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EphB2-dependent signaling promotes neuronal excitotoxicity and inflammation in the acute phase of ischemic stroke

ABSTRACT: Local cerebral hypoperfusion causes ischemic stroke while driving multiple cell-specific responses including inflammation, glutamate-NMDAR-mediated neurotoxicity, edema formation and angiogenesis. Despite the relevance of these pathophysiological mechanisms for disease progression and outcome, molecular determinants controlling the onset of these processes are only partially understood. In this context, our study intended to investigate the functional role of EphB2 – a receptor tyrosine kinase that is crucial for synapse function and binds to membrane-associated ephrin-B ligands. Cerebral ischemia was induced in EphB2-deficient mice by transient middle cerebral artery occlusion followed by different times (6, 12, 24 and 48 h) of reperfusion. Histological, neurofunctional and transcriptome analyses indicated an increase in EphB2 phosphorylation under these conditions and attenuated progression of stroke in EphB2-deficient mice. Moreover, while infiltration of microglia/macrophages and astrocytes into the peri-infarct region was not altered, expression of the pro-inflammatory mediators MCP-1 or IL-6 was decreased in these mice. In fact, in vitro analyses indicated that binding of EphB2 to astrocytic ephrin-B ligands stimulates NF-κB-mediated cytokine expression via the MAPK pathway. Further magnetic resonance imaging of the EphB2-deficient ischemic brain revealed a lower level of neuronal cytotoxic edema formation within 6 h upon onset of reperfusion. On the mechanistic level, absence of neuronal EphB2 decreased the mitochondrial Ca2+ load upon activation of NMDAR but not AMPAR. Moreover, activation of EphB2 by ephrin-B2 enhanced the NMDA-evoked excitotoxic neuronal cell death in vitro while neuron-specific loss of ephrin-B2 reduced the extent of cerebral tissue damage in the acute phase of ischemic stroke. Collectively, EphB2 may promote the immediate response to an ischemia-reperfusion event in the central nervous system by (i) pro-inflammatory activation of astrocytes via ephrin-B-dependent signalling and (ii) amplification of the NMDA-evoked neuronal excitotoxicity.

ORGANISM(S): Mus musculus

PROVIDER: GSE120565 | GEO | 2019/02/13

REPOSITORIES: GEO

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Project description:Cerebral ischemia/reperfusion injury (CI/RI), including neurological behavior deficits, cerebral infarction, blood-brain barrier (BBB) dysfunction, and neuroinflammation, et al. is a severe challenge in treatment of ischemic stroke. Traditional Chinese medicine (TCM) with the characteristics of multi-components and multi-functions for multiple targets/pathways has been historically used in the treatment of stroke and post stroke recovery in China. QiShenYiQi (QSYQ), a representative component-based Chinese medicine, is capable of reducing organ injury caused by ischemia/reperfusion via multiple mechanisms. Recently, we have previously reported that the positive action of QSYQ against the acute phase of CI/RI is partly via modulation of neuroinflammatory response. However, the effects and underlying mechanisms of QSYQ on subacute phase of CI/RI remain unknown, which are aimed to investigate in present study. The pharmacological action of QSYQ treatment on brain damage was estimated in the experimental stroke rats underwent 90 min ischemia and 8 days reperfusion by assessing the neurological and locomotor deficits, cerebral infarction, brain edema, and BBB integrity. Furthermore, we used TMT-based quantitative proteomics technology to identify significantly differentially expressed proteins following QSYQ treatment, which could give important clues for revealing the possible mechanism underlying the positive role of QSYQ in CI/RI. Besides, immunohistochemistry, western blot analysis, RT-qPCR, and rat ELISA kits were executed to further verify the accuracy of proteomics analysis results. As a consequence, we found that treatment with QSYQ (600mg/kg) for 7 days obviously improved neurological and behavioral impairment, attenuated infarct volume and brain edema, and alleviated BBB breakdown in stroke rats. Bioinformatics analysis suggested that differentially expressed protein galectin-3 mediated inflammatory response was closely related to the beneficial effect of QSYQ. Results of immunohistochemistry, western blot analysis and RT-qPCR showed that the model rats treated with QSYQ (600mg/kg) markedly downregulated the mRNA and protein expression level of galectin-3 in brain tissues compared to the untreated stroke rats. In addition, the decrease of mRNA level in brain tissues and contents in serum of TNF-α and IL-6 following QSYQ treatment were also observed. These interesting finding manifested that the effective action of QSYQ against subacute phase of CI/RI was partly via regulating galectin-3 mediated inflammatory reaction.

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EphB2-dependent signaling promotes neuronal excitotoxicity and inflammation in the acute phase of ischemic stroke

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