Folate regulation of axonal regeneration in the rodent central nervous system through DNA methylation

Folate-mediated transgenerational inheritance of sperm DNA methylation patterns correlate with spinal axon regeneration

In mammals, the molecular mechanisms underlying transgenerational inheritance of phenotypic traits in serial generations of progeny after ancestral environmental exposures, without variation in DNA sequence, remain elusive. We've recently described transmission of a beneficial trait in rats and mice, in which F0 supplementation of methyl donors, including folic acid, generates enhanced axon regeneration after sharp spinal cord injury in untreated F1 to F3 progeny linked to differential DNA methylation levels in spinal cord tissue. To test whether the transgenerational effect of folic acid is transmitted via the germline, we performed whole-genome methylation sequencing on sperm DNA from F0 mice treated with either folic acid or vehicle control, and their F1, F2, and F3 untreated progeny. Transgenerational differentially methylated regions (DMRs) are observed in each consecutive generation and distinguish folic acid from untreated lineages, predominate outside of CpG islands and in regions of the genome that regulate gene expression, including promoters, and overlap at both the differentially methylated position (DMP) and gene levels. These findings indicate that molecular changes between generations are caused by ancestral folate supplementation. In addition, 29,719 DMPs exhibit serial increases or decreases in DNA methylation levels in successive generations of untreated offspring, correlating with a serial increase in the phenotype across generations, consistent with a 'wash-in' effect. Sibship-specific DMPs annotate to genes that participate in axon- and synapse-related pathways.

Spatial Transcriptomics and Single-Nucleus Multi-Omics Analysis Revealing the Impact of High Maternal Folic Acid Supplementation on Offspring Brain Development

Background: Folate, an essential vitamin B9, is crucial for diverse biological processes, including neurogenesis. Folic acid (FA) supplementation during pregnancy is a standard practice for preventing neural tube defects (NTDs). However, concerns are growing over the potential risks of excessive maternal FA intake. Objectives/Methods: Here, we employed a mouse model and spatial transcriptomic and single-nucleus multi-omics approaches to investigate the impact of high maternal FA supplementation during the periconceptional period on offspring brain development. Results: Maternal high FA supplementation affected gene pathways linked to neurogenesis and neuronal axon myelination across multiple brain regions, as well as gene expression alterations related to learning and memory in thalamic and ventricular regions. Single-nucleus multi-omics analysis revealed that maturing excitatory neurons in the dentate gyrus (DG) are particularly vulnerable to high maternal FA intake, leading to aberrant gene expressions and chromatin accessibility in pathways governing ribosomal biogenesis critical for synaptic formation. Conclusions: Our findings provide new insights into specific brain regions, cell types, gene expressions and pathways that can be affected by maternal high FA supplementation.

Roles of Kdm6a and Kdm6b in regulation of mammalian neural regeneration

Epigenetic regulation of neuronal transcriptomic landscape is emerging to be a key coordinator of mammalian neural regeneration. Here we investigated roles of two histone 3 lysine 27 (H3K27) demethylases Kdm6a/b in controlling neuroprotection and axon regeneration. Deleting either Kdm6a or Kdm6b led to enhanced sensory axon regeneration in PNS, whereas in the CNS only deleting Kdm6a in retinal ganglion cells (RGCs) significantly enhanced optic nerve regeneration. Moreover, both Kdm6a and Kdm6b functioned to regulate RGC survival but with different mechanisms. Mechanistically, Kdm6a regulates RGC regeneration via distinct pathway from that of Pten and co-deleting Kdm6a and Pten resulted in long distance optic nerve regeneration passing the optic chiasm. In addition, RNA-seq profiling revealed that Kdm6a deletion switched the RGC transcriptomics into a developmental-like state and suppressed several known repressors of neural regeneration. Klf4 was identified as a direct downstream target of Kdm6a-H3K27me3 signaling in both sensory neurons and RGCs to regulate axon regeneration. These findings not only revealed different roles of Kdm6a and Kdm6b in regulation of neural regeneration and their underlying mechanisms, but also identified Kdm6a-mediated histone demethylation signaling as a novel epigenetic target for supporting CNS neural regeneration.

The bioenergetics of traumatic brain injury and its long-term impact for brain plasticity and function

Mitochondria provide the energy to keep cells alive and functioning and they have the capacity to influence highly complex molecular events. Mitochondria are essential to maintain cellular energy homeostasis that determines the course of neurological disorders, including traumatic brain injury (TBI). Various aspects of mitochondria metabolism such as autophagy can have long-term consequences for brain function and plasticity. In turn, mitochondria bioenergetics can impinge on molecular events associated with epigenetic modifications of DNA, which can extend cellular memory for a long time. Mitochondrial dysfunction leads to pathological manifestations such as oxidative stress, inflammation, and calcium imbalance that threaten brain plasticity and function. Hence, targeting mitochondrial function may have great potential to lessen the outcomes of TBI.

Bibliometric Analysis and a Call for Increased Rigor in Citing Scientific Literature: Folic Acid Fortification and Neural Tube Defect Risk as an Example

The health benefits of vitamin B9 (folate) are well documented, particularly in regard to neural tube defects during pregnancy; however, much remains to be learned regarding the health effects and risks of consuming folic acid supplements and foods fortified with folic acid. In 2020, our laboratory conducted a population-based analysis of the Food Fortification Initiative (FFI) dataset to determine the strength of the evidence regarding the prevalence of neural tube defects (NTD) at the national level in response to mandatory fortification of cereal grains with folic acid. We found a very weak correlation between the prevalence of NTDs and the level of folic acid fortification irrespective of the cereal grain fortified (wheat, maize, or rice). We found a strong linear relationship between reduced NTDs and higher socioeconomic status (SES). Our paper incited a debate on the proper statistics to employ for population-level data. Subsequently, there has been a large number of erroneous citations to our original work. The objective here was to conduct a bibliometric analysis to quantitate the accuracy of citations to Murphy and Westmark's publication entitled, "Folic Acid Fortification and Neural Tube Defect Risk: Analysis of the Food Fortification Initiative Dataset". We found a 70% inaccuracy rate. These findings highlight the dire need for increased rigor in citing scientific literature, particularly in regard to biomedical research that directly impacts public health policy.

Scaffold design considerations for peripheral nerve regeneration

Peripheral nerve injury (PNI) represents a serious clinical and public health problem due to its high incurrence and poor spontaneous recovery. Compared to autograft, which is still the best current practice for long-gap peripheral nerve defects in clinics, the use of polymer-based biodegradable nerve guidance conduits (NGCs) has been gaining momentum as an alternative to guide the repair of severe PNI without the need of secondary surgery and donor nerve tissue. However, simple hollow cylindrical tubes can barely outperform autograft in terms of the regenerative efficiency especially in critical sized PNI. With the rapid development of tissue engineering technology and materials science, various functionalized NGCs have emerged to enhance nerve regeneration over the past decades. From the aspect of scaffold design considerations, with a specific focus on biodegradable polymers, this review aims to summarize the recent advances in NGCs by addressing the onerous demands of biomaterial selections, structural designs, and manufacturing techniques that contributes to the biocompatibility, degradation rate, mechanical properties, drug encapsulation and release efficiency, immunomodulation, angiogenesis, and the overall nerve regeneration potential of NGCs. In addition, several commercially available NGCs along with their regulation pathways and clinical applications are compared and discussed. Lastly, we discuss the current challenges and future directions attempting to provide inspiration for the future design of ideal NGCs that can completely cure long-gap peripheral nerve defects.

Spatial Transcriptomics and Single-Nucleus Multi-omics Analysis Revealing the Impact of High Maternal Folic Acid Supplementation on Offspring Brain Development

Folate, an essential vitamin B9, is crucial for diverse biological processes including neurogenesis. Folic acid (FA) supplementation during pregnancy is a standard practice for preventing neural tube defects (NTDs). However, concerns are growing over the potential risks of excessive maternal FA intake. Here, we employed mouse model and spatial transcriptomics and single-nucleus multi-omics approaches to investigate the impact of high maternal FA supplementation during the periconceptional period on offspring brain development. Maternal high FA supplementation affected gene pathways linked to neurogenesis and neuronal axon myelination across multiple brain regions, as well as gene expression alterations related to learning and memory in thalamic and ventricular regions. Single-nucleus multi-omics analysis revealed that maturing excitatory neurons in the dentate gyrus (DG) are particularly vulnerable to high maternal FA intake, leading to aberrant gene expressions and chromatin accessibility in pathways governing ribosomal biogenesis critical for synaptic formation. Our findings provide new insights into specific brain regions, cell types, gene expressions and pathways that can be affected by maternal high FA supplementation.

