miR-208b/499通过甲状腺素信号通路抑制猪骨骼肌能量代谢提高饲料效率的作用机理研究

Skeletal muscle is the biggest tissue in pig, which consumes about 60% energy. It is an important approach to improve the feed efficiency by decreasing the energy consuming of the skeletal muscle tissue. Our study found that miR-208b and miR-499 were up-regulated in the skeletal muscle tissue of pigs that have better feed efficiency. However, almost all the mitochondrial genes were down-regulated in these pigs. In addition, GWAS results showed that miR-208b was associated with the feed efficiency trait. It has been reported that the energy metabolism was increased and the feed efficiency was decreased when miR-208a was inhibited in heart tissue in mice. Previous studies confirm that the mitochondrial genes can be regulated by the thyroid hormone signaling pathway. Our studied indicated that the activation of the thyroid hormone signaling pathway was negatively regulated by miR-208b and miR-499. According to these studies, we deduced that in the skeletal muscle of pig, miR-208b and miR-499 could negatively regulate the thyroid hormone signaling pathway, which leads to energy metabolism of mitochondrial deceasing. The energy metabolism of the skeletal muscle was decreased and the feed efficiency was increased accordingly. In this project, the transcriptional regulation of miR-208b and miR-499 will be investigated. The target genes of miR-208b and miR-499 will be identified. The molecular mechanism of miR-208b and miR-499 in the regulation of thyroid hormone signaling pathway and in the energy metabolism of mitochondrial will be studied. Moreover, the function of miR-208b and miR-499 on the energy metabolism and feed efficiency will be studied in the pig. Our study will reveal the molecular mechanism of miR-208b and miR-499 on the regulation of energy metabolism in the skeletal muscle tissue of pig. It will offered useful information for improvement of the feed efficiency trait in pig.

骨骼肌是猪最大的组织，约消耗机体60%的能量，降低骨骼肌能量代谢是提高猪饲料效率(FE)的重要途径。我们发现在FE高的猪骨骼肌中miR-208b/499上调，而绝大多数线粒体基因下调。GWAS分析发现 miR-208b与猪FE关联。小鼠中，抑制心脏miR-208a可增加能量代谢，降低FE。线粒体基因受甲状腺素信号调控，我们发现miR-208b/499能抑制甲状腺素信号通路。因此，我们假设miR-208b/499是通过抑制甲状腺素信号通路降低线粒体能量代谢，从而降低骨骼肌能量代谢，提高猪FE。本项目拟在猪骨骼肌细胞中研究miR-208b/499表达调控规律；鉴定其靶基因；揭示其调控甲状腺素信号通路及线粒体能量代谢的分子机理；在个体水平上研究miR-208b/499对猪能量代谢及FE的作用。研究结果将阐明miR-208b/499调控猪骨骼肌能量代谢的分子机理，为猪FE性状改良提供重要理论依据。

饲料成本占养猪总成本的60%以上，提高饲料效率降低饲料成本是提高养猪经济效益的重要手段。已有的研究表明饲料效率与机体生长、代谢等因素密切相关，但是目前猪饲料效率的分子调控机理仍不甚清楚，已报道的猪饲料效率主效基因及信号通路还很少，miR-208b/499是申请人鉴定的与猪饲料效率密切相关的两个miRNA，研究这两个miRNA有利于解析猪饲料效率的分子调控机理，同时也可为猪饲料效率改良提供新的靶点和标记。.本研究取得了以下研究结果:.第一，.发现miR-208b/499通过靶向TCF12基因，抑制成肌分化、促进成肌细胞增殖。.第二，.发现miR-208b/499通过靶向FNIP1基因，激活PGC1a/AMPK信号通路，上调线粒体基因表达及能量代谢。.第三，.发现饲料效率好的猪骨骼肌组织糖进入线粒体的速度较快，但是氧化磷酸化速度较慢，整个骨骼肌组织能量代谢减慢。推测饲料效率好的猪糖转化成能量时效率更高，能量损失更少。.第四，.发现饲料效率好的猪肝脏组织维生素A的合成及分解代谢增强。维生素A代谢通路增强有利于激活合成通路，同时也有可以影响机体能量代谢通路。.科学意义：. 我们的研究结果表明适当抑制骨骼肌能量代谢有利于提高猪饲料效率。这些研究结果为解析了猪饲料效率的分子调控机理提供了重要理论基础；也为猪饲料效率改良提供了新的候选基因及分子靶点，未来可以针对这些基因进行分子标记开发及标记辅助选育；也可以针对这些靶基因、信号通路开发相应的饲料添加剂，调控猪饲料效率。