The Role of TRIM28 Phosphorylation in the Mechanical Regulation of Skeletal Muscle

项目摘要/摘要 机械刺激在调节骨骼肌质量和维持肌肉方面起着重要作用。 群众对疾病预防和生活质量有很大贡献。尽管机械设备之间的联系 信号和肌肉质量的调节已经被认识到几十年了，分子机制 驾驶这一过程目前还不得而知。因此，我们研究的长期目标是定义分子 机械刺激调节骨骼肌群的事件。这个项目的主要目标是 确定TRIM28磷酸化的变化在多大程度上有助于机械 肌肉质量的调节。我们之所以关注这个话题，是因为TRIM28可以控制mTOR(A)的活动 被广泛认为与肌肉质量的机械调节有关的一种蛋白激酶)。最近的一项研究还 确定TRIM28是一种与关键的生肌转录因子(例如，MEF2和 MyoD)，并且已经证明TRIM28上S473残基的磷酸化可以起到开关的作用 释放Mef2和MyoD的转录活性。这很耐人寻味，因为 MyoD和Mef2被广泛地参与肌肉质量的调节，以及最近的一种磷酸蛋白质组 我们实验室的分析显示，机械刺激导致TRIM28显著增加(S473) 磷酸化。此外，我们还发现，TRIM28的S473拟磷突变体的表达是 足以诱导肥大，并且肥大效应依赖于仿磷素 突变。综合这些观察结果，我们得出了我们的核心假设：TRIM28基因的增加(S473) 磷酸化是机械刺激促进血管紧张素转换酶增加的一个基本部分。 肌肉发达。为了严格检验这一假设，我们将首先使用生物化学、分子生物学的组合 以及对小鼠的基因干预。重要的是，基于老鼠的研究将使我们能够：i)深入了解 TRIM28(S473D)诱导肥大的机制，以及ii)定义了肌纤维和 TRIM28(S473)磷酸化的卫星细胞特异性变化在机械负荷诱导的肥大中起作用。 除了以老鼠为基础的研究外，我们还将进行人体试验，以确定主要的 小鼠的结论可以转化为人类的情况。总的来说，这个项目的成果是 预计将建立TRIM28作为一种新的肌肉质量调节器，并阐明一些基本的 S473磷酸化改变控制其肥大效应的机制。结果是 也有望揭示TRIM28依赖途径的存在，它不仅能使机械 刺激可诱导肥大，也可激活卫星细胞的增殖和融合。这样的结果 不仅极大地提高了我们对机械刺激如何调节肌肉质量的理解，而且 他们还将为未来的研究创造一个新的里程碑，旨在开发一种 了解这一非常重要的过程。

Project Summary / Abstract Mechanical stimuli play a major role in the regulation of skeletal muscle mass, and the maintenance of muscle mass contributes significantly to disease prevention and quality of life. Although the link between mechanical signals and the regulation of muscle mass has been recognized for decades, the molecular mechanisms that drive this process are still not known. Hence, the long-term goal of our research is to define the molecular events via which mechanical stimuli regulate skeletal muscle mass. The primary objective of this project is to determine the extent to which changes in the phosphorylation of TRIM28 contribute to the mechanical regulation of muscle mass. We are focusing on this topic because TRIM28 can control the activity of mTOR (a kinase that has been widely implicated in the mechanical regulation of muscle mass). A recent study also identified TRIM28 as a scaffold protein that interacts with key myogenic transcription factors (e.g., Mef2 and MyoD), and it has been shown that phosphorylation of the S473 residue on TRIM28 can act as a switch that unleashes the transcriptional activity of Mef2 and MyoD. This is intriguing because alterations in the activity of MyoD and Mef2 have been widely implicated in the regulation of muscle mass, and a recent phosphoproteomic analysis from our lab revealed that mechanical stimulation leads to a profound increase in TRIM28(S473) phosphorylation. Moreover, we discovered that the expression of a S473 phosphomimetic mutant of TRIM28 is sufficient to induce hypertrophy, and that the hypertrophic effect is dependent on the phosphomimetic mutation. Combined, these observations led us to our central hypothesis: an increase in TRIM28(S473) phosphorylation is a fundamental part of the pathway via which mechanical stimuli promote an increase in muscle mass. To rigorously test this hypothesis, we will first use of a combination of biochemical, molecular and genetic interventions in mice. Importantly, the mouse-based studies will enable us to: i) gain insight into the mechanisms via which TRIM28(S473D) induces hypertrophy, and ii) define the role that both myofiber and satellite cell specific changes in TRIM28(S473) phosphorylation play in mechanical load-induced hypertrophy. In addition to the mouse-based studies, we will also perform a human trial to determine whether the primary conclusions from mice can be translated to the human condition. Collectively, the outcomes of this project are expected to establish TRIM28 as a novel regulator of muscle mass and shed light on some of the basic mechanisms through which alterations in S473 phosphorylation control its hypertrophic effect. The outcomes are also expected to reveal the existence of a TRIM28-dependent pathway that not only enables mechanical stimuli to induce hypertrophy, but also the activation of satellite cell proliferation and fusion. Such outcomes would not only dramatically advance our understanding of how mechanical stimuli regulate muscle mass, but they would also create a new landmark for future studies that are aimed at developing a comprehensive understanding of this highly important process.