Understanding the Role GPRC6a During Tau Metabolism

包括阿尔茨海默病（AD）在内的Tau病由年龄相关的神经退行性疾病组成， 而这些疾病并不存在改善病情的治疗方法。我们的团队发现了一种独特的相互作用， 精氨酸代谢和tau蛋白病。精氨酸代谢影响多种生物过程， 对Tau生物学有很大的影响。我们假设L-精氨酸作为一个传感器的氨基酸 精氨酸的缺乏启动自噬以补充氨基酸水平。精氨酸酶1 （Arg 1）仍然是能够代谢半必需氨基酸L-的几种不同酶之一。 精氨酸。事实上，Arg和一氧化氮合酶（NOS）存在许多同种型。我们在细胞中展示 和tau蛋白病的动物模型，增加Arg 1在减少tau表型的许多方面的益处 （由tau效应组成的标志）。一些精液发现显示溶酶体和细胞质精氨酸 调节雷帕霉素复合物1（mTORC 1）的机制靶点的传感器。GPRC 6a是G蛋白偶联的 一种结合L-α氨基酸（包括L-精氨酸）的受体，可作为细胞外精氨酸传感器， mTORC 1。我们的初步数据表明，AD患者中的丝氨酸敏感mTORC 1通路的激活增加， 大脑和tau蛋白病的动物模型。我们发现精氨酸产生和代谢酶， 与对照组相比，AD患者海马中精氨酸感受器和mTORC 1复合物增加 年龄匹配的大脑我们还发现，tau蛋白使大脑中的总精氨酸水平增加了35%，增加了基础精氨酸水平。 细胞外精氨酸水平和脑中神经元刺激后精氨酸释放。此外，委员会认为， GPRC 6a的新型变构拮抗剂清除细胞系、原代神经元和小鼠中各种形式的tau。 GPRC 6a的遗传减少也减少了tau蛋白的表达，并且似乎调节了细胞内的几种细胞因子。 精氨酸传感器我们认为tau蛋白病（包括AD）会导致精氨酸代谢受损和解偶联， 的mTORC 1信号传导，这导致超mTORC 1激活，创造一个积极的饲料- 前向环以增加tau表型。我们将检验以下假设： GPRC 6a的变构拮抗剂或shRNA调节酪氨酸敏感mTORC 1信号传导，诱导自噬 并在体外和体内增加tau的清除。我们将使用四环素诱导的tau细胞系与照片- 测量tau代谢可转换荧光示踪剂，测量tau的分裂tau-GFP构建体 寡聚化和原代神经元以确定GPRC 6a和tau命运的作用。我们将确定是否 GPRC 6a的遗传敲除和药理学抑制在体外和体内影响tau生物学。成功 在本申请中，将提供一种新的受体靶点，其可影响尼古丁敏感mTORC 1信号传导。 此外，我们的目标是确定一种全新的药物，靶向GPCR 6a，以减轻tau蛋白， 表型为tau蛋白病和AD提供了新的策略。

Tauopathies including Alzheimer's disease (AD) consist of age-associated neurodegenerative diseases for which no disease-modifying treatments exist. Our group has uncovered a unique interaction between the arginine metabolism and tauopathies. Arginine metabolism affects multiple biological processes that show considerable influence upon tau biology. We hypothesize that L-arginine acts as a sensor for amino acid abundance and that the depletion of arginine initiates autophagy to replenish amino acid levels. Arginase 1 (Arg1) remains one of several different enzymes capable of metabolizing the semi-essential amino acid L- arginine. In fact numerous isoforms exist for Arg and nitric oxide synthases (NOS). We demonstrate in cells and animal models of tauopathy the benefits of increasing Arg1 in reducing many aspects of the tau phenotype (hallmarks comprised of tau effects). Several seminal findings show lysosomal and cytoplasmic arginine sensors that modulate mechanistic target of rapamycin complex 1 (mTORC1). GPRC6a is a G-protein coupled receptor that binds L-α amino acids including L-arginine and may serve as an extracellular arginine sensor for mTORC1. Our preliminary data indicates increased activation of the arginine-sensing mTORC1 pathway in AD brains and animal models of tauopathies. We show that arginine producing and metabolizing enzymes, arginine sensors, and mTORC1 complexes increase in the hippocampus of AD patients compared to control aged matched brains. We also find that tau increased total arginine levels in the brain by 35%, increased basal levels of extracellular arginine and arginine release following neuronal stimulation in the brain. Furthermore, novel allosteric antagonist to GPRC6a clears various forms of tau in cell lines, primary neurons, and mice. Genetic reduction of GPRC6a also reduced tau expression and seemingly regulates several intracellular arginine sensors. We posit that tauopathies (including AD) cause impaired arginine metabolism and uncoupling of arginine-sensing mTORC1 signaling, which lead to hyper-mTORC1 activation creating a positive feed- forward loop to augment the tau phenotype. We will test the hypothesis that decreased GPRC6a signaling from allosteric antagonists or shRNA to GPRC6a modulate arginine-sensing mTORC1 signaling, induces autophagy and increases tau clearance in vitro and in vivo. We will use tetracycline inducible tau cell lines with a photo- switchable fluorescent tracer to measure tau metabolism, split tau-GFP constructs that measure tau oligomerization, and primary neurons to determine the role of GPRC6a and tau fate. We will determine if genetic knockdown and pharmacological inhibition of GPRC6a impacts tau biology in vitro and in vivo. Success in this application would provide a new receptor target that may impact arginine-sensing mTORC1 signaling. Furthermore, we aim to identify an entirely new class of drugs that targets GPCR6a to mitigate the tau phenotype provide new strategies for tauopathies and AD.