Effects And Mechanism Of Capsaicin On Different Muscle Fiber Types

Capsaicin is an active substance extracted from peppers.In recent years,many studies already show that capsaicincan activate multiple receptors such as transient receptor potential vanilloid 1(TRPV1)channel and cannabinoid receptors.And few studies indicate that capsaicin can promote myosin heavy chain I(MyHC I)fiber expression and oxidative metabolism,but its effect on signaling pathways have not been elucidated;the distribution of receptors on different muscles is not clear,whether capsaicin has different effects on different types of muscles has not been reported.Thus,the aim of this study is to investigate the effects of capsaicin on skeletal muscle fiber types in vitro and in vivoand explore its mechanism.Firstly,in vitro,C2C12 was treated with capsaicin at a concentration of 1,10 ?M for 2 d,3 d and 4 d to observe the effect of capsaicin on the muscle fiber type and related receptors.Western Blot was used to detect the expression of myosin heavy chain types,TRPV1 receptor,cannabinoid receptors and related intracellular signaling molecules.Immunocytochemistry was used to detect the expression of MyHC I type fiber.Calcium probe was used to detect the effect of capsaicin and corresponding receptor blockers on intracellular transient calcium concentration.The results showed that:(1)1,10 ?M capsaicin could promote the expression of MyHC I type fiber and thebest treatment time is 2 d.(2)10 ?M capsaicin could promote TRPV1 and CB2 receptors protein expression.(3)10 ?M capsaicin treatment for 2 d significantly promoted Calcineurin,MEF2 c protein expression and AMPK phosphorylation.(4)The blockers of TRPV1 and CB1 receptors couldn't completely reverse the effect that capsaicin promoted the rise of intracellular transient calcium.(5)2 ?MBAPTA-AM couldn't completely reverse the significant effect that capsaicin increased AMPK phosphorylation.Secondly,in vivo,we selected 56 Sprague-Dawley(SD)rats(21 days old)which have an average body weight of 65 ± 3g.42 SD rats were randomly assigned to three groups with thesame gender and similar average initial body weight,each group had 14 repeats(7 male,7 female).The first group was control group(given the normal diet),the second group was 0.01% capsaicin group(add 0.01% capsaicin to the diet),the third group was 0.02% capsaicin group(add 0.02% capsaicin to the diet).Rats were maintained in the institutional animal facility on a 12 h light/dark cycle with food and water ad libitum for 28 days after 3 days pre-experiment.The expression of capsaicin receptor in the gastrocnemius and soleus muscle of the remaining 14 21-day-old rats was detected by Western Blot.After the trial,Western Blot was used to detect the heavy chain types,TRPV1 receptor,cannabinoid receptors and related intracellular signaling molecules of gastrocnemius and soleus muscle.Enzyme staining was used to detect the muscle fiber type of gastrocnemius sections.qPCR was used to detect the expression level of four myosin heavy chain types.C holesterol(CHO)and triglyceride(TG)in the serum were meas ured using colorimetry.Hexokinase(HK),lactate dehydrogenase(LDH)and succinate dehydrogenase(SDH)activity in the gastrocnemius muscle were detected as well.The results showed that:(1)Capsaicin could activate TRPV1 and cannabinoid receptors,causing intracellular calcium concerntration increase,therby promoting the muscle fiber type transformed from fast type to slow type.(2)Capsaicin could reduce the weight of SD rats,promoting body fat oxidation and energy consumption,and increas ing the weight of the gastrocnemius muscle.(3)The expression of TRPV1 and CB2 receptors in the soleus muscle were significantly lower than that in gastrocnemius,but the expression of C B1 receptor has no different between the gastrocnemius and soleus muscle.Capsaicin could significantly promote the expression of CB1 and CB2 receptor s protein in the soleus muscle.(4)Capsaicin could activate the signaling pathways of TRPV1 and cannabinoid receptors in the gastrocnemius and soleus muscle,but the TRPV1 signaling pathway was more active in the soleus muscle.(5)The activation of PKA/AMPK pathway in the gastrocnemius and soleus muscle was similar.The activity of inflammation in the soleus muscle was more pronounced than in the gastrocnemius,but the phosphorylation of mTOR in the gastrocnemius muscle was higher than that in the soleus muscle.In summary,capsaicin could promote the expression of MyHC I,TRPV1 and CB2 receptors protein expression in C2C12.And capsaicin could affect the expression of intracellular calcium signaling molecules through different receptors.The expression of TRPV1 and C B2 receptors in the gastrocnemius and soleus muscle was different.Through these receptors,capsaicin could promote skeletal muscle weight while changing muscle fiber types from glycolytic fiber to oxidative fiber.The activation of TRPV1 and inflammation-related signaling pathway of capsaicin in the soleus muscle was higher than in the gastrocnemius.And the activation of mTOR pathway in the gastrocnemius muscle was higher than in the soleus muscle.