versus vehicle-treated animals showed a differential upregulation of transcripts involved in neurotransmission, neuronal differentiation, regeneration, axonal guidance, and synaptic plasticity. Interestingly, genes involved in the inflammatory response were significantly downregulated. Behavioral analysis demonstrated that chronic optogenetic stimulation of the ChR2-NSCs enhanced forelimb use on the stroke-affected side and motor activity in an open field test. Together these data suggest that excitatory stimulation of grafted NSCs elicits beneficial effects in experimental stroke model through cell replacement and non-cell replacement, anti-inflammatory/neurotrophic effects.

Molecular mechanisms in the regulation of adult neurogenesis during stress

Coping with stress is fundamental for mental health, but understanding of the molecular neurobiology of stress is still in its infancy. Adult neurogenesis is well known to be regulated by stress, and conversely adult neurogenesis regulates stress responses. Recent studies in neurogenic cells indicate that molecular pathways activated by glucocorticoids, the main stress hormones, are modulated by crosstalk with other stress-relevant mechanisms, including inflammatory mediators, neurotrophic factors and morphogen signalling pathways. This Review discusses the pathways that are involved in this crosstalk and thus regulate this complex relationship between adult neurogenesis and stress.

S-Nitrosylation in neurogenesis and neuronal development

BACKGROUND

Nitric oxide (NO) is a pleiotropic messenger molecule. The multidimensional actions of NO species are, in part, mediated by their redox nature. Oxidative posttranslational modification of cysteine residues to regulate protein function, termed S-nitrosylation, constitutes a major form of redox-based signaling by NO.

SCOPE OF REVIEW

S-Nitrosylation directly modifies a number of cytoplasmic and nuclear proteins in neurons. S-Nitrosylation modulates neuronal development by reaction with specific proteins, including the transcription factor MEF2. This review focuses on the impact of S-nitrosylation on neurogenesis and neuronal development.

MAJOR CONCLUSIONS

Functional characterization of S-nitrosylated proteins that regulate neuronal development represents a rapidly emerging field. Recent studies reveal that S-nitrosylation-mediated redox signaling plays an important role in several biological processes essential for neuronal differentiation and maturation.

GENERAL SIGNIFICANCE

Investigation of S-nitrosylation in the nervous system has elucidated new molecular and cellular mechanisms for neuronal development. S-Nitrosylated proteins in signaling networks modulate key events in brain development. Dysregulation of this redox-signaling pathway may contribute to neurodevelopmental disabilities such as autism spectrum disorder (ASD). Thus, further elucidation of the involvement of S-nitrosylation in brain development may offer potential therapeutic avenues for neurodevelopmental disorders. This article is part of a Special Issue entitled Redox regulation of differentiation and de-differentiation.

Stem cell transplantation for neuroprotection in stroke

Stem cell-based therapies for stroke have expanded substantially over the last decade. The diversity of embryonic and adult tissue sources provides researchers with the ability to harvest an ample supply of stem cells. However, the optimal conditions of stem cell use are still being determined. Along this line of the need for optimization studies, we discuss studies that demonstrate effective dose, timing, and route of stem cells. We recognize that stem cell derivations also provide uniquely individual difficulties and limitations in their therapeutic applications. This review will outline the current knowledge, including benefits and challenges, of the many current sources of stem cells for stroke therapy.

ATM-dependent phosphorylation of MEF2D promotes neuronal survival after DNA damage

Mutations in the ataxia telangiectasia mutated (ATM) gene, which encodes a kinase critical for the normal DNA damage response, cause the neurodegenerative disorder ataxia-telangiectasia (AT). The substrates of ATM in the brain are poorly understood. Here we demonstrate that ATM phosphorylates and activates the transcription factor myocyte enhancer factor 2D (MEF2D), which plays a critical role in promoting survival of cerebellar granule cells. ATM associates with MEF2D after DNA damage and phosphorylates the transcription factor at four ATM consensus sites. Knockdown of endogenous MEF2D with a short-hairpin RNA (shRNA) increases sensitivity to etoposide-induced DNA damage and neuronal cell death. Interestingly, substitution of endogenous MEF2D with an shRNA-resistant phosphomimetic MEF2D mutant protects cerebellar granule cells from cell death after DNA damage, whereas an shRNA-resistant nonphosphorylatable MEF2D mutant does not. In vivo, cerebella in Mef2d knock-out mice manifest increased susceptibility to DNA damage. Together, our results show that MEF2D is a substrate for phosphorylation by ATM, thus promoting survival in response to DNA damage. Moreover, dysregulation of the ATM-MEF2D pathway may contribute to neurodegeneration in AT.

