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

项目概要/摘要 机械刺激在骨骼肌质量的调节和肌肉的维持中起着重要作用 大众对预防疾病和提高生活质量作出了重大贡献。虽然机械之间的联系 信号和肌肉质量的调节已经被认识了几十年， 驱动这个过程仍然是未知的。因此，我们研究的长期目标是确定 机械刺激调节骨骼肌质量的事件。该项目的主要目标是 确定TRIM 28磷酸化的变化在多大程度上有助于机械性的 调节肌肉质量。我们关注这个话题是因为TRIM 28可以控制mTOR的活性（a 广泛参与肌肉质量的机械调节的激酶）。最近的一项研究还 将TRIM 28鉴定为与关键肌原性转录因子（例如，Mef 2和 MyoD），并且已经显示TRIM 28上的S473残基的磷酸化可以充当开关， 释放Mef 2和MyoD的转录活性。这是有趣的，因为在活动的变化， MyoD和Mef 2广泛参与肌肉质量的调节，最近的磷酸化蛋白质组学研究表明， 我们实验室的分析显示，机械刺激导致TRIM 28（S473）的显著增加。 磷酸化此外，我们发现TRIM 28的S473磷酸模拟突变体的表达是 足以诱导肥大，并且肥大效应依赖于磷酸化模拟物 突变综合起来，这些观察结果使我们得出了我们的中心假设：TRIM 28（S473）的增加 磷酸化是机械刺激促进细胞凋亡增加的途径的基本部分。 肌肉质量.为了严格检验这一假设，我们将首先使用生物化学、分子生物学和生物化学的组合， 以及对老鼠的基因干预。重要的是，基于小鼠的研究将使我们能够：i）深入了解 TRIM 28（S473 D）诱导肥大的机制，以及ii）定义肌纤维和肌纤维在肌纤维中的作用。 TRIM 28（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。 除了基于小鼠的研究，我们还将进行人体试验，以确定是否主要 从老鼠身上得出的结论可以应用到人类身上。总的来说，该项目的成果是 预计将TRIM 28作为一种新的肌肉质量调节剂，并揭示了一些基本的 S473磷酸化改变控制其肥大作用的机制。成果 还有望揭示TRIM 28依赖性通路的存在，该通路不仅使机械 刺激诱导肥大，还可激活卫星细胞增殖和融合。这种结果 不仅会极大地推进我们对机械刺激如何调节肌肉质量的理解， 他们还将为未来的研究创造一个新的里程碑， 了解这个非常重要的过程。

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.