Epigenetic modulation of gene expression governs the brain's response to injury

Regulating DNA methylation could reduce neuronal ischemia response and apoptosis after ischemia-reperfusion injury

BACKGROUND

Ischemia-reperfusion injury (IRI) is an important pathophysiological condition that can cause cell injury and large-scale tissue injury in the nervous system. Previous studies have shown that epigenetic regulation may play a role in the pathogenesis of IRI.

METHODS

In this study, we isolated mouse cortical neurons and constructed an oxygen-glucose deprivation/reoxygenation (OGD) model to explore the change in DNA methylation and its effect on the expression of corresponding genes.

RESULTS

We found that DNA methylation in neurons increased with hypoxia duration and that hypermethylation of numerous promoters and 3'-untranslated regions increased. We performed Gene Ontology enrichment analysis to study gene function and Kyoto Encyclopedia of Genes and Genomes pathway analysis to identify the pathways associated with gene regulation. The results showed that hypermethylation-related genes expressed after OGD were related to physiological pathways such as neuronal projection, ion transport, growth and development, while hypomethylation-related genes were related to pathological pathways such as the external apoptosis signaling pathway, neuronal death regulation, and regulation of oxidative stress. However, the changes in DNA methylation were specific for certain genes and may have been related to OGD-induced neuronal damage. Importantly, we integrated transcription and DNA methylation data to identify several candidate target genes, including hypomethylated Apoe, Pax6, Bmp4, and Ptch1 and hypermethylated Adora2a, Crhr1, Stxbp1, and Tac1. This study further indicated the effect of DNA methylation on gene function in brain IRI from the perspective of epigenetics, and the identified genes may become new targets for achieving neuroprotection in the brain after IRI.

The Role of the lncRNA MALAT1 in Neuroprotection against Hypoxic/Ischemic Injury

Hypoxic and ischemic brain injury can cause neurological disability and mortality, and has become a serious public health problem worldwide. Long-chain non-coding RNAs are involved in the regulation of many diseases. Metastasis-related lung adenocarcinoma transcript 1 (MALAT1) is a type of long non-coding RNA (lncRNA), known as long intergenic non-coding RNA (lincRNA), and is highly abundant in the nervous system. The enrichment of MALAT1 in the brain indicates that it may be associated with important functions in pathophysiological processes. Accordingly, the role of MALAT1 in neuronal cell hypoxic/ischemic injury has been gradually discovered over recent years. In this article, we summarize recent research regarding the neuroprotective molecular mechanism of MALAT1 and its regulation of pathophysiological processes of brain hypoxic/ischemic injury. MALAT1 may function as a regulator through interaction with proteins or RNAs to perform its role, and may therefore serve as a therapeutic target in cerebral hypoxia/ischemia.

HDAC1 Expression, Histone Deacetylation, and Protective Role of Sodium Valproate in the Rat Dorsal Root Ganglia After Sciatic Nerve Transection

Nerve injury is an important reason of human disability and death. We studied the role of histone deacetylation in the response of the dorsal root ganglion (DRG) cells to sciatic nerve transection. Sciatic nerve transection in the rat thigh induced overexpression of histone deacetylase 1 (HDAC1) in the ipsilateral DRG at 1-4 h after axotomy. In the DRG neurons, HDAC1 initially upregulated at 1 h but then redistributed from the nuclei to the cytoplasm at 4 h after axotomy. Histone H3 was deacetylated at 24 h after axotomy. Deacetylation of histone H4, accumulation of amyloid precursor protein, a nerve injury marker, and GAP-43, an axon regeneration marker, were observed in the axotomized DRG on day 7. Neuronal injury occurred on day 7 after axotomy along with apoptosis of DRG cells, which were mostly the satellite glial cells remote from the site of sciatic nerve transection. Administration of sodium valproate significantly reduced apoptosis not only in the injured ipsilateral DRG but also in the contralateral ganglion. It also reduced the deacetylation of histones H3 and H4, prevented axotomy-induced accumulation of amyloid precursor protein, which indicated nerve injury, and overexpressed GAP-43, a nerve regeneration marker, in the axotomized DRG. Therefore, HDAC1 was involved in the axotomy-induced injury of DRG neurons and glial cells. HDAC inhibitor sodium valproate demonstrated the neuroprotective activity in the axotomized DRG.

