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

 描述(由申请人提供)： 在美国，每年有超过150万人被诊断出患有癌症。恶病质(定义为脂肪组织和骨骼肌丢失导致的非自愿体重下降)和厌食症(食物摄入量减少)在高达80%的患者中存在，导致在这种情况下出现的功能表现、生活质量和生存能力下降；然而，缺乏针对这种情况的治疗。Ghrelin是一种新的合成代谢激素，能增加能量摄入，减少能量消耗，减少炎症，导致肌肉和脂肪质量增加；尽管，其在癌症恶病质发病中的作用机制尚未完全清楚。到目前为止，唯一识别Ghrelin的受体是生长激素促分泌素受体1a(GHSR-1a)，该受体不存在于肌肉或脂肪组织中。最近的数据表明，Ghrelin的一些作用是不依赖于GHSR-1a的。这项建议的目的是表征Ghrelin和GHSR-1a激动剂在肌肉和脂肪组织中的作用机制，并建立这些机制在癌症恶病质中依赖于GHSR-1a的程度。我们假设Ghrelin通过引起：1)依赖于GHSR-1a的食欲增加、GH/IGF-I和炎症的下调，以及2)不依赖于GHSR-1a的通过直接作用于肌肉细胞的蛋白分解减少，从而改善癌症恶病质。我们还假设，在肿瘤诱导的恶病质中，Ghrelin通过GHSR-1a依赖和独立的机制增加脂肪生成和抑制脂质氧化和脂肪分解。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。利用我们已经建立的GHSR-1a WT和KO小鼠体内模型(Lewis肺癌[LLC]诱导恶病质)，我们将确定在这种情况下，GHSR-1a激活在调节肌肉质量和力量、炎症、蛋白质分解和蛋白质合成方面的作用。2)研究Ghrelin在肌肉中非依赖于GHSR-1a的作用机制。基于我们的初步数据显示，ghrelin不是阻止顺铂诱导的C2C12细胞蛋白分解所必需的GHSR-1a，并且ghrelin部分阻止了LLC诱导的GHSR-1a KO恶病质，我们将在我们的LLC诱导恶病质模型中研究这些作用，并在体外研究来自GHSR-1a KO小鼠的C2C12细胞和1RY心肌细胞培养的这些作用。我们将描述介导Ghrelin的这些GHSR-1a非依赖性效应的途径，并进行实验以确定负责这些效应的替代受体。3)确定GHSR-1a在介导Ghrelin在脂肪组织中的作用。如我们的顺铂模型所示，我们将研究Ghrelin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，我们还将确定GHSR-1a在体内和体外介导Ghrelin对脂肪的影响的作用。迫切需要开发预防或治疗癌症相关脂肪和肌肉萎缩的疗法，因为它们显著降低了患有癌症的退伍军人的生活质量。本提案将深入了解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不依赖的，并对这两条途径进行表征，并鉴定这种新的受体。综上所述，这些实验将确定在这种情况下Ghrelin的保护作用的调节机制，解决临床需求并填补文献中的空白。最终，这些结果将使我们能够更好地针对这一点 治疗这种疾病的途径和新疗法的开发。其他情况，如慢性阻塞性肺疾病、心力衰竭和老年人的虚弱也与此有关 肌肉和脂肪的减少，并将受益于这项提议将带来的知识进步。

 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.