Study On The Role Of Nucleo-mitochondrial Imbalance In Aging Skeletal Muscle Sarcopenia Based On PGC1α Pathway

Objective:Mitochondrial dysfunction in skeletal muscle is considered to be one of the causes of sarcopenia.Nuclear and mitochondrial genomes closely coordinate mitochondrial functions,and the molecular mechanisms of the two genomes mediating aging are still controversial.Therefore,it is necessary to study the relationship between mitochondrial dysfunction and mitochondrial dysfunction in sarcopenia.To provide underlying data and key information for the development of possible interventions that may offset or delay age-related diseases and improve the quality of life of older persons.Methods:(1)The experimental animals were divided into 3 months of age(3 M),12 months of age(12 M),22 months of age(22M),22 months of age combined with PGC-1α activator ZLN005 group(22M+ZLN005).(2)Mouse skeletal muscle mass index(SMI)was measured by weight method,the morphology of mouse skeletal muscle cross-sectional facial muscle cells was observed by HE staining,the size change trend of gastnemius cross-sectional area(CSA)was quantitatively analyzed,and the muscle strength of upper limbs and limbs was measured by grip test,which was used to detect the phenotype of age-related sarcopenia.(3)ATP content in skeletal muscle was detected by luciferase,ROS content in muscle fiber was detected by DCFH-DA fluorescent probe,mitochondrial ridge density was detected by transmission electron microscopy and cytology quantization,mitochondrial DNA copy number was detected by q PCR.m RNA levels of mitochondrial and nuclear encoded mitochondrial respiratory chain complex were detected by q PCR to detect nucleo-mitochondrial imbalance and mitochondrial function in skeletal muscle.(4)Western blotting detected the expression of age-related total proteins PGC-1α,NRF1,NRF2,and TFAM.Quantitative age-related ratio of TFAM to mitochondrial copy number confirmed the mechanism of PGC-1α pathway in sarcosis.Western blotting detected the expression of age-related total proteins PGC-1α,NRF1,NRF2,and TFAM.Quantitative age-related ratio of TFAM to mitochondrial copy number confirmed the mechanism of PGC-1α pathway in sarcopenia.Results:(1)Phenotype detection of skeletal muscle sarcopenia in mice of each group: In aging mice,the gripping power of forelimbs and limbs was weakened(P<0.05),and the SMI value was decreased(P<0.05).The color of gastrocnemius muscle fibers was significantly increased,the shape of some muscle fibers was irregular,the shape of some muscle fibers was small and round,the number of nuclei was increased,and nuclear inmigration and centralization appeared,and the collagen deposition in the muscle fiber space was significantly increased.The muscle fiber cross-sectional area(CSA)decreased intensively.(2)With the increase of age,the content of ATP in skeletal muscle of mice decreased and the content of ROS increased;Under electron microscope,the morphology of grain is irregular,the mitochondrial cristae arrangement is broken obviously,and the density of mitochondrial cristae is reduced.The mitochondrial DNA copy number was decreased,the CYTB level of respiratory chain complex Ⅲ related gene encoded by mitochondria was decreased(P<0.05),and the COX2 level of complex Ⅳ related gene was decreased,but there was no statistical significance(P >0.05).In addition,the levels of respiratory chain complex Ⅲ related gene CYCS and complex Ⅳ related gene COX4 encoded by nuclear mitochondria were increased(P<0.05).(3)PGC-1α plays a role in skeletal sarcopenia by regulating nucleo-mitochondrial imbalance: With the increase of age,the expression of total gastrocnemius PGC-1α protein decreased(P<0.05),the expression of NRF1 protein was not statistically significant(P > 0.05),the expression of NRF2 protein decreased(P<0.05),and the expression of TFAM protein decreased(P<0.05).The ratio of total gastrocnemius protein TFAM to mitochondrial copy number was decreased(P<0.05).Compared with 22 M group,total protein expression of PGC-1α in gastnemius muscle was increased(P<0.05),gripping power of forelimbs and limbs was increased(P<0.05),SMI was increased(P<0.05),muscle fiber shape was more regular,and no nucleus centralization was observed.Increased ATP content in skeletal muscle;The level of CYTB of respiratory chain complex Ⅲ related gene encoded by mitochondria was increased(P<0.05),the level of CYCS of respiratory chain complex Ⅲ related gene encoded by nuclear mitochondria was increased(P<0.05),and the level of COX2 of respiratory chain complex Ⅳ related gene encoded by mitochondria was increased(P<0.05).The level of respiratory chain complex Ⅳ related gene COX4 was increased(P<0.05).Mitochondrial crest density increased,mitochondrial DNA copy number increased,total gastrocnemius TFAM protein expression increased(P<0.05),ratio of total protein TFAM to mitochondrial copy number increased(P<0.05).Conclusion:(1)Mitochondrial dysfunction in skeletal muscle tissues of sarcopenia is related to nucleo-mitochondrial imbalance,and the transcription levels of oxidative phosphorylation subunits encoded by both nucleus and mitochondria are changed,which occurs before mitochondrial DNA damage.(2)Mitochondrial morphological changes and decreased mitochondrial function in skeletal muscle showed age-dependent changes,which occurred in the middle-aged group prior to the onset of sarcopenia.(3)PGC-1a pathway improves mitochondrial morphology and function in skeletal muscle cells with sarcopenia,which may be related to PGC-1a regulating nucleus-mitochondrial imbalance and regulating TFAM/mt DNA ratio.