Histone deacetylase expression in white matter oligodendrocytes after stroke

Epigenetic modifications in the motor cortex caused by exercise or pharmacological inhibition of histone deacetylases (HDACs) after intracerebral hemorrhage (ICH)

Epigenetic regulation is expected to provide an enriched platform for neurorehabilitation of post-stroke patients. Acetylation of specific lysine residues in histones is a potent epigenetic target essential for transcriptional regulation. Exercise modulates histone acetylation and gene expression in neuroplasticity in the brain. This study sought to examine the effect of epigenetic treatment using a histone deacetylase (HDAC) inhibitor, sodium butyrate (NaB), and exercise on epigenetic markers in the bilateral motor cortex after intracerebral hemorrhage (ICH) to identify a more enriched neuronal condition for neurorehabilitation. Forty-one male Wistar rats were randomly divided into five groups: sham (n = 8), control (n = 9), NaB, exercise (n = 8), and NaB and exercise (n = 8). Intraperitoneal administration of an HDAC inhibitor (300 mg/kg NaB) and treadmill exercise (11 m/min for 30 min) was conducted five days a week for approximately-four weeks. ICH specifically decreased the acetylation level of histone H4 in the ipsilateral cortex, and HDAC inhibition with NaB increased the acetylation level of histone H4 over the sham level, accompanied by an improvement in motor function as assessed by the cylinder test. Exercise increased the acetylation levels of histones (H3 and H4) in the bilateral cortex. Synergistic effects of exercise and NaB were not observed during histone acetylation. Pharmacological treatment with a HDAC inhibitor and exercise can provide an enriched epigenetic platform for neurorehabilitation in an individual manner.

The NG2-glia is a potential target to maintain the integrity of neurovascular unit after acute ischemic stroke

The neurovascular unit (NVU) plays a critical role in health and disease. In the current review, we discuss the critical role of a class of neural/glial antigen 2 (NG2)-expressing glial cells (NG2-glia) in regulating NVU after acute ischemic stroke (AIS). We first introduce the role of NG2-glia in the formation of NVU during development as well as aging-induced damage to NVU and accompanying NG2-glia change. We then discuss the reciprocal interactions between NG2-glia and the other component cells of NVU, emphasizing the factors that could influence NG2-glia. Damage to the NVU integrity is the pathological basis of edema and hemorrhagic transformation, the most dreaded complication after AIS. The role of NG2-glia in AIS-induced NVU damage and the effect of NG2-glia transplantation on AIS-induced NVU damage are summarized. We next discuss the role of NG2-glia and the effect of NG2-glia transplantation in oligodendrogenesis and white matter repair as well as angiogenesis which is associated with the outcome of the patients after AIS. Finally, we review the current strategies to promote NG2-glia proliferation and differentiation and propose to use the dental pulp stem cells (DPSC)-derived exosome as a promising strategy to reduce AIS-induced injury and promote repair through maintaining the integrity of NVU by regulating endogenous NG2-glia proliferation and differentiation.

Histone Deacetylase 3 Inhibition Decreases Cerebral Edema and Protects the Blood–Brain Barrier After Stroke

We have previously shown that selective inhibition of histone deacetylase 3 (HDAC3) decreases infarct volume and improves long-term functional outcomes after stroke. In this study, we examined the effects of HDAC3 inhibition on cerebral edema and blood–brain barrier (BBB) leakage and explored its underlying mechanisms. Adult male Wistar rats were subjected to 2-h middle cerebral artery occlusion (MCAO) and randomly treated i.p. with either vehicle or a selective HDAC3 inhibitor (RGFP966) at 2 and 24 h after stroke. Modified neurological severity scores (mNSS) were calculated at 2 h, 1 day, and 3 days. H&E, Evans blue dye (EBD) assay, and fluorescein isothiocyanate (FITC)-dextran were employed to assess cerebral edema and BBB leakage. Western blot for matrix metalloproteinase-9 (MMP9), MMP-9 zymography, and immunostaining for HDAC3, GFAP, Iba-1, albumin, aquaporin-4, claudin-5, ZO-1, and NF-kB were performed. Early RGFP966 administration decreased cerebral edema (p = 0.002) and BBB leakage, as measured by EBD assay, FITC-dextran, and albumin extravasation (p < 0.01). RGFP966 significantly increased tight junction proteins (claudin-5 and ZO-1) in the peri-infarct area. RGFP966 also significantly decreased HDAC3 in GFAP + astrocytes, which correlated with better mNSS (r = 0.67, p = 0.03) and decreased cerebral edema (r = 0.64, p = 0.04). RGFP966 decreased aquaporin-4 in GFAP + astrocytes (p = 0.002), as well as, the inflammatory markers Iba-1, NF-kB, and MMP9 in the ischemic brain (p < 0.05). Early HDAC3 inhibition decreases cerebral edema and BBB leakage. BBB protection by RGFP966 is mediated in part by the upregulation of tight junction proteins, downregulation of aquaporin-4 and HDAC3 in astrocytes, and decreased neuroinflammation.

