Regulation Of Skeletal-muscle Function By Geniposide

Skeletal muscle approximately accounts for 40%of body weight and plays a vital role in exercising,maintaining posture and regulating metabolic homeostasis.Geniposide is a natural product belonging to iridoid glycosides and has many bioactive effects.In this study,there are two parts to explore the effects of geniposide on regulating skeletal-muscle function,including the effect of geniposide on skeletal-muscle fibrosis and the effect of geniposide on glucose utilization in skeletal muscle.Geniposide has the effect on attenuating skeletal-muscle fibrosis.Firstly,there was an in vitro experiment.The expression of fibrotic makers was determined in mouse myoblast cells?C2C12 myotubes?treated with geniposide in concentration gradients?0,0.05,0.1,0.2,0.4,0.8mg/mL?and time gradients?0,1,2,4,8,12 h?.Geniposide could significantly inhibit the exprssion of fibrotic makers in vitro?the optimum concentration point was 0.4 mg/mL and the optimum time point was 12 h?.Secondly,there was an in vivo experiment.An acute contusion model of gastrocnemius?GAS?in mouse was builded and mice were treated with geniposide?25 mg/kg?by an intraperitoneal injection.Histological analysis?the staining of hematoxylin and eosin,sirius red and immunohistochemistry?of GAS in mice at the indicated time points?0,7,14,21 d?revealed that geniposide could attenuate the condition of fibrotic process in injured skeletal muscle.It was proved that geniposide was a natural compound containing the effect on attenuation of skeletal-muscle fibrosis in vitro and in vivo.Lastly,C2C12 myotubes were respectively stimulated with transforming growth factor-??TGF-??inducing fibrotic process and transfected with Smad4 inducing Smad4 overexpression to explore molecular mechanism in vitro.Results indicated that genipside?0.4 mg/mL?inhibited the TGF-?-induced fibrotic process and the anti-fibrotic effect of geniposide was altered by TGF-?and Smad4.Therefore,geniposide inhibited skeletal-muscle fibrosis through regulating TGF-?/Smad4signaling pathway.Geniposide promotes glucose utilization in skeletal muscle.The composition of myofiber in skeletal muscle and transcription factor forkhead box transcription factor O1?FoxO1?are related closely with skeletal-muscle glucose homeostasis.Firstly,the effect of geniposide on conversion of muscle-fibers specification in skeletal muscle was explored.C2C12 myotubes and mice were treated with geniposide.By observing the quantity of myofiber phenotype under immunofluorescence staining in C2C12 myotubes,analyzing the proportion of fast and slow myofibers under tissue section strain?the staining of hematoxylin and eosin,succinate dehydrogenase and ATPase?in skeletal muscle and determining genes expression related myofibers at mRNA level in myocytes,results showed that geniposide promoted the shift from slow to fast fiber type of muscle phenotype in virto and in vivo.Additionally,at mRNA and protein levels,geniposide decreased the expression of FoxO1,pyruvate dehydrogenase kinase4?PDK4?and phosphorylated pyruvate dehydrogenase?P-PDH?in vitro and in vivo.To further investigate the effect of geniposide on glucose metabolism in skeletal muscle,a series of indexes related with glucose utilization(PDH activity,the content of pyruvate and acetyl coenzyme A,glycolysis capacity,¹⁴C glucose oxidation,respiratory exchange ratio,glucose tolerance test)were determined and results illustrated that geniposide promoted glucose utilization in vitro and in vivo.Lastly,C2C12 myotubes were transfected with FoxO1 to explore molecular mechanism in vitro.Results indicated that the above effect of geniposide was altered by FoxO1 and geniposide played a role in promoting a slow-to-fast fiber-type switch and glucose utilization in skeletal muscle through regulating FoxO1.In summary,geniposide can attenuate fibrosis and promote glucose utilization in skeletal muscle.