Serum binding folate receptor autoantibodies lower in autistic boys and positively-correlated with folate

Folate receptor autoantibody (FRAA) has caught increasing attention since its discovery in biological fluids of patients with autism spectrum disorder (ASD), but quantification and understanding of its function are still in their infancy. In this study, we aimed to quantify serum binding-FRAA and explore its relation with serum folate, vitamin B12 (VB12) and ferritin. We quantitated serum binding-FRAA in 132 ASD children and 132 typically-developing (TD) children, as well as serum levels of folate, VB12 and ferritin. The results showed that serum binding-FRAA in the ASD group was significantly lower than that in the TD group (p < 0.0001). Further analysis showed that the difference between these two groups was attributed to boys in each group, not girls. There was no statistically significant difference in folate levels between the ASD and TD groups (p > 0.05). However, there was significant difference in boys between these two groups, not girls. Additionally, the combination of nitrite and binding-FRAA showed potential diagnostic value in patients with ASD (AUC > 0.7). Moreover, in the ASD group, the level of folate was consistent with that of binding-FRAA, whereas in the TD group, the binding-FRAA level was high when the folate level was low. Altogether, these differences revealed that the low serum FRAA in autistic children was mediated by multiple factors, which deserves more comprehensive investigation with larger population and mechanistic studies.

O-GlcNAc signaling increases neuron regeneration through one-carbon metabolism in Caenorhabditis elegans

Cellular metabolism plays an essential role in the regrowth and regeneration of a neuron following physical injury. Yet, our knowledge of the specific metabolic pathways that are beneficial to neuron regeneration remains sparse. Previously, we have shown that modulation of O-linked β-N-acetylglucosamine (O-GlcNAc) signaling, a ubiquitous post-translational modification that acts as a cellular nutrient sensor, can significantly enhance in vivo neuron regeneration. Here, we define the specific metabolic pathway by which O-GlcNAc transferase (ogt-1) loss of function mediates increased regenerative outgrowth. Performing in vivo laser axotomy and measuring subsequent regeneration of individual neurons in C. elegans, we find that glycolysis, serine synthesis pathway (SSP), one-carbon metabolism (OCM), and the downstream transsulfuration metabolic pathway (TSP) are all essential in this process. The regenerative effects of ogt-1 mutation are abrogated by genetic and/or pharmacological disruption of OCM and the SSP linking OCM to glycolysis. Testing downstream branches of this pathway, we find that enhanced regeneration is dependent only on the vitamin B12 independent shunt pathway. These results are further supported by RNA sequencing that reveals dramatic transcriptional changes by the ogt-1 mutation, in the genes involved in glycolysis, OCM, TSP, and ATP metabolism. Strikingly, the beneficial effects of the ogt-1 mutation can be recapitulated by simple metabolic supplementation of the OCM metabolite methionine in wild-type animals. Taken together, these data unearth the metabolic pathways involved in the increased regenerative capacity of a damaged neuron in ogt-1 animals and highlight the therapeutic possibilities of OCM and its related pathways in the treatment of neuronal injury.

Genome-wide study reveals novel roles for formin-2 in axon regeneration as a microtubule dynamics regulator and therapeutic target for nerve repair

Peripheral nerves regenerate successfully; however, clinical outcome after injury is poor. We demonstrated that low-dose ionizing radiation (LDIR) promoted axon regeneration and function recovery after peripheral nerve injury (PNI). Genome-wide CpG methylation profiling identified LDIR-induced hypermethylation of the Fmn2 promoter, exhibiting injury-induced Fmn2 downregulation in dorsal root ganglia (DRGs). Constitutive knockout or neuronal Fmn2 knockdown accelerated nerve repair and function recovery. Mechanistically, increased microtubule dynamics at growth cones was observed in time-lapse imaging of Fmn2-deficient DRG neurons. Increased HDAC5 phosphorylation and rapid tubulin deacetylation were found in regenerating axons of neuronal Fmn2-knockdown mice after injury. Growth-promoting effect of neuronal Fmn2 knockdown was eliminated by pharmaceutical blockade of HDAC5 or neuronal Hdac5 knockdown, suggesting that Fmn2deletion promotes axon regeneration via microtubule post-translational modification. In silico screening of FDA-approved drugs identified metaxalone, administered either immediately or 24-h post-injury, accelerating function recovery. This work uncovers a novel axon regeneration function of Fmn2 and a small-molecule strategy for PNI.

Lactoferrin deficiency during lactation increases the risk of depressive-like behavior in adult mice

BACKGROUND

Lactoferrin is an active protein in breast milk that plays an important role in the growth and development of infants and is implicated as a neuroprotective agent. The incidence of depression is currently increasing, and it is unclear whether the lack of lactoferrin during lactation affects the incidence of depressive-like behavior in adulthood.

RESULTS

Lack of lactoferrin feeding during lactation affected the barrier and innate immune functions of the intestine, disrupted the intestinal microflora, and led to neuroimmune dysfunction and neurodevelopmental delay in the hippocampus. When exposed to external stimulation, adult lactoferrin feeding-deficient mice presented with worse depression-like symptoms; the mechanisms involved were activation of the LPS-TLR4 signalling pathway in the intestine and hippocampus, reduced BDNF-CREB signaling pathway in hippocampus, increased abundance of depression-related bacteria, and decreased abundance of beneficial bacteria.

CONCLUSIONS

Overall, our findings reveal that lactoferrin feeding deficient during lactation can increase the risk of depressive-like behavior in adults. The mechanism is related to the regulatory effect of lactoferrin on the development of the "microbial-intestinal-brain" axis.

Subacute and Chronic Spinal Cord Injury: A Scoping Review of Epigenetics and Secondary Health Conditions

Background

Epigenetics studies the impact of environmental and behavioral factors on stable phenotypic changes; however, the state of the science examining epigenomic mechanisms of regulation related to secondary health conditions (SHCs) and neuroepigenetics in chronic spinal cord injury (SCI) remain markedly underdeveloped.

Objective

This scoping review seeks to understand the state of the science in epigenetics and secondary complications following SCI.

Methods

A literature search was conducted, yielding 277 articles. The inclusion criteria were articles (1) investigating SCI and (2) examining epigenetic regulation as part of the study methodology. A total of 23 articles were selected for final inclusion.

Results

Of the 23 articles 52% focused on histone modification, while 26% focused on DNA methylation. One study had a human sample, while the majority sampled rats and mice. Primarily, studies examined regeneration, with only one study looking at clinically relevant SHC, such as neuropathic pain.

Discussion

The findings of this scoping review offer exciting insights into epigenetic and neuroepigenetic application in SCI research. Several key genes, proteins, and pathways emerged across studies, suggesting the critical role of epigenetic regulation in biological processes. This review reinforced the dearth of studies that leverage epigenetic methods to identify prognostic biomarkers in SHCs. Preclinical models of SCI were genotypically and phenotypically similar, which is not reflective of the heterogeneity found in the clinical population of persons with SCI. There is a need to develop better preclinical models and more studies that examine the role of genomics and epigenomics in understanding the diverse health outcomes associated with traumatic SCI.

DNMT1 involved in the analgesic effect of folic acid on gastric hypersensitivity through downregulating ASIC1 in adult offspring rats with prenatal maternal stress

AIMS

Gastric hypersensitivity (GHS) is a characteristic pathogenesis of functional dyspepsia (FD). DNA methyltransferase 1 (DNMT1) and acid-sensing ion channel 1 (ASIC1) are associated with GHS induced by prenatal maternal stress (PMS). The aim of this study was to investigate the mechanism of DNMT1 mediating the analgesic effect of folic acid (FA) on PMS-induced GHS.