High Mobility Group A1 Regulates Transcription Levels of Oligodendrocyte Marker Genes in Cultured Oligodendrocyte Precursor Cells

Oligodendrocyte precursor cells (OPCs) serve as progenitor cells of terminally differentiated oligodendrocytes. Past studies have confirmed the importance of epigenetic system in OPC differentiation to oligodendrocytes. High mobility group A1 (HMGA1) is a small non-histone nuclear protein that binds DNA and modifies the chromatin conformational state. However, it is still completely unknown about the roles of HMGA1 in the process of OPC differentiation. In this study, we prepared primary OPC cultures from the neonatal rat cortex and examined whether the loss- and gain-of-function of HMGA1 would change the mRNA levels of oligodendrocyte markers, such as Cnp, Mbp, Myrf, and Plp during the process of OPC differentiation. In our system, the mRNA levels of Cnp, Mbp, Myrf, and Plp increased depending on the oligodendrocyte maturation step, but the level of Hmga1 mRNA decreased. When HMGA1 was knocked down by a siRNA approach, the mRNA levels of Cnp, Mbp, Myrf, and Plp were smaller in OPCs with Hmga1 siRNA compared to the ones in the control OPCs. On the contrary, when HMGA1 expression was increased by transfection of the Hmga1 plasmid, the mRNA levels of Cnp, Mbp, Myrf, and Plp were slightly larger compared to the ones in the control OPCs. These data may suggest that HMGA1 participates in the process of OPC differentiation by regulating the mRNA expression level of myelin-related genes.

Effect of Neurorepair for Motor Functional Recovery Enhanced by Total Saponins From Trillium tschonoskii Maxim. Treatment in a Rat Model of Focal Ischemia

Trillium tschonoskii Maxim. (TTM), is a perennial herb from Liliaceae, that has been widely used as a traditional Chinese medicine treating cephalgia and traumatic hemorrhage. The present work was designed to investigate whether the total saponins from Trillium tschonoskii Maxim. (TSTT) would promote brain remodeling and improve gait impairment in the chronic phase of ischemic stroke. A focal ischemic model of male Sprague-Dawley (SD) rats was established by permanent middle cerebral artery occlusion (MCAO). Six hours later, rats were intragastrically treated with TSTT (120, 60, and 30 mg/kg) and once daily up to day 30. The gait changes were assessed by the CatWalk-automated gait analysis system. The brain tissues injuries, cerebral perfusion and changes of axonal microstructures were detected by multimodal magnetic resonance imaging (MRI), followed by histological examinations. The axonal regeneration related signaling pathways including phosphatidylinositol 3-kinases (PI3K)/protein kinase B (AKT)/glycogen synthase kinase-3 (GSK-3)/collapsin response mediator protein-2 (CRMP-2) were measured by western blotting. TSTT treatment significantly improved gait impairment of rats. MRI analysis revealed that TSTT alleviated tissues injuries, significantly improved cerebral blood flow (CBF), enhanced microstructural integrity of axon and myelin sheath in the ipsilesional sensorimotor cortex and internal capsule. In parallel to MRI findings, TSTT preserved myelinated axons and promoted oligodendrogenesis. Specifically, TSTT interventions markedly up-regulated expression of phosphorylated GSK-3, accompanied by increased expression of phosphorylated PI3K, AKT, but reduced phosphorylated CRMP-2 expression. Taken together, our results suggested that TSTT facilitated brain remodeling. This correlated with improving CBF, encouraging reorganization of axonal microstructure, promoting oligodendrogenesis and activating PI3K/AKT/GSK-3/CRMP-2 signaling, thereby improving poststroke gait impairments.

HDAC2/3 inhibitor MI192 mitigates oligodendrocyte loss and reduces microglial activation upon injury: A potential role of epigenetics

Background:

During development, oligodendrocyte (OL) lineage cells are susceptible to injury, leading to life-long clinical neurodevelopmental deficits, which lack effective treatments. Drugs targeting epigenetic modifications that inhibit histone deacetylases (HDACs) protect from many clinical neurodegenerative disorders.

Aim:

This study aimed to investigate the therapeutic potential of histone deacetylase 2/3 (HDAC2/3) inhibitor MI192 on white matter (WM) pathology in a model of neonatal rat brain injury.

Methods:

Wistar rats (8.5-day-old, n = 32) were used to generate brain tissues. The tissues were cultured and then randomly divided into four groups and treated as following: group I (sham); the tissues were cultured under normoxia, group II (vehicle); DMSO only, group III (injury, INJ); the tissues were exposed to 20 minutes oxygen-glucose deprivation (OGD) insult, and group IV (INJ + MI192); the tissues were subjected to the OGD insult and then treated with the MI192 inhibitor. On culture day 10, the tissues were fixed for biochemical and histological examinations.

