PDF(Pubmed)
Abstract：
Here, we investigated the mechanisms by which aging-related reductions of the levels of Numb in skeletal muscle fibers contribute to loss of muscle strength and power, two critical features of sarcopenia. Numb is an adaptor protein best known for its critical roles in development, including asymmetric cell division, cell-type specification, and termination of intracellular signaling. Numb expression is reduced in old humans and mice. We previously showed that, in mouse skeletal muscle fibers, Numb is localized to sarcomeres where it is concentrated near triads; conditional inactivation of Numb and a closely related protein Numb-like (Numbl) in mouse myofibers caused weakness, disorganization of sarcomeres, and smaller mitochondria with impaired function. Here, we found that a single knockout of Numb in myofibers causes reduction in tetanic force comparable to a double Numb, Numbl knockout. We found by proteomics analysis of protein complexes isolated from C2C12 myotubes by immunoprecipitation using antibodies against Numb that Septin 7 is a potential Numb-binding partner. Septin 7 is a member of the family of GTP-binding proteins that organize into filaments, sheets, and rings, and is considered part of the cytoskeleton. Immunofluorescence evaluation revealed a partial overlap of staining for Numb and Septin 7 in myofibers. Conditional, inducible knockouts of Numb led to disorganization of Septin 7 staining in myofibers. These findings indicate that Septin 7 is a Numb-binding partner and suggest that interactions between Numb and Septin 7 are critical for structural organization of the sarcomere and muscle contractile function.
摘要：
这里,我们研究了骨骼肌纤维中与衰老相关的Numb水平降低导致肌肉力量和力量丧失的机制，肌肉减少症的两个关键特征。Numb是一种以其在发育中的关键作用而闻名的衔接蛋白，包括不对称细胞分裂，细胞类型规格，和细胞内信号的终止。在老年人和小鼠中Numb表达减少。我们之前表明，在小鼠骨骼肌纤维中，Numb位于肌节，集中在三联体附近；小鼠肌纤维中Numb和密切相关的Numb样蛋白（Numbl）的条件性失活引起虚弱，肉瘤的解体，和功能受损的较小线粒体。这里,我们发现，在肌纤维中单次敲除Numb会导致强直力降低，Numbl淘汰赛。我们通过使用抗Numb抗体的免疫沉淀从C2C12肌管分离的蛋白质复合物的蛋白质组学分析发现，Septin7是潜在的Numb结合伴侣。Septin7是组织成丝的GTP结合蛋白家族的成员，床单,和戒指，被认为是细胞骨架的一部分。免疫荧光评估显示肌纤维中Numb和Septin7的染色部分重叠。有条件的,可诱导的Numb敲除导致肌纤维中Septin7染色的混乱。这些发现表明Septin7是Numb结合伴侣，并表明Numb和Septin7之间的相互作用对于肌节的结构组织和肌肉收缩功能至关重要。
