ASTROCYTIC INTEGRINS IN CEREBRAL VESSEL FORMATION

该提案的长期目标是了解中枢神经系统（CNS）中血管稳定性的调节。为了实现这一目标，我们将研究中枢神经系统中稳定血管形成所需的细胞相互作用的机制。具体来说，我们将研究整合素在中枢神经系统血管稳定中发挥的细胞类型特异性作用。对于中枢神经系统血管变得完全胜任，内皮细胞与其他细胞类型的相互作用 are required. CNS脉管系统由于选择性渗透特性（血脑屏障）而不同于其他血管床。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，其基础知之甚少。我们先前已经确定了一种细胞粘附受体，整合素avb 8，最近被鉴定为正常小鼠脑血管发育所必需的，由星形胶质细胞表达。 而不是内皮细胞或平滑肌细胞。整合素b8亚基敲除小鼠在妊娠晚期死于脑出血，这为支持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。我们假设星形胶质细胞avb 8对内皮细胞的作用本质上是旁分泌的，因为我们的初步数据表明avb 8是培养的星形胶质细胞中TGF-β活化的主要分子介质。TGF-β可能是提供指导性线索并协调增殖和分化的候选分子。 星形胶质细胞和内皮细胞之间的分化事件;活性TGF-β、内皮糖蛋白和Alk-1的内皮受体的功能丧失，导致人类脑动静脉畸形的发展（HHT-1和2）。由于TGF-β在组织中普遍表达，几乎完全处于无活性（潜伏）状态，因此avb 8依赖性TGF-β 1的表达在组织中几乎完全处于无活性状态。 星形胶质细胞将潜伏性TGF-b转化为活性TGF-b可能是将活性TGF-b提呈给中枢神经系统内皮细胞的主要调节步骤。因此，我们的新发现支持了这一假设：星形胶质细胞整合素介导的潜伏性转化为活性TGF-β对正常脑血管系统的发育和稳定至关重要。这将在三个特定的目标进行测试：1）测试星形胶质细胞调节TGF-β活性的假设。2)验证星形胶质细胞整合素在体外改变内皮功能的假设。3)为了验证整合素介导的星形胶质细胞释放TGF-β在脑胶质细胞凋亡中的作用， 体内血管形成/稳定。这些研究将为内皮细胞和星形胶质细胞之间的相互作用提供机制性见解，这可能导致开发针对脑血管畸形、中风和脑水肿治疗的新型疗法。

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.