Laboratoire de Génomique Fonctionnelle et Myogenèse, UMR866 Laboratoire Dynamique Musculaire et Métabolisme, INRA, 2 place Viala, Montpellier Cedex, France.
Am J Physiol Cell Physiol. 2011 May;300(5):C1122-38. doi: 10.1152/ajpcell.00214.2010. Epub 2011 Jan 19.
Expression of Wnt proteins is known to be important for developmental processes such as embryonic pattern formation and determination of cell fate. Previous studies have shown that Wn4 was involved in the myogenic fate of somites, in the myogenic proliferation, and differentiation of skeletal muscle. However, the function of this factor in adult muscle homeostasis remains not well understood. Here, we focus on the roles of Wnt4 during C2C12 myoblasts and satellite cells differentiation. We analyzed its myogenic activity, its mechanism of action, and its interaction with the anti-myogenic factor myostatin during differentiation. Established expression profiles indicate clearly that both types of cells express a few Wnts, and among these, only Wnt4 was not or barely detected during proliferation and was strongly induced during differentiation. As attested by myogenic factors expression pattern analysis and fusion index determination, overexpression of Wnt4 protein caused a strong increase in satellite cells and C2C12 myoblast differentiation leading to hypertrophic myotubes. By contrast, exposure of satellite and C2C12 cells to small interfering RNA against Wnt4 strongly diminished this process, confirming the myogenic activity of Wnt4. Moreover, we reported that Wnt4, which is usually described as a noncanonical Wnt, activates the canonical β-catenin pathway during myogenic differentiation in both cell types and that this factor regulates negatively the expression of myostatin and the regulating pathways associated with myostatin. Interestingly, we found that recombinant myostatin was sufficient to antagonize the differentiation-promoting activities of Wnt4. Reciprocally, we also found that the genetic deletion of myostatin renders the satellite cells refractory to the hypertrophic effect of Wnt4. These results suggest that the Wnt4-induced decrease of myostatin plays a functional role during hypertrophy. We propose that Wnt4 protein may be a key factor that regulates the extent of differentiation in satellite and C2C12 cells.
Wnt 蛋白的表达对于胚胎形态发生和细胞命运决定等发育过程非常重要。先前的研究表明，Wn4 参与了体节的肌生成命运、骨骼肌的肌生成增殖和分化。然而，这个因子在成年肌肉稳态中的功能仍不清楚。在这里，我们专注于 Wnt4 在 C2C12 成肌细胞和卫星细胞分化中的作用。我们分析了它的肌生成活性、作用机制以及在分化过程中与抗肌生成因子肌肉生长抑制素的相互作用。已建立的表达谱清楚地表明，这两种类型的细胞都表达了一些 Wnts，而在这些 Wnts 中，只有 Wnt4 在增殖过程中不表达或几乎检测不到，而在分化过程中强烈诱导。正如肌生成因子表达模式分析和融合指数测定所证明的那样，Wnt4 蛋白的过表达导致卫星细胞和 C2C12 成肌细胞分化的强烈增加，导致肥大的肌管。相比之下，用针对 Wnt4 的小干扰 RNA 暴露卫星和 C2C12 细胞强烈削弱了这个过程，证实了 Wnt4 的肌生成活性。此外，我们报道了 Wnt4，通常被描述为非经典 Wnt，在两种细胞类型的肌生成分化过程中激活经典的 β-连环蛋白途径，并且该因子负调控肌肉生长抑制素的表达和与肌肉生长抑制素相关的调节途径。有趣的是，我们发现重组肌肉生长抑制素足以拮抗 Wnt4 促进分化的活性。相反，我们还发现肌肉生长抑制素的基因缺失使卫星细胞对 Wnt4 的肥大效应产生抗性。这些结果表明，Wnt4 诱导的肌肉生长抑制素减少在肥大过程中发挥功能作用。我们提出 Wnt4 蛋白可能是调节卫星细胞和 C2C12 细胞分化程度的关键因素。
