Effects Of Arginine On The Skeletal Muscle Fiber Type Transformation And Its Mechanism

Muscle fiber type is one of the important factors affecting the quality of meat,and it was regulated by nutrition.It has been shown that arginine(Arg)improves pork quality,and it may be closely related to muscle fiber type transformation.Thereforore,in order to investigate the effect of Arg on the transformation of skeletal muscle fiber types and its underlying mechanism,the present study explored the effects and the possible molecular mechanism of Arg on muscle fiber type transformation in mice.On this basis,we investigated the effect of Arg on muscle fiber type transformation in C2C12 cells.Subsequently,exogenous addition of the specific AMPK or Sirt1 inhibitor and siRNA-mediated RNA interference technology will be used to investigate whether Arg affects themuscle fiber type transformation via the AMPK-and Sirt1-dependent signaling pathway.The main research contents and results are as follows: Test 1: Effect of arg on skeletal muscle fiber type transformation in miceThe aim of this study is to explore the effects and the underlying mechanism of dietary Arg supplementation on themuscle fiber type transformation in mice.Forty-eight(21-day-old)healthy male Kunming mice were randomly divided into 4 groups of 12 mice each,representing supplementation with 0%,0.25%,0.5%,or 1.0% arginine to the basal diet.The experiment lasted for 42 days.Four mice each treatment were sacrificed and tibialis anterior(TA)muscle and soleus(SOL)muscle were collected and used for real-time PCR,western blot and metabolic enzyme activity analysis.The results shown that dietary Arg supplementation significantly increased the protein expression of slow-MyHC,phosphorylated AMPK,phosphorylated LKB1,significantly inhibited fast-MyHC protein expression,and 0.5% treatment showed better effect.Compared to the control group,0.5% Arg supplementation significantly increased the mRNA levels of MyHC I,MyHC IIa,Tnnc1,Tnni1,Tnnt1,AMPK?2,Sirt1,PGC-1?,and MEF2 C and significantly decreased the mRNA level of the MyHC IIb.Meanwhile,the activities of succinate dehydrogenase(SDH)and malate dehydrogenase(MDH)in skeletal muscle were significantly increased,and the activity of lactate dehydrogenase(LDH)was significantly decreased.In addition,the activity of T-AOC?T-SOD and GSH-Px in skeletal muscles were significantly increased,and the content of MDA was significantly decreased.These results revealed that Arg induced a fast-to-slow fiber type transition,may be mediated via Sirt1-and AMPK-dependent signaling pathway.Test 2: Arg regulates the muscle fiber type transformation through Sirt1/AMPK signaling pathwayFirstly,we investigatedthe effect of Arg on muscle fiber type transformation in C2C12 cells.Subsequently,exogenous addition of the specific AMPK or Sirt1 inhibitor and siRNA-mediated RNA interference technology will be used to investigate whether Arg affects the muscle fiber type transformation via the Sirt1/AMPK signaling pathway.The results showed that 100 ?g/mL Arg significantly promoted the protein expression of slow-MyHC,while significantly reduced the protein expression of fast-MyHC.The protein expression of phosphorylated AMPK,Sirt1,PGC-1?,as well as the activity of NOS and NO,were significantly upregulated.However,inhibition of AMPK and Sirt1 activities markedly attenuated thes effects.And arginine activates AMPK in a Sirt1-dependent mechanism.In summary,our data confirm that Arg can promote the conversion of muscle fibers from fast to slow muscle fiber in both in vitro and in vivo experiments,which may be mediated by the upregualtion of the Sirt1/AMPK signaling pathway.