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Proteomics analysis of 3 months induced RAmKO mice muscle

ABSTRACT: Maintaining skeletal muscle mass is of high importance as muscle atrophy like during sarcopenia or cachexia lead to a decrease in independence and a higher risk of morbidity and mortality. A leading compound in the treatment against ageing and cancer is rapamycin, an inhibitor of mechanistic target of rapamycin complex 1 (mTORC1). Whether the treatment with mTORC1 