Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, 6-155 Jackson Hall, 321 Church Street SE, Minneapolis, MN 55455, USA.
Skelet Muscle. 2011 Oct 13;1(1):32. doi: 10.1186/2044-5040-1-32.
γ-cytoplasmic (γ-cyto) actin levels are elevated in dystrophin-deficient mdx mouse skeletal muscle. The purpose of this study was to determine whether further elevation of γ-cyto actin levels improve or exacerbate the dystrophic phenotype of mdx mice.
We transgenically overexpressed γ-cyto actin, specifically in skeletal muscle of mdx mice (mdx-TG), and compared skeletal muscle pathology and force-generating capacity between mdx and mdx-TG mice at different ages. We investigated the mechanism by which γ-cyto actin provides protection from force loss by studying the role of calcium channels and stretch-activated channels in isolated skeletal muscles and muscle fibers. Analysis of variance or independent t-tests were used to detect statistical differences between groups.
Levels of γ-cyto actin in mdx-TG skeletal muscle were elevated 200-fold compared to mdx skeletal muscle and incorporated into thin filaments. Overexpression of γ-cyto actin had little effect on most parameters of mdx muscle pathology. However, γ-cyto actin provided statistically significant protection against force loss during eccentric contractions. Store-operated calcium entry across the sarcolemma did not differ between mdx fibers compared to wild-type fibers. Additionally, the omission of extracellular calcium or the addition of streptomycin to block stretch-activated channels did not improve the force-generating capacity of isolated extensor digitorum longus muscles from mdx mice during eccentric contractions.
The data presented in this study indicate that upregulation of γ-cyto actin in dystrophic skeletal muscle can attenuate force loss during eccentric contractions and that the mechanism is independent of activation of stretch-activated channels and the accumulation of extracellular calcium.
γ-细胞浆（γ-cyto）肌动蛋白水平在缺乏肌营养不良蛋白的 mdx 小鼠骨骼肌中升高。本研究的目的是确定γ-cyto 肌动蛋白水平的进一步升高是否改善或加剧 mdx 小鼠的肌营养不良表型。
我们在 mdx 小鼠的骨骼肌中转基因过表达 γ-cyto 肌动蛋白（mdx-TG），并在不同年龄比较 mdx 和 mdx-TG 小鼠的骨骼肌病理学和产生力的能力。我们通过研究钙通道和牵张激活通道在分离的骨骼肌和肌纤维中的作用，研究 γ-cyto 肌动蛋白提供防止力丧失的保护机制。方差分析或独立 t 检验用于检测组间的统计学差异。
与 mdx 骨骼肌相比，mdx-TG 骨骼肌中的 γ-cyto 肌动蛋白水平升高了 200 倍，并整合到细肌丝中。γ-cyto 肌动蛋白的过表达对大多数 mdx 肌肉病理学参数几乎没有影响。然而，γ-cyto 肌动蛋白对离心收缩时的力丧失提供了统计学上显著的保护作用。与野生型纤维相比，mdx 纤维的肌浆网钙库操纵性钙内流没有差异。此外，在离心收缩期间，省略细胞外钙或添加链霉素阻断牵张激活通道并没有改善分离的趾长伸肌的力产生能力。
本研究提供的数据表明，在肌营养不良的骨骼肌中上调 γ-cyto 肌动蛋白可以减轻离心收缩时的力丧失，其机制独立于牵张激活通道的激活和细胞外钙的积累。
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