Results:

The results showed that inhibition of HDAC2/3 activity alleviated WM pathology. Specifically, MI192 treatment significantly reduced cell death, minimized apoptosis, and mitigates the loss of the MBP⁺ OLs and their precursors (NG₂⁺ OPCs). Additionally, MI192 decreased the density of reactive microglia (OX−42⁺). These findings demonstrate that the inhibition of HDAC2/3 activity post-insult alleviates WM pathology through mechanism(s) including preserving OL lineage cells and suppressing microglial activation.

Conclusion:

The findings of this study suggest that HDAC2/3 inhibition is a rational strategy to preserve WM or reverse its pathology upon newborn brain injury.

Trillium tschonoskii rhizomes' saponins induces oligodendrogenesis and axonal reorganization for ischemic stroke recovery in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Trillium tschonoskii Maxim. is one of traditional Chinese medical herbs that has been utilized to treat brain damages and cephalalgia. The neuroprotective effect of total saponins from Trillium tschonoskii rhizome (TSTT) has been demonstrated efficacy in rats following ischemia. However, the axonal remodeling effect of TSTT and the detailed mechanisms after ischemic stroke have not been investigated.

AIM OF THE STUDY

We aimed to estimate therapeutic role of TSTT in axonal remodeling using magnetic resonance imaging (MRI) technique, and explored possible mechanisms underlying this process followed by histological assays in ischemic rats.

METHODS

Male Sprague-Dawley (SD) rats underwent permanently focal cerebral ischemia induced by occluding right permanent middle cerebral artery. TSTT was intragastrically administrated 6 h after surgery and once daily for consecutive 15 days. Neurological function was assessed by the motor deficit score and beam walking test. T2 relaxation mapping and diffusion tensor imaging (DTI) were applied for detecting cerebral tissues damages and microstructural integrity of axons. Luxol fast blue (LFB) and transmission electron microscope (TEM) were performed to evaluate histopathology in myelinated axons. Double immunofluorescent staining was conducted to assess oligodendrogenesis. Furthermore, the protein expressions regarding to axonal remodeling related signaling pathways were detected by Western blot assays.

RESULTS

TSTT treatment (65, 33 mg/kg) markedly improved motor function after ischemic stroke. T2 mapping MRI demonstrated that TSTT decreased lesion volumes, and DTI further confirmed that TSTT preserved axonal microstructure of the sensorimotor cortex and internal capsule. Meanwhile, diffusion tensor tractography (DTT) showed that TSTT elevated correspondent density and length of fiber in the internal capsule. These MRI measurements were confirmed by histological examinations. Notably, TSTT significantly increased Ki67/NG2, Ki67/CNPase double-labeled cells along the boundary zone of ischemic cortex and striatum. Meanwhile, TSTT treatment up-regulated the phosphorylation level of Ser 9 in GSK-3β, and down-regulated phosphorylated β-catenin and CRMP-2 expression.

CONCLUSION

Taken together, our findings indicated that TSTT (65, 33 mg/kg) enhanced post-stroke functional recovery, amplified endogenous oligodendrogenesis and promoted axonal regeneration. The beneficial role of TSTT might be correlated with GSK-3/β-catenin/CRMP-2 modulating axonal reorganization after ischemic stroke.

Histone deacetylase HDAC4 participates in the pathological process of myocardial ischemia-reperfusion injury via MEKK1/JNK pathway by binding to miR-206

Histone deacetylases (HDACs) and microRNAs (miRs) have been reported to exert pivotal roles on the pathogenesis of myocardial ischemia-reperfusion injury (MIRI). Therefore, the present study was performed to define the underlying role of HDAC4 and miR-206 in the pathological process of MIRI. An IRI rat model was established. The interaction between HDAC4 and the promoter region of miR-206 was determined using ChIP, and that between miR-206 and mitogen-activated protein kinase kinase kinase 1 (MEKK1) was determined using dual luciferase reporter gene assay. After the loss- or gain-of-function assay in cardiomyocytes, western blot analysis, RT-qPCR, TUNEL, and ELISA assay were performed to define the roles of HDAC4, miR-206, and MEKK1. Up-regulation of HDAC4 and down-regulation of miR-206 occurred in rat myocardial tissues and cardiomyocytes in MIRI. HDAC4 down-regulation or miR-206 up-regulation contributed to reduced cell apoptosis and the levels of tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), and malondialdehyde (MDA), while elevating the superoxide dismutase (SOD) and glutathione (GSH) contents. Meanwhile, HDAC4 silencing promoted the expression of miR-206, which targeted and negatively regulated MEKK1. Then inhibition of JNK phosphorylation reduced the cardiomyocyte apoptosis to alleviate MIRI. Coherently, HDAC4 silencing could up-regulate the expression of miR-206 to reduce cardiomyocyte apoptosis and inhibit oxidative stress, and exerting a protective effect on MIRI via the MEKK1/JNK pathway.