METHODS

GHS was quantified by electromyogram recordings. The expression of DNMT1, DNMT3a, DNMT3b, and ASIC1 were detected by western blot, RT-PCR, and double-immunofluorescence. Neuronal excitability and proton-elicited currents of dorsal root ganglion (DRG) neurons were determined by whole-cell patch clamp recordings.

RESULTS

The expression of DNMT1, but not DNMT3a or DNMT3b, was decreased in DRGs of PMS rats. FA alleviated PMS-induced GHS and hyperexcitability of DRG neurons. FA also increased DNMT1 and decreased ASIC1 expression and sensitivity. Intrathecal injection of DNMT1 inhibitor DC-517 attenuated the effect of FA on GHS alleviation and ASIC1 downregulation. Overexpression of DNMT1 with lentivirus not only rescued ASIC1 upregulation and hypersensitivity, but also alleviated GHS and hyperexcitability of DRG neurons induced by PMS.

CONCLUSIONS

These results indicate that increased DNMT1 contributes to the analgesic effect of FA on PMS-induced GHS by reducing ASIC1 expression and sensitivity.

Folic acid relieves bone cancer pain by downregulating P2X2/3 receptors in rats

BACKGROUND

Bone cancer pain (BCP) remains a clinical challenge due to the limited and side effects of therapeutic methods. Folic acid has been known as an FDA approved dietary supplement and proved to have an analgesic effect in neuropathic pain. Here we investigate the role and mechanism of folic acid in bone cancer pain of a rat model.

METHODS

Walker 256 tumor cells were inoculated into the left tibia of rats to induce bone cancer pain model. Pain reflex were assessed by paw withdrawal threshold (PWT) response to Von Frey filaments and paw withdrawal latency (PWL) response to thermal stimulation. Folic acid was injected intraperitoneally to evaluate its analgesic effect in rats with bone cancer pain. Western blotting and qPCR were used to determine P2X2/3 receptor protein and mRNA levels in ipsilateral L4-6 dorsal root ganglion (DRG) and spinal dorsal horn (SDH).

RESULTS

The PWT and PWL of rats with bone cancer pain were obviously decreased compared to the naïve and sham rats. Interestingly, continuous folic acid treatment significantly increased the PWT and PWL of rats with bone cancer pain. P2X2 and P2X3 receptors were clearly upregulated at both mRNA and protein expression in L4-6 DRG and SDH of rats with bone cancer pain. P2X2 and P2X3 receptors were mainly localized with CGRP (calcitonin gene-related peptide) or IB4 (isolectin B4) positive neurons in L4-6 DRG of rats with bone cancer pain. Notably, continuous folic acid treatment significantly reduced the expression of P2X2 and P2X3 receptors in L4-6 DRG and SDH of rats with bone cancer pain. Finally, intrathecal injection of A317491 (a selective antagonist of P2X2/3 receptors) markedly elevated the PWT and PWL of rats with bone cancer pain.

CONCLUSION

These results suggest that folic acid has an effective antinociceptive effect on bone cancer pain, which is mediated by downregulating P2X2/3 receptors in L4-6 DRG and SDH of rats with bone cancer pain. Folic acid may be a novel therapeutic strategy in cancer patients for pain relief.

Epigenetic and epitranscriptomic regulation of axon regeneration

Effective axonal regeneration in the adult mammalian nervous system requires coordination of elevated intrinsic growth capacity and decreased responses to the inhibitory environment. Intrinsic regenerative capacity largely depends on the gene regulatory network and protein translation machinery. A failure to activate these pathways upon injury is underlying a lack of robust axon regeneration in the mature mammalian central nervous system. Epigenetics and epitranscriptomics are key regulatory mechanisms that shape gene expression and protein translation. Here, we provide an overview of different types of modifications on DNA, histones, and RNA, underpinning the regenerative competence of axons in the mature mammalian peripheral and central nervous systems. We highlight other non-neuronal cells and their epigenetic changes in determining the microenvironment for tissue repair and axon regeneration. We also address advancements of single-cell technology in charting transcriptomic and epigenetic landscapes that may further facilitate the mechanistic understanding of differential regenerative capacity in neuronal subtypes. Finally, as epigenetic and epitranscriptomic processes are commonly affected by brain injuries and psychiatric disorders, understanding their alterations upon brain injury would provide unprecedented mechanistic insights into etiology of injury-associated-psychiatric disorders and facilitate the development of therapeutic interventions to restore brain function.

Purified regenerating retinal neurons reveal regulatory role of DNA methylation-mediated Na+/K+-ATPase in murine axon regeneration

While embryonic mammalian central nervous system (CNS) axons readily grow and differentiate, only a minority of fully differentiated mature CNS neurons are able to regenerate injured axons, leading to stunted functional recovery after injury and disease. To delineate DNA methylation changes specifically associated with axon regeneration, we used a Fluorescent-Activated Cell Sorting (FACS)-based methodology in a rat optic nerve transection model to segregate the injured retinal ganglion cells (RGCs) into regenerating and non-regenerating cell populations. Whole-genome DNA methylation profiling of these purified neurons revealed genes and pathways linked to mammalian RGC regeneration. Moreover, whole-methylome sequencing of purified uninjured adult and embryonic RGCs identified embryonic molecular profiles reactivated after injury in mature neurons, and others that correlate specifically with embryonic or adult axon growth, but not both. The results highlight the contribution to both embryonic growth and adult axon regeneration of subunits encoding the Na⁺/K⁺-ATPase. In turn, both biochemical and genetic inhibition of the Na⁺/K⁺-ATPase pump significantly reduced RGC axon regeneration. These data provide critical molecular insights into mammalian CNS axon regeneration, pinpoint the Na⁺/K⁺-ATPase as a key regulator of regeneration of injured mature CNS axons, and suggest that successful regeneration requires, in part, reactivation of embryonic signals.

Transgenerational epigenetic inheritance of axonal regeneration after spinal cord injury

Human epidemiological studies reveal that dietary and environmental alterations influence the health of the offspring and that the effect is not limited to the F1 or F2 generations. Non-Mendelian transgenerational inheritance of traits in response to environmental stimuli has been confirmed in non-mammalian organisms including plants and worms and are shown to be epigenetically mediated. However, transgenerational inheritance beyond the F2 generation remains controversial in mammals. Our lab previously discovered that the treatment of rodents (rats and mice) with folic acid significantly enhances the regeneration of injured axons following spinal cord injury in vivo and in vitro, and the effect is mediated by DNA methylation. The potential heritability of DNA methylation prompted us to investigate the following question: Is the enhanced axonal regeneration phenotype inherited transgenerationally without exposure to folic acid supplementation in the intervening generations? In the present review, we condense our findings showing that a beneficial trait (i.e., enhanced axonal regeneration after spinal cord injury) and accompanying molecular alterations (i.e., DNA methylation), triggered by an environmental exposure (i.e., folic acid supplementation) to F0 animals only, are inherited transgenerationally and beyond the F3 generation.

Folic acid attenuates chronic visceral pain by reducing clostridiales abundance and hydrogen sulfide production

Irritable bowel syndrome (IBS) related chronic visceral pain affects 20% of people worldwide. The treatment options are very limited. Although the scholarly reviews have appraised the potential effects of the intestinal microbiota on intestinal motility and sensation, the exact mechanism of intestinal microbiota in IBS-like chronic visceral pain remains largely unclear. The purpose of this study is to investigate whether Folic Acid (FA) attenuated visceral pain and its possible mechanisms. Chronic visceral hyperalgesia was induced in rats by neonatal colonic inflammation (NCI). 16S rDNA analysis of fecal samples from human subjects and rats was performed. Patch clamp recording was used to determine synaptic transmission of colonic-related spinal dorsal horn. Alpha diversity of intestinal flora was increased in patients with IBS, as well as the obviously increased abundance of Clostridiales order (a main bacteria producing hydrogen sulfide). The hydrogen sulfide content was positive correlation with visceral pain score in patients with IBS. Consistently, NCI increased Clostridiales frequency and hydrogen sulfide content in feces of adult rats. Notably, the concentration of FA was markedly decreased in peripheral blood of IBS patients compared with non-IBS human subjects. FA supplement alleviated chronic visceral pain and normalized the Clostridiales frequency in NCI rats. In addition, FA supplement significantly reduced the frequency of sEPSCs of neurons in the spinal dorsal horn of NCI rats. Folic Acid treatment attenuated chronic visceral pain of NCI rats through reducing hydrogen sulfide production from Clostridiales in intestine.

