星形胶质细胞通过CXCL5/CXCR2信号轴诱导慢性缺血性脑白质髓鞘形成障碍的病理机制研究

Chronic cerebral hypoperfusion usually leads to ischemic white matter lesion and consequently cause cognitive impairment. However, there is no effective treatment for this cerebral lesion, which is probably due to the unclear molecular mechanism of its occurrence and development. The pathological feature of ischemic white matter lesion involves reactive astrogliosis and myelination dysfunction. Our preliminary results showed that chronic cerebral hyoperfusion resulted in up-regulation of chemokine CXCL5 within astrocytes and that functional inhibition of CXCR2, which is the receptor of CXCL5 located on the membrane of astrocytes, by its antagonist down-regulated the transcription factor SP1, which plays an important role in cell proliferation. Our further research showed treatment of mouse primary oligodendrocyte progenitor cells (OPCs) with recombinant CXCL5 cytokines could suppress expression of Olig2 genes, which is a differentiation marker for OPCs. Collectively, we come up with a scientific hypothesis that chronic cerebral hyoperfusion leads to up-regulation of chemokine CXCL5 and subsequently acts on astrocyte themselves and OPCs through the CXCL5/CXCR2 axis in the manner of autocrine and paracrine, contributing to reactive astrogliosis, dysfunction of OPCs differentiation and eventually myelination deficits. The aim of the current project is to unravel the molecular mechanism of myelination deficits within white matter after chronic cerebral hyoperfusion in virtue of approaches of cellular biology, molecular biology and experiment animals and obtain novel intervention targets for repair and treatment of ischemic white matter lesion.

慢性脑血流低灌注可导致缺血性脑白质损伤，最终引起认知障碍，目前尚无有效治疗方法，缘于其发生发展的分子机制仍不明确。其病理特征包括反应性星形细胞胶质化和髓鞘形成障碍。以此为切入点，我们前期研究发现，慢性脑血流低灌注引起星形胶质细胞趋化因子CXCL5表达升高，而抑制其受体CXCR2功能则下调转录因子SP1表达，后者对细胞增殖具有重要作用。进一步研究发现，采用CXCL5刺激少突胶质前体细胞（OPCs）可抑制Olig2表达，后者是OPCs分化标志物。因此，我们提出科学假设：慢性脑血流低灌注导致星形胶质细胞CXCL5高表达，其通过CXCL5/CXCR2信号轴以自分泌与旁分泌方式作用于自身与OPCs，导致星形胶质细胞过度增殖与OPCs成熟分化障碍，最终引起髓鞘形成障碍。本项目拟借助分子生物学、细胞生物学和实验动物手段，尝试揭示慢性脑血流低灌注后髓鞘形成障碍的分子机制，从而为其修复和治疗提供干预靶点。

研究背景：慢性脑血流低灌注导致缺氧性脑白质损伤(WMI)，引起认知能力下降。星形胶质细胞在WMI和修复过程中发挥重要作用，但其潜在机制尚不清楚。研究目标旨在探索慢性缺血性脑白质损伤后星形胶质细胞CXCL5表达和功能，探索CXCL5-CXCR2信号轴对少突胶质细胞髓鞘形成障碍的机制。主要研究内容：1.探索趋化因子CXCL5在慢性脑缺血性损伤小鼠血清、脑组织和星形胶质细胞中表达；2.采用星形胶质细胞CXCL5-/-条敲（cKO）小鼠，研究慢性脑缺血性白质损伤模型中，敲除CXCl5表达对小鼠认知功能、脑白质和髓鞘的影响；3.探索星形胶质细胞CXCL5调控少突胶质细胞髓鞘形成和脑白质损伤的机制。重要结果：CXCL5在双侧颈动脉狭窄（BCAS）小鼠血清及胼胝体(CC)显著升高，主要表达于星形胶质细胞，CXCL5条件敲除（cKO）小鼠髓鞘、WMI和认知功能改善。重组CXCL5 (rCXCL5)对体外少突胶质前体细胞增殖分化无直接影响。星形胶质细胞特异性CXCL5过表达加重慢性脑缺血引起的WMI和认知功能下降，而清除小胶质细胞后则抵消这种作用。星形胶质细胞CXCL5对小胶质细胞介导的炎症反应有轻度影响，同时显著阻碍小胶质细胞对髓鞘碎片的吞噬，抑制CXCL5受体CXCR2可挽救小胶质细胞对髓鞘碎片的吞噬。关键数据：1.慢性脑缺血诱导星形胶质细胞CXCL5表达上调，敲除CXCL5促进髓鞘形成；2.星形胶质细胞CXCL5通过阻碍小胶质细胞吞噬髓鞘碎片促进慢性缺血性脑白质损伤修复。科学意义：本项目为基础科学研究，发现在慢性缺血性脑白质损伤模型中，星形胶质细胞CXCL5-CXCR2信号通路介导了一种新的星形胶质细胞-小胶质细胞通路，诱导髓鞘形成障碍和脑白质损伤，为揭示脑白质损伤的病理机制提供新的思路，有助于为治疗药物研发提供新靶点。