MMPs, Integrins and Microglial activation in HAND

描述(由申请人提供)：经典的小胶质细胞激活可能有助于HIV相关神经疾病(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，对基质金属蛋白酶活性的抑制阻止了小胶质细胞对包括内毒素在内的刺激的激活。此外，米诺环素是一种有效的基质金属蛋白酶表达和活性的抑制剂，可以阻止渗透性脱髓鞘和猴免疫缺陷病毒(SIV)感染所引起的小胶质细胞激活。MMPs激活小胶质细胞的机制尚不完全清楚。然而，令人感兴趣的是，MMPs有可能为小胶质细胞上高表达的整合素产生配体。整合素依赖的信号转而可以刺激与激活表型相关的变化。数据表明，抑制小胶质细胞整合素的表达或功能，会阻止小胶质细胞的吞噬和迁移，这一机制可能是重要的。此外，最近 研究表明，在多种疾病模型中，选择整合素拮抗剂可以显著减少小胶质细胞的激活和相关的神经毒性。在以前的出版物中，我们已经证明HIV蛋白可以增加脑源性细胞释放的基质金属蛋白酶，并且手部患者的脊髓液样本中的基质金属蛋白酶水平增加。在目前的应用中，我们假设这些MMP产生特定的细胞黏附分子(CAM)片段，进而与小胶质细胞整合素结合。我们对CAM片段的关注基于几个考虑因素。由于CAM靠近细胞表面，因此很容易接触到，这是一个可能集中基质金属蛋白酶活性的区域。我们和其他人已经证明，MMPs刺激这些分子的胞外脱落，在脑炎患者的脊髓液样本中可以检测到可溶性形式的升高。此外，我们最近发表的数据显示，至少一个CAM的脱落区可以与小胶质细胞整合素相互作用，该整合素与激活的表型有很好的联系。在目前的R21提案中，我们计划识别与HIV相关的可能增加的小胶质细胞整合素结合配体，调查这些配体刺激经典的促炎小胶质细胞激活的假设，并确定这种激活是否具有足够的幅度对脆弱的神经元有害。我们将关注在中枢神经系统中广泛表达的CaM，包括含有细胞间黏附分子(ICAM)和突触CAM(SynCAM)的免疫球蛋白(Ig)结构域，以及钙粘附素。我们还将关注在其他疾病模型中介导小胶质细胞激活的整合素，如LFA-1和Mac-1。这一双重PI授权依赖于与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。在HIV感染的背景下，MMPs促进小胶质细胞激活的可能性尚未得到测试，而且具有临床意义，因为它将允许使用MMPI来尝试减少这种激活。进一步研究构成基质金属蛋白酶依赖效应的受体也具有临床意义。至少一个可溶性的CAM可以与LFA-1相互作用，LFA-1是一种小胶质细胞整合素，已经开发出临床上可以耐受的拮抗剂。

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.