HDAC1 deregulation promotes neuronal loss and deficit of motor function in stroke pathogenesis

Stroke is a common cause of death worldwide and leads to disability and cognitive dysfunction. Ischemic stroke and hemorrhagic stroke are major categories of stroke, accounting for 68% and 32% of strokes, respectively. Each year, 15 million people experience stroke worldwide, and the stroke incidence is rising. Epigenetic modifications regulate gene transcription and play a major role in stroke. Accordingly, histone deacetylase 1 (HDAC1) participates in DNA damage repair and cell survival. However, the mechanisms underlying the role of HDAC1 in stroke pathogenesis are still controversial. Therefore, we investigated the role of HDAC1 in stroke by using a rat model of endothelin-1-induced brain ischemia. Our results revealed that HDAC1 was deregulated following stroke, and its expressional level and enzymatic activity were decreased. We also used MS-275 to inhibit HDAC1 function in rats exposed to ischemic insult. We found that HDAC1 inhibition promoted the infarct volume, neuronal loss, DNA damage, neuronal apoptosis after stroke, and levels of reactive oxygen species and inflammation cytokines. Additionally, HDAC1 inhibition deteriorated the behavioral outcomes of rats with ischemic insult. Overall, our findings demonstrate that HDAC1 participates in ischemic pathogenesis in the brain and possesses potential for use as a therapeutic target.

Convergent epigenetic regulation of glial plasticity in myelin repair and brain tumorigenesis: A focus on histone modifying enzymes

Brain regeneration and tumorigenesis are complex processes involving in changes in chromatin structure to regulate cellular states at the molecular and genomic level. The modulation of chromatin structure dynamics is critical for maintaining progenitor cell plasticity, growth and differentiation. Oligodendrocyte precursor cells (OPC) can be differentiated into mature oligodendrocytes, which produce myelin sheathes to permit saltatory nerve conduction. OPCs and their primitive progenitors such as pri-OPC or pre-OPC are highly adaptive and plastic during injury repair or brain tumor formation. Recent studies indicate that chromatin modifications and epigenetic homeostasis through histone modifying enzymes shape genomic regulatory landscape conducive to OPC fate specification, lineage differentiation, maintenance of myelin sheaths, as well as brain tumorigenesis. Thus, histone modifications can be convergent mechanisms in regulating OPC plasticity and malignant transformation. In this review, we will focus on the impact of histone modifying enzymes in modulating OPC plasticity during normal development, myelin regeneration and tumorigenesis.

Epigenetic Landscape Changes Due to Acupuncture Treatment: From Clinical to Basic Research

Acupuncture has been widely used for treating diseases since the ancient days in China, but the mechanism by which acupuncture exerts such powerful roles is unclear. Epigenetics, including DNA methylation, histone modification, and post-transcriptional regulation of miRNAs, is the study of heritable changes in gene expression that do not include DNA sequence alterations. Epigenetics has become a new strategy for the basic and clinical research of acupuncture in the last decade. Some investigators have been trying to illustrate the mechanism of acupuncture from an epigenetics perspective, which has shed new lights on the mechanisms and applications of acupuncture. Moreover, the introduction of epigenetics into the regulatory mechanism in acupuncture treatment has provided more objective and scientific support for acupuncture theories and brought new opportunities for the improvement of acupuncture studies. In this paper, we reviewed the literatures that has demonstrated that acupuncture could directly or indirectly affect epigenetics, in order to highlight the progress of acupuncture studies correlated to epigenetic regulations. We do have to disclose that the current evidence in this review is not enough to cover all the complex interactions between multiple epigenetic modifications and their regulations. However, the up-to-date results can help us to better understand acupuncture's clinical applications and laboratory research.

Inhibition of CD147 improves oligodendrogenesis and promotes white matter integrity and functional recovery in mice after ischemic stroke

White matter damage is an important contributor to long-term neurological deficit after stroke. Our previous study has shown that inhibition of CD147 ameliorates acute ischemic stroke in mice. In this study, we aimed to investigate whether inhibition of CD147 promotes white matter repair and long-term functional recovery after ischemic stroke.Male adult C57BL/6 mice were subjected to transient (1-h) middle cerebral artery occlusion (tMCAO). Anti-CD147 function-blocking antibody (αCD147) was injected intravenously once daily for 3 days beginning 4 h after onset of ischemia. Sensorimotor and cognitive functions were evaluated up to 28 days after stroke. We found that αCD147 treatment not only prevented neuronal and oligodendrocyte cell death in the acute phase, but also profoundly protected white matter integrity and reduced brain atrophy and tissue loss in the late phase, leading to improved sensorimotor and cognitive functions for at least 28 days after stroke. Mechanistically, we found that αCD147 treatment increased the number of proliferating NG2(+)/PDGFRα(+) oligodendrocyte precursor cells (OPCs) and newly generated mature APC(+)/Sox10(+) oligodendrocytes after stroke, possibly through upregulation of SDF-1/CXCR4 axis in OPCs. In conclusion, inhibition of CD147 promotes long-term functional recovery after stroke, at least in part, by enhancing oligodendrogenesis and white matter repair.

