National Key Laboratory of Agrobiotechnology, China Agricultural University, Beijing 100193, China.
Dev Growth Differ. 2010 Oct;52(8):725-33. doi: 10.1111/j.1440-169X.2010.01209.x.
Skeletal myoblasts withdrawing from cell cycle is a prerequisite for myodifferentiation, while upon proliferation/differentiation transformation, a large portion of myoblasts will undergo apoptosis. Skeletal fibroblasts, residing in muscle tissue both during and post myogenesis, have been proofed to play pivotal roles in muscle development, while their effect on myoblast apoptosis being coincident with differentiation has not been reported. Using a membrane insert co-culture system, we studied it and found that the mitochondrial pathway played a crucial role in myoblast apoptosis during differentiation, and fibroblasts promoted not only cell cycle withdrawal but also myoblast survival in a paracrine fashion, which was coupled with upregulations of β1 integrin, phosphorylated Akt and anti-apoptotic protein Bcl2. To determine the effect of β1 integrin in the process, we transfected myoblasts with siRNA specific for β1 integrin before co-culture and found that β1 integrin knockdown abolished anti-apoptotic ability of myoblasts and inhibited Akt activation and Bcl2 expression. Blockage of PI3K/Akt pathway with wortmannin also seriously impaired the protective effect of fibroblasts on myoblasts and fibroblast-induced Bcl2 expression. The data demonstrated that fibroblasts protected myoblasts from intrinsic apoptosis associated with differentiation, and β1 integrin-PI3K/Akt pathway activation was required for the process.
成肌细胞退出细胞周期是肌分化的前提条件，而在增殖/分化转化过程中，大部分成肌细胞将经历凋亡。骨骼肌成纤维细胞在肌发生过程中和之后都存在于肌肉组织中，已经证明它们在肌肉发育中起着关键作用，而它们对成肌细胞凋亡的影响与分化同时发生的情况尚未报道。使用膜插入共培养系统，我们对此进行了研究，发现线粒体途径在分化过程中成肌细胞凋亡中起关键作用，成纤维细胞不仅以旁分泌方式促进细胞周期退出，而且还促进成肌细胞存活，这与β1 整合素、磷酸化 Akt 和抗凋亡蛋白 Bcl2 的上调有关。为了确定β1 整合素在该过程中的作用，我们在共培养前用针对β1 整合素的 siRNA 转染成肌细胞，发现β1 整合素敲低消除了成肌细胞的抗凋亡能力，并抑制了 Akt 激活和 Bcl2 表达。用 wortmannin 阻断 PI3K/Akt 通路也严重损害了成纤维细胞对成肌细胞的保护作用和成纤维细胞诱导的 Bcl2 表达。该数据表明，成纤维细胞保护成肌细胞免于与分化相关的内在凋亡，并且β1 整合素-PI3K/Akt 通路的激活是该过程所必需的。
