Calpain-mediated proteolysis of tropomodulin isoforms leads to thin filament elongation in dystrophic skeletal muscle.
Calpain-mediated proteolysis of tropomodulin isoforms leads to thin filament elongation in dystrophic skeletal muscle.
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DOI：
10.1091/mbc.e13-10-0608
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发表时间：
2014-03
影响因子：
3.3
通讯作者：
Fowler VM
中科院分区：
文献类型：
--
作者：
Gokhin DS;Tierney MT;Sui Z;Sacco A;Fowler VM
在两种不同的Duchenne肌营养不良小鼠模型中，钙蛋白酶介导的细丝尖端封端蛋白原调节蛋白的蛋白分解导致肌动蛋白亚单位与尖端的结合，并增加了细丝长度。这一机制以一种依赖于使用和疾病严重程度的方式影响不同的骨骼肌。Duchenne肌营养不良症(DMD)可导致肌膜机械不稳定和断裂，细胞内钙蛋白酶过度活跃，以及肌肉结构蛋白的蛋白分解。在这里，我们确定了两个肌节原调节蛋白(Tmod)亚型，Tmod1和Tmod4，作为m-Calain的新的蛋白水解靶，Tmod1对Calain介导的切割的敏感性是∼原位切割的10倍。在mdx小鼠中，营养不良比目鱼肌中m-calain水平的增加与细丝尖端Tmod1的丢失有关，导致∼细丝长度增加11%。在mdx/mtr小鼠中，在更严重的DMD模型中，Tmod1在胫前肌和比目鱼肌的细丝尖端消失，而Tmod4另外从比目鱼肌消失，导致∼10和∼在TA和比目鱼肌的细丝长度分别增加12%。在mdx和mdx/mtr小鼠中，TA和比目鱼肌都显示了α-肌动蛋白、星云蛋白M1M2M3结构域、Tmod3和胞浆γ-肌动蛋白的正常定位，表明m-Calain不会导致营养不良骨骼肌中其他肌节和肌动蛋白细胞骨架蛋白的大规模蛋白分解。这些结果表明，Tmod蛋白分解和由此产生的细丝长度错误是可能导致DMD病理的新机制，以一种依赖于使用和疾病严重程度的方式影响肌肉。
Calpain-mediated proteolysis of the thin filament pointed-end–capping protein tropomodulin results in actin subunit association onto pointed ends and increased thin filament lengths in two different murine models of Duchenne muscular dystrophy. This mechanism affects different skeletal muscles in a use- and disease severity–dependent manner. Duchenne muscular dystrophy (DMD) induces sarcolemmal mechanical instability and rupture, hyperactivity of intracellular calpains, and proteolytic breakdown of muscle structural proteins. Here we identify the two sarcomeric tropomodulin (Tmod) isoforms, Tmod1 and Tmod4, as novel proteolytic targets of m-calpain, with Tmod1 exhibiting ∼10-fold greater sensitivity to calpain-mediated cleavage than Tmod4 in situ. In mdx mice, increased m-calpain levels in dystrophic soleus muscle are associated with loss of Tmod1 from the thin filament pointed ends, resulting in ∼11% increase in thin filament lengths. In mdx/mTR mice, a more severe model of DMD, Tmod1 disappears from the thin filament pointed ends in both tibialis anterior (TA) and soleus muscles, whereas Tmod4 additionally disappears from soleus muscle, resulting in thin filament length increases of ∼10 and ∼12% in TA and soleus muscles, respectively. In both mdx and mdx/mTR mice, both TA and soleus muscles exhibit normal localization of α-actinin, the nebulin M1M2M3 domain, Tmod3, and cytoplasmic γ-actin, indicating that m-calpain does not cause wholesale proteolysis of other sarcomeric and actin cytoskeletal proteins in dystrophic skeletal muscle. These results implicate Tmod proteolysis and resultant thin filament length misspecification as novel mechanisms that may contribute to DMD pathology, affecting muscles in a use- and disease severity–dependent manner.