Effect Of Lauric Acid On Skeletal Muscle Fiber Type And Metabolism And Its Mechanism

Skeletal muscle is an important site for metabolism of nutrients in animals.Skeletal muscle fiber type is closely related to the quality of animal meat products.Fatty acids can serve both as energy substrate and regulater of physiological and metabolic processes.In this study,we investigated the effect of lauric acid on skeleatl muscle fiber type,metabolism and its posssible machanism.We used C57 mice and C2C12 cell line as research model.Lauric acid were fed with diet or added in cell cultural medium,and the expression of myosin heavy chain in skeletal muscle and C2C12 cells were detected,the proportion of different fiber types in gastrocnemius muscle was analyzed by histochemical staining.Then colorimetric assay,Western Blot and qPCR were used to detect the variations of glucose and fatty acid metabolism-related proteins,genes and enzymes in skeletal muscle and C2C12 cells.Finally we used Cas9 gene knockout technology and siRNA interference method to investigate the involvement of GPR84 and TLR4 within the effect of lauric acid on skeletal muscle fiber type.The main results were as follows:(1)Lauric acid significantly increased MHCIIb expression in skeletal muscle and C2C12 cells,increasing the proportion of glycolytic fibers in gastrocnemius muscle and the diameter of C2C12 myotubes;(2)Lauric acid significantly increased the mRNA expression of key genes involved in glycolysis,such as LDH2 and HK2,in skeletal muscle and C2C12 cells.And lauric acid supplementation significantly decreased the catalytic activity of LDH in skeletal muscle.(3)Lauric acid significantly decreased the intracellular TG content and the mRNA expression of lipid synthesis-related genes of C2C12 cells.(4)Lauric acid had no significant effect on GPR84 expression and its downstream PI3K/AKT pathway in skeletal muscle and C2C12 cells;After GPR84 knockdown,the effect of lauric acid on muscle LDH activity and muscle fiber type were not reversed.(5)Lauric acid can activate the TLR4/MyD88/IKK pathway in skeletal muscle and C2C12 cells.After interfering the activity of this pathway,the regulatory effects of lauric acid on mRNA expression of genes involved in glycolysis,lipid synthesis and muscle fiber type were reversed.In summary,lauric acid activates the TLR4/MyD88/IKK pathway,which regulating mRNA expression of key genes involved in glycolysis and lipid synthesis,ultimately leading to an increase in glycolytic fibers.