From OPC to Oligodendrocyte: An Epigenetic Journey

Oligodendrocytes provide metabolic and functional support to neuronal cells, rendering them key players in the functioning of the central nervous system. Oligodendrocytes need to be newly formed from a pool of oligodendrocyte precursor cells (OPCs). The differentiation of OPCs into mature and myelinating cells is a multistep process, tightly controlled by spatiotemporal activation and repression of specific growth and transcription factors. While oligodendrocyte turnover is rather slow under physiological conditions, a disruption in this balanced differentiation process, for example in case of a differentiation block, could have devastating consequences during ageing and in pathological conditions, such as multiple sclerosis. Over the recent years, increasing evidence has shown that epigenetic mechanisms, such as DNA methylation, histone modifications, and microRNAs, are major contributors to OPC differentiation. In this review, we discuss how these epigenetic mechanisms orchestrate and influence oligodendrocyte maturation. These insights are a crucial starting point for studies that aim to identify the contribution of epigenetics in demyelinating diseases and may thus provide new therapeutic targets to induce myelin repair in the long run.

Differential roles of epigenetic regulators in the survival and differentiation of oligodendrocyte precursor cells

During development or after brain injury, oligodendrocyte precursor cells (OPCs) differentiate into oligodendrocytes to supplement the number of oligodendrocytes. Although mechanisms of OPC differentiation have been extensively examined, the role of epigenetic regulators, such as histone deacetylases (HDACs) and DNA methyltransferase enzymes (DNMTs), in this process is still mostly unknown. Here, we report the differential roles of epigenetic regulators in OPC differentiation. We prepared primary OPC cultures from neonatal rat cortex. Our cultured OPCs expressed substantial amounts of mRNA for HDAC1, HDAC2, DNMT1, and DNMT3a. mRNA levels of HDAC1 and HDAC2 were both decreased by the time OPCs differentiated into myelin-basic-protein expressing oligodendrocytes. However, DNMT1 or DNMT3a mRNA level gradually decreased or increased during the differentiation step, respectively. We then knocked down those regulators in cultured OPCs with siRNA technique before starting OPC differentiation. While HDAC1 knockdown suppressed OPC differentiation, HDAC2 knockdown promoted OPC differentiation. DNMT1 knockdown also suppressed OPC differentiation, but unlike HDAC1/2, DNMT1-deficient cells showed cell damage during the later phase of OPC differentiation. On the other hand, when OPCs were transfected with siRNA for DNMT3a, the number of OPCs was decreased, indicating that DNMT3a may participate in OPC survival/proliferation. Taken together, these data demonstrate that each epigenetic regulator has different phase-specific roles in OPC survival and differentiation.

Brain Functional Reserve in the Context of Neuroplasticity after Stroke

Stroke is the second cause of death and more importantly first cause of disability in people over 40 years of age. Current therapeutic management of ischemic stroke does not provide fully satisfactory outcomes. Stroke management has significantly changed since the time when there were opened modern stroke units with early motor and speech rehabilitation in hospitals. In recent decades, researchers searched for biomarkers of ischemic stroke and neuroplasticity in order to determine effective diagnostics, prognostic assessment, and therapy. Complex background of events following ischemic episode hinders successful design of effective therapeutic strategies. So far, studies have proven that regeneration after stroke and recovery of lost functions may be assigned to neuronal plasticity understood as ability of brain to reorganize and rebuild as an effect of changed environmental conditions. As many neuronal processes influencing neuroplasticity depend on expression of particular genes and genetic diversity possibly influencing its effectiveness, knowledge on their mechanisms is necessary to understand this process. Epigenetic mechanisms occurring after stroke was briefly discussed in this paper including several mechanisms such as synaptic plasticity; neuro-, glio-, and angiogenesis processes; and growth of axon.

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.

Epigenetic modifications-insight into oligodendrocyte lineage progression, regeneration, and disease

Myelination by oligodendrocytes in the central nervous system permits high-fidelity saltatory conduction from neuronal cell bodies to axon terminals. Dysmyelinating and demyelinating disorders impair normal nervous system functions. Consequently, an understanding of oligodendrocyte differentiation that moves beyond the genetic code into the field of epigenetics is essential. Chromatin reprogramming is critical for steering stage-specific differentiation processes during oligodendrocyte development. Fine temporal control of chromatin remodeling through ATP-dependent chromatin remodelers and sequential histone modifiers shapes a chromatin regulatory landscape conducive to oligodendrocyte fate specification, lineage differentiation, and maintenance of cell identity. In this Review, we will focus on the biological functions of ATP-dependent chromatin remodelers and histone deacetylases in myelinating oligodendrocyte development and implications for myelin regeneration in neurodegenerative diseases.

Cell Death Mechanisms in Stroke and Novel Molecular and Cellular Treatment Options

As a result of ischemia or hemorrhage, blood supply to neurons is disrupted which subsequently promotes a cascade of pathophysiological responses resulting in cell loss. Many mechanisms are involved solely or in combination in this disorder including excitotoxicity, mitochondrial death pathways, and the release of free radicals, protein misfolding, apoptosis, necrosis, autophagy and inflammation. Besides neuronal cell loss, damage to and loss of astrocytes as well as injury to white matter contributes also to cerebral injury. The core problem in stroke is the loss of neuronal cells which makes recovery difficult or even not possible in the late states. Acute treatment options that can be applied for stroke are mainly targeting re-establishment of blood flow and hence, their use is limited due to the effective time window of thrombolytic agents. However, if the acute time window is exceeded, neuronal loss starts due to the activation of cell death pathways. This review will explore the most updated cellular death mechanisms leading to neuronal loss in stroke. Ischemic and hemorrhagic stroke as well as subarachnoid hemorrhage will be debated in the light of cell death mechanisms and possible novel molecular and cellular treatment options will be discussed.

