Mechanisms of Adhesion GPCR Action

摘要/摘要：GPR56/ADGRG1 是一种去孤儿脑粘附 G 蛋白偶联受体 (AGPCR) 具有生理配体胶原蛋白。我们提出新证据表明 GPR56 存在于人体表面 和小鼠血小板。考虑到自主血小板激活会导致血栓，这是非常有趣的 形成是由血小板与暴露在血管损伤部位的胶原蛋白相互作用介导的。我们 发现血小板 GPR56 的药理激活足以引发生理性血小板激活 伤口愈合（止血）和血液凝固（血栓形成）所需的程序。此外，Gpr56敲除 在小鼠血管壁损伤模型中，小鼠患有严重的出血性疾病和凝块形成的严重缺陷。 我们假设 GPR56 是介导初始 G 蛋白 12/13 依赖性的血小板胶原蛋白受体 当血小板沿着暴露的胶原蛋白滚动/移位到其稳定粘附的部位时，血小板形状发生变化 血管伤口的滞后边缘。我们将研究血小板 GPR56 介导的 G 蛋白信号传导， 血小板形状变化、体外血小板活化以及 GPR56 在小鼠止血模型中的作用 血栓形成。我们发现了令人信服的初步证据，表明 Gpr56 敲除小鼠的血小板显着 当小鼠血液在高浓度下流过固定胶原蛋白表面时，其粘附缺陷 剪切力。我们认为 GPR56 并不直接参与稳定的血小板粘附，而是随着血小板的翻滚而参与 穿过胶原蛋白表面，GPR56 被刺激引起形状变化，从而使血小板能够稳定地 通过不同的非 GPCR 胶原蛋白受体粘附。在发现血小板上的 GPR56 之前，我们提出了 AGPCR 激活的一般模型，需要锚定受体 N 端，并且剪切力介导 受体解离导致 AGPCR 束缚激动剂暴露以诱导 G 蛋白信号传导。的 血小板携带的 GPR56 所经历的条件与该理论模型非常吻合。我们的工作 还包括使用新开发的光交联激动剂探针进行生化研究来定义 相关 AGPCR、GPR56 和 GPR114 的激动剂结合位点。

Summary/Abstract: GPR56/ADGRG1 is a deorphanized brain Adhesion G protein Coupled Receptor (AGPCR) with a physiological ligand, collagen. We present new evidence that GPR56 is present on the surface of human and mouse platelets. This is very intriguing considering that autonomous platelet activation that leads to clot formation is mediated by platelet interactions with collagen that becomes exposed at sites of vessel injury. We found that pharmacological activation of platelet GPR56 is sufficient to elicit the physiological platelet activation program required for wound healing (hemostasis) and blood clotting (thrombosis). Moreover, Gpr56 knockout mice have a severe bleeding disorder and dramatic defects in clot formation in mouse vessel wall injury models. We hypothesize that GPR56 is the platelet collagen receptor that mediates the initial G protein 12/13-dependent platelet shape changes while platelets roll/translocate along exposed collagen to their site of stable adhesion at the lagging edges of blood vessel wounds. We will investigate platelet GPR56-mediated G protein signaling, platelet shape changes, in vitro platelet activation, and the role of GPR56 in mouse models of hemostasis and thrombosis. We found compelling preliminary evidence that platelets from Gpr56 knockout mice are dramatically defective in adhering to an immobilized collagen surface when mouse blood is flowed over the surface at high shear force. We propose that GPR56 is not directly involved in stable platelet adhesion, but as platelets tumble across the collagen surface, GPR56 is stimulated to cause the shape changes that allow platelets to then stably adhere via distinct non-GPCR collagen receptors. Before discovering GPR56 on platelets we proposed a general model of AGPCR activation that required anchoring of the receptor N-termini, and shear force-mediated receptor dissociation that leads to exposure of the AGPCR tethered agonists to induce G protein signaling. The conditions experienced by platelet-borne GPR56 align remarkably well with this theoretical model. Our work also includes conducting biochemical studies using newly developed photo-crosslinking agonist probes to define the agonist binding sites of the related AGPCRs, GPR56 and GPR114.