MMPs, Integrins and Microglial activation in HAND

描述（由申请方提供）：经典小胶质细胞活化可能导致HIV相关神经系统疾病（HAND）发生的神经元损伤。新出现的证据表明，基质金属蛋白酶（MMPs）可能在刺激这种激活中发挥关键作用。例如，MMP活性的抑制阻断了响应于包括脂多糖的刺激的小胶质细胞活化。此外，米诺环素，MMP的表达和活性的有效抑制剂，废除小胶质细胞的激活发生的渗透性脱髓鞘，以及与猿猴免疫缺陷病毒（SIV）感染。 MMPs可能激活小胶质细胞的机制尚未完全了解。然而，令人感兴趣的是MMPs产生在小胶质细胞上高度表达的整合素配体的潜力。整合素依赖性信号传导又可以刺激与活化表型相关的变化。数据显示，抑制小胶质细胞整联蛋白的表达或功能，阻断小胶质细胞的吞噬作用和迁移，这一机制可能是重要的。此外，最近 研究表明，选择的整联蛋白拮抗剂可以大大减少多种疾病模型中的小胶质细胞活化和相关的神经毒性。 在以前的出版物中，我们已经表明，HIV蛋白可以增加MMP从脑源性细胞的释放，并且MMP水平在HAND患者的脊髓液样品中增加。在本申请中，我们假设这些MMPs产生特异性细胞粘附分子（CAM）片段，所述片段又将接合小胶质细胞整联蛋白。我们对CAM片段的关注基于几个考虑。CAM由于其接近细胞表面而容易接近，细胞表面是MMP活性可能集中的区域。我们和其他人已经表明，基质金属蛋白酶刺激这些分子的胞外域脱落，并且可以在脑炎症患者的脊髓液样品中检测到可溶性形式的水平升高。此外，我们最近发表的数据表明，脱落域的至少一个CAM可以与小胶质细胞整合素，已被很好地链接到一个激活的表型。 在目前的R21提案中，我们计划识别可能与HIV相关增加的小胶质细胞整合素结合配体，研究这些配体刺激经典的促炎小胶质细胞活化的假设，并确定这种活化是否足够大，对脆弱的神经元有害。我们将重点关注在中枢神经系统中广泛表达的CAM，包括含有细胞间粘附分子（ICAM）和突触CAM（synCAM）的免疫球蛋白（IG）结构域，以及钙粘蛋白。我们还将关注在其他疾病模型中介导小胶质细胞活化的整合素，如LFA-1和Mac- 1。这种双重PI补助金依赖于与MMPs（KC）以及小胶质细胞和多巴胺能神经元（KMZ）相关的专业知识。 MMP在HIV背景下促进小胶质细胞活化的可能性尚未测试和临床相关，因为它将允许使用MMP抑制剂来尝试减少这种活化。对MMP依赖性作用的基础受体的进一步研究也具有临床相关性。至少一种可溶性CAM可以与LFA-1相互作用，LFA-1是一种小胶质细胞整联蛋白，已经开发了临床上可耐受的拮抗剂。

DESCRIPTION (provided by applicant): Classical microglial activation may contribute to neuronal injury occurring with HIV associated neurological disorders (HAND). Emerging evidence suggests that matrix metalloproteinases (MMPs) could play a critical role in stimulating such activation. For example, inhibition of MMP activity blocks microglial activation in response to stimuli including lipopolysaccharide. In addition, minocycline, a potent inhibitor of MMP expression and activity, abrogates microglial activation occurring with osmotic demyelination as well as with simian immunodeficiency viral (SIV) infection. The mechanisms by which MMPs might activate microglia are not completely understood. Of interest, however, is the potential for MMPs to generate ligands for integrins that are highly expressed on microglia. Integrin dependent signaling can in turn stimulate changes associated with an activated phenotype. That this mechanism could be important is underlined by data showing that inhibition of microglial integrin expression, or function, blocks microglial phagocytosis and migration. In addition, recent studies have shown that select integrin antagonists can substantially reduce microglial activation and associated neurotoxicity in more than one disease model. In previous publications we have shown that HIV proteins can increase MMP release from brain derived cells, and that MMP levels are increased in spinal fluid samples from patients with HAND. In the present application, we hypothesize that these MMPs generate specific cell adhesion molecule (CAM) fragments that will in turn engage microglial integrins. Our focus on CAM fragments is based on several considerations. CAMs are easily accessible by virtue of their proximity to the cell surface, an area where MMP activity may be concentrated. We and others have shown that MMPs stimulate ectodomain shedding of these molecules, and elevated levels of soluble forms can be detected in spinal fluid samples from patients with brain inflammation. Moreover, we have recently published data showing that the shed domain of at least one CAM can interact with a microglial integrin that has been well linked to an activated phenotype. In the present R21 proposal we plan to identify microglial integrin-binding ligands that may be increased in association with HIV, to investigate the hypothesis that these ligands stimulate classical, pro-inflammatory microglial activation, and to determine whether this activation is of sufficient magnitude to be inimical to vulnerable neurons. We will focus on CAMs that are widely expressed in the CNS, including the immunoglobulin (Ig) domain containing intercellular cell adhesion molecules (ICAMs) and synaptic CAMs (synCAMs), as well as the cadherins. We will also focus on integrins that mediate microglial activation in other disease models, such as LFA-1 and Mac- 1. This dual PI grant relies on expertise related to MMPs (KC), as well as microglia and dopaminergic neurons (KMZ). The possibility that MMPs contribute to microglial activation in the setting of HIV is yet untested and clinically relevant, in that it would allow MMP inhibitor to be used in an attempt to reduce such activation. Further study of the receptors that underlie MMP dependent effects is also clinically relevant. At least one soluble CAM can interact with LFA-1, a microglial integrin for which a clinically tolerable antagonist has been developed.