HDAC Inhibitor Sodium Butyrate-Mediated Epigenetic Regulation Enhances Neuroprotective Function of Microglia During Ischemic Stroke
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Cerebral ischemia leads to neuroinflammation and activation of microglia which further contribute to stroke pathology. Understanding regulation of microglial activation will aid in the development of therapeutic strategies that mitigate microglia-mediated neurotoxicity in neuropathologies, including ischemia. In this study, we investigated the epigenetic regulation of microglial activation by studying histone modification histone 3-lysine 9-acetylation (H3K9ac) and its regulation by histone deacetylase (HDAC) inhibitors. In vitro analysis of activated microglia showed that HDAC inhibitor, sodium butyrate (SB), alters H3K9ac enrichment and transcription at the promoters of pro-inflammatory (Tnf-α, Nos2, Stat1, Il6) and anti-inflammatory (Il10) genes while inducing the expression of genes downstream of the IL10/STAT3 anti-inflammatory pathway. In an experimental mouse (C57BL/6NTac) model of middle cerebral artery occlusion (MCAO), we observed that SB mediates neuroprotection by epigenetically regulating the microglial inflammatory response, via downregulating the expression of pro-inflammatory mediators, TNF-α and NOS2, and upregulating the expression of anti-inflammatory mediator IL10, in activated microglia. Interestingly, H3K9ac levels were found to be upregulated in activated microglia distributed in the cortex, striatum, and hippocampus of MCAO mice. A similar upregulation of H3K9ac was detected in lipopolysaccharide (LPS)-activated microglia in the Wistar rat brain, indicating that H3K9ac upregulation is consistently associated with microglial activation in vivo. Altogether, these results show evidence of HDAC inhibition being a promising molecular switch to epigenetically modify microglial behavior from pro-inflammatory to anti-inflammatory which could mitigate microglia-mediated neuroinflammation.
KeywordsMicroglia H3K9ac HDAC inhibitors Ischemia Neuroinflammation Epigenetics
This research was funded by the NUHS seed fund for basic science research (Grant No. T1-BSRG 2014-02; WBS No. R181-000-166-112).
RP, graduate student conceived the study, designed and performed experiments, and wrote the manuscript. TVA performed tMCAO and in vivo SB treatment. NG performed in vitro experiments relating to pSTAT3 targets and analyzed data. TVA, NG, and STD provided intellectual contribution and edited the manuscript. STD is the principal investigator of the study.
Compliance with Ethical Standards
Conflict of Interest
The authors declare that they have no competing interests.
Ethics Approval and Consent to Participate
All animal procedures were carried out in accordance with the National University of Singapore Institutional Animal Care and Use committee (IACUC) guidelines (NUS/IACUC/R15-0051). All efforts were made to minimize pain and number of animals used.
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