Mechanotransduction: Does PLD Regulate mTOR and Skeletal Muscle Growth?

描述(由申请人提供)： 机械刺激在肌肉质量的调节中起着重要作用，而肌肉质量的维持对疾病的预防和生活质量的提高具有重要意义。虽然机械刺激和肌肉质量调节之间的联系已经被认识到几十年了，但将机械信息转化为控制这一过程的分子事件所涉及的机制还没有确定。然而，这一领域正在取得重大进展，最近发现，通过雷帕霉素敏感(RS)途径发出的信号对于机械诱导的骨骼肌生长是必要的。由于雷帕霉素是一种被称为哺乳动物雷帕霉素靶点(MTOR)的蛋白激酶的抑制剂，许多研究人员得出结论，mTOR信号对于机械诱导的生长是必要的。然而，目前还缺乏直接证据表明mTOR是该信号通路中的雷帕霉素敏感元件，而且涉及RS信号通路机械激活的机制尚不清楚。因此，这一应用的重点是确定机械刺激如何激活RS信号通路和骨骼肌生长。我们的初步研究结果暗示了磷脂酶D(PLD)介导的磷脂酸(PA)产生的作用，并导致了以下假设：机械刺激诱导依赖于PLD的PA增加，随后结合并激活mTOR信号和骨骼肌生长。为了验证这一假设，将在两个特定目标下结合使用体内和体外模型以及一系列药理学和分子干预。第一个特定目的是确定PLD介导的PA产生是否足以诱导RS信号和骨骼肌生长，以及PLD介导的PA产生是否对于机械诱导的RS信号和生长是必需的。第二个目标是确定mTOR是否是机械诱导的RS信号和骨骼肌生长的RS元件，并确定mTOR激酶活性和与PA的结合是否是这些事件所必需的。综上所述，这些研究将填补机械刺激对RS信号机制理解的一个重要空白，并阐明mTOR的作用以及PLD和PA在这一途径中潜在的新功能。这些研究广泛应用于与健康相关的研究，并可能导致旨在预防卧床、制动、航天、衰老、恶病质和营养不良等情况下骨骼肌萎缩的治疗方法的开发。

DESCRIPTION (provided by applicant): Mechanical stimuli play a major role in the regulation of muscle mass, and the maintenance of muscle mass contributes significantly to disease prevention and the quality of life. Although a link between mechanical stimuli and the regulation of muscle mass has been recognized for decades, the mechanisms involved in converting mechanical information into the molecular events that control this process have not been defined. Nevertheless, significant advancements are being made in this field, and it has recently been established that signaling through a rapamycin-sensitive (RS) pathway is necessary for mechanically-induced growth of skeletal muscle. Since rapamycin is an inhibitor of a protein kinase called the mammalian target of rapamycin (mTOR), many investigators have concluded that mTOR signaling is necessary for mechanically-induced growth. There is, however, a lack of direct evidence that mTOR is the rapamycin-sensitive (RS) element in this pathway, and the mechanisms involved in the mechanical activation of the RS signaling pathway are not known. Therefore, the focus of this application is aimed at defining how mechanical stimuli activate the RS signaling pathway and skeletal muscle growth. The findings of our preliminary studies implicate a role for phospholipase D (PLD) mediated phosphatidic acid (PA) production and led to the following hypothesis: Mechanical stimuli induce a PLD-dependent increase in PA, which subsequently binds and activates mTOR signaling and skeletal muscle growth. To test this hypothesis, a combination of in vivo and ex vivo models in conjunction with a series of pharmacological and molecular interventions will be employed under two specific aims. The goal of the first specific aim is to determine whether PLD-mediated PA production is sufficient for the induction of RS signaling and skeletal muscle growth, and whether PLD-mediated PA production is necessary for mechanically-induced RS signaling and growth. The goal of the second aim is to determine whether mTOR is the RS element that confers mechanically-induced RS signaling and skeletal muscle growth, and also determine whether mTOR kinase activity and binding to PA are necessary for these events. Taken together, these studies will fill an important gap in the mechanistic understanding of RS signaling by mechanical stimulation and elucidate the role of mTOR and the potentially novel functions of PLD and PA in this pathway. These studies have broad application to health-related research and could lead to the development of therapies aimed at preventing skeletal muscle atrophy during conditions such as bed rest, immobilization, spaceflight, aging, cachexia and dystrophy.