Potential for cell therapy in Parkinson's disease using genetically programmed human embryonic stem cell-derived neural progenitor cells

Neural transplantation is a promising strategy for restoring dopaminergic dysfunction and modifying disease progression in Parkinson's disease (PD). Human embryonic stem cells (hESCs) are a potential resource in this regard because of their ability to provide a virtually limitless supply of homogenous dopaminergic progenitors and neurons of appropriate lineage. The recent advances in developing robust cell culture protocols for directed differentiation of hESCs to near pure populations of ventral mesencephalic (A9-type) dopaminergic neurons has heightened the prospects for PD cell therapy. Here, we focus our review on current state-of-the-art techniques for harnessing hESC-based strategies toward development of a stem cell therapeutic for PD. Importantly, we also briefly describe a novel genetic-programming approach that may address many of the key challenges that remain in the field and that may hasten clinical translation.

Isogenic human iPSC Parkinson's model shows nitrosative stress-induced dysfunction in MEF2-PGC1α transcription

Parkinson's disease (PD) is characterized by loss of A9 dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc). An association has been reported between PD and exposure to mitochondrial toxins, including environmental pesticides paraquat, maneb, and rotenone. Here, using a robust, patient-derived stem cell model of PD allowing comparison of A53T α-synuclein (α-syn) mutant cells and isogenic mutation-corrected controls, we identify mitochondrial toxin-induced perturbations in A53T α-syn A9 DA neurons (hNs). We report a pathway whereby basal and toxin-induced nitrosative/oxidative stress results in S-nitrosylation of transcription factor MEF2C in A53T hNs compared to corrected controls. This redox reaction inhibits the MEF2C-PGC1α transcriptional network, contributing to mitochondrial dysfunction and apoptotic cell death. Our data provide mechanistic insight into gene-environmental interaction (GxE) in the pathogenesis of PD. Furthermore, using small-molecule high-throughput screening, we identify the MEF2C-PGC1α pathway as a therapeutic target to combat PD.

An Update on Translating Stem Cell Therapy for Stroke from Bench to Bedside

With a constellation of stem cell sources available, researchers hope to utilize their potential for cellular repair as a therapeutic target for disease. However, many lab-to-clinic translational considerations must be given in determining their efficacy, variables such as the host response, effects on native tissue, and potential for generating tumors. This review will discuss the current knowledge of stem cell research in neurological disease, mainly stroke, with a focus on the benefits, limitations, and clinical potential.

Ethanol diverts early neuronal differentiation trajectory of embryonic stem cells by disrupting the balance of lineage specifiers

Background

Ethanol is a toxin responsible for the neurodevelopmental deficits of Fetal Alcohol Spectrum Disorders (FASD). Recent evidence suggests that ethanol modulates the protein expression of lineage specifier transcription factors Oct4 (Pou5f1) and Sox2 in early stages of mouse embryonic stem (ES) cell differentiation. We hypothesized that ethanol induced an imbalance in the expression of Oct4 and Sox2 in early differentiation, that dysregulated the expression of associated and target genes and signaling molecules and diverted cells from neuroectodermal (NE) formation.

Methodology/Principal Findings

We showed modulation by ethanol of 33 genes during ES cell differentiation, using high throughput microfluidic dynamic array chips measuring 2,304 real time quantitative PCR assays. Based on the overall gene expression dynamics, ethanol drove cells along a differentiation trajectory away from NE fate. These ethanol-induced gene expression changes were observed as early as within 2 days of differentiation, and were independent of cell proliferation or apoptosis. Gene expression changes were correlated with fewer βIII-tubulin positive cells of an immature neural progenitor phenotype, as well as a disrupted actin cytoskeleton were observed. Moreover, Tuba1a and Gapdh housekeeping genes were modulated by ethanol during differentiation and were replaced by a set of ribosomal genes with stable expression.

Conclusions/Significance

These findings provided an ethanol-response gene signature and pointed to the transcriptional dynamics underlying lineage imbalance that may be relevant to FASD phenotype.

