The misfolded myosin response in health and disease

肌病是一种遗传性、进行性的心脏和骨骼肌疾病，通常会导致患者严重的身体损伤和过早死亡。通常，横纹肌的基本收缩机构肌节的成分突变被发现是疾病发生和发展的原因。虽然肌节的组成已为人所知，但其组装的分子调控以及保证肌瘤发生的辅助蛋白如Unc45b或Hsp90a的相互作用仍不完全清楚。Unc45b和Hsp90a被认为具有调节肌球蛋白折叠的特殊功能。有趣的是，携带这两个肌球蛋白伴侣蛋白功能缺失突变的动物模型显示出大量的肌肉结构紊乱、肌丝解体和运动性严重受损，证实了辅助和调节蛋白在将结构成分组装成完全功能的肌节和肌丝中的重要性。最近，含有甲基转移酶集合和myND结构域的蛋白1(Smyd1)被确定为Unc45b和Hsp90a的相互作用伙伴，但也包括肌肉肌球蛋白，这表明Smyd1类似于Unc45b或Hsp90a，甚至与Unc45b或Hsp90a一起参与体内肌球蛋白折叠和组装的调节。Unc45b、Hsp90a或Smyd1b的突变导致错误折叠肌球蛋白的积累，随后诱导称为错误折叠肌球蛋白反应(MMR)的复杂基因程序，最终导致肌原纤维在发育过程中的损害。在拟议的研究中，我们现在的目标是(1)分析明确的Smyd1突变(在第一个资助期确定)和(2)Smyd1丢失对成人肌肉功能和结构的作用。此外，我们的目标是(3)确定Smyd1特异性的非组蛋白甲基化靶点及其在肌瘤发生和错误折叠的肌球蛋白反应中的生物学作用。除了我们对斑马鱼的分析外，我们还将(4)确定Smyd1缺失的作用以及人类Smyd1变体对人类诱导多能干细胞来源的心肌细胞(hiPSC-CMS)发育和功能的影响。最后，我们的目标是(5)定义和表征由体内错误折叠的肌球蛋白反应激活的因子、通路和信号网络(生物信息学数据集)。综上所述，拟议的研究最终将有助于进一步剖析肌节组装的遗传和分子基础，特别是肌球蛋白折叠，这将对开发更具体的治疗横纹肌疾病的策略至关重要。

Myopathies are inherited, progressive diseases of heart and skeletal muscle that often lead to severe physical impairment and premature death of affected patients. Frequently, mutations in constituents of the basic contractile apparatus of striated muscle, the sarcomere, were found to be causative for disease onset and progression. Although the composition of the sarcomere is well known, the molecular regulation of its assembly and the interplay of auxiliary proteins such as Unc45b or Hsp90a that guarantee sarcomerogenesis are still incompletely understood. Unc45b and Hsp90a are known to specifically function to regulate myosin folding. Interestingly, animal models carrying loss-of-function mutations in these two myosin chaperones display massively disorganized muscle structures, myofilament disassembly and a severely impaired motility, substantiating the importance of auxiliary and regulatory proteins in the assembly of structural components into fully functional sarcomeres and myofilaments.Very recently, the methyltransferase SET- and MYND-domain-containing protein 1 (Smyd1) was identified as an interaction partner of Unc45b and Hsp90a but also muscle Myosin, suggesting that Smyd1, similar to or even together with Unc45b or Hsp90a, to be involved in the regulation of myosin folding and assembly in vivo. Mutation of Unc45b, Hsp90a or Smyd1b leads to the accumulation of misfolded myosin, the subsequent induction of a complex gene program termed the misfolded myosin response (MMR) and finally the impairment of myofibril formation during development.In the proposed research we now aim (1) to dissect the role of defined Smyd1 mutations (identified during the first funding period) and (2) of loss of Smyd1 on adult muscle function and structure. Furthermore, we aim (3) to identify Smyd1-specific non-histone methylation targets and their biological role in sarcomerogenesis and the misfolded myosin response. In addition to our analyses in zebrafish, we will (4) define the role of Smyd1 loss and the impact of human Smyd1 variants on development and function in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs). Finally, we aim (5) to define and characterize factors, pathways and signaling networks (bioinformatics datasets) activated by the misfolded myosin response in vivo.In summary, the proposed research will ultimately help to further dissect the genetic and molecular underpinnings of sarcomere assembly and particularly myosin folding, which will be essential for the development of more specific strategies to treat diseases of striated muscle.