ASTROCYTIC INTEGRINS IN CEREBRAL VESSEL FORMATION

这项建议的长期目标是了解中枢神经系统(CNS)中血管稳定性的调节。为了这个目标，我们将研究中枢神经系统稳定血管形成所需的细胞相互作用的潜在机制。具体地说，我们将研究整合素在中枢神经系统血管稳定中所起的细胞类型的特定作用。为使中枢神经系统血管功能完全正常，内皮细胞与其他类型细胞的相互作用 都是必需的。中枢神经系统的血管系统不同于其他血管床，因为它具有选择性的通透性(血脑屏障)。这些特性是由于星形胶质细胞和内皮细胞之间的旁分泌相互作用，其基础尚不清楚。我们先前已经确定，一种细胞黏附受体，整合素avb8，最近被证实对正常小鼠脑血管发育是必不可少的，是由星形胶质细胞表达的。 而不是内皮细胞或平滑肌细胞。整合素b8亚单位敲除小鼠在脑出血妊娠晚期死亡，为星形胶质细胞在脑血管发育/稳定中的作用提供了第一个遗传学证据。我们的初步数据表明，在培养的星形胶质细胞中，avb8是转化生长因子-b激活的主要分子介质，因此我们推测，星形细胞avb8对内皮细胞的作用本质上是旁分泌的。转化生长因子-β可能是提供指导线索和协调增殖和 星形胶质细胞和内皮细胞之间的分化事件；活性转化生长因子-b、endoglin和ALK-1的内皮受体功能丧失，导致人类脑动静脉畸形的发生(HHT-1和2)。由于转化生长因子-b在几乎完全处于非活性(潜伏)状态的组织中普遍表达，因此依赖于avb8的 星形胶质细胞将潜在的转化生长因子-b转化为活性的转化生长因子-b可能是向中枢神经系统内皮细胞呈递转化生长因子-b的重要调节步骤。因此，我们的新发现支持这一假设：星形细胞整合素介导的潜伏的转化为活性的转化生长因子-b对于正常脑血管的发育和稳定是必不可少的。这将在三个特定的目标中得到检验：1)检验星形胶质细胞调节转化生长因子-β活性的假设。2)在体外验证星形细胞整合素改变内皮功能的假说。3)验证整合素介导的星形胶质细胞释放转化生长因子-b在脑内发挥作用的假说。 血管形成/稳定，体内。这些研究将从机制上深入了解内皮细胞和星形胶质细胞之间的相互作用，这可能导致针对脑血管畸形、中风和脑水肿的新疗法的开发。

The long-term goal of this proposal is to understand the regulation of vessel stability in the central nervous system (CNS). Towards this goal, we will investigate the mechanisms underlying cellular interactions required for stable vessel formation in the CNS. Specifically, we will investigate the cell-type specific roles that integrins play in CNS vessel stabilization. For CNS vessels to become fully competent, interactions of endothelial ceils with other cell types are required. The CNS vasculature is distinct from other vascular beds because of selective permeability properties (blood-brain-barrier). These properties are due to paracrine interactions between astrocytes and endothelial cells, the basis of which are poorly understood. We have previously determined that a cell-adhesion receptor, integrin avb8, recently identified as being essential for normal murine cerebral vascular development, is expressed by astrocytes and not by endothelial cells or smooth muscle cells. Integrin b8 subunit knock-out mice die at late gestation of cerebral hemorrhage providing the first genetic evidence to support a role for astrocytes in cerebral vascular development/stabilization. We hypothesize that action of astrocytic avb8 on endothelial cells is paracrine in nature since our preliminary data suggests that that avb8 is the major molecular mediator of TGF-b activation in cultured astrocytes. TGF-b is likely candidate molecule to provide instructional cues and to orchestrate proliferation and differentiation events between astrocytes and endothelial cells; loss of function of the endothelial receptors for active TGF-b, endoglin and Alk-1, lead to the development of brain arteriovenous malformations in humans (HHT-1 and 2). Because TGF-b is ubiquitously expressed in tissues almost entirely in an inactive (latent) state, the avb8-dependent conversion of latent to active TGF-b by astrocytes could be a major regulatory step in the presentation of active TGF-b to CNS endothelial cells. Thus, our novel findings support the hypothesis: astrocytic integrin mediated conversion of latent to active TGF-b is essential for the development and stabilization of a normal cerebral vasculature. This wilt be tested in three specific aims: 1) To test the hypothesis that astrocytes regulate the activity of TGF-b. 2) To test the hypothesis that astrocytic integrins modify endothelial function, in vitro. 3) To test the hypothesis that the integrin-mediated release of TGF-b by astrocytes plays a role in cerebral vessel formation/stabilization, in vivo. These studies will provide mechanistic insight into the reciprocal interactions between endothelial cells and astrocytes, which may lead to the development of novel therapeutics targeted at the treatment of brain vascular malformations, stroke and cerebral edema.