Regenerative Drug Discovery Using Ear Pinna Punch Wound Model in Mice

The ear pinna is a complex tissue consisting of the dermis, cartilage, muscles, vessels, and nerves. Ear pinna healing is a model of regeneration in mammals. In some mammals, including rabbits, punch wounds in the ear pinna close spontaneously; in common-use laboratory mice, they remain for life. Agents inducing ear pinna healing are potential regenerative drugs. We tested the effects of selected bioactive agents on 2 mm ear pinna wound closure in BALB/c mice. Our previous research demonstrated that a DNA methyltransferase inhibitor, zebularine, remarkably induced ear pinna regeneration. Although experiments with two other demethylating agents, RG108 and hydralazine, were unsuccessful, a histone deacetylase inhibitor, valproic acid, was another epigenetic agent found to increase ear hole closure. In addition, we identified a pro-regenerative activity of 4-ketoretinoic acid, a retinoic acid metabolite. Attempts to counteract the regenerative effects of the demethylating agent zebularine, with folates as methyl donors, failed. Surprisingly, a high dose of methionine, another methyl donor, promoted ear hole closure. Moreover, we showed that the regenerated areas of ear pinna were supplied with nerve fibre networks and blood vessels. The ear punch model proved helpful in testing the pro-regenerative activities of small-molecule compounds and observations of peripheral nerve regeneration.

Genetic and epigenetic mechanisms influencing acute to chronic postsurgical pain transitions in pediatrics: Preclinical to clinical evidence

Background

Chronic postsurgical pain (CPSP) in children remains an important problem with no effective preventive or therapeutic strategies. Recently, genomic underpinnings explaining additional interindividual risk beyond psychological factors have been proposed.

Aims

We present a comprehensive review of current preclinical and clinical evidence for genetic and epigenetic mechanisms relevant to pediatric CPSP.

Methods

Narrative review.

Results

Animal models are relevant to translational research for unraveling genomic mechanisms. For example, Cacng2, p2rx7, and bdnf mutant mice show altered mechanical hypersensitivity to injury, and variants of the same genes have been associated with CPSP susceptibility in humans; similarly, differential DNA methylation (H1SP) and miRNAs (miR-96/7a) have shown translational implications. Animal studies also suggest that crosstalk between neurons and immune cells may be involved in nociceptive priming observed in neonates. In children, differential DNA methylation in regulatory genomic regions enriching GABAergic, dopaminergic, and immune pathways, as well as polygenic risk scores for enhanced prediction of CPSP, have been described. Genome-wide studies in pediatric CPSP are scarce, but pathways identified by adult gene association studies point to potential common mechanisms.

Conclusions

Bench-to-bedside genomics research in pediatric CPSP is currently limited. Reverse translational approaches, use of other -omics, and inclusion of pediatric/CPSP endophenotypes in large-scale biobanks may be potential solutions. Time of developmental vulnerability and longitudinal genomic changes after surgery warrant further investigation. Emergence of promising precision pain management strategies based on gene editing and epigenetic programing emphasize need for further research in pediatric CPSP-related genomics.

Gut Microbiota–Brain Axis as a Potential Modulator of Psychological Stress after Spinal Cord Injury

A growing body of evidence from preclinical and clinical studies has associated alterations of the gut microbiota–brain axis with the progression and development of a number of pathological conditions that also affect cognitive functions. Spinal cord injuries (SCIs) can be produced from traumatic and non-traumatic causes. It has been reported that SCIs are commonly associated with anxiety and depression-like symptoms, showing an incidence range between 11 and 30% after the injury. These psychological stress-related symptoms are associated with worse prognoses in SCIs and have been attributed to psychosocial stressors and losses of independence. Nevertheless, emotional and mental modifications after SCI could be related to changes in the volume of specific brain areas associated with information processing and emotions. Additionally, physiological modifications have been recognized as a predisposing factor for mental health depletion, including the development of gut dysbiosis. This condition of imbalance in microbiota composition has been shown to be associated with depression in clinical and pre-clinical models. Therefore, the understanding of the mechanisms underlying the relationship between SCIs, gut dysbiosis and psychological stress could contribute to the development of novel therapeutic strategies to improve SCI patients’ quality of life.

DNA methylation maintenance at the p53 locus initiates biliary-mediated liver regeneration

In cases of extensive liver injury, biliary epithelial cells (BECs) dedifferentiate into bipotential progenitor cells (BPPCs), then redifferentiate into hepatocytes and BECs to accomplish liver regeneration. Whether epigenetic regulations, particularly DNA methylation maintenance enzymes, play a role in this biliary-mediated liver regeneration remains unknown. Here we show that in response to extensive hepatocyte damages, expression of dnmt1 is upregulated in BECs to methylate DNA at the p53 locus, which represses p53 transcription, and in turn, derepresses mTORC1 signaling to activate BEC dedifferentiation. After BEC dedifferentiation and BPPC formation, DNA methylation at the p53 locus maintains in BPPCs to continue blocking p53 transcription, which derepresses Bmp signaling to induce BPPC redifferentiation. Thus, this study reveals promotive roles and mechanisms of DNA methylation at the p53 locus in both dedifferentiation and redifferentiation stages of biliary-mediated liver regeneration, implicating DNA methylation and p53 as potential targets to stimulate regeneration after extensive liver injury.

Loss of the N-acetylgalactosamine side chain of the GPI-anchor impairs bone formation and brain functions and accelerates the prion disease pathology

Glycosylphosphatidylinositol (GPI) is a posttranslational glycolipid modification of proteins that anchors proteins in lipid rafts on the cell surface. Although some GPI-anchored proteins (GPI-APs), including the prion protein PrP^C, have a glycan side chain composed of N-acetylgalactosamine (GalNAc)−galactose−sialic acid on the core structure of GPI glycolipid, in vivo functions of this GPI-GalNAc side chain are largely unresolved. Here, we investigated the physiological and pathological roles of the GPI-GalNAc side chain in vivo by knocking out its initiation enzyme, PGAP4, in mice. We show that Pgap4 mRNA is highly expressed in the brain, particularly in neurons, and mass spectrometry analysis confirmed the loss of the GalNAc side chain in PrP^C GPI in PGAP4-KO mouse brains. Furthermore, PGAP4-KO mice exhibited various phenotypes, including an elevated blood alkaline phosphatase level, impaired bone formation, decreased locomotor activity, and impaired memory, despite normal expression levels and lipid raft association of various GPI-APs. Thus, we conclude that the GPI-GalNAc side chain is required for in vivo functions of GPI-APs in mammals, especially in bone and the brain. Moreover, PGAP4-KO mice were more vulnerable to prion diseases and died earlier after intracerebral inoculation of the pathogenic prion strains than wildtype mice, highlighting the protective roles of the GalNAc side chain against prion diseases.

Developmental and Injury-induced Changes in DNA Methylation in Regenerative versus Non-regenerative Regions of the Vertebrate Central Nervous System

BACKGROUND

Because some of its CNS neurons (e.g., retinal ganglion cells after optic nerve crush (ONC)) regenerate axons throughout life, whereas others (e.g., hindbrain neurons after spinal cord injury (SCI)) lose this capacity as tadpoles metamorphose into frogs, the South African claw-toed frog, Xenopus laevis, offers unique opportunities for exploring differences between regenerative and non-regenerative responses to CNS injury within the same organism. An earlier, three-way RNA-seq study (frog ONC eye, tadpole SCI hindbrain, frog SCI hindbrain) identified genes that regulate chromatin accessibility among those that were differentially expressed in regenerative vs non-regenerative CNS [11]. The current study used whole genome bisulfite sequencing (WGBS) of DNA collected from these same animals at the peak period of axon regeneration to study the extent to which DNA methylation could potentially underlie differences in chromatin accessibility between regenerative and non-regenerative CNS.