Myocyte enhancer factor 2C in hematopoiesis and leukemia

MEF2C is a selectively expressed transcription factor involved in different transcriptional complexes. Originally identified as an essential regulator of muscle development, ectopic expression of MEF2C as a result of chromosomal rearrangements is now linked to leukemia. Specifically, high MEF2C expression has been linked to mixed lineage leukemia-rearranged acute myeloid leukemia as well as to the immature subgroup of T-cell acute lymphoblastic leukemia. This review focuses on the role of MEF2C in the hematopoietic system and on aberrant MEF2C expression in human leukemia.

MEF2C Haploinsufficiency features consistent hyperkinesis, variable epilepsy, and has a role in dorsal and ventral neuronal developmental pathways

MEF2C haploinsufficiency syndrome is an emerging neurodevelopmental disorder associated with intellectual disability, autistic features, epilepsy, and abnormal movements. We report 16 new patients with MEF2C haploinsufficiency, including the oldest reported patient with MEF2C deletion at 5q14.3. We detail the neurobehavioral phenotype, epilepsy, and abnormal movements, and compare our subjects with those previously reported in the literature. We also investigate Mef2c expression in the developing mouse forebrain. A spectrum of neurofunctional deficits emerges, with hyperkinesis a consistent finding. Epilepsy varied from absent to severe, and included intractable myoclonic seizures and infantile spasms. Subjects with partial MEF2C deletion were statistically less likely to have epilepsy. Finally, we confirm that Mef2c is present both in dorsal primary neuroblasts and ventral gamma-aminobutyric acid(GABA)ergic interneurons in the forebrain of the developing mouse. Given interactions with several key neurodevelopmental genes such as ARX, FMR1, MECP2, and TBR1, it appears that MEF2C plays a role in several developmental stages of both dorsal and ventral neuronal cell types.

High-frequency hippocampal oscillations activated by optogenetic stimulation of transplanted human ESC-derived neurons

After transplantation, individual stem cell-derived neurons can functionally integrate into the host CNS; however, evidence that neurons derived from transplanted human embryonic stem cells (hESCs) can drive endogenous neuronal network activity in CNS tissue is still lacking. Here, using multielectrode array recordings, we report activation of high-frequency oscillations in the β and γ ranges (10-100 Hz) in the host hippocampal network via targeted optogenetic stimulation of transplanted hESC-derived neurons.

The MEF2C-Related and 5q14.3q15 Microdeletion Syndrome

Disorders related to the autosomal transcription factor MEF2C located in 5q14.3 were first described in 2009 and have since evolved to one of the more common microdeletion syndromes. Mutational screening in a larger cohort revealed heterozygous de novo mutations of MEF2C in about 1% of patients with moderate to severe intellectual disability, and the phenotype is similar in patients with intragenic deletions and multigenic microdeletions. Clinically, MEF2C-related disorders are characterized by severe intellectual disability with absent speech and limited walking abilities, hypotonia, seizures, and a variety of minor brain anomalies. The majority of patients show a similar facial gestalt with broad forehead, flat nasal bridge, hypotonic mouth, and small chin, as well as strabismus, but this phenotype is clinically not well recognized. The course of the disease is generally quite uniform, but patients with point mutations and smaller deletions seem to have a higher chance of walking skills and a lower risk of refractory seizures. Patients in whom the microdeletion also includes the RASA1 gene show features of the respective capillary and arterio-venous malformations and fistula syndrome. The phenotypic overlap with Rett syndrome is explained by a shared pathway and, accordingly, diminished MECP2 and CDKL5 expression is measureable in patients with MEF2C defects. Further research of this pathway may therefore eventually lead to a common therapeutic target.

