Delineating the roles of GPR55 in cellular metabolism and energy homeostasis

G蛋白偶联受体(GPCR超家族)在细胞通讯中发挥着重要作用。因此，它们调节循环激素和其他生物活性分子在细胞面向血液的膜上的影响，以调节不同的细胞/组织过程，例如，感觉知觉、新陈代谢和饱腹感。考虑到它们与神经系统疾病、炎症和代谢疾病、糖尿病和心脏功能障碍有关，它们是人体内最大和最成功的可用药靶标。然而，尽管目前对GPCR生物学产生了极大的兴趣，但该家族中许多成员的功能仍然知之甚少，但它们很可能代表着治疗重大公共卫生问题的重要治疗靶点，如肥胖症、糖尿病和心血管疾病。该项目旨在探索一种名为GPR55的脂质感知GPCR与影响肥胖、炎症、心脏功能和关键代谢组织(如白色脂肪、肝脏、骨骼肌和心脏)对胰岛素反应的过程之间的联系。这些组织是体内胰岛素的主要靶点，是糖(葡萄糖)和脂肪储存和代谢的主要部位，对荷尔蒙的反应。GPR55受到一种名为LPI的循环脂质的刺激，我们发现它可以改善这些代谢组织对胰岛素的反应，并有助于降低它们衍生的细胞中的炎症驱动。关键是，如果细胞与GPR55抑制剂共同处理，这种LPI介导的反应就会丢失。引人注目的是，我们发现这种脂质感受器缺陷的动物表现出组织对胰岛素的反应性降低，代谢能力受损，心脏功能下降。代谢能力在很大程度上依赖于线粒体；线粒体是细胞内代表细胞“能量生成器”的结构。值得注意的是，缺乏GPR55的动物表现出线粒体生物学上的变化，这与“燃烧”脂肪的能力降低一致。与此相一致，我们发现缺乏GPR55的动物会患上肥胖症，抑制培养的脂肪细胞(脂肪细胞)中的受体会诱导有助于制造更多脂肪的蛋白质，这将加剧肥胖的过程。GPR55与上述过程的分子调控的确切联系目前尚不清楚。本申请中描述的研究将利用来自啮齿动物和人类来源的培养细胞以及小鼠组织进行实验室分析，以帮助剖析GPR55不仅在胰岛素作用和炎症方面发挥的作用，而且在控制组织脂肪(脂肪)和心脏功能方面发挥的作用。该项目还将探索GPR55激活是否有助于缓解喂食高脂肪卡路里饮食的小鼠的脂肪增加、组织对胰岛素敏感性的丧失和心脏功能障碍。在这些研究结束时，从动物身上提取的组织将被处理以进行生化分析和最先进的全细胞/组织蛋白质图谱--一种方法将识别哪些蛋白质在缺乏GPR55的小鼠组织中上调或下调，或者在GPR55已被选择性药物激活/抑制的细胞中上调或下调。这种方法将产生丰富的信息，可能会揭示与GPR55相关的新蛋白质，以调控胰岛素的作用方式或脂肪的储存或“燃烧”方式。重要的是，大规模的蛋白质图谱可以标记出以前没有与GPR55联系在一起的蛋白质，但这些蛋白质可能是其他领域研究人员工作的核心，从而为科学界提供了宝贵的数据资源。总而言之，我们的初步研究表明，GPR55可能作为一种新的组织内代谢调节器发挥作用，并表明了解它如何调节胰岛素作用、脂肪代谢和心脏功能可能为治疗与肥胖和II型糖尿病等疾病相关的代谢紊乱提供新的药理学机会。

The G-protein coupled receptor (GPCR) superfamily play crucial roles in cell communication. As such, they mediate the effects of circulating hormones and other biologically active molecules across the blood-facing membranes of cells to regulate diverse cell/tissue processes including, for example, sensory perception, metabolism and satiety. Given their involvement in neurological disorders, inflammatory and metabolic diseases, diabetes and cardiac dysfunction they represent the largest and most successful class of "druggable" targets in the human body. However, despite the immense current interest in GPCR biology, the function of numerous members of this family remain poorly understood, but which may well represent important therapeutic targets for treatment of major public health issues, such as obesity, diabetes and cardiovascular disease. This project aims to explore links between a lipid sensing GPCR, called GPR55, and processes influencing adiposity, inflammation, cardiac function and response to insulin within key metabolic tissues, such as white fat, liver, skeletal muscle and heart. These tissues are major targets for insulin in the body and represent the principal sites where sugar (glucose) and fat are stored and metabolised in response to the hormone. GPR55 is stimulated by a circulating lipid called LPI, which we find improves the response of these metabolic tissues to insulin and also helps lower inflammatory drive in cells derived from them. Crucially, this LPI-mediated response is lost if cells are co-treated with a GPR55 inhibitor. Strikingly, we have discovered that animals deficient in this lipid sensor exhibit reduced tissue responsiveness to insulin, impaired metabolic capacity and a decline in cardiac performance. Metabolic capacity is crucially dependent upon mitochondria; structures within cells representing the cell's "energy generator". Significantly, animals lacking GPR55 show changes in mitochondrial biology consistent with a reduced ability to "burn" fat. In line with this, we find animals lacking GPR55 develop obesity and that inhibiting the receptor in cultured adipocytes (fat cells) induces proteins that help make more fat, which would augment the process of obesity. Precisely how GPR55 links to the molecular regulation of the above processes is currently unclear. The studies described in this application will utilise cells in culture from rodent and human origin as well as mouse tissues for laboratory-based analysis to help dissect out the role GPR55 plays not only with respect to insulin action and inflammation, but in control of tissue adiposity (fatness) and cardiac function. The project will also explore whether GPR55 activation helps mitigate the increase in fat gain, the loss in tissue sensitivity to insulin and cardiac dysfunction in mice fed a high fat calorie diet. Tissues taken from animals at the end of such studies will be processed for biochemical analysis and state-of-the-art whole cell/tissue protein profiling - an approach that will identify which proteins become up- or down-regulated in tissues of mice lacking GPR55 or in cells in which GPR55 has been activated/inhibited with selective drugs. This methodology will generate a wealth of information, potentially unveiling novel proteins that connect with GPR55 to regulate how insulin works or fat is stored or "burnt". Importantly, the large scale protein profiling may flag-up proteins that have not previously been linked to GPR55, but which may be central to the work of researchers in other fields thus providing an invaluable data resource to the scientific community. Collectively, our pilot studies indicate GPR55 may function as a novel metabolic regulator within tissues and suggest that understanding how it regulates insulin action, lipid metabolism and cardiac function may offer new pharmacological opportunities for treatment of metabolic disorders associated with conditions such as obesity and type II diabetes.