RESULTS

Consistent with the hypothesis that DNA of regenerative CNS is more accessible than that of non-regenerative CNS, DNA from both the regenerative tadpole hindbrain and frog eye was less methylated than that of the non-regenerative frog hindbrain. Also, consistent with observations of CNS injury in mammals, DNA methylation in non-regenerative frog hindbrain decreased after SCI. However, contrary to expectations that the level of DNA methylation would decrease even further with axotomy in regenerative CNS, DNA methylation in these regions instead increased with injury. Injury-induced differences in CpG methylation in regenerative CNS became especially enriched in gene promoter regions, whereas non-CpG methylation differences were more evenly distributed across promoter regions, intergenic, and intragenic regions. In non-regenerative CNS, tissue-related (i.e., regenerative vs. non-regenerative CNS) and injury-induced decreases in promoter region CpG methylation were significantly correlated with increased RNA expression, but the injury-induced, increased CpG methylation seen in regenerative CNS across promoter regions was not, suggesting it was associated with increased rather than decreased chromatin accessibility. This hypothesis received support from observations that in regenerative CNS, many genes exhibiting increased, injury-induced, promoter-associated CpG-methylation also exhibited increased RNA expression and association with histone markers for active promoters and enhancers. DNA immunoprecipitation for 5hmC in optic nerve regeneration found that the promoter-associated increases seen in CpG methylation were distinct from those exhibiting changes in 5hmC.

CONCLUSIONS

Although seemingly paradoxical, the increased injury-associated DNA methylation seen in regenerative CNS has many parallels in stem cells and cancer. Thus, these axotomy-induced changes in DNA methylation in regenerative CNS provide evidence for a novel epigenetic state favoring successful over unsuccessful CNS axon regeneration. The datasets described in this study should help lay the foundations for future studies of the molecular and cellular mechanisms involved. The insights gained should, in turn, help point the way to novel therapeutic approaches for treating CNS injury in mammals.

Epigenetic control of ion channel expression and cell-specific splicing in nociceptors: Chronic pain mechanisms and potential therapeutic targets

Ion channels underlie all forms for electrical signaling including the transmission of information about harmful events. Voltage-gated calcium ion channels have dual function, they support electrical signaling as well as intracellular calcium signaling through excitation-dependent calcium entry across the plasma membrane. Mechanisms that regulate ion channel forms and actions are essential for myriad cell functions and these are targeted by drugs and therapeutics. When disrupted, the cellular mechanisms that control ion channel activity can contribute to disease pathophysiology. For example, alternative pre-mRNA splicing is a major step in defining the precise composition of the transcriptome across different cell types from early cellular differentiation to programmed apoptosis. An estimated 30% of disease-causing mutations are associated with altered alternative splicing, and mis-splicing is a feature of numerous highly prevalent diseases including neurodegenerative, cancer, and chronic pain. Here we discuss the important role of epigenetic regulation of gene expression and cell-specific alternative splicing of calcium ion channels in nociceptors, with emphasis on how these processes are disrupted in chronic pain, the potential therapeutic benefit of correcting or compensating for aberrant ion channel splicing in chronic pain.

Factors influencing the outcome of cardiogenic cerebral embolism: a literature review

OBJECTIVE

The onset of cardiogenic cerebral embolism is sudden, dangerous, and often has high morbidity and mortality. Improving understanding of factors contributing to outcomes of cardiogenic cerebral embolism will improve prognostic and therapeutic capabilities.

METHODS

Through PubMed and Google Scholar, this paper examined and analyzed the factors implicated in the outcome of patients with cardiogenic cerebral embolism using the key terms 'cardiogenic cerebral embolism', 'atrial fibrillation', 'stroke related diseases', 'collateral circulation', 'emboli profile', 'epigenetic' up to 28 February 2021. Full texts of the retrieved articles were accessed. In general, in these literatures, National Institute Health of Stroke Scale (NIHSS) score ≥ 17, modified Rankin Scale (mRS) score ≥ 2, stroke recurrence, death caused by stroke are regarded as the criteria of poor prognosis. As long as one of these conditions occurs, it is judged as poor prognosis.

RESULTS

Factors influencing patient outcomes including patient outcome include severity of neurological impairment, types and severity of combined heart diseases, establishment of cerebral collateral circulation, treatments, components of emboli causing cardiogenic cerebral embolism, existence and control of other system complications, distribution and expression of inflammatory immune cells and molecules in the course of cardiogenic cerebral embolism, and epigenetic changes related to disease prognosis.

CONCLUSION

Regarding to prevention and treatment of cardiogenic cerebral embolism, the related factors, such as clinical setting, emboli pathological profile, and epigenetic changes should be emphasized so that outcomes and recurrence of cardiogenic cerebral embolism can be improvised.

The role of dietary supplements that modulate one-carbon metabolism on stroke outcome

PURPOSE OF REVIEW

Ischemic stroke results in disability and mortality worldwide. Nutrition is a modifiable risk factor for stroke. For example, deficiencies in one-carbon metabolism have been linked to increased risk of stroke through elevated levels of homocysteine. Some countries world-wide fortify their diets with folates to prevent neural tube defects, but deficiencies in other one-carbon metabolites, such as vitamin B12 and choline are still present in many populations. The aim of this review is to understand the current evidence on how dietary supplementation by nutrients which modulate one-carbon metabolism impact stroke outcome.

RECENT FINDINGS

The results from clinical studies evaluating lowering homocysteine through B-vitamin supplementation on stroke risk remain unclear. Other clinical and preclinical studies have shown increasing dietary intake of one-carbon metabolism has some benefit on stroke outcome. Preclinical studies have shown that increased levels of nutrients which modulate one-carbon metabolism help facilitate recovery in damage models of the central nervous system. One the mechanisms driving these changes is neuroplasticity.

SUMMARY

The data suggest that increasing dietary nutrients that modulate one-carbon metabolites in patients that are at a higher risk for and suffer from central nervous system diseases, such as stroke, could benefit in addition to other therapies.

Spinal Cord Injury Changes the Structure and Functional Potential of Gut Bacterial and Viral Communities

Emerging data indicate that gut dysbiosis contributes to many human diseases, including several comorbidities that develop after traumatic spinal cord injury (SCI). To date, all analyses of SCI-induced gut dysbiosis have used 16S rRNA amplicon sequencing. This technique has several limitations, including being susceptible to taxonomic "blind spots," primer bias, and an inability to profile microbiota functions or identify viruses. Here, SCI-induced gut dysbiosis was assessed by applying genome- and gene-resolved metagenomic analysis of murine stool samples collected 21 days after an experimental SCI at the 4th thoracic spine (T4) or 10th thoracic spine (T10) spinal level. These distinct injuries partially (T10) or completely (T4) abolish sympathetic tone in the gut. Among bacteria, 105 medium- to high-quality metagenome-assembled genomes (MAGs) were recovered, with most (n = 96) representing new bacterial species. Read mapping revealed that after SCI, the relative abundance of beneficial commensals (Lactobacillus johnsonii and CAG-1031 spp.) decreased, while potentially pathogenic bacteria (Weissella cibaria, Lactococcus lactis _A, Bacteroides thetaiotaomicron) increased. Functionally, microbial genes encoding proteins for tryptophan, vitamin B6, and folate biosynthesis, essential pathways for central nervous system function, were reduced after SCI. Among viruses, 1,028 mostly novel viral populations were recovered, expanding known murine gut viral species sequence space ∼3-fold compared to that of public databases. Phages of beneficial commensal hosts (CAG-1031, Lactobacillus, and Turicibacter) decreased, while phages of pathogenic hosts (Weissella, Lactococcus, and class Clostridia) increased after SCI. Although the microbiomes and viromes were changed in all SCI mice, some of these changes varied as a function of spinal injury level, implicating loss of sympathetic tone as a mechanism underlying gut dysbiosis.IMPORTANCE To our knowledge, this is the first article to apply metagenomics to characterize changes in gut microbial population dynamics caused by a clinically relevant model of central nervous system (CNS) trauma. It also utilizes the most current approaches in genome-resolved metagenomics and viromics to maximize the biological inferences that can be made from these data. Overall, this article highlights the importance of autonomic nervous system regulation of a distal organ (gut) and its microbiome inhabitants after traumatic spinal cord injury (SCI). By providing information on taxonomy, function, and viruses, metagenomic data may better predict how SCI-induced gut dysbiosis influences systemic and neurological outcomes after SCI.