MEF2C enhances dopaminergic neuron differentiation of human embryonic stem cells in a parkinsonian rat model

Human embryonic stem cells (hESCs) can potentially differentiate into any cell type, including dopaminergic neurons to treat Parkinson's disease (PD), but hyperproliferation and tumor formation must be avoided. Accordingly, we use myocyte enhancer factor 2C (MEF2C) as a neurogenic and anti-apoptotic transcription factor to generate neurons from hESC-derived neural stem/progenitor cells (NPCs), thus avoiding hyperproliferation. Here, we report that forced expression of constitutively active MEF2C (MEF2CA) generates significantly greater numbers of neurons with dopaminergic properties in vitro. Conversely, RNAi knockdown of MEF2C in NPCs decreases neuronal differentiation and dendritic length. When we inject MEF2CA-programmed NPCs into 6-hydroxydopamine—lesioned Parkinsonian rats in vivo, the transplanted cells survive well, differentiate into tyrosine hydroxylase-positive neurons, and improve behavioral deficits to a significantly greater degree than non-programmed cells. The enriched generation of dopaminergic neuronal lineages from hESCs by forced expression of MEF2CA in the proper context may prove valuable in cell-based therapy for CNS disorders such as PD.

MicroRNA-21 dysregulates the expression of MEF2C in neurons in monkey and human SIV/HIV neurological disease

MicroRNAs (miRNAs) have important roles in regulating a plethora of physiological and pathophysiogical processes including neurodegeneration. In both human immunodeficiency virus (HIV)-associated dementia in humans and its monkey model simian immunodeficiency virus encephalitis (SIVE), we find miR-21, a miRNA largely known for its link to oncogenesis, to be significantly upregulated in the brain. In situ hybridization of the diseased brain sections revealed induction of miR-21 in neurons. miR-21 can be induced in neurons by prolonged N-methyl--aspartic acid receptor stimulation, an excitotoxic process active in HIV and other neurodegenerative diseases. Introduction of miR-21 into human neurons leads to pathological functional defects. Furthermore, we show that miR-21 specifically targets the mRNA of myocyte enhancer factor 2C (MEF2C), a transcription factor crucial for neuronal function, and reduces its expression. MEF2C is dramatically downregulated in neurons of HIV-associated dementia patients, as well as monkeys with SIVE. Together, this study elucidates a novel role for miR-21 in the brain, not only as a potential signature of neurological disease, but also as a crucial effector of HIV-induced neuronal dysfunction and neurodegeneration.

Ascl1/Mash1 is a novel target of Gli2 during Gli2-induced neurogenesis in P19 EC cells

The Sonic Hedgehog (Shh) signaling pathway is important for neurogenesis in vivo. Gli transcription factors, effector proteins of the Shh signaling pathway, have neurogenic properties in vivo, which are still poorly understood. To study the molecular basis of neurogenic properties of Gli2, we used a well-established embryonic stem cell model, the P19 embryonal carcinoma (EC) cell line, which can be induced to differentiate into neurons in the presence of retinoic acid (RA). We found that, in the absence of RA, overexpression of Gli2 induced P19 EC cells to differentiate into neurons, but not astrocytes during the first ten days of differentiation. To our knowledge, this is the first indication that the expression of Gli factors can convert EC cells into neurons. Furthermore, Gli2 upregulated expression of the neurogenic basic helix-loop-helix (bHLH) factors, such as NeuroD, Neurog1 and Ascl1/Mash1 in P19 EC cells. Using chromatin immunoprecipitation assays, we showed that Gli2 bound to multiple regulatory regions in the Ascl1 gene, including promoter and enhancer regions during Gli2-induced neurogenesis. In addition, Gli2 activated the Ascl1/Mash1 promoter in vitro. Using the expression of a dominant-negative form of Gli2, fused to the Engrailed repression domain, we observed a reduction in gliogenesis and a significant downregulation of the bHLH factors Ascl1/Mash1, Neurog1 and NeuroD, leading to delayed neurogenesis in P19 EC cells, further supporting the hypothesis that Ascl1/Mash1 is a direct target of Gli2. In summary, Gli2 is sufficient to induce neurogenesis in P19 stem cells at least in part by directly upregulating Ascl1/Mash1. Our results provide mechanistic insight into the neurogenic properties of Gli2 in vitro, and offer novel plausible explanations for its in vivo neurogenic properties.