PON1 Hypermethylation and PON3 Hypomethylation are Associated with Risk of Cerebral Infarction

OBJECTIVE

Paraoxonase (PON) family genes are closely related to the etiology and prognosis of cerebral infarction. This study explored the association of the promoter methylation of PON family genes (PON1, PON2 and PON3) with the risk of cerebral infarction.

MATERIALS AND METHODS

In this study, 152 patients with confirmed cerebral infarction were selected as the case group, and 152 healthy controls were selected as the control group. The quantitative methylation-specific PCR (qMSP) was used to determine the promoter methylation levels of PON1, PON2 and PON3 genes. The methylation level was expressed as a methylation reference percentage (PMR).

RESULTS

Our results indicated that PON1 methylation was significantly higher in the case group than in the control group (P = 0.0001). On the contrary, PON3 methylation was significantly lower in the case group than in the control group (P = 0.002). In addition, we found that PON2 gene had a very low level of methylation in both case and control groups (PMR = 0). Subgroup analysis showed that PON1 and PON3 methylation were associated with cerebral infarction only in males (PON1, P = 0.0002; PON3, P = 0.007). Interestingly, the methylation levels of PON1 and PON3 were correlated with each other (case: r = 0.418, P = 0.0001; control: r = 0.3, P = 0.0002). Further multiple regression analysis suggested that elevated methylation levels of PON3 were a protective factor for cerebral infarction [OR (95%CI) = 0.979 (0.96, 0.999), β = -0.021, P = 0.035)], highdensity lipoprotein (HDL) and uric acid (UA) also were protective factors for cerebral infarction [HDL, OR (95% CI) = 0.01 (0.003, 0.033), P < 0.0001); UA, OR (95% CI) = 0.995 (0.991, 0.998), P = 0.003)]. The ROC curve analysis found that the combination of PON3, HDL, and UA had a good predictive power for cerebral infarction (AUC=0.878, 95% CI=0.839-0.918, sensitivity 73.7%, specificity 89.7%, P < 0.0001).

CONCLUSION

PON1 and PON3 promoter methylation levels in peripheral blood were closely related. PON1 and PON3 methylation were associated with the risk of cerebral infarction in men. PON3 promoter methylation combined with HDL and UA could be used as potential biomarkers for the diagnosis of cerebral infarction.

Neutrophil-Related Oxidants Drive Heart and Brain Remodeling After Ischemia/Reperfusion Injury

The inflammatory response associated with myocardial and brain ischemia/reperfusion injury (IRI) is a critical determinant of tissue necrosis, functional organ recovery, and long-term clinical outcomes. In the post-ischemic period, reactive oxygen species (ROS) are involved in tissue repair through the clearance of dead cells and cellular debris. Neutrophils play a critical role in redox signaling due to their early recruitment and the large variety of released ROS. Noteworthy, ROS generated during IRI have a relevant role in both myocardial healing and activation of neuroprotective pathways. Anatomical and functional differences contribute to the responses in the myocardial and brain tissue despite a significant gene overlap. The exaggerated activation of this signaling system can result in adverse consequences, such as cell apoptosis and extracellular matrix degradation. In light of that, blocking the ROS cascade might have a therapeutic implication for cardiomyocyte and neuronal loss after acute ischemic events. The translation of these findings from preclinical models to clinical trials has so far failed because of differences between humans and animals, difficulty of agents to penetrate into specific cellular organs, and specifically unravel oxidant and antioxidant pathways. Here, we update knowledge on ROS cascade in IRI, focusing on the role of neutrophils. We discuss evidence of ROS blockade as a therapeutic approach for myocardial infarction and ischemic stroke.