A Variation in FGF14 Is Associated with Downbeat Nystagmus in a Genome-Wide Association Study

Downbeat nystagmus (DBN) is a frequent form of acquired persisting central fixation nystagmus, often associated with other cerebellar ocular signs, such as saccadic smooth pursuit or gaze-holding deficits. Despite its distinct clinical features, the underlying etiology of DBN often remains unclear. Therefore, a genome-wide association study (GWAS) was conducted in 106 patients and 2609 healthy controls of European ancestry to identify genetic variants associated with DBN. A genome-wide significant association (p < 5 × 10^-8) with DBN was found for a variation on chromosome 13 located within the fibroblast growth factor 14 gene (FGF14). FGF14 is expressed in Purkinje cells (PCs) and a reduction leads to a decreased spontaneous firing rate and excitability of PCs, compatible with the pathophysiology of DBN. In addition, mutations in the FGF14 gene cause spinocerebellar ataxia type 27. Suggestive associations (p < 1 × 10^-05) could be detected for 15 additional LD-independent loci, one of which is also located in the FGF14 gene. An association of a region containing the dihydrofolate reductase (DHFR) and MutS Homolog 3 (MSH3) genes on chromosome 5 was slightly below the genome-wide significance threshold. DHFR is relevant for neuronal regulation, and a dysfunction is known to induce cerebellar damage. Among the remaining twelve suggestive associations, four genes (MAST4, TPPP, FTMT, and IDS) seem to be involved in cerebral pathological processes. Thus, this GWAS analysis has identified a potential genetic contribution to idiopathic DBN, including suggestive associations to several genes involved in postulated pathological mechanisms of DBN (i.e., impaired function of cerebellar PCs).

Maternal folic acid supplementation prevents autistic behaviors in a rat model induced by prenatal exposure to valproic acid

Maternal FA supplementation at 4 mg kg⁻¹ rescued the development delay, anxiety and core autism-like behaviors, and restored the abnormal synaptic spine morphology and synaptic protein expression in mPFC in the male offspring prenatally exposed to VPA.

The inorganic chemicals that surround us: role of tellurium, selenium and zinc on behavioural functions in mammals

Living organisms live in continuous interaction with its environment. During this process changes in one can induce adaptive responses on the other. Many factors in the environment have been studied with the notorious distinction of been rare or to be of high intensity strength in its interaction with living organisms. However, little attention has been put on some factors that have constant interaction with organisms but usually have low intensity strength, such as the case of the inorganic chemical environment that surrounds us. In this review, the interaction between the chemical element and living organisms is discussed under a theoretical model of interaction between compartments, giving attention to tellurium (Te), zinc (Zn) and selenium (Se) on some cognitive functions in human and animals. After studies in our laboratory of the phenotypic expression of the HSR (Hand Skill Relative) gene in school children community living in geographic zone rich in minerals and mines of La Rioja province, Argentine, where Te was found to be in higher non-toxic concentrations, a translational experimental model to maturing rats exposed to this trace element was made. Te was found to increase some parameters related to locomotion in an open field induced by novelty and exploratory motivation. At the same time, inhibition of lateralized responses, survival responses and social activity was also observed. Some of these changes, particularly those related to lateralization had similarity with that found previously in children of La Rioja province. Discussion of similarities and discrepancies of biologic effects between animals and humans, about the possible meaning of Te and its interaction with Zn and Se with relevance to humans was analyzed.

DNA methylation and hydroxymethylation have distinct genome-wide profiles related to axonal regeneration

Alterations in environmentally sensitive epigenetic mechanisms (e.g., DNA methylation) influence axonal regeneration in the spinal cord following sharp injury. Conventional DNA methylation detection methods using sodium bisulphite treatment do not distinguish between methylated and hydroxymethylated forms of cytosine, meaning that past studies report a composite of 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC). To identify the distinct contributions of DNA methylation modifications to axonal regeneration, we collected spinal cord tissue after sharp injury from untreated adult F3 male rats with enhanced regeneration of injured spinal axons or controls, derived from folate- or water-treated F0 lineages, respectively. Genomic DNA was profiled for genome-wide 5hmC levels, revealing 658 differentially hydroxymethylated regions (DhMRs). Genomic profiling with whole genome bisulphite sequencing disclosed regeneration-related alterations in composite 5mC + 5hmC DNA methylation levels at 2,260 differentially methylated regions (DMRs). While pathway analyses revealed that differentially hydroxymethylated and methylated genes are linked to biologically relevant axon developmental pathways, only 22 genes harbour both DhMR and DMRs. Since these differential modifications were more than 60 kilobases on average away from each other, the large majority of differential hydroxymethylated and methylated regions are unique with distinct functions in the axonal regeneration phenotype. These data highlight the importance of distinguishing independent contributions of 5mC and 5hmC levels in the central nervous system, and denote discrete roles for DNA methylation modifications in spinal cord injury and regeneration in the context of transgenerational inheritance.

Ancestral Folate Promotes Neuronal Regeneration in Serial Generations of Progeny

Folate supplementation in F0 mating rodents increases regeneration of injured spinal axons in vivo in 4 or more generations of progeny (F1-F4) in the absence of interval folate administration to the progeny. Transmission of the enhanced regeneration phenotype to untreated progeny parallels axonal growth in neuron culture after in vivo folate administration to the F0 ancestors alone, in correlation with differential patterns of genomic DNA methylation and RNA transcription in treated lineages. Enhanced axonal regeneration phenotypes are observed with diverse folate preparations and routes of administration, in outbred and inbred rodent strains, and in two rodent genera comprising rats and mice, and are reversed in F4-F5 progeny by pretreatment with DNA demethylating agents prior to phenotyping. Uniform transmission of the enhanced regeneration phenotype to progeny together with differential patterns of DNA methylation and RNA expression is consistent with a non-Mendelian mechanism. The capacity of an essential nutritional co-factor to induce a beneficial transgenerational phenotype in untreated offspring carries broad implications for the diagnosis, prevention, and treatment of inborn and acquired disorders.

Nitrous Oxide Impairs Axon Regeneration after Nervous System Injury in Male Rats

BACKGROUND

Nitrous oxide can induce neurotoxicity. The authors hypothesized that exposure to nitrous oxide impairs axonal regeneration and functional recovery after central nervous system injury.

METHODS

The consequences of single and serial in vivo nitrous oxide exposures on axon regeneration in four experimental male rat models of nervous system injury were measured: in vitro axon regeneration in cell culture after in vivo nitrous oxide administration, in vivo axon regeneration after sharp spinal cord injury, in vivo axon regeneration after sharp optic nerve injury, and in vivo functional recovery after blunt contusion spinal cord injury.

RESULTS

In vitro axon regeneration 48 h after a single in vivo 70% N2O exposure is less than half that in the absence of nitrous oxide (mean ± SD, 478 ± 275 um; n = 48) versus 210 ± 152 um (n = 48; P < 0.0001). A single exposure to 80% N2O inhibits the beneficial effects of folic acid on in vivo axonal regeneration after sharp spinal cord injury (13.4 ± 7.1% regenerating neurons [n = 12] vs. 0.6 ± 0.7% regenerating neurons [n = 4], P = 0.004). Serial 80% N2O administration reverses the benefit of folic acid on in vivo retinal ganglion cell axon regeneration after sharp optic nerve injury (1277 ± 180 regenerating retinal ganglion cells [n = 7] vs. 895 ± 164 regenerating retinal ganglion cells [n = 7], P = 0.005). Serial 80% N2O exposures reverses the benefit of folic acid on in vivo functional recovery after blunt spinal cord contusion (estimate for fixed effects ± standard error of the estimate: folic acid 5.60 ± 0.54 [n = 9] vs. folic acid + 80% N2O 5.19 ± 0.62 [n = 7], P < 0.0001).

CONCLUSIONS

These data indicate that nitrous oxide can impair the ability of central nervous system neurons to regenerate axons after sharp and blunt trauma.

