HCN2通道介导少突胶质细胞缺血损伤的机制及其在血管性痴呆中的作用研究

The oligodendrocytes (OLGs) are one of the main target cells in ischemic brain injury. Recent evidence showed that the mechanisms of OLGs damage after ischemia is different from that of excitatory toxicity in neuron. Under the ischemia condition, OLGs are damaged in a Ca2+-dependent manner mediated by non-glutamate receptor. The hyperpolarization-activated cyclic nucleotide-gated cation channel 2 (HCN2) is expressed in OLGs and has a certain permeability for Ca2+. Our previous studies have shown that chronic cerebral ischemia can induce stable cognitive impairment corresponding with increased expression of HCN2 in hippocampal CA1 region of rats. But the neuronal loss in hippocampal CA1 only can be observed in the early stage of ischemia. Is the cognitive impairment in the prolonged stage of ischemia caused by the OLGs damage? And whether there is a relationship between OLGs damage and the inceresed HCN2 expression is also unclear. This study will focus on whether/how HCN2 subunit regulate the OLGs damage after ischemia, and furtherly explore the role of OLGs damage in the development and progression of cognitive impairment induced by chronic brain hypoperfusion. The research will provide new therapy ideas and drug targets for the treatment of vascular dementia from the point of OLGs damage in a way different from the traditional excitatory neurotoxicity.

少突胶质细胞（OLGs）是缺血性脑损伤的主要靶细胞之一。然而与神经元缺血损伤不同的是，最新证据显示OLGs的缺血损伤是由非谷氨酸受体所介导的钙内流增多引起。超极化激活的环核苷酸门控阳离子通道2（HCN2通道）在OLGs中表达且对钙离子具有一定通透性。并且，我们前期研究表明：大鼠慢性脑缺血后出现持续的认知障碍并伴随海马CA1区HCN2的表达上调，但是神经元的丢失只出现在缺血早期。那么，在缺血延长期大鼠认知障碍的产生是否由非神经元因素即OLGs的损伤所造成？以及OLGs损伤是否与HCN2的表达上调有关？目前不是很清楚。因此，本课题拟从细胞及动物水平上探讨HCN2通道是否参与了缺血后OLGs的损伤及可能机制；并进一步明确其在慢性脑缺血所致认知障碍发生发展过程中的作用。基于非谷氨酸受体从OLGs病变的角度为临床上血管性痴呆的治疗提供新的思路和靶点。

少突胶质细胞（oligodendrocytes, OLGs）是缺血性脑损伤的主要靶细胞之一。然而与神经元缺血损伤不同的是，有证据显示OLGs的缺血损伤是由非谷氨酸受体所介导的钙内流增多引起。超极化激活的环核苷酸门控阳离子通道2（hyperpolarization-activated cyclic nucleotide-gated cation channel 2, HCN2通道）在OLGs中表达且对钙离子具有一定通透性。本研究借助HCN通道阻断剂ZD7288，在离体细胞模型中采用氧糖剥夺/复灌（oxygen-glucose deprivation/reperfusion, OGD-R）模型，证实了HCN通道参与了OLGs的缺血损伤，其机制可能部分是通过抑制钙内流，从而阻断钙蛋白酶（Calpain）-凋亡诱导因子（apoptosis inducing factor, AIF）及Calpain-半胱氨酸天冬氨酸蛋白水解酶12（Caspase 12）途径所介导。然而，出乎预期地是，本研究发现离子型谷氨酸受体及电压依赖性钙离子通道也参与了OLGs的缺血损伤。在整体动物模型中，本研究进一步发现ZD7288可以改善小鼠局灶性脑缺血/复灌（MACO-R）所致的焦虑样症状。同时，在慢性脑缺血（Chronic Cerebral Hypoperfusion, CCH）模型中，本研究发现杏仁核中HCN1表达上调与大鼠焦虑样行为有关，而杏仁核中HCN2与CCH所致的焦虑样行为无关。综上结果，本研究为探讨HCN通道参与OLGs缺血损伤及缺血后行为学改变的机制奠定了坚实的工作基础。同时，对于认识HCN通道亚型之间的功能区别提供了线索。