Abstract：
Vitamin A is an essential nutrient in animals, playing important roles in animal health. In the pig industry, proper supplementation of vitamin A in the feed can improve pork production performance, while deficiency or excessive intake can lead to growth retardation or disease. However, the specific molecular mechanisms through which vitamin A operates on pig skeletal muscle growth as well as muscle stem cell function remain unexplored. Therefore, in this study, we isolated the pig primary skeletal muscle stem cells (pMuSCs) and treated with retinoic acid (RA), the natural metabolite of vitamin A, and then examined the myogenic capacity of pMuSCs via immunostaining, real-time PCR, CCK8 and western-blot analysis. Unexpectedly, the RA caused a significant decrease in the proliferation and differentiation of pMuSCs. Mechanistically, the RA addition induced the activation of retinoic acid receptor gamma (RARγ), which inhibited the myogenesis through the blockage of protein translation of the master myogenic regulator myogenic differentiation 1 gene (MYOD). Specifically, RARγ inactivate AKT kinase (AKT) signalling and lead to dephosphorylation of eukaryotic translation initiation factor 4E binding protein 1 (eIF4EBP1), which in turn repress the eukaryotic translation initiation factor 4E (eIF4E) complex and block mRNA translation of MYOD. Inhibition of AKT could rescue the myogenic defects of RA-treated pMuSCs. Our findings revealed that retinoid acid signalling inhibits the skeletal muscle stem cell proliferation and differentiation in pigs. Therefore, the vitamin A supplement in the feedstuff should be cautiously optimized to avoid the potential adverse consequences on muscle development associated with the excessive levels of retinoic acid.
摘要：
维生素A是动物的必需营养素,在动物健康中发挥着重要作用。在养猪业,饲料中适当补充维生素A可以提高猪肉生产性能,而摄入不足或过量会导致生长迟缓或疾病。然而,维生素A对猪骨骼肌生长以及肌肉干细胞功能起作用的具体分子机制仍未被探索。因此,在这项研究中，我们分离了猪原代骨骼肌干细胞（pMuSCs）并用维甲酸（RA）处理，维生素A的天然代谢产物,然后通过免疫染色检查pMuSCs的成肌能力，实时PCR，CCK8和蛋白质印迹分析。出乎意料的是,RA导致pMuSCs的增殖和分化显著降低。机械上,RA的添加诱导了视黄酸受体γ（RARγ）的激活，通过阻断主要的生肌调节因子肌分化1基因（MYOD）的蛋白质翻译来抑制肌生成。具体来说,RARγ使AKT激酶（AKT）信号失活，并导致真核翻译起始因子4E结合蛋白1（eIF4EBP1）的去磷酸化，进而抑制真核翻译起始因子4E（eIF4E）复合物并阻断MYOD的mRNA翻译。抑制AKT可以挽救RA处理的pMuSC的肌源性缺陷。我们的发现表明，类维生素A酸信号抑制猪骨骼肌干细胞的增殖和分化。因此,应谨慎优化饲料中的维生素A补充剂，以避免视黄酸水平过高对肌肉发育的潜在不利后果。