Chromatin remodeling and epigenetic regulation of oligodendrocyte myelination and myelin repair

Oligodendrocytes are essential for the development, function, and health of the vertebrate central nervous system. These cells maintain axon myelination to ensure saltatory propagation of action potentials. Oligodendrocyte develops from neural progenitor cells, in a step-wise process that involves oligodendrocyte precursor specification, proliferation, and differentiation. The lineage progression requires coordination of transcriptional and epigenetic circuits to mediate the stage-specific intricacies of oligodendrocyte development. Epigenetic mechanisms involve DNA methylation, histone modifications, ATP-dependent chromatin remodeling, and non-coding RNA modulation that regulate the chromatin state over regulatory genes, which must be expressed or repressed to establish oligodendrocyte identity and lineage progression. In this review, we will focus on epigenetic programming associated with histone modification enzymes, chromatin remodeling, and non-coding RNAs that regulate oligodendrocyte lineage progression, and discuss how these mechanisms might be harnessed to induce myelin repair for treatment of demyelinating diseases such as multiple sclerosis.

Monocarboxylate transporter 1 and the vulnerability of oligodendrocyte lineage cells to metabolic stresses

AIMS

Oligodendrocytes, especially oligodendrocyte precursor cells, are known to be sensitive to hypoxic and metabolic stresses. Vulnerability of oligodendrocytes is considered a contributing factor to white matter dysfunction. However, little is known about the energy processing characteristics of oligodendrocyte lineage cells under basal and metabolic stress conditions. The aim of this study was to identify the energy requirements and cellular responses of oligodendrocytes at different developmental stages.

METHODS

We compared the metabolic stress responses between myelinating oligodendrocytes (OLs) and oligodendrocyte precursor cells (OPCs). Differential regulation of cellular response was also investigated.

RESULTS

We found that, following cerebral ischemia, monocarboxylate transporter 1 (MCT1) expression was upregulated in the peri-infarct striatum but not in the cortex of the brain. In vitro ischemia models were used to induce oligodendrocyte stress as well. An increase in MCT1 expression was detected in OPCs after a mild oxygen-glucose deprivation. Double-labeled immunohistochemical analysis revealed that OPCs and OLs responded differently to metabolic stresses and that the susceptibility to metabolic stresses of OPCs and OLs was associated with their distinct expression profiles of MCT1.

CONCLUSION

Taken together, this study shows that MCT1 plays a role in the responses of OPCs and OLs to metabolic and ischemic stresses and suggests that redistribution of energy substrates is a determinant in white matter injury.

The Role of the Oligodendrocyte Lineage in Acute Brain Trauma

An acute brain injury is commonly characterized by an extended cellular damage. The post-injury process of scar formation is largely determined by responses of various local glial cells and blood-derived immune cells. The role of astrocytes and microglia have been frequently reviewed in the traumatic sequelae. Here, we summarize the diverse contributions of oligodendrocytes (OLs) and their precursor cells (OPCs) in acute injuries. OLs at the lesion site are highly sensitive to a damaging insult, provoked by Ca²⁺ overload after hyperexcitation originating from increased levels of transmitters. At the lesion site, differentiating OPCs can replace injured oligodendrocytes to guarantee proper myelination that is instrumental for healthy brain function. In contrast to finally differentiated and non-dividing OLs, OPCs are the most proliferative cells of the brain and their proliferation rate even increases after injury. There exist even evidence that OPCs might also generate some type of astrocyte beside OLs. Thereby, OPCs can contribute to the generation and maintenance of the glial scar. In the future, detailed knowledge of the molecular cues that help to prevent injury-evoked glial cell death and that control differentiation and myelination of the oligodendroglial lineage will be pivotal in developing novel therapeutic approaches.

Epigenetics in Stroke Recovery

Abstract: While the death rate from stroke has continually decreased due to interventions in the hyperacute stage of the disease, long-term disability and institutionalization have become common sequelae in the aftermath of stroke. Therefore, identification of new molecular pathways that could be targeted to improve neurological recovery among survivors of stroke is crucial. Epigenetic mechanisms such as post-translational modifications of histone proteins and microRNAs have recently emerged as key regulators of the enhanced plasticity observed during repair processes after stroke. In this review, we highlight the recent advancements in the evolving field of epigenetics in stroke recovery.

