Japanese Center for Research on Women in Sport, Juntendo University Graduate School of Health and Sports Science, Chiba 270-1695, Japan.
Research Institute for Diseases of Old Age, Juntendo University Graduate School of Medicine, Tokyo 113-8421, Japan.
Cells. 2020 Nov 23;9(11):2524. doi: 10.3390/cells9112524.
Perlecan is an extracellular matrix molecule anchored to the sarcolemma by a dystrophin-glycoprotein complex. Perlecan-deficient mice are tolerant to muscle atrophy, suggesting that perlecan negatively regulates mechanical stress-dependent skeletal muscle mass. Delocalization of neuronal nitric oxide synthase (nNOS) from the sarcolemma to the cytosol triggers protein degradation, thereby initiating skeletal muscle atrophy. We hypothesized that perlecan regulates nNOS delocalization and activates protein degradation during this process. To determine the role of perlecan in nNOS-mediated mechanotransduction, we used sciatic nerve transection as a denervation model of gastrocnemius muscles. Gastrocnemius muscle atrophy was significantly lower in perinatal lethality-rescued perlecan-knockout (-Tg) mice than controls (WT-Tg) on days 4 and 14 following surgery. Immunofluorescence microscopy showed that cell membrane nNOS expression was reduced by denervation in WT-Tg mice, with marginal effects in -Tg mice. Moreover, levels of atrophy-related proteins-i.e., FoxO1a, FoxO3a, atrogin-1, and Lys48-polyubiquitinated proteins-increased in the denervated muscles of WT-Tg mice but not in -Tg mice. These findings suggest that during denervation, perlecan promotes nNOS delocalization from the membrane and stimulates protein degradation and muscle atrophy by activating FoxO signaling and the ubiquitin-proteasome system.
纤维连接蛋白是一种细胞外基质分子，通过 dystrophin-glycoprotein 复合物锚定在肌膜上。纤维连接蛋白缺失的小鼠对肌肉萎缩具有耐受性，这表明纤维连接蛋白负调控机械应激依赖性骨骼肌质量。神经元型一氧化氮合酶（nNOS）从肌膜向细胞质的易位会触发蛋白质降解，从而引发骨骼肌萎缩。我们假设纤维连接蛋白在这个过程中调节 nNOS 的易位并激活蛋白质降解。为了确定纤维连接蛋白在 nNOS 介导的机械转导中的作用，我们使用坐骨神经横断作为比目鱼肌去神经模型。与对照组（WT-Tg）相比，围产期致死性拯救纤维连接蛋白敲除（-Tg）小鼠在手术后第 4 天和第 14 天，腓肠肌萎缩明显较低。免疫荧光显微镜显示，WT-Tg 小鼠的细胞膜 nNOS 表达在去神经后减少，-Tg 小鼠的影响较小。此外，在 WT-Tg 去神经肌肉中，与萎缩相关的蛋白质（即 FoxO1a、FoxO3a、atrogin-1 和 Lys48-多聚泛素化蛋白）的水平增加，但 -Tg 小鼠中则没有增加。这些发现表明，在去神经过程中，纤维连接蛋白通过激活 FoxO 信号通路和泛素-蛋白酶体系统促进 nNOS 从膜易位，并刺激蛋白质降解和肌肉萎缩。
