Functional analysis of the fiber type-specific gene regulation in skeletal muscle: Modulation of NFAT function by post-translational modifications

骨骼肌的主要特征之一是其可塑性。肌肉纤维可以响应生理需求而改变，例如耐力活动，但也可以不活动，年龄依赖性萎缩或肌肉营养不良。这涉及改变协同基因程序，导致纤维类型的不同收缩和代谢特征。运动蛋白肌球蛋白重链（MyHC）的慢型和快型是每种纤维类型的主要特征。从快纤维到慢纤维的转变（快到慢转化）由钙调神经磷酸酶/NFATc（活化T细胞的核因子）-信号传导途径介导，并且可以通过添加Ca 2 +-离子载体在培养的细胞中诱导。该更新提案研究了蛋白质1-4的额外调节途径，包括c1的C-末端变体，通过翻译后修饰（PTM）在钙调磷酸酶下游，并专注于通过骨骼肌中蛋白质的乙酰化或SUMO化微调NFATc信号传导。在其他细胞模型中，例如T细胞的免疫应答，通过转录因子的乙酰化或SUMO化的修饰可以诱导或抑制其靶基因的转录激活，这取决于启动子环境。在这里，一个可能的调节机制，通过乙酰化或SUMO化的蛋白质，导致激活的慢纤维和抑制的快纤维类型的基因程序在慢纤维将进行调查。这包括蛋白质1-4和c1亚型中功能性乙酰化/SUMO化受体位点的鉴定以及启动子依赖性修饰的研究。初步数据表明，乙酰化和SUMO化的NFATc，分别基因激活和抑制的相关性。此外，我们将寻找结合位点邻近NFATc反应元件和转录辅因子。细胞培养的初步实验将通过分析人类模型系统中的快-慢转化来完成，目的是更好地了解骨骼肌纤维中高效的调控机制，以及纤维类型特异性基因程序的交替激活和抑制。蛋白质的其他调节机制可以进一步阐明具有临床意义的纤维类型特异性基因调节，例如神经肌肉疾病。此外，它还可能对横纹肌中NFATc信号通路的调节产生更广泛的影响。

One of the major characteristics of the skeletal muscle is its plasticity. Muscle fibers can be altered in response to physiological demands e.g. endurance activity, but also inactivity, age-dependent atrophy or muscle dystrophies. This involves the alteration of concerted gene programs resulting in the different contractile and metabolic features of fibre types. The slow and fast isoforms of the motor protein myosin heavy chain (MyHC) are a main characteristic of each fiber type. A shift from fast to slow fibers (fast-to-slow transformation) is mediated by the calcineurin/NFATc (nuclear factor of activated T cells)-signaling pathway and can be induced in cultured cells by addition of Ca2+-Ionophore. This renewal proposal investigates an additional regulatory pathway of proteins 1-4, including the C-terminal variants of c1, downstream of calcineurin by post-translational modifications (PTMs) and focus on the fine-tuning of NFATc signaling by acetylation or SUMOylation of proteins in skeletal muscle. In other cell models, e.g. immune response of T-cells, a modification by acetylation or SUMOylation of transcription factors can induce or repress transcriptional activation of their target genes depending on the promoter context. Here, a possible regulatory mechanism by acetylation or SUMOylation of proteins leading to the activation of the slow and inhibition of the fast fiber type gene program in slow fibers will be investigated. This includes the identification of functional acetylation/SUMOylation acceptor sites in the proteins 1-4 and c1 Isoforms and the investigation of a modification in a promoter-dependant manner. Preliminary data indicate a correlation of gene activation and repression by acetylated and SUMOylated NFATc, respectively. Furthermore, we will search for binding sites adjacent to NFATc response elements and for transcriptional cofactors. The initial experiments in cell culture will be completed by the analysis of a fast-to-slow transformation in a human model system.The objectives are a better understanding of the highly efficient regulatory mechanisms in skeletal muscle fibers with their alternating activation and inhibition of fiber type-specific gene programs. Additional regulatory mechanisms of proteins could further elucidate fiber type-specific gene regulations with clinical implications, in respect to e.g. neuromuscular diseases. In addition, it might also have a broader impact on the regulation of NFATc signaling pathway in the cross-striated cardiac muscle.