Epitranscriptomic profiling of N6-methyladenosine-related RNA methylation in rat cerebral cortex following traumatic brain injury

Background

N6-methyladenosine (m6A) is the most prevalent post-transcriptional modification of eukaryotic mRNA. It has been reported that there is a stimulus-dependent regulation of m6A in the mammalian central nervous system in response to sensory experience, learning, and injury. The mRNA m6A methylation pattern in rat cortex after traumatic brain injury (TBI) has not been investigated.

Results

In this study, we conducted a genome-wide profiling of mRNA m6A methylation in rat cortex via methylated RNA immunoprecipitation sequencing (MeRIP-Seq). After TBI, the expressions of METTL14 and FTO were significantly down-regulated in rat cerebral cortex. Using MeRIP-Seq, we identified a total of 2165 significantly changed peaks, of which 1062 were significantly up-regulated and 1103 peaks were significantly down-regulated. These m6A peaks were located across 1850 genes. The analysis of both m6A peaks and mRNA expression revealed that there were 175 mRNA significantly altered methylation and expression levels after TBI. Moreover, it was found that functional FTO is necessary to repair neurological damage caused by TBI but has no effect on the spatial learning and memory abilities of TBI rats by using FTO inhibitor FB23–2.

Conclusion

This study explored the m6A methylation pattern of mRNA after TBI in rat cortex and identified FTO as possible intervention targets in the epigenetic modification of TBI.

Decoding epigenetic codes: new frontiers in exploring recovery from spinal cord injury

Spinal cord injury that results in severe neurological disability is often incurable. The poor clinical outcome of spinal cord injury is mainly caused by the failure to reconstruct the injured neural circuits. Several intrinsic and extrinsic determinants contribute to this inability to reconnect. Epigenetic regulation acts as the driving force for multiple pathological and physiological processes in the central nervous system by modulating the expression of certain critical genes. Recent studies have demonstrated that post-SCI alteration of epigenetic landmarks is strongly associated with axon regeneration, glial activation and neurogenesis. These findings not only establish a theoretical foundation for further exploration of spinal cord injury, but also provide new avenues for the clinical treatment of spinal cord injury. This review focuses on the epigenetic regulation in axon regeneration and secondary spinal cord injury. Together, these discoveries are a selection of epigenetic-based prognosis biomarkers and attractive therapeutic targets in the treatment of spinal cord injury.

Elimination of human folypolyglutamate synthetase alters programming and plasticity of somatic cells

Folates are vital cofactors for the regeneration of S-adenosyl methionine, which is the methyl source for DNA methylation, protein methylation, and other aspects of one-carbon (C1) metabolism. Thus, folates are critical for establishing and preserving epigenetic programming. Folypolyglutamate synthetase (FPGS) is known to play a crucial role in the maintenance of intracellular folate levels. Therefore, any modulation in FPGS is expected to alter DNA methylation and numerous other metabolic pathways. To explore the role of polyglutamylation of folate, we eliminated both isoforms of FPGS in human cells (293T), producing FPGS knockout (FPGS^ko) cells. The elimination of FPGS significantly decreased cell proliferation, with a major effect on oxidative phosphorylation and a lesser effect on glycolysis. We found a substantial reduction in global DNA methylation and noteworthy changes in gene expression related to C1 metabolism, cell division, DNA methylation, pluripotency, Glu metabolism, neurogenesis, and cardiogenesis. The expression levels of NANOG, octamer-binding transcription factor 4, and sex-determining region Y-box 2 levels were increased in the mutant, consistent with the transition to a stem cell-like state. Gene expression and metabolite data also indicate a major change in Glu and GABA metabolism. In the appropriate medium, FPGS^ko cells can differentiate to produce mainly cells with characteristics of either neural stem cells or cardiomyocytes.-Srivastava, A. C., Thompson, Y. G., Singhal, J., Stellern, J., Srivastava, A., Du, J., O'Connor, T. R., Riggs, A. D. Elimination of human folypolyglutamate synthetase alters programming and plasticity of somatic cells.

Chromatin modification and epigenetic control in functional nerve regeneration

The repair and functional recovery of the nervous system is a highly regulated process that requires the coordination of many different components including the proper myelination of regenerated axons. Dysmyelination and remyelination failures after injury result in defective nerve conduction, impairing normal nervous system functions. There are many convergent regulatory networks and signaling mechanisms between development and regeneration. For instance, the regulatory mechanisms required for oligodendrocyte lineage progression could potentially play fundamental roles in myelin repair. In recent years, epigenetic chromatin modifications have been implicated in CNS myelination and functional nerve restoration. The pro-regenerative transcriptional program is likely silenced or repressed in adult neural cells including neurons and myelinating cells in the central and peripheral nervous systems limiting the capacity for repair after injury. In this review, we will discuss the roles of epigenetic mechanisms, including histone modifications, chromatin remodeling, and DNA methylation, in the maintenance and establishment of the myelination program during normal oligodendrocyte development and regeneration. We also discuss how these epigenetic processes impact myelination and axonal regeneration, and facilitate the improvement of current preclinical therapeutics for functional nerve regeneration in neurodegenerative disorders or after injury.

Intrinsic mechanisms of neuronal axon regeneration

Permanent disabilities following CNS injuries result from the failure of injured axons to regenerate and rebuild functional connections with their original targets. By contrast, injury to peripheral nerves is followed by robust regeneration, which can lead to recovery of sensory and motor functions. This regenerative response requires the induction of widespread transcriptional and epigenetic changes in injured neurons. Considerable progress has been made in recent years in understanding how peripheral axon injury elicits these widespread changes through the coordinated actions of transcription factors, epigenetic modifiers and, to a lesser extent, microRNAs. Although many questions remain about the interplay between these mechanisms, these new findings provide important insights into the pivotal role of coordinated gene expression and chromatin remodelling in the neuronal response to injury.

Photoperiod-induced neurotransmitter plasticity declines with aging: An epigenetic regulation?

Neuroplasticity has classically been understood to arise through changes in synaptic strength or synaptic connectivity. A newly discovered form of neuroplasticity, neurotransmitter switching, involves changes in neurotransmitter identity. Chronic exposure to different photoperiods alters the number of dopamine (tyrosine hydroxylase, TH+) and somatostatin (SST+) neurons in the paraventricular nucleus (PaVN) of the hypothalamus of adult rats and results in discrete behavioral changes. Here, we investigate whether photoperiod-induced neurotransmitter switching persists during aging and whether epigenetic mechanisms of histone acetylation and DNA methylation may contribute to this neurotransmitter plasticity. We show that this plasticity in rats is robust at 1 and at 3 months but reduced in TH+ neurons at 12 months and completely abolished in both TH+ and SST+ neurons by 18 months. De novo expression of DNMT3a catalyzing DNA methylation and anti-AcetylH3 assessing histone 3 acetylation were observed following short-day photoperiod exposure in both TH+ and SST+ neurons at 1 and 3 months while an overall increase in DNMT3a in SST+ neurons paralleled neuroplasticity reduction at 12 and 18 months. Histone acetylation increased in TH+ neurons and decreased in SST+ neurons following short-day exposure at 3 months while the total number of anti-AcetylH3+ PaVN neurons remained constant. Reciprocal histone acetylation in TH+ and SST+ neurons indicates the importance of studying epigenetic regulation at the circuit level for identified cell phenotypes. The findings may be useful for developing approaches for noninvasive treatment of disorders characterized by neurotransmitter dysfunction.

Epigenetic Regulation Of Axon Regeneration and Glial Activation in Injury Responses

Injury to the nervous system triggers a multicellular response in which epigenetic mechanisms play an important role in regulating cell type-specific transcriptional changes. Here, we summarize recent progress in characterizing neuronal intrinsic and extrinsic chromatin reconfigurations and epigenetic changes triggered by axonal injury that shape neuroplasticity and glial functions. We specifically discuss regeneration-associated transcriptional modules comprised of transcription factors and epigenetic regulators that control axon growth competence. We also review epigenetic regulation of neuroinflammation and astroglial responses that impact neural repair. These advances provide a framework for developing epigenetic strategies to maximize adaptive alterations while minimizing maladaptive stress responses in order to enhance axon regeneration and achieve functional recovery after injury.

