Understanding the Role GPRC6a During Tau Metabolism

包括阿尔茨海默病(AD)在内的神经退行性疾病包括与年龄相关的神经退行性疾病 目前还没有治疗疾病的方法。我们的团队发现了一种独特的相互作用 精氨酸代谢与肌萎缩侧索硬化症精氨酸代谢影响多个生物过程，表明 对tau生物学有相当大的影响。我们推测L-精氨酸是氨基酸的感受器。 大量的精氨酸和精氨酸的耗尽启动了自噬来补充氨基酸水平。精氨酸酶1 (Arg1)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，精氨酸和一氧化氮合酶(NOS)存在多种异构体。我们在细胞中展示了 和tau病的动物模型增加arg1在减少tau表型的许多方面的好处 (由陶效应组成的特征)。几个精液发现显示溶酶体和细胞质精氨酸 调节雷帕霉素复合体1(MTORC1)机制靶点的传感器。GPRC6a是一种偶联的G蛋白 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感受器 MTORC1.我们的初步数据表明阿尔茨海默病患者精氨酸敏感的mTORC1通路激活增加 大脑和紧张症的动物模型。我们证明了精氨酸的产生和代谢酶， 与对照组相比，AD患者海马区精氨酸感受器和mTORC1复合体增加 年龄匹配的大脑。我们还发现，tau使大脑中的总精氨酸水平增加了35%，增加了基础 脑神经刺激后细胞外精氨酸和精氨酸释放的水平。此外， 新的GPRC6a变构拮抗剂可清除细胞系、原代神经元和小鼠中各种形式的tau。 GPRC6a的遗传减少也减少了tau的表达，似乎调节了几个细胞内 精氨酸传感器。我们假设牛磺酸疾病(包括阿尔茨海默病)会导致精氨酸代谢受损和解偶联 精氨酸敏感的mTORC1信号，这导致了高mTORC1的激活，产生了一个正反馈- 前向环，以增加tau表型。我们将测试以下假设：GPRC6a信号从 变构拮抗剂或GPRC6a的shRNA调节精氨酸敏感的mTORC1信号，诱导自噬 并在体外和体内增加tau的清除量。我们将使用四环素诱导的tau细胞系与照片- 测量tau代谢的可切换荧光示踪剂，测量tau的分离式tau-GFP构建 寡聚和原代神经元的作用决定了GPRC6a和tau的命运。我们将确定是否 GPRC6a的基因敲除和药物抑制在体外和体内都会影响tau生物学。成功 这一应用将提供一个新的受体靶点，可能影响精氨酸敏感的mTORC1信号。 此外，我们的目标是确定一类针对GPCR6a的全新药物，以缓解tau 表型为治疗tauopathy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.