PPARα促进过氧化物酶体自噬抑制缺血性脑卒中后星形胶质细胞过度活化的作用和机制

The excessive activation of astrocytes and the formation of glial scar are the important causes that hinder the recovery of neurological function in the chronic phase of cerebral ischemia. However, its precise mechanism has not yet been clarified. We found that astrocyte activation as well as accumulation of dysfunction peroxisomes increased remarkably in the boundary area near infarct core after cerebral ischemia; in addition, we found that oleoylethanolamide (OEA), an activator of peroxisome proliferator-activated receptor α (PPARα), help to promote the recovery of neurological function, inhibit excessive astroctye activation and reduce the accumulation of abnormal peroxisomes. As we know that pexophagy plays an important role in maintaining cellular homeostasis, so we propose a hypothesis that PPARα inhibites the excessive activation of astrocytes by promoting pexophagy after ischemic stroke. To test this hypothesis, focal cerebral ischemia will be induced by middle cerebral artery occlusion (MCAO) in mice; and an in vitro model of astrocyte activation will be induced by oxygen-glucose deprivation (OGD) in primary cultures of mouse astrocytes. In the present project, we will elucidate the role of pexophagy in the excessive activation of astrocytes after ischemia stroke, and subsequently the effects of PPARα on pexophagy and astrocyte activation. Our results will help to clarify the molecular mechanism of astrocyte activation after brain ischemia, and provide a theoretical basis for the determination of PPARα as a promising drug target for promoting neurological function recovery after brain ischemia.

星形胶质细胞过度活化继而形成胶质疤痕是阻碍脑缺血后神经功能恢复的重要因素，其调控机制尚未阐明。我们发现脑缺血后慢性期损伤周边星形胶质细胞大量激活，功能异常的过氧化物酶体明显增多;同时PPARα激动剂OEA可抑制脑缺血后星形胶质细胞过度活化，促进神经功能的恢复，并可减少脑缺血后异常增生的过氧化物酶体。因此基于过氧化物酶体自噬在维持细胞稳态中的重要作用，我们提出假设：PPARα通过促进过氧化物酶体自噬抑制脑缺血后星形胶质细胞过度活化。本项目拟采用小鼠MCAO脑缺血模型和低强度缺糖缺氧（OGD）诱导体外星形胶质细胞活化模型，研究过氧化物酶体自噬在脑缺血后星形胶质细胞过度活化中的作用；研究PPARα对脑缺血后过氧化物酶体自噬和星形胶质细胞过度活化的作用和机制。本项目研究结果有助于阐明脑缺血后星形胶质细胞过度活化的分子机制，并为确定以PPARα为靶点寻找促进脑缺血后神经功能恢复药物提供理论依据。

星形胶质细胞过度活化继而形成胶质疤痕是阻碍脑缺血后神经功能恢复的重要因素，其调控机制尚未阐明。我们前期研究发现脑缺血后慢性期损伤周边星形胶质细胞大量激活，功能异常的过氧化物酶体明显增多;同时PPARα激动剂OEA可抑制脑缺血后星形胶质细胞过度活化，促进神经功能的恢复，并可减少脑缺血后异常增生的过氧化物酶体。因此基于过氧化物酶体自噬在维持细胞稳态中的重要作用，本项目应用PPARα功能缺失小鼠（PPARα null）小鼠和PPARα激动剂油酰乙醇胺（oleoylethanolamide, OEA），在线拴法建立的大脑中动脉栓塞(middle cerebral artery occlusion, MCAO)脑缺血模型和缺糖缺氧/复氧（oxygen-glucose deprivation/ reoxygenation，OGD/R）诱导的体外星形胶质细胞活化模型上观察脑缺血后过氧化物酶体自噬在星形胶质细胞活化中的作用；研究PPARα对自噬和星形胶质细胞过度活化的作用和机制。重要研究结果包括1.脑缺血损伤慢性期星形胶质过度活化形成胶质疤痕过程中，存在星形胶质细胞自噬流障碍，导致过氧化物酶体在细胞内堆积。2.PPARα null加重脑缺血后星形胶质细胞内自噬流障碍，促进星形胶质细胞的激活，延缓运动神经功能恢复。3.PPARα激动剂OEA可抑制脑缺血后星形胶质细胞的过度激活，改善自噬流障碍，减少过氧化物酶体在胞内的堆积。自噬流抑制剂氯喹可拮抗OEA对脑缺血后慢性损伤的保护作用。以上研究结果提示PPARα通过促进过氧化物酶体自噬，对抗脑缺血后星形胶质细胞过度活化，改善脑缺血后慢性损伤。本项目的研究结果不但有助于加深我们对脑缺血后星形胶质细胞过度活化分子机制的认识，对基于PPARα为靶点寻找和发现对缺血性脑卒中慢性期损伤有效的治疗药物也具有十分重要的意义。