Astrocytes-Mediated Regulation of Wnt/b-Catenin Pathway in Ischemic Brain

项目总结 脑血管相关星形胶质细胞末端足在脑血管的形成和发展中起重要作用 维持血脑屏障(BBB)，调节神经血管偶联和 脑血流量(CBF)。缺血性卒中引起脑组织结构和生化改变 血管周围星形胶质细胞，但潜在的分子机制和后续的影响 脑血管损伤/修复还不是很清楚。在此之前，我们展示了作为对 缺血缺氧、反应性星形胶质细胞刺激Na+/H+交换异构体1蛋白(NHE1) 中和酸性phi的活性。这会导致细胞内Na+超载，星形细胞肿胀， 谷氨酸摄取受损，加剧了脑缺血损伤。我们最近的研究 结果表明，选择性缺失星形胶质细胞中的Nhe1(Astro-KO)可消除缺血性卒中- 介导性星形胶质细胞增生，保护血脑屏障功能，减少脑血管损伤 局灶性脑缺血(短暂性大脑中动脉闭塞)小鼠模型。尽管 星形胶质细胞Nhe1缺失对缺血脑的神经保护作用 参与这一过程的分子机制尚不完全清楚。我们的预赛 研究表明，Wnt信号通路基因是最显著上调的基因 Nhe1 Astro-KO缺血脑。最重要的是，在Astro-KO小鼠中靶向缺失Nhe1 导致WNT 7a/b和−连环蛋白表达升高，并伴有 紧密连接蛋白与缺血后血管紧密连接结构的保存 卒中。这些新的发现使我们假设星形胶质细胞Nhe1基因的缺失促进了 Wnt/−连环蛋白介导的信号机制对缺血组织修复的影响我们会调查的 Nhe1 Astro-KO小鼠Wnt7a/b基因表达增加导致1)增加 血管内皮细胞中WnT/−连环蛋白信号转导，2)改善血脑屏障结构， 功能完整性，以及3)通过血管生成和血管修复促进血管恢复 缺血性卒中后的脑血流调节。完成三个具体目标将产生 寻找促进血管修复的新知识和新的治疗药物 缺血性中风。

PROJECT SUMMARY Cerebral vessel-associated astrocyte end-feet play an important role in formation and maintenance of the blood-brain barrier (BBB), and regulation of neurovascular coupling and cerebral blood flow (CBF). Ischemic stroke causes structural and biochemical changes of the perivascular astrocytes, but the underlying molecular mechanisms and subsequent impact on cerebral vessel damage/repair are not well understood. Previously, we show that in response to ischemia and hypoxia, reactive astrocytes stimulate Na+/H+ exchanger isoform 1 protein (NHE1) activity to counteract the acidic pHi. This leads to intracellular Na+ overload, astrocytic swelling, and impaired glutamate uptake, which aggravates ischemic brain damage. Our recent study shows that selective deletion of Nhe1 in astrocytes (Astro-KO) abolished ischemic stroke- mediated astrogliosis, preserved BBB function, and reduced cerebral vessel damage in a mouse model of focal ischemic stroke (transient middle cerebral artery occlusion). Despite the neuroprotective effects conferred by astrocytic Nhe1 deletion in ischemic brains, the precise molecular mechanisms involved in the process are not completely understood. Our preliminary study reveals that Wnt signaling pathway genes are the most significantly upregulated genes in Nhe1 Astro-KO ischemic brains. Most importantly, targeted deletion of Nhe1 in Astro-KO mice caused elevation of Wnt 7a/b and −catenin protein, accompanied with increased expression of tight junction protein (TJ) and preservation of TJ structures in the blood vessels after ischemic stroke. These new findings led us to hypothesize that deletion of astrocytic Nhe1 promotes ischemic tissue repair by Wnt/−catenin mediated signaling mechanisms. We will investigate that increased Wnt7a/b gene expression in Nhe1 Astro-KO mice leads to 1) increased Wnt/−catenin signaling in vascular endothelial cells, 2) improves the BBB structural and functional integrity, and 3) promotes vascular recovery by angiogenesis and restore of the cerebral flow regulation after ischemic stroke. Completion of three specific aims will generate new knowledge and identify novel therapeutic agents for promoting vascular repairs after ischemic stroke.