维生素A对肉牛脂肪沉积及其调控的研究进展

维生素A是肉牛维持正常生理功能、生化代谢及生长发育所必需的一类脂溶性维生素,机体自身不能合成,必须由饲粮供给。饲粮中维生素A不仅影响肉牛视觉和骨骼发育,也对肉牛脂肪沉积和肌肉大理石花纹形成等发挥着重要调控作用。在生产中,肉牛处在不同生理阶段对维生素A的需要量也不同,胎牛和犊牛阶段补充维生素A可增强肌内脂肪细胞发育和脂肪细胞增生,促进肌内脂肪沉积;育肥期限饲维生素A可提高肉牛的肌内脂肪沉积和大理石花纹等级。大理石花纹与牛肉的嫩度和风味密切相关,是衡量牛肉品质的重要指标。维生素A在肉牛体内通过其活性代谢产物视黄醇、视黄醛和视黄酸促进脂肪的形成,并在成脂定型、成脂分化和脂质蓄积的每个阶段都发挥重要作用。脂肪沉积过程受转录因子过氧化物酶体增殖物激活受体（peroxisome proliferator-activated receptors,PPARs）、CCAAT增强子结合蛋白（CCAAT-enhancer binding proteins,C/EBPs）和Janus激酶-信号转导及转录激活因子（JAK-STAT）信号转导通路等调控。表观遗传修饰的DNA甲基化和去甲基化也可通过调控脂肪形成过程中相关基因的表达参与脂肪细胞的分化和脂肪组织的生长发育,从而影响肉牛的脂肪沉积。作者主要介绍了脂肪组织不同阶段的形成过程和维生素A的生物学功能;重点阐述了肉牛在不同生理阶段补充和限饲维生素A,通过转录因子的表达、表观遗传修饰等途径来影响成脂相关信号通路调控脂肪沉积的机理,以期为促进维生素A改善肉牛品质和高档牛肉生产提供参考。

Research Progress of Vitamin A on Fat Deposition and Its Regulation in Beef Cattle

Vitamin A is a kind of fat-soluble vitamin, it's necessary for maintaining normal physiological function, biochemical metabolism and growth and development of beef cattle, it cannot be synthesized by the body and must be supplied by diet. Vitamin A not only affects the visual and skeletal development of beef cattle, but also plays an important role in the regulation of fat deposition and muscle marbling formation in beef cattle. The requirement of vitamin A is different at different physiological stages of beef cattle in production, vitamin A supplementation at the fetal and calf stages can enhance intramuscular adipocyte development and adipocyte proliferation and promote intramuscular fat deposition, and vitamin A restriction during the fattening period can improve intramuscular fat deposition and marbling grade in beef cattle. Marbling is closely related to the tenderness and flavor of beef, and is an important indicator to measure the quality of beef. Vitamin A promotes fat formation through retinol, retinaldehyde and retinoic acid in beef cattle, and can play important roles in each stage of adipogenesis, adipogenic differentiation and accumulation. The process of fat deposition is regulated by the transcription factors peroxisome proliferator-activated receptors (PPARs), CCAAT-erbinding protein (C/EBPs) and Janus kinase-signal transduction and activation of transcription (JAK-STAT) signal transduction pathways. Epigenetically modified DNA methylation and demethylation can also be involved in adipocyte differentiation and adipose tissue growth and development by regulating the expression of related genes during adipogenesis, thus affecting fat deposition in beef cattle. This review focused on the definition of vitamin A, its biological function and the process of adipose tissue formation, and emphatically expounded the mechanism of vitamin A supplementation and feeding restriction in beef cattle at different physiological stages, which affected the regulation of fat deposition by adipogenesis-related signaling pathways through the expression levels of transcription factors and epigenetic modifications, in order to promote vitamin A to improve beef cattle quality and high-grade beef production and provide a reference.