Mechanisms of action of ghrelin in muscle and adipose tissue in cancer cachexia

 描述（由申请人提供）： 美国每年有超过150万人被诊断患有癌症。恶病质（定义为由于脂肪组织和骨骼肌损失导致的非自愿体重减轻）和厌食症（食物摄入减少）存在于高达80%的这些患者中，导致在这种情况下观察到的功能表现、生活质量和生存率下降;然而，缺乏对这种疾病的治疗。Ghrelin是一种新的合成代谢激素，增加能量摄入，减少能量消耗和炎症，导致肌肉和脂肪量增加;尽管其在癌症恶病质背景下的作用机制尚未完全了解。迄今为止，唯一确定的生长激素释放肽受体是生长激素促分泌素受体1a（GHSR-1a），这种受体不存在于肌肉或脂肪组织中。最近的数据表明，ghrelin的一些作用是GHSR-1a独立的。本提案的目的是表征生长激素释放肽和GHSR-1a激动剂在肌肉和脂肪组织中的作用机制，并确定这些机制在癌症恶病质中依赖GHSR-1a的程度。我们假设ghrelin通过诱导以下因素改善癌症恶病质：1）GHSR-1a依赖性食欲增加、GH/IGF-I和炎症下调，2）GHSR-1a非依赖性蛋白水解减少，直接作用于肌肉细胞。我们还假设生长激素释放肽通过GHSR-1a依赖性和非依赖性机制在肿瘤诱导的恶病质中增加脂肪生成并下调脂质氧化和脂解。我们的具体目标是：1）确定ghrelin受体GHSR-1a在介导ghrelin在肿瘤诱导的啮齿动物肌肉恶病质中的作用。使用我们在GHSR-1a WT和KO小鼠中已经建立的体内模型（刘易斯肺癌[LLC]诱导的恶病质），我们将确定GHSR-1a激活在这种情况下调节肌肉质量和力量、炎症、蛋白水解和蛋白合成中的作用。2)描述生长激素释放肽在肌肉中的作用机制，不依赖于GHSR-1a。基于我们的初步数据显示，GHSR-1a不是生长素释放肽防止C2 C12细胞中顺铂诱导的蛋白水解所必需的，并且生长素释放肽部分地防止GHSR-1a KO小鼠中LLC诱导的恶病质，我们将在我们的LLC诱导的恶病质模型中体内研究这些作用，并在来自GHSR-1a KO小鼠的C2 C12细胞和1 ry肌细胞培养物中体外研究这些作用。我们将表征介导这些生长激素释放肽的GHSR-1a-独立的影响的途径，并进行实验，以确定负责这些影响的替代受体。3)确定GHSR-1a在脂肪组织中介导ghrelin效应的作用。如我们的顺铂模型中所示，我们将研究生长素释放肽在预防LLC肿瘤诱导的脂肪萎缩中的作用以及在这种情况下脂肪生成、脂解和脂质氧化的相对贡献。使用我们的GHSR-1a WT和KO动物，我们还将建立GHSR-1a在体内和体外介导生长素释放肽在脂肪中的作用。迫切需要开发用于预防或治疗癌症相关脂肪和肌肉萎缩的疗法，因为它们显着降低了癌症退伍军人的生活质量。本提案将提供深入了解ghrelin的作用机制，确定这些作用中哪些是GHSR-1a依赖的，哪些是GHSR-1a独立的，表征这两种途径并鉴定这种新型受体。总之，这些实验将确定在这种情况下介导生长激素释放肽的保护作用的机制，解决临床需求并填补文献中的空白。最终，这些结果将允许更好地针对这一点 途径和开发新的治疗方法。其他疾病如慢性阻塞性肺病、心力衰竭和老年人身体虚弱也与此有关 肌肉和脂肪的损失，并将受益于知识的进步，这一建议将带来。

 DESCRIPTION (provided by applicant): More than 1,500,000 individuals in the US are diagnosed with cancer every year. Cachexia (defined as an involuntary weight loss due to adipose tissue and skeletal muscle loss), and anorexia (decreased food intake) are present in up to 80% of these patients, contributing to the decrease in functional performance, quality of life and survival seen in this setting; however, treatments for this condition are lacking. Ghrelin is a novel anabolic hormone that increases energy intake and decreases energy expenditure and inflammation leading to an increase in muscle and fat mass; although, its mechanisms of action in the setting of cancer cachexia are not fully understood. To this date, the only identify receptor for ghrelin is the growth hormone secretagogue receptor 1a (GHSR-1a) and this receptor is not present in muscle or adipose tissue. Recent data has shown that some of ghrelin's effects are GHSR-1a-independent. The objectives of this proposal are to characterize the mechanisms of action of ghrelin and GHSR-1a agonists in muscle and adipose tissue and to establish the extent to which these mechanisms are GHSR-1a-dependent in cancer cachexia. We hypothesize that ghrelin ameliorates cancer cachexia by inducing: 1) GHSR-1a- dependent increases in appetite, GH/IGF-I and downregulation of inflammation, and 2) GHSR-1a-independent decreases in proteolysis by acting directly on muscle cells. We also hypothesize that ghrelin increases lipogenesis and downregulates lipid oxidation and lipolysis in tumor-induced cachexia through GHSR-1a- dependent and independent mechanisms. Our specific aims are: 1) To determine the role of the ghrelin receptor GHSR-1a in mediating the effects of ghrelin in tumor-induced cachexia in rodent muscle. Using our already established in-vivo model (Lewis Lung Carcinoma [LLC]-induced cachexia) in GHSR-1a WT and KO mice, we will determine the role of GHSR-1a activation in modulating muscle mass and strength, inflammation, proteolysis and protein synthesis in this setting. 2) To characterize GHSR-1a-independent mechanisms of action of ghrelin in muscle. Based on our preliminary data showing that the GHSR-1a is not necessary for ghrelin to prevent cisplatin-induced proteolysis in C2C12 cells, and that ghrelin partially prevent LLC-induced cachexia in GHSR-1a KO, we will study these effects in- vivo in our LLC-induced cachexia model and in-vitro in C2C12 cells and 1ry myocyte culture from GHSR-1a KO mice. We will characterize the pathways mediating these GHSR-1a-independent effects of ghrelin and perform experiments to identify the alternate receptor responsible for these effects. 3) To establish the role of GHSR-1a in mediating the effects of ghrelin in adipose tissue. As shown in our cisplatin model, we will study the role of ghrelin in preventing fat atrophy induced by LLC tumor and the relative contribution of lipogenesis, lipolysis and lipid oxidation in this setting. Using our GHSR-1a WT and KO animals we will also establish the role of GHSR-1a in mediating ghrelin's effect in fat in-vivo and in-vitro. The development of therapies for the prevention or treatment of cancer-related fat and muscle wasting is desperately needed because they significantly reduce quality of life in Veterans with cancer. The present proposal will provide insight into ghrelin's mechanisms of action, determine which of these effects are GHSR- 1a-dependent and which are GHSR-1a-independent, characterize these two pathways and identify this novel receptor. Taken together, these experiments will determine the mechanisms mediating ghrelin's protective effects in this setting, addressing a clinical need and filling a void in the literature. Ultimately, these results will allow for better targeting of this pathway and the development of novel therapies for this condition. Other conditions such as chronic obstructive pulmonary disease, heart failure and frailty of the elderly are also associated with muscle and fat loss and will benefit from the advance in knowledge that this proposal will bring.