基于CaN/NFAT信号通路研究胍基乙酸促进猪肌纤维类型转化的分子机制

The muscle fiber type is one of the main factors to affect the meat quality. In our previous research, we found that dietary guanidinoacetic acid supplementation could improve the meat quality, and regulate the transformation of muscle fiber type in finishing pigs. However, the relevant mechanism is still unclear. Several studies have found that mitochondrial function and CaN/NFAT signaling pathway have important regulatory effects on the skeletal muscle fiber type transformation. This project intends to investigate the effects of dietary guanidinoacetic acid supplementation on meat quality and energy reserves of skeletal muscle in finishing pigs, and explore the biological mechanism to promote the synthesis and function of mitochondria, and clarify the regulation of key genes and proteins in CaN/NFAT signaling pathway by RT-PCR and Western-Blot techniques. On this basis, the in vitro experiment is used to further explore the molecular mechanism of muscle fiber type transformation by guanidinoacetic acid supplementation through CaN/NFAT signaling pathway. The results are expected to clarify the effect and the regulatory mechanism of guanidinoacetic acid on muscle fiber type transformation in finishing pigs, which may provide important theoretical basis for improving pork quality through nutritional techniques.

肌纤维类型是影响肉品质的重要因素之一。申请人前期发现，日粮补充胍基乙酸可以改善猪肉品质，促进肌纤维类型的转化，但其中的相关机制尚不清楚。研究发现线粒体功能和CaN/NFAT信号通路对骨骼肌肌纤维类型转化有重要的调控作用。因此，本项目拟在前期工作基础上，以育肥猪为研究对象，研究胍基乙酸对育肥猪肉质和骨骼肌能量状态的影响，采用RT-PCR和Western-Blot等技术，探讨胍基乙酸促进线粒体的合成与功能改善的生物学机制，明确CaN/NFAT信号通路中关键基因及蛋白表达的规律；在此基础上，采用体外细胞模型，进一步探讨胍基乙酸通过CaN/NFAT信号通路调控肌纤维类型转化的分子机制。研究结果有望阐明胍基乙酸对肌纤维类型转化的影响及其调控机制，为通过营养调控技术改善猪肉品质提供重要理论依据。

肌纤维类型是影响肉品质的重要因素之一。研究表明，日粮补充胍基乙酸可以改善猪肉品质，促进肌纤维类型的转化，但其中的相关机制尚不清楚。本研究发现：日粮添加胍基乙酸一定程度上提高了育肥猪的平均日增重，降低其料重比，提高了育肥猪的生产性能，但胍基乙酸的添加对育肥猪的屠宰性能和肌肉中的营养成分均无显著影响；同时添加胍基乙酸显著降低了育肥猪背最长肌的滴水损失、蒸煮损失，显著提高了半腱肌pH45min；其中0.10 %胍基乙酸组半腱肌的蒸煮损失显著降低。日粮中添加胍基乙酸显著提高了宰后育肥猪背最长肌和半腱肌中糖原、肌酸、磷酸肌酸和ATP的含量，并通过降低HIF-1的转录水平和糖酵解过程中乳酸脱氢酶的活性，从而降低宰后肌肉中乳酸积累，延缓pH的下降，进而提高系水力。日粮中添加胍基乙酸提高了肌浆中Ca2+浓度，通过上调PPARGC1A的表达，进一步激活CaN/NFAT通路中关键因子CaM、CaN和NFATc1的基因和蛋白的表达，提高了CaN和Ca2+-ATPase的活性，同时通过提高线粒体MMP水平和呼吸链复合酶活性，以及TFAM的基因和蛋白的表达，改善线粒体功能和合成，促进育肥猪肌纤维类型由IIb型向I和IIa型转化。体外细胞试验结果表明，胍基乙酸可以通过激活CaN/NFAT通路，调控骨骼肌细胞的肌纤维转化。本研究结果初步阐明了胍基乙酸对肌纤维类型转化的影响及其调控机制，为通过营养调控技术改善猪肉品质提供重要理论依据。