| Objective:As the largest energy metabolizing tissue in the human body,the mass and function of skeletal muscle diminish significantly with age,therefore the prevention and treatment of aging-related skeletal muscle function and mass decline has received widespread attention,and the related mechanisms need to be urgently elucidated.Time-restricted feeding(TRF),which restricts the eating window to a certain time frame,is a dietary pattern with multiple protective effects in metabolic and cardiovascular aspects,but its protective effects on aging-related skeletal muscle are not yet clear.To this end,this study investigates the effects of TRF intervention on aging skeletal muscle and provides a preliminary investigation of its mechanisms.Methods:8-week-old male C57BL/6N mice were housed until 14 months of age and randomly divided into an all-day maintenance diet group,an 8 h TRF maintenance diet group,an all-day high-fat diet group,and an 8 h TRF high-fat diet group,of which the8-h TRF group was fed only during ZT15-ZT23(22:00-6:00)each day.The intervention period was from 14 months to 21 months of age,and skeletal muscle function was evaluated during the intervention period using grasping force,balance beam,spinning stick,and hanging test;frailty index to evaluate aging;Micro-CT live scan to estimate lean volume of mice;and metabolic cage monitoring to assess basal metabolism of mice.At the end of the intervention,mice were executed and weighed to calculate skeletal muscle wet weight and skeletal muscle index;HE staining to observe the cross-sectional area of skeletal muscle;immunofluorescence staining to observe the ratio of fast and slow gastrocnemius muscle in different groups of mice;Western blot to detect autophagy protein expression.Results:(1)Basal metabolic evaluation:The results of the study showed that from the 3rd month of the intervention,the body weight of the 8 h TRF maintenance diet group was significantly lower than that of the all-day maintenance diet group;the body weight of the 8 h TRF high-fat diet group was significantly lower than that of the all-day high-fat diet group(P<0.01).The body weight of the all-day high-fat diet group was significantly higher than that of the all-day maintenance diet group(P<0.01).The metabolic cage results showed that between the groups,there was no significant difference in caloric intake throughout the day.The 8 h TRF maintenance diet group was more active throughout the day compared to the all-day maintenance diet group;the 8 h TRF high-fat diet group was significantly more active than the all-day high-fat diet group(P<0.01).The results of frailty index showed that the frailty index of mice in the all-day high-fat diet group was higher compared with the all-day maintenance diet group(P<0.01);(2)Aging condition:The frailty index results showed that the frailty index of mice in the all-day high-fat diet group was higher compared with the all-day maintenance diet group(P<0.01).(3)Skeletal muscle function evaluation:Compared with the all-day maintenance diet group,the relative grip strength decreased by 0.27 N/g,the bar-turning dwell time decreased by 53.70 s,and the hanging time shortened by62.24 s in the all-day high-fat diet group(P<0.01),while the relative grip strength increased by 0.07 N/g,the bar-turning dwell time increased by 17.11 s,the hanging time prolonged by 36.73 s,and the balance beam score increased in the 8-h TRF maintenance diet group.36.73 s,and the balance beam score increased by 0.90 points(P<0.05);compared with the all-day high-fat diet group,the 8-h TRF high-fat diet group increased relative grip strength by 0.16 N/g,bar rotation dwell time by 17.98 s,and suspension length by 14.52 s(P<0.01).(4)Skeletal muscle quality evaluation:Micro-CT results showed that the lean volume ratio of the all-day high-fat diet group decreased significantly compared with the all-day maintenance diet group(P<0.01),and there was no change in the lean volume ratio of the 8-h TRF maintenance diet group(P>0.05);HE staining showed that the cross-sectional area of the gastrocnemius muscle increased by68.08μm~2(P<0.05)in the 8-h TRF high-fat diet group compared with the all-day high-fat diet group,and there was no significant change in the cross-sectional area of the gastrocnemius muscle in the all-day high-fat diet group compared with the all-day maintenance diet group,and the cross-sectional area of the gastrocnemius muscle increased by 56.85 um~2(P<0.01)in the 8-h TRF maintenance diet group;there was no significant change in the cross-sectional area of flounder muscle between the groups;the results of fast and slow muscle staining of gastrocnemius muscle showed that the percentage of slow muscle fibers was increased by 6.75%in the 8 h TRF maintenance diet group compared with the all-day maintenance diet group(P<0.05).(5)Detection of autophagy level:Western blot results showed that Beclin1 protein expression was significantly higher(P<0.01)and p62 protein expression was significantly lower(P<0.01)in the all-day high-fat diet group compared with the all-day maintenance diet group;Beclin1 protein expression was lower(P<0.05)in the 8 h TRF high-fat diet group compared with the all-day high-fat diet group,p62 and p-mTOR/mTOR protein expression was significantly higher(P<0.01).Conclusion:TRF intervention reduced body weight and increased activity in mice without reducing caloric intake;improved skeletal muscle function in aged mice,as evidenced by improved grip strength,balance,and coordination;increased muscle fiber cross-sectional area and maintained unchanged lean volume;high-fat diet may lead to excessive autophagy in mouse skeletal muscle,while TRF reduced high-fat-induced excessive autophagy,suggesting that maintaining autophagy homeostasis may be the mechanism by which TRF improves aging-related skeletal muscle function and quality. |
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