Mechanisms of obesity-linked muscle atrophy and n-3 fatty acids

项目摘要 肥胖是退伍军人社区和全国各地流行比例的临床问题。它不利 影响几乎所有器官，导致代谢功能障碍，包括慢性炎症、胰岛素抵抗 以及糖尿病、血脂异常和心血管疾病。肥胖症的一个未被充分认识的并发症是， 导致肌肉萎缩这种消耗导致肌肉无力和脆弱，这增加了 福尔斯，降低生活质量，并与合并症的发生率和 mortality.来自动物和病人的证据表明，肥胖会通过以下方式降低肌肉的大小和力量： 损害肌生成（即，纤维修复）和通过减弱蛋白质合成和加速蛋白质水解。 先前的研究已经记录了多种蛋白水解系统的激活-泛素-蛋白酶体， 自噬和半胱天冬酶-3系统-在肥胖db/db小鼠和最近的研究，我们的实验室表明， 通过将培养的C2 C12肌管与棕榈酸盐一起孵育，可以复制反应，棕榈酸盐是人体最重要的 丰富的饱和脂肪酸。棕榈酸盐加速C2 C12肌管中的蛋白质降解速率， 减少胰岛素信号传导并刺激所有三种蛋白水解系统， 小鼠最近，我们扩展了这些发现，证明棕榈酸诱导的内质网应激也 有助于萎缩相关基因和蛋白表达的产生。肌生成抑制素（Myostatin，MSTs）， BMP/TGF β超家族，通过诱导萎缩相关的蛋白水解， 酶和肌因子在肥胖患者和动物的肌肉中增加。新的初步数据 证明棕榈酸酯诱导MSP 4 mRNA。根据这些发现，我们建议调查是否 肥胖症通过激活C/EBP而促进体内肌管和骨骼肌中的MMP 3表达， CREB转录因子通过两种新发现的与ER应激和Akt- 调节的磷酸二酯酶（PDE 3/4）（Aim 1）。肌肉萎缩会增加萎缩的表现- 相关蛋白，部分是通过Akt破坏胰岛素和IGF-1信号传导，Akt激活分解代谢 然而，MclO如何降低Akt活性仍然是未知的。在目标2中，我们 研究MSTN相关的microRNA-29抑制及其靶点之一的表达增加是否 - 磷酸酶和张力蛋白同源物（PTEN）有助于Akt失调和FoxO介导的 骨骼肌和肌管中的基因表达。在目标3中，我们将测试膳食中提供的omega-3是否 多不饱和脂肪酸（n-3 PUFA）对db/db小鼠的作用逆转了肥胖相关的功能障碍性MMP 3信号传导 和蛋白质分解代谢反应导致肌肉萎缩。最近的动物和患者研究提供了 有证据表明，施用n-3 PUFA可以在癌症、肾衰竭和 其他与萎缩相关的疾病。我们的初步数据表明，n-3多不饱和脂肪酸，二十二碳六烯酸， DHA，防止棕榈酸诱导的MMP 3表达和Akt-FoxO和ER应激的变化 与肌肉萎缩基因表达相关的信号。我们建议，这些有益的效果是实现 通过逆转肥胖相关的功能失调信号，产生MMP 3和其他蛋白质分解代谢反应， 最终导致肌肉萎缩目标3的结果将提供新的临床前证据， 使用n-3 PUFA作为一种具有成本效益的治疗方法来对抗肥胖对 退伍军人的骨骼肌质量。

PROJECT SUMMARY Obesity is a clinical issue of epidemic proportion in the Veteran community and across the country. It adversely affects almost every organ and causes metabolic dysfunction including chronic inflammation, insulin resistance and diabetes, dyslipidemias, and cardiovascular disease. An underappreciated complication of obesity is that it causes muscle atrophy. This wasting leads to muscle weakness and frailty which increases the incidence of falls, reduces the quality of life, and is associated with a higher incidence of co-morbidities and risks of mortality. Evidence from animals and patients indicates that obesity decreases muscle size and strength by impairing myogenesis (i.e., fiber repair) and by attenuating protein synthesis and accelerating proteolysis. Previous studies have documented activation of multiple proteolytic systems - the ubiquitin-proteasome, autophagy and caspase-3 systems - in obese db/db mice and recent studies by our lab indicate that these responses can be duplicated by incubating cultured C2C12 myotubes with palmitate, one of the body’s most abundant saturated fatty acids. Palmitate accelerates the rate of protein degradation in C2C12 myotubes by reducing insulin signaling and stimulating all three of the proteolytic systems that are up-regulated in obese mice. We have extended these findings by recently demonstrating that palmitate-induced ER stress also contributes to the production of atrophy-related gene and protein expression. Myostatin (MSTN), a member of the BMP/TGFß superfamily, contributes to protein degradation by inducing atrophy-related proteolytic enzymes and the myokine is increased in muscle of obese patients and animals. New preliminary data demonstrate that palmitate induces MSTN mRNA. Based on these findings, we propose to investigate whether obesity contributes to MSTN expression in myotubes and skeletal muscle in vivo by activating the C/EBP and CREB transcription factors via two newly identified signaling mechanisms linked to ER stress and Akt- regulated phosphodiesterases (PDE3/4), respectively (Aim 1). MSTN increases the expression of atrophy- related proteins, in part, by impairing insulin and IGF-1 signaling through Akt, which activates the catabolic FoXO transcription factors), however, it remains unknown how MSTN reduces Akt activity. In Aim 2, we will investigate whether MSTN-related suppression of microRNA-29 and increased expression of one of its targets - phosphatase and tensin homolog (PTEN) contributes to Akt dysregulation and increased FoxO-mediated gene expression in skeletal muscle and myotubes. In Aim 3, we will test whether dietary provision of omega-3 polyunsaturated fatty acids (n-3 PUFA) to db/db mice reverses obesity-related dysfunctional MSTN signaling and protein catabolic responses that lead to muscle atrophy. Recent animal and patient studies provide evidence that administration of n-3 PUFA can produce muscle-sparing effects in cancer, kidney failure and other atrophy-associated conditions. Our preliminary data demonstrate that a n-3 PUFA, docosahexaenoic acid (DHA), prevents the palmitate-induced changes in MSTN expression and Akt-FoxO and ER stress signaling that are linked to muscle atrogene expression. We propose that these beneficial effects are achieved by reversing obesity-related dysfunctional signaling that produce MSTN and other protein catabolic responses which ultimately lead to muscle atrophy. Results from Aim 3 will provide new preclinical evidence to support the feasibility of using of n-3 PUFA as a cost-effective therapy to counter the adverse effects of obesity on skeletal muscle mass in Veterans.