Class IIa histone deacetylases affect neuronal remodeling and functional outcome after stroke

We have previously demonstrated that stroke induces nuclear shuttling of class IIa histone deacetylase 4 (HDAC4). Stroke-induced nuclear shuttling of HDAC4 is positively and significantly correlated with improved indices of neuronal remodeling in the peri-infarct cortex. In this study, using a rat model for middle cerebral artery occlusion (MCAO), we tested the effects of selective inhibition of class IIa HDACs on functional recovery and neuronal remodeling when administered 24hr after stroke. Adult male Wistar rats (n = 15-17/group) were subjected to 2 h MCAO and orally gavaged with MC1568 (a selective class IIa HDAC inhibitor), SAHA (a non-selective HDAC inhibitor), or vehicle-control for 7 days starting 24 h after MCAO. A battery of behavioral tests was performed. Lesion volume measurement and immunohistochemistry were performed 28 days after MCAO. We found that stroke increased total HDAC activity in the ipsilateral hemisphere compared to the contralateral hemisphere. Stroke-increased HDAC activity was significantly decreased by the administration of SAHA as well as by MC1568. However, SAHA significantly improved functional outcome compared to vehicle control, whereas selective class IIa inhibition with MC1568 increased mortality and lesion volume and did not improve functional outcome. In addition, MC1568 decreased microtubule associated protein 2 (MAP2, dendrites), phosphorylated neurofilament heavy chain (pNFH, axons) and myelin basic protein (MBP, myelination) immunoreactivity in the peri-infarct cortex. Quantitative RT-PCR of cortical neurons isolated by laser capture microdissection revealed that MC1568, but not SAHA, downregulated CREB and c-fos expression. Additionally, MC1568 decreased the expression of phosphorylated CREB (active) in neurons. Taken together, these findings demonstrate that selective inhibition of class IIa HDACs impairs neuronal remodeling and neurological outcome. Inactivation of CREB and c-fos by MC1568 likely contributes to this detrimental effect.

CD200 restrains macrophage attack on oligodendrocyte precursors via toll-like receptor 4 downregulation

There are numerous barriers to white matter repair after central nervous system injury and the underlying mechanisms remain to be fully understood. In this study, we propose the hypothesis that inflammatory macrophages in damaged white matter attack oligodendrocyte precursor cells via toll-like receptor 4 signaling thus interfering with this endogenous progenitor recovery mechanism. Primary cell culture experiments demonstrate that peritoneal macrophages can attack and digest oligodendrocyte precursor cells via toll-like receptor 4 signaling, and this phagocytosis of oligodendrocyte precursor cells can be inhibited by using CD200-Fc to downregulate toll-like receptor 4. In an in vivo model of white matter ischemia induced by endothelin-1, treatment with CD200-Fc suppressed toll-like receptor 4 expression in peripherally circulating macrophages, thus restraining macrophage phagocytosis of oligodendrocyte precursor cells and leading to improved myelination. Taken together, these findings suggest that deleterious macrophage effects may occur after white matter ischemia, whereby macrophages attack oligodendrocyte precursor cells and interfere with endogenous recovery responses. Targeting this pathway with CD200 may offer a novel therapeutic approach to amplify endogenous oligodendrocyte precursor cell-mediated repair of white matter damage in mammalian brain.

The Emerging Role of Epigenetics in Cerebral Ischemia

Despite great progresses in the treatment and prevention of ischemic stroke, it is still among the leading causes of death and serious long-term disability all over the world, indicating that innovative neural regenerative and neuroprotective agents are urgently needed for the development of therapeutic approaches with greater efficacy for ischemic stroke. More and more evidence suggests that a spectrum of epigenetic processes play an important role in the pathophysiology of cerebral ischemia. In the present review, we first discuss recent developments in epigenetic mechanisms, especially their roles in the pathophysiology of cerebral ischemia. Specifically, we focus on DNA methylation, histone deacetylase, histone methylation, and microRNAs (miRNAs) in the regulation of vascular and neuronal regeneration after cerebral ischemia. Additionally, we highlight epigenetic strategies for ischemic stroke treatments, including the inhibition of histone deacetylase enzyme and DNA methyltransferase activities, and miRNAs. These therapeutic strategies are far from clinic use, but preliminary data indicate that neuroprotective agents targeting these pathways can modulate neural cell regeneration and promote brain repair and functional recovery after cerebral ischemia. A better understanding of how epigenetics influences the process and progress of cerebral ischemia will pave the way for discovering more sensitive and specific biomarkers and new targets and therapeutics for ischemic stroke.

