PI3K/Akt信号通路参与淫羊藿素治疗失负荷性肌肉萎缩机制的研究

Skeletal muscle undergoes rapid and profound atrophy in response to decreased mechanical loading, e.g., limb immobilization, bed rest, denervation, hindlimb suspension and spaceflight. The known consequences are loss of muscle mass, decrease in muscle strength, reduction of functional capacity and increase in fatigue. Loss of muscle strength impairs the ability to maintain posture and perform a wide range of movements and motions, reduces bone strength and increases fracture risk, physical frailty and subsequent mortality..Counteracting muscle atrophy associated with mechanical unloading/inactivity is of great clinical need and challenge. Currently, some physical therapies and pharmacological agents are attempted to attenuate muscle atrophy. However, their practical and long-term application is limited by various implications..Natural products derived from Chinese herbs that have been clinically prescribed in China for thousands of years might be a potential candidate to counteract muscle atrophy with minimal adverse effects. It has been well established that disuse/inactivity-induced muscle loss is mediated by a decrease in protein synthesis and an increase in protein degradation. Phosphatidylinositol 3 kinase (PI3K)/Akt signaling pathway is critical for regulating the balance between protein synthesis and degradation during disuse/inactivity-induced muscle atrophy. Epimedium is a frequently used herb to strengthen musculoskeletal system in Traditional Chinese Medicine. Epimedium-derived flavonoid (EF) has demonstrated safety and efficacy in treating postmenopausal osteoporosis in our published clinical trials. Interestingly, it has been reported that EF showed an anabolic effect on the activation of PI3K/Akt pathway in non-muscle tissues. Our preliminary study further showed that icaritin, intestinal metabolite of EF, can activate PI3K/Akt pathway and enhance muscle force in skeletal muscle in osteoporotic rats. This motivates our hypothesis that icaritin could counteract disuse/inactivity-induced skeletal muscle atrophy with involvement of PI3K/Akt signaling pathway. .In this proposal, the applicants will test the hypothesis in a rat model of hindlimb suspension- induced skeletal muscle atrophy to examine: 1) the effect of icaritin on the muscle atrophic changes in muscle mass, fiber cross-sectional area, fiber type distribution, muscle and myofibril protein content, and muscle contractile properties; 2) the influence of icaritin on the activation status of PI3K/Akt signaling pathway; 3) the involvement of PI3K/Akt signaling pathway in the effect of icaritin on skeletal muscle atrophy..This study will provide new insight that natural product icaritin may be a novel muscle anabolic agent to counteract muscle atrophy induced by mechanical unloading, thereby, reduce falling and fracture risk, and improve independence and quality of life.

骨骼肌在力学载荷降低或缺失时（肢体固定，长期卧床，神经损伤或太空飞行等）会发生快速明显的萎缩。防治这种失负荷性或废用性肌肉萎缩面临极大临床挑战。失负荷/废用性肌肉萎缩主要由PI3K/Akt信号通路介导的肌细胞内蛋白合成减少和降解增加所致。我们前期发表的两项治疗骨质疏松临床试验证实了淫羊藿总黄酮对人体主要系统的安全性。淫羊藿总黄酮主要成分淫羊藿苷可激活非肌肉组织内的PI3K/Akt信号通路而促进蛋白合成和抑制蛋白降解。我们前期研究证实淫羊藿苷血清代谢产物淫羊藿素可以激活骨质疏松大鼠骨骼肌内PI3K/Akt信号通路并增强肌力，从而形成本研究的假说：淫羊藿素可能激活失负荷性肌肉内的PI3K/Akt信号通路并预防此类肌肉萎缩。本研究将应用大鼠后肢悬吊致肌肉萎缩模型，观察淫羊藿素预防失负荷性肌肉萎缩的疗效和PI3K/Akt信号通路在此过程中的作用。本研究将为治疗失负荷性/废用性肌肉萎缩提供新的视角。

骨骼肌在力学载荷降低或缺失时（肢体固定，长期卧床，神经损伤或太空飞行等）会发生快速明显的萎缩。表现为肌肉质量以及力量的下降，肌肉功能的降低。肌肉萎缩降低了保持姿势和执行各种动作和运动的能力，降低了骨骼强度，增加骨折风险，身体虚弱和随后的死亡率。..目前试图减轻肌肉萎缩的治疗方法有，物理疗法，如抗阻运动和电刺激，以及药物治疗，例如胰岛素样生长因子-I，促蛋白合成类固醇，肌抑素抑制剂，和β2肾上腺素能受体激动剂。然而，由于各种因素使它们的实际操作和长期应用受限，如患者体质因素使物理治疗顺应性低，或者药物治疗有耐药性风险，以及心血管和前列腺癌，心脏肥大和功能障碍的风险。..中国草药天然产品已被在中国医学上使用几千年，其可能是一个潜在的可用于治疗肌肉萎缩并且对人体安全的药物。失负荷/废用性肌肉萎缩主要由 PI3K/Akt 信号通路介导的肌细胞内蛋白合成减少和降解增加所致。淫羊藿是一种在中国传统医学常用的以加强肌肉骨骼系统的草药。本研究表明，淫羊藿素（ICT），淫羊藿衍生的类黄酮肠道代谢物，可以提高的PI3K的p110催化亚基的磷酸化水平在和促进C2C12细胞中PI3K/Akt信号通路的表达。该研究还表明，高剂量淫羊藿素治疗能显著缓解28天后肢悬吊所致萎缩的大鼠比目鱼肌中PI3K-p110及其与蛋白合成相关的下游标记物（Akt，mTOR，p70S6K和4EBP1）的磷酸化水平的下降，并抑制蛋白降解相关标记在蛋白水平（FOXO1，FOXO3a）和mRNA表达水平（Atrogin-1，MuRF-1）的升高。此外，高剂量淫羊藿素可以显著缓解比目鱼肌肉重量，肌纤维横截面积和肌肉功能参数（单次收缩力，单位面积强直收缩力，肌肉收缩时间，半弛豫时间）的下降。渥曼青霉素，PI3K的在p110催化亚基的特异性抑制剂，可抑制淫羊藿素在体外和体内实验中的治疗效果，表明淫羊藿素对抗失负荷性肌肉萎缩需要PI3K / Akt信号通路的参与。..上述研究提供了一种新的见解，即天然产物淫羊藿素可能是一种新的对抗失负荷性肌肉萎缩肌肉合成促进药物，从而减少摔倒和骨折风险，并提高独立性和生活质量。