Several skeletal muscle diseases are characterized by fibrosis, the excessive accumulation of extracellular matrix. Transforming growth factor-β (TGF-β) and connective tissue growth factor (CCN2/CTGF) are two profibrotic factors augmented in fibrotic skeletal muscle, together with signs of reduced vasculature that implies a decrease in oxygen supply. We observed that fibrotic muscles are characterized by the presence of positive nuclei for hypoxia-inducible factor-1α (HIF-1α), a key mediator of the hypoxia response. However, it is not clear how a hypoxic environment could contribute to the fibrotic phenotype in skeletal muscle. We evaluated the role of hypoxia and TGF-β on CCN2 expression in vitro. Fibroblasts, myoblasts and differentiated myotubes were incubated with TGF-β1 under hypoxic conditions. Hypoxia and TGF-β1 induced CCN2 expression synergistically in myotubes but not in fibroblasts or undifferentiated muscle progenitors. This induction requires HIF-1α and the Smad-independent TGF-β signaling pathway. We performed in vivo experiments using pharmacological stabilization of HIF-1α or hypoxia-induced via hindlimb ischemia together with intramuscular injections of TGF-β1, and we found increased CCN2 expression. These observations suggest that hypoxic signaling together with TGF-β signaling, which are both characteristics of a fibrotic skeletal muscle environment, induce the expression of CCN2 in skeletal muscle fibers and myotubes.

中文翻译：

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缺氧在骨骼肌纤维化中的作用：缺氧和TGF-β信号之间的协同作用上调了CCN2 / CTGF在肌肉纤维中的表达。

几种骨骼肌疾病的特征是纤维化，细胞外基质的过度积累。转化生长因子-β（TGF-β）和结缔组织生长因子（CCN2 / CTGF）是纤维化骨骼肌中增加的两个纤维化因子，同时伴有血管减少的迹象，这意味着氧供应减少。我们观察到纤维化肌肉的特征是存在缺氧诱导因子-1α（HIF-1α）的正核，缺氧诱导因子-1α是缺氧反应的关键介体。但是，目前尚不清楚低氧环境如何促进骨骼肌的纤维化表型。我们评估了缺氧和TGF-β对体外CCN2表达的作用。在缺氧条件下，将成纤维细胞，成肌细胞和分化的肌管与TGF-β1孵育。缺氧和TGF-β1在肌管中协同诱导CCN2表达，但在成纤维细胞或未分化的肌肉祖细胞中不协同诱导CCN2表达。这种诱导需要HIF-1α和非Smad的TGF-β信号通路。我们进行了体内实验，使用了HIF-1α的药理稳定作用或通过后肢局部缺血引起的缺氧，以及肌肉注射TGF-β1，我们发现CCN2表达增加。这些观察结果表明，缺氧信号传导和TGF-β信号传导都是纤维化骨骼肌环境的特征，它们诱导了骨骼肌纤维和肌管中CCN2的表达。我们进行了体内实验，使用了HIF-1α的药理稳定作用或通过后肢局部缺血引起的缺氧，以及肌肉注射TGF-β1，我们发现CCN2表达增加。这些观察结果表明，缺氧信号传导和TGF-β信号传导都是纤维化骨骼肌环境的特征，它们诱导了骨骼肌纤维和肌管中CCN2的表达。我们进行了体内实验，使用了HIF-1α的药理稳定作用或通过后肢局部缺血引起的缺氧，以及肌肉注射TGF-β1，我们发现CCN2表达增加。这些观察结果表明，缺氧信号传导和TGF-β信号传导都是纤维化骨骼肌环境的特征，它们诱导了骨骼肌纤维和肌管中CCN2的表达。