Thrombin signaling and HIV dementia

描述（由申请人提供）：病理学证据表明，凝血酶及其主要受体蛋白酶激活受体-1（PAR-1）的水平升高与HIV脑炎相关。凝血酶可以通过受损的血脑屏障进入中枢神经系统，也可以由脑实质的免疫激活细胞产生。凝血酶的潜在作用可能对HIVD的发病机制很重要，包括其降解支持细胞粘附和存活的基质蛋白的能力，以及其通过PAR发出信号的能力。内皮细胞PAR的活化与细胞形状的改变、趋化因子释放的增加和粘附分子表达的增加有关。神经元PAR的激活也已得到证实，并被认为是凝血酶对这些细胞的一些先前报道的作用的基础，包括神经毒性和神经突收缩。有趣的是，HIV痴呆（HIVD）与神经突退缩的证据有关，包括树突简化和突触密度降低。然而，对负责的机制并不十分了解。 在目前的R21申请中，我们提出测试凝血酶作用于特定神经元PAR以通过激活糖原合成酶激酶3b（GSK 3b）（细胞形状和存活的关键介质）来刺激神经突收缩的假设。GSK 3b已被证明磷酸化微管相关蛋白，包括tau蛋白，并增加tau蛋白的磷酸化已被链接到神经突起收缩在许多实验范例。我们还将确定凝血酶对GSK 3b作用的机制。虽然以前的研究表明，G蛋白亚型通常与Rho GT3活性的改变相关，可以影响GSK 3b的活性，但没有人表明与腺苷酸环化酶活性降低相关的G蛋白亚型也可以这样做。因此，我们将测试凝血酶刺激神经元影响PKA依赖性丝氨酸磷酸化的减少和RhoA依赖性GSK 3b酪氨酸磷酸化的增加的假设。这些实验的结果应该促使未来的研究，以确定是否其他HIVD相关的刺激，导致神经突回缩的目标类似的途径。最终，我们希望获得更好的理解机制，有助于改变神经元形态的HIVD设置，并确定它是否可能是有用的目标GSK 3b和/或特定的G蛋白偶联受体。

DESCRIPTION (provided by applicant): Pathological evidence suggests that levels of both thrombin and its principal receptor, proteinase activated receptor-1 (PAR-l), are increased in associated with HIV encephalitis. Thrombin can enter the CNS through a damaged blood brain barrier, and it is also produced by immune activated cells of the brain parenchyma. Potential effects of thrombin which may be important to the pathogenesis of HIVD include its ability to degrade matrix proteins that support cell adhesion and survival, as well as its ability to signal through PARs. Activation of endothelial cell PARs has been linked to changes in cell shape, increased chemokine release, and increased adhesion molecule expression. Activation of neuronal PARs has also been demonstrated and is thought to underlie some of the previously reported effects of thrombin on these cells, including neurotoxicity and neurite retraction. Of interest, HIV dementia (HIVD) has been associated with evidence of neurite retraction including dendritic simplification and reduced synaptic density. The responsible mechanisms, however, are not well understood. In the present R21 application, we propose to test the hypothesis that thrombin acts on specific neuronal PARs to stimulate neurite retraction through the activation of glycogen synthase kinase 3b (GSK3b), a critical mediator of cell shape and survival. GSK3b has been shown to phosphorylate microtubule-associated proteins including tau, and increased phosphorylation of tau has been linked to neurite retraction in a number of experimental paradigms. We will also identify the mechanisms that underlie thrombin's effects on GSK3b. While previous studies have suggested that G protein subtypes typically associated with alterations in Rho GTPase activity can affect the activity of GSK3b, none have shown that those linked to decreased adenylate cyclase activity can do the same. We will therefore test the hypothesis that thrombin stimulation of neurons affects both a decrease in PKA-dependent serine phosphorylation and an increase in RhoA dependent tyrosine phosphorylation of GSK3b. The results from these experiments should prompt future studies to determine whether other HIVD related stimuli that cause neurite retraction target similar pathways. Ultimately, we hope to gain a better understanding of mechanisms that contribute to altered neuronal morphology in the setting of HIVD, and to determine whether it may be useful to target GSK3b and/or specific G protein coupled receptors.