Rhesus Brain Transcriptomic Landscape in an ex vivo Model of the Interaction of Live Borrelia Burgdorferi With Frontal Cortex Tissue Explants

Lyme neuroborreliosis (LNB) is the most dangerous manifestation of Lyme disease caused by the spirochete Borrelia burgdorferi which can reach the central nervous system most commonly presenting with lymphocytic meningitis; however, the molecular basis for neuroborreliosis is still poorly understood. We incubated explants from the frontal cortex of three rhesus brains with medium alone or medium with added live Borrelia burgdorferi for 6, 12, and 24 h and isolated RNA from each group was used for RNA sequencing with further bioinformatic analysis. Transcriptomic differences between the ex vivo model of live Borrelia burgdorferi with rhesus frontal cortex tissue explants and the controls during the progression of the infection were identified. A total of 2249, 1064, and 420 genes were significantly altered, of which 80.7, 52.9, and 19.8% were upregulated and 19.3, 47.1, 80.2% were downregulated at 6, 12, and 24 h, respectively. Gene ontology and KEGG pathway analyses revealed various pathways related to immune and inflammatory responses during the spirochete infection were enriched which is suggested to have a causal role in the pathogenesis of neurological Lyme disease. Moreover, we propose that the overexpressed FOLR2 which was demonstrated by the real-time PCR and western blotting could play a key role in neuroinflammation of the neuroborreliosis based on PPI analysis for the first time. To our knowledge, this is the first study to provide comprehensive information regarding the transcriptomic signatures that occur in the frontal cortex of the brain upon exposure to Borrelia burgdorferi, and suggest that FOLR2 is a promising target that is associated with neuroinflammation and may represent a new diagnostic or therapeutic marker in LNB.

Excess Folic Acid Supplementation Before and During Pregnancy and Lactation Activates Fos Gene Expression and Alters Behaviors in Male Mouse Offspring

Periconceptional folic acid (FA) supplementation is recommended to prevent neural tube defects and other birth defects. After 20 years mandate food fortification with FA, serum concentration of folate and unmetabolized FA increased significantly in the North American population. But whether excess FA intake impairs neurodevelopment and behavior is still controversial. Here, we treated mice with approximately 2.5-fold (moderate dose of FA, MFA) or 10-fold (high dose of FA, HFA) the dietary requirement of FA 1 week before mating and throughout pregnancy and lactation, and examined behaviors in adult male offspring using open field test, three-chamber sociability and social novelty test, elevated plus maze, rotarod and Morris water maze. We found that early life MFA supplementation increased long-term body weight gain in adults, elevated anxiety-like behavior, and impaired social preference, motor learning and spatial learning ability without modifying motor ability and spatial memory. In contrast, HFA supplementation only induced mild behavioral abnormality. RNA sequencing revealed that FA supplementation altered the expression of brain genes at weaning, among which Fos and related genes were significantly up-regulated in MFA mice compared with control and HFA mice. Quantitative real time-PCR (qRT-PCR) and western blots confirmed the increase of these genes. Our results suggested that FA supplementation during early life stage affected gene expression in weaning mice, and exhibited long-term impairments in adult behaviors in a dose-sensitive manner.

Folic Acid Modulates Matrix Metalloproteinase-9 Expression Following Spinal Cord Injury

Background

Treatment of spinal cord injury (SCI) induced neuropathic pain (NP) proves to be extremely clinically challenging as the mechanism behind SCINP is poorly understood. Matrix metalloproteinase (MMP) is largely responsible for the early disruption of the blood spinal cord barrier. This system initiates macrophage infiltration and degradation of myelin, which plays a pivotal role in how NP occurs. In a recent study, we demonstrated that folic acid (FA) treatment to cSCI rats reduced NP and improved functional recovery by repressing MMP-2 expression. We hypothesize that MMP-2 expression is suppressed because FA actively methylates the DNA sequence that encodes for the MMP-2 protein. However, modulation of MMP-2 expression for alleviation of NP is only pertinent to the mid- to late-phase of injury. Therefore, we need to explore alternate therapeutic methods to target the early- to mid-phase of injury to wholly alleviate NP.

Purpose

Furthering our previous findings on inhibiting MMP-2 expression by FA in mid- and late- phase following cSCI in rats, we hypothesized that FA will methylate and suppress MMP-9 expression during the early- phase, day 1, 3, 7 post cSCI and mid- phase (day 18 post cSCI), in comparison with MMP-2 expression during mid- and the late-phase of cSCI.

Methods

Adult male Sprague Dawley rats (250–270g) underwent cSCI, using a NYU impactor, with 12.5 gm/cm injury. The spinal cord-injured animals were treated intraperitoneally (i.p.) with a standardized dose of FA (80 μg/kg body weight) on day 1, 2, 3, prior to cSCI, followed by daily injection up to 14 or 17 days post-cSCI in different experiments. Animals were euthanized on day 1, 3, 7 post cSCI (early- phase), day 18 post cSCI (mid- phase), and day 42 post cSCI (late-phase) and the epicenter region of injured spinal cord were harvested for MMP-9 and MMP-2 expression analysis by Western blots technique.

Results

i) During early-phase on day 1, 3, and 7, the quantitation displayed no statistical significance in MMP-9 expression, between water- and FA- injected rats. ii) On day 18 post-cSCI, FA significantly modulates the expression of MMP-9 (p = 0.043) iii) Comparing results with MMP-2 expression and inhibition, FA significantly modulates the expression of MMP-2 on day 18 post cSCI (FA- and water-injected rats (p = 0.003). iv) In addition, FA significantly modulates the expression of MMP-2 on day 42 post-cSCI comparing FA- and water- injected rat groups (p = 0.034).

Conclusion

We report that FA administration results in alleviating cSCI-induced NP by inhibiting MMP-9 in the proposed mid- phase of cSCI. However, FA administration resulted in MMP-2 decline during both mid- through late- phase following cSCI. Our study elucidates a new phase of cSCI, the mid-phase. We conclude that further investigation on discovering and quantifying the nature of the mid- phase of SCI injury is needed.

Folic acid contributes to peripheral nerve injury repair by promoting Schwann cell proliferation, migration, and secretion of nerve growth factor

After peripheral nerve injury, intraperitoneal injection of folic acid improves axon quantity, increases axon density and improves electromyography results. However, the mechanisms for this remain unclear. This study explored whether folic acid promotes peripheral nerve injury repair by affecting Schwann cell function. Primary Schwann cells were obtained from rats by in vitro separation and culture. Cell proliferation, assayed using the Cell Counting Kit-8 assay, was higher in cells cultured for 72 hours with 100 mg/L folic acid compared with the control group. Cell proliferation was also higher in the 50, 100, 150, and 200 mg/L folic acid groups compared with the control group after culture for 96 hours. Proliferation was markedly higher in the 100 mg/L folic acid group compared with the 50 mg/L folic acid group and the 40 ng/L nerve growth factor group. In Transwell assays, the number of migrated Schwann cells dramatically increased after culture with 100 and 150 mg/L folic acid compared with the control group. In nerve growth factor enzyme-linked immunosorbent assays, treatment of Schwann cell cultures with 50, 100, and 150 mg/L folic acid increased levels of nerve growth factor in the culture medium compared with the control group at 3 days. The nerve growth factor concentration of Schwann cell cultures treated with 100 mg/L folic acid group was remarkably higher than that in the 50 and 150 mg/L folic acid groups at 3 days. Nerve growth factor concentration in the 10, 50, and 100 mg/L folic acid groups was higher than that in the control group at 7 days. The nerve growth factor concentration in the 50 mg/L folic acid group was remarkably higher than that in the 10 and 100 mg/L folic acid groups at 7 days. In vivo, 80 μg/kg folic acid was intraperitoneally administrated for 7 consecutive days after sciatic nerve injury. Immunohistochemical staining showed that the number of Schwann cells in the folic acid group was greater than that in the control group. We suggest that folic acid may play a role in improving the repair of peripheral nerve injury by promoting the proliferation and migration of Schwann cells and the secretion of nerve growth factors.