Non-coding RNA-mediated epigenetic regulation of liver fibrosis

Hepatic stellate cells (HSC) activation plays a key role in liver fibrosis. Numerous studies have indicated that non-coding RNAs (ncRNAs) control liver fibrosis and fibroblasts proliferation. Greater knowledge of the role of the ncRNAs-mediated epigenetic mechanism in liver fibrosis could improve understanding of the liver fibrosis pathogenesis. The aim of this review is to describe the present knowledge about the ncRNAs significantly participating in liver fibrosis and HSC activation, and look ahead on new perspectives of ncRNAs-mediated epigenetic mechanism research. Moreover, we will discuss examples of non-coding RNAs that interact with histone modification or DNA methylation to regulate gene expression in liver fibrosis. Diverse classes of ncRNAs, ranging from microRNAs (miRs) to long non-coding RNAs (LncRNAs), have emerged as key regulators of several important aspects of function, including cell proliferation, activation, etc. In addition, recent advances suggest the important role of ncRNAs transcripts in epigenetic gene regulation. Targeting the miRs and LncRNAs can be a promising direction in liver fibrosis treatment. We discuss new perspectives of miRs and LncRNAs in liver fibrosis and HSC activation, mainly including interaction with histone modification or DNA methylation to regulate gene expression. These epigenetic mechanisms form powerful ncRNAs surveillance systems that may represent new targets for liver fibrosis therapeutic intervention.

Promoting brain remodeling to aid in stroke recovery

Endogenous brain repair after stroke involves a set of highly interactive processes, such as angiogenesis, neurogenesis, oligodendrogenesis, synaptogenesis, and axonal outgrowth, which together orchestrate neurological recovery. During the past several years, there have been advances in our understanding of miRNAs and histone deacetylases (HDACs) in brain repair processes after stroke. Emerging data indicate the important role of exosomes for intercellular communication in promoting coupled brain remodeling processes. These advances will likely have a major impact on the development of restorative therapies for ischemic brain repair, consequently leading to improvement of neurological function. In this review, we provide an update on our current understanding of cellular and molecular mechanisms of miRNAs, exosomes, and HDACs in brain restorative processes after stroke.

Stroke Induces Nuclear Shuttling of Histone Deacetylase 4

BACKGROUND AND PURPOSE

Histone deacetylases (HDACs) 4 and 5 are abundantly expressed in the brain and have been implicated in the regulation of neurodegeneration. Under physiological conditions, HDACs 4 and 5 are expressed in the cytoplasm of brain cells where they cannot directly access chromatin. In response to external stimuli, they can shuttle to the nucleus and regulate gene expression. However, the effect of stroke on nuclear shuttling of HDACs 4 and 5 remains unknown.

METHODS

Using a rat model of middle cerebral artery occlusion, we examined the subcellular localization of HDACs 4 and 5 in the peri-infarct cortex during brain repair after stroke.

RESULTS

Stroke significantly increased nuclear HDAC4 immunoreactivity in neurons, but not in astrocytes or in oligodendrocytes, of the peri-infarct cortex at 2, 7, and 14 days after middle cerebral artery occlusion. Neurons with nuclear HDAC4 immunoreactivity distributed across all layers of the peri-infarct cortex and were Ctip2+ excitatory and parvalbumin+ inhibitory neurons. These neurons were not TUNEL or BrdU positive. Furthermore, nuclear HDAC4 immunoreactivity was positively and significantly correlated with increased dendritic, axonal, and myelin densities as determined by microtubule-associated protein 2, phosphorylated neurofilament heavy chain, and myelin basic protein, respectively. Unlike HDAC4, stroke did not alter nuclear localization of HDAC5.

CONCLUSIONS

Our data show that stroke induces nuclear shuttling of HDAC4 in neurons in the peri-infarct cortex, and that increased nuclear HDAC4 is strongly associated with neuronal remodeling but not with neuronal cell death, suggesting a role for nuclear HDAC4 in promoting neuronal recovery after ischemic injury.

Oligodendroglial Development: New Roles for Chromatin Accessibility

In the central nervous system, the generation of mature oligodendrocytes from their progenitors is a critical step in myelination, which is essential for normal nervous system function. Thus, understanding the regulatory mechanism underlying oligodendroglial development is of great importance, especially for the development of new therapeutic strategies that promote remyelination in demyelinating diseases, such as multiple sclerosis. Previous studies have focused on genetic patterns and revealed a network of cell signaling pathways and related transcription factors involved in oligodendroglial lineage development. Recently, epigenetic regulation, which refers to regulation of gene expression by adjusting the environment of the genes has been shown to play a profound role during oligodendroglial development. In this review, we summarize the recent data demonstrating the effects of chromatin modification and remodeling in regulating oligodendroglial development and discuss the use of high-throughput analysis and bio-informatics in future studies.

Epigenetic mechanisms of neuroplasticity and the implications for stroke recovery

Ischemic stroke is a devastating brain injury and an important cause of neurologic disability worldwide and across the lifespan. Despite the physical, social, and economic burdens of this disease there is only a single approved medicine for the treatment of acute stroke, and its use is unfortunately limited to the small fraction of patients presenting within the narrow therapeutic window. Following stroke, there is a period of plasticity involving cell genesis, axon growth, and synaptic modulation that is essential to spontaneous recovery. Treatments focusing on neuroprotection and enhancing recovery have been the focus of intense preclinical studies, but translation of these treatments into clinical use has been disappointing thus far. The important role of epigenetic mechanisms in disease states is becoming increasingly apparent, including in ischemic stroke. These regulators of gene expression are poised to be critical mediators of recovery following stroke. In this review we discuss evidence for the role of epigenetics in neuroplasticity and the implications for stroke recovery.