The transcriptional response to chronic stress and glucocorticoid receptor blockade in the hippocampal dentate gyrus

The dentate gyrus (DG) of the hippocampus plays a crucial role in learning and memory. This subregion is unique in its ability to generate new neurons throughout life and integrate these new neurons into the hippocampal circuitry. Neurogenesis has further been implicated in hippocampal plasticity and depression. Exposure to chronic stress affects DG function and morphology and suppresses neurogenesis and long-term potentiation (LTP) with consequences for cognition. Previous studies demonstrated that glucocorticoid receptor (GR) blockade by a brief treatment with the GR antagonist mifepristone (RU486) rapidly reverses the stress and glucocorticoid effects on neurogenesis. The molecular pathways underlying both the stress-induced effects and the RU486 effects on the DG are, however, largely unknown. The aim of this study was therefore (1) to investigate by microarray analysis which genes and pathways in the DG are sensitive to chronic stress and (2) to investigate to what extent blockade of GR can normalize these stress-induced effects on DG gene expression. Chronic stress exposure affected the expression of 90 genes in the DG (P < 0.01), with an overrepresentation of genes involved in brain development and morphogenesis and synaptic transmission. RU486 treatment of stressed animals affected expression of 107 genes; however, mostly different genes than those responding to stress. Interestingly, we found CREBBP to be normalized by RU486 treatment to levels observed in control animals, suggesting that CREB-signaling may play a central role in mediating the chronic stress effects on neurogenesis, LTP and calcium currents. The identified genetic pathways provide insight into the stress-induced adaptive plasticity of the hippocampal DG that is so central in learning and memory and will direct future studies on the functional outcome and modulation of these stress effects.

Mutations in MEF2C from the 5q14.3q15 microdeletion syndrome region are a frequent cause of severe mental retardation and diminish MECP2 and CDKL5 expression

The etiology of mental retardation remains elusive in the majority of cases. Microdeletions within chromosomal bands 5q14.3q15 were recently identified as a recurrent cause of severe mental retardation, epilepsy, muscular hypotonia, and variable minor anomalies. By molecular karyotyping we identified two novel 2.4- and 1.5-Mb microdeletions of this region in patients with a similar phenotype. Both deletions contained the MEF2C gene, which is located proximally to the previously defined smallest region of overlap. Nevertheless, due to its known role in neurogenesis, we considered MEF2C as a phenocritical candidate gene for the 5q14.3q15 microdeletion phenotype. We therefore performed mutational analysis in 362 patients with severe mental retardation and found two truncating and two missense de novo mutations in MEF2C, establishing defects in this transcription factor as a novel relatively frequent autosomal dominant cause of severe mental retardation accounting for as much as 1.1% of patients. In these patients we found diminished MECP2 and CDKL5 expression in vivo, and transcriptional reporter assays indicated that MEF2C mutations diminish synergistic transactivation of E-box promoters including that of MECP2 and CDKL5. We therefore conclude that the phenotypic overlap of patients with MEF2C mutations and atypical Rett syndrome is due to the involvement of a common pathway.

mu-opioid receptor-stimulated synthesis of reactive oxygen species is mediated via phospholipase D2

We have recently shown that the activation of the rat mu-opioid receptor (MOPr, also termed MOR1) by the mu-agonist [D-Ala(2), Me Phe(4), Glyol(5)]enkephalin (DAMGO) leads to an increase in phospholipase D2 (PLD2) activity and an induction of receptor endocytosis, whereas the agonist morphine which does not induce opioid receptor endocytosis fails to activate PLD2. We report here that MOPr-mediated activation of PLD2 stimulates production of reactive oxygen molecules via NADH/NADPH oxidase. Oxidative stress was measured with the fluorescent probe dichlorodihydrofluorescein diacetate and the role of PLD2 was assessed by the PLD inhibitor D-erythro-sphingosine (sphinganine) and by PLD2-small interfering RNA transfection. To determine whether NADH/NADPH oxidase contributes to opioid-induced production of reactive oxygen species, mu-agonist-stimulated cells were pre-treated with the flavoprotein inhibitor, diphenylene iodonium, or the specific NADPH oxidase inhibitor, apocynin. Our results demonstrate that receptor-internalizing agonists (like DAMGO, beta-endorphin, methadone, piritramide, fentanyl, sufentanil, and etonitazene) strongly induce NADH/NADPH-mediated ROS synthesis via PLD-dependent signaling pathways, whereas agonists that do not induce MOPr endocytosis and PLD2 activation (like morphine, buprenorphine, hydromorphone, and oxycodone) failed to activate ROS synthesis in transfected human embryonic kidney 293 cells. These findings indicate that the agonist-selective PLD2 activation plays a key role in the regulation of NADH/NADPH-mediated ROS formation by opioids.