Beneficial and deleterious effects of cannabinoids in the brain: the case of ultra-low dose THC

This article reviews the neurocognitive advantages and drawbacks of cannabinoid substances, and discusses the possible physiological mechanisms that underlie their dual activity. The article further reviews the neurocognitive effects of ultra-low doses of ∆9-tetrahydrocannabinol (THC; 3-4 orders of magnitude lower than the conventional doses) in mice, and proposes such low doses of THC as a possible remedy for various brain injuries and for the treatment of age-related cognitive decline.

Histone acetylation and DNA methylation in ischemia/reperfusion injury

Ischemic/reperfusion (I/R) injury causes a series of serious clinical problems associated with high morbidity and mortality in various disorders, such as acute kidney injury (AKI), myocardial infarction, ischemic stroke, circulatory arrest, and peripheral vascular disease. The pathophysiology and pathogenesis of I/R injury is complex and multifactorial. Recent studies have revealed that epigenetic regulation is critically involved in the pathogenesis of I/R-induced tissue injury. In this review, we will sum up recent advances on the modification, regulation, and implication of histone modifications and DNA methylation in I/R injury-induced organ dysfunction. Understandings of I/R-induced epigenetic alterations and regulations will aid in the development of potential therapeutics.

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.

The vagal ganglia transcriptome identifies candidate therapeutics for airway hyperreactivity

Mainstay therapeutics are ineffective in some people with asthma, suggesting a need for additional agents. In the current study, we used vagal ganglia transcriptome profiling and connectivity mapping to identify compounds beneficial for alleviating airway hyperreactivity (AHR). As a comparison, we also used previously published transcriptome data from sensitized mouse lungs and human asthmatic endobronchial biopsies. All transcriptomes revealed agents beneficial for mitigating AHR; however, only the vagal ganglia transcriptome identified agents used clinically to treat asthma (flunisolide, isoetarine). We also tested one compound identified by vagal ganglia transcriptome profiling that had not previously been linked to asthma and found that it had bronchodilator effects in both mouse and pig airways. These data suggest that transcriptome profiling of the vagal ganglia might be a novel strategy to identify potential asthma therapeutics.

Adaptive Plasticity in the Retina: Protection Against Acute Injury and Neurodegenerative Disease by Conditioning Stimuli

Although both preclinical and clinical conditioning studies in heart and brain lead the field of conditioning medicine, investigations of retinal conditioning still number more than 100. In this brief review, we highlight findings to date from animal and cell culture models of conditioning that provide demonstrated protection in acute and chronic retinal injury and disease models. The multitude of stimuli used to condition the retina, the signaling mediators and pathways identified, and the injury- and disease-resilient phenotypes documented are discussed herein, along with our recommendations for the kinds of studies needed to continue to advance this promising field. In our view, the robust protection afforded by these adaptive epigenetic responses to conditioning stress provides significant incentives for both furthering our investment in bench research and underwriting clinical trials, so that the full potential of this therapy can be realized.

Trans-resveratrol enriched maternal diet protects the immature hippocampus from perinatal asphyxia in rats

Trans-resveratrol (tRESV), a polyphenol with antioxidant properties, is common in many food sources, hence easily accessible for study as a maternal dietary supplement in perinatal asphyxia (PA). Hypoxic-ischemic encephalopathy secondary to PA affects especially vulnerable brain areas such as hippocampus and is a leading cause of neonatal morbidity. The purpose of this study is to identify new epigenetic mechanisms of brain inflammation and injury related to PA and to explore the benefit of tRESV enriched maternal diet. The hippocampal interleukin 1 beta (IL-1b), tumour necrosis factor alpha (TNFα) and S-100B protein, at 24-48h after 90min of asphyxia were assessed in postnatal day 6 rats whose mothers received either standard or tRESV enriched diet. The expression of non-coding microRNAs miR124, miR132, miR134, miR146 and miR15a as epigenetic markers of hippocampus response to PA was determined 24h post-asphyxia. Our results indicate that neural response to PA could be epigenetically controlled and that tRESV reduces asphyxia-related neuroinflammation and neural injury. Moreover, tRESV could increase, through epigenetic mechanisms, the tolerance to asphyxia, with possible impact on the neuronal maturation. Our data support the neuroprotective quality of tRESV when used as a supplement in the maternal diet on the offspring's outcome in PA.