Project description:The rapid accumulation of self-renewed polarized microglia in the penumbra is the critical neuroinflammatory process after the onset of ischemic stroke, leading to secondary demyelination and neuronal loss. HDAC3 has been reported to regulate cell proliferation of tumour cells and modulate neuroinflammation. However, the mechanism by which HDAC3 regulates microgliosis and microglial polarization remains ambiguous. Herein, we demonstrated that microglia-specific ablation of HDAC3 (HDAC3-miKO) ameliorated poststroke long-term functional and histological outcomes. Starting with unbiased RNA seq of microglia, we identified mitosis as the most significant process reversed by loss of HDAC3. Notably, HDAC3-miKO specifically inhibited the proliferation of M1-like microglia but not M2-like microglia, resulting in microglial transition to an M1-like state. Moreover, ATAC-seq (Assay for Transposase-Accessible Chromatin using sequencing) revealed that HDAC3 deletion induced drastic closing of accessible regions enriched with motifs for PU.1. Taken together, we uncovered for the first time that HDAC3/PU.1-mediated differential proliferation-related reprogramming in different microglia populations drives poststroke inflammatory state transition of microglia and thereby contributes to the pathophysiology of ischemic stroke.
Project description:The rapid accumulation of self-renewed polarized microglia in the penumbra is the critical neuroinflammatory process after the onset of ischemic stroke, leading to secondary demyelination and neuronal loss. HDAC3 has been reported to regulate cell proliferation of tumour cells and modulate neuroinflammation. However, the mechanism by which HDAC3 regulates microgliosis and microglial polarization remains ambiguous. Herein, we demonstrated that microglia-specific ablation of HDAC3 (HDAC3-miKO) ameliorated poststroke long-term functional and histological outcomes. Starting with unbiased RNA seq of microglia, we identified mitosis as the most significant process reversed by loss of HDAC3. Notably, HDAC3-miKO specifically inhibited the proliferation of M1-like microglia but not M2-like microglia, resulting in microglial transition to an M1-like state. Moreover, ATAC-seq (Assay for Transposase-Accessible Chromatin using sequencing) revealed that HDAC3 deletion induced drastic closing of accessible regions enriched with motifs for PU.1. Taken together, we uncovered for the first time that HDAC3/PU.1-mediated differential proliferation-related reprogramming in different microglia populations drives poststroke inflammatory state transition of microglia and thereby contributes to the pathophysiology of ischemic stroke.
Project description:BackgroundNeuroinflammation, which is mainly mediated by excessive microglia activation, plays a major role in ischemic stroke. Overactivated microglia secrete numerous inflammatory cytokines, causing excessive inflammatory responses and ultimately exacerbating ischemic brain injury. Hence, compounds that attenuate neuroinflammation could become promising drug candidates for ischemic stroke. Fraxetin has an anti-inflammatory effect in many inflammatory diseases. However, whether it possesses an anti-inflammatory capacity in microglia-mediated neuroinflammation after ischemic brain injury is unknown. Our study aimed to investigate the suppression effect of fraxetin on neuroinflammation in lipopolysaccharide (LPS)-activated microglia and establish whether fraxetin could alleviate ischemic brain injury in a rodent model of ischemic stroke.MethodsFor the in vitro experiment, primary microglia were obtained from 1-day-old C57/BL6J mice. The cells were activated with LPS and treated with fraxetin at a non-cytotoxic concentration. Real-time PCR, enzyme-linked immunosorbent assays, and immunofluorescence staining were used to evaluate the anti-inflammatory effects of fraxetin. The potential molecular mechanisms were explored and verified through RNA-sequencing analysis, western blotting and real-time PCR. For the in vivo experiment, focal ischemia was induced by middle cerebral artery occlusion (MCAO) in 8-week-old male C57/BL6J mice. Fraxetin (5 mg/kg) or an equal volume of saline was injected into mice intraperitoneally after MCAO, and 2% 2,3,5-triphenyltetrazolium chloride staining was applied to measure infarct volume. Behavioral tests were conducted to measure neurological deficits in the mice. Real-time PCR, western blotting, and immunofluorescence staining were used to examine the expression of inflammatory cytokines and microglia activation in the ischemic penumbra.ResultsFraxetin effectively inhibited the expression of proinflammatory cytokines including inducible nitric oxide synthase, tumor necrosis factor-α, interleukin-1 beta, and interleukin-6 in LPS-activated microglia. Fraxetin also suppressed the PI3K/Akt/NF-κB signaling pathway in activated microglia, which contributed to its anti-inflammatory effects. Furthermore, the administration of fraxetin attenuated ischemic brain injury and behavioral deficits after stroke. Finally, fraxetin was found to attenuate the activation of microglia both in vitro and in vivo.ConclusionsOur results suggest that fraxetin has a suppression effect on microglia-mediated neuroinflammation, and this effect is associated with the PI3K/Akt/NF-κB signaling pathway. Fraxetin may therefore have potential neuroprotective properties for ischemic stroke.
Project description:Stroke is the most common type of cerebrovascular disease and is a leading cause of disability and death. Ischemic stroke accounts for approximately 80% of all strokes. The remaining 20% of strokes are hemorrhagic in nature. To date, therapeutic options for acute ischemic stroke are very limited. Recent research suggests that shifting microglial phenotype from the pro-inflammatory M1 state toward the anti-inflammatory and tissue-reparative M2 phenotype may be an effective therapeutic strategy for ischemic stroke. The dietary phytochemical curcumin has shown promise in experimental stroke models, but its effects on microglial polarization and long-term recovery after stroke are unknown. Here we address these gaps by subjecting mice to distal middle cerebral artery occlusion (dMCAO) and administering curcumin intraperitoneally (150 mg/kg) immediately after ischemia and 24 h later. Histological studies revealed that curcumin post-treatment significantly reduced cerebral ischemic damage 3 days after dMCAO. Sensorimotor functions-as measured by the adhesive removal test and modified Garcia scores-were superior in curcumin-treated mice at 3, 5, 7 and 10 days after stroke. RT-PCR measurements revealed an elevation of M2 microglia/macrophage phenotypic markers and a reduction in M1 markers in curcumin-treated brains 3 days after dMCAO. Immunofluorescent staining further showed that curcumin treatment significantly increased the number of CD206+Iba1+ M2 microglia/macrophages and reduced the number of CD16+Iba1+ M1 cells 10 days after stroke. In vitro studies using the BV2 microglial cell line confirmed that curcumin inhibited lipopolysaccharide (LPS) and interferon-γ (IFN-γ)-induced M1 polarization. Curcumin treatment concentration-dependently reduced the expression of pro-inflammatory cytokines, including TNF-α, IL-6 and IL-12p70, in the absence of any toxic effect on microglial cell survival. In conclusion, we demonstrate that curcumin has a profound regulatory effect on microglial responses, promoting M2 microglial polarization and inhibiting microglia-mediated pro-inflammatory responses. Curcumin post-treatment reduces ischemic stroke-induced brain damage and improves functional outcomes, providing new evidence that curcumin might be a promising therapeutic strategy for stroke.
Project description:To detect chromatin loops maintaining genomic interactions among enhancer and promoter regions in microglia after ischemic stroke, we performed H3K27ac HiChIP of FACS-sorted CD45intCD11bint microglia from sham-operated and post-ischemic day 6 mouse brains.
Project description:To investigate time-dependent changes in gene expression in microglia after ischemic stroke, we performed RNA-seq of FACS-sorted microglia from mouse brains at multiple time points after middle cerebral artery occlusion (MCAO).