Effects And Mechanism Of Sesamol On Skeletal Muscle Fiber-Type Conversion In Obese States

Objective: The present research aimed to explore the effects and potential mechanism of sesamol on skeletal muscle fiber-type conversion in obese states,and find the specific action pathway of sesamol in preventing and treating obesity,which will provide scientific data of sesamol for the treatment of obesity.Methods: C57BL/6J male mice aged 8 weeks were randomly divided into three groups(n=8 per group): normal diet group,high-fat diet group and sesamol intervention group.The experiment was maintained for 16 weeks.Five days before the sacrifice,the exhaustive swimming experiment was performed.C2C12 myotubes were divided into five groups: control group,high-fat environment control group(PA:0.25 mmol/L),and low/medium/high concentration sesamol group(PA+SEM;PA: 0.25 mmol/L;SEM: 12.5/25/50 μmol/L).Moreover,sesamol intervention after pretreatment with SIRT1 specific inhibitor group(PA+SEM+EX-527;PA: 0.25 mmol/L;SEM: 50 μmol/L;EX-527:25 μmol/L)was set up.Glucose uptake and consumption experiments were used to measure the insulin sensitivity of C2C12 myotubes;Biochemical methods were used to detect lipid profile and metabolic enzyme activities in skeletal muscle and C2C12 myotubes;Oil red O staining were used to observe lipid accumulation in skeletal muscle and C2C12 myotubes;ATPase staining was used to observe skeletal muscle fiber composition;Mito-Tracker Green staining was used to observe the mitochondrial content of C2C12 myotubes;Western blot was used to detect mitochondrial content markers: COX2,COX5 A,mitochondrial biogenesis markers: PGC-1α,TFAM,NRF1,and muscle fiber-type markers: My HC I,My HC Ⅱa/b,My HC Ⅱx;Immunofluorescence was used to observe the expressions of My HC I and My HC Ⅱa/b in C2C12 myotubes.Results:(1)Sesamol increased the exhaustive swimming time(P<0.05);(2)Sesamol elevated insulin-stimulated glucose uptake and glucose consumption in C2C12 myotubes(P<0.05).In addition,sesamol decreased TG and TC contents in skeletal muscle and C2C12 myotubes(P<0.05),and reduced lipid droplet accumulation in skeletal muscle and C2C12 myotubes;(3)Sesamol up-regulated the expressions of mitochondrial content markers: COX2,COX5 A,and mitochondrial biogenesis markers: PGC-1α,TFAM,NRF1 in skeletal muscle and C2C12 myotubes(P<0.05),and increased the mitochondrial content of C2C12 myotubes;(4)Sesamol elevated SDH activity and reduced LDH activity in skeletal muscle and C2C12 myotubes(P<0.05),and increased type I fiber content in skeletal muscle.Meanwhile,sesamol up-regulated the level of type I muscle fiber markers: My HC I,and down-regulated the expressions of type Ⅱ muscle fiber markers: My HC Ⅱa/b and My HC Ⅱx in C2C12 myotubes(P<0.05).Moreover,sesamol elevated SIRT1 level and the phosphorylation of AMPK in skeletal muscle and C2C12myotubes(P<0.05);(5)After pretreatment with the SIRT1 inhibitor,EX-527,sesamol failed to up-regulate the expression of SIRT1 and phosphorylation of AMPK(P<0.05).Of note,sesamol failed to increase insulin-stimulated glucose uptake,and reduce lipid droplets and the contents of TG and TC in C2C12 myotubes when SIRT1 was inhibited by EX-527(P<0.05).Meanwhile,the sesamol-induced increases of mitochondrial content,the expressions of mitochondrial content markers and mitochondrial biogenesis markers were blocked by EX-527(P<0.05).Additionally,the levels of My HC proteins were reversed with EX527(P<0.05).Conclusions:(1)Sesamol can reverse muscle fiber-type conversion in obese states and ameliorate obesity-related muscular glucose and lipid metabolism disorders;(2)The mechanism of sesamol in reversing myofiber-type conversion in obese situation is to activate the SIRT1/AMPK pathway,thereby promoting mitochondrial biogenesis and up-regulating type I fiber marker expression,down-regulating type Ⅱmuscle fiber markers expression.