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

项目摘要 脑血管相关星形胶质细胞终足在脑胶质细胞的形成和分化中起重要作用。 维持血脑屏障（BBB），调节神经血管偶联， 脑血流量（CBF）。缺血性中风引起脑组织的结构和生化变化， 血管周围星形胶质细胞，但潜在的分子机制和随后的影响， 脑血管损伤/修复尚未得到很好的理解。之前，我们表明，在响应 缺血缺氧、反应性星形胶质细胞刺激Na+/H+交换蛋白1（NHE 1） 活性以抵消酸性pH。这导致细胞内Na+超载，星形胶质细胞肿胀， 以及谷氨酸吸收受损，这加剧了缺血性脑损伤。我们最近的研究 显示星形胶质细胞中Nhe 1的选择性缺失（Astro-KO）消除了缺血性中风- 介导的星形胶质细胞增生，保留BBB功能，减少脑血管损伤， 局部缺血性中风（短暂性大脑中动脉闭塞）的小鼠模型。尽管 在缺血性脑中星形胶质细胞Nhe 1缺失所赋予的神经保护作用， 参与该过程的分子机制尚未完全了解。我们的初步 一项研究表明，Wnt信号通路基因是最显着上调的基因， Nhe 1 Astro-KO缺血性脑。最重要的是，Astro-KO小鼠中Nhe 1的靶向缺失 引起Wnt 7a/B和β-连环蛋白的升高，伴随着 紧密连接蛋白（TJ）和缺血后血管中TJ结构的保存 中风这些新的发现使我们假设星形胶质细胞Nhe 1的缺失促进了 通过Wnt/β-catenin介导的信号传导机制进行缺血组织修复。我们将调查 Nhe 1 Astro-KO小鼠中Wnt 7 a/B基因表达增加导致1）增加 血管内皮细胞中的Wnt/β-catenin信号传导，2）改善BBB结构， 功能完整性，以及3）通过血管生成促进血管恢复， 缺血性卒中后的脑血流调节三个具体目标的完成将产生 新的知识，并确定新的治疗药物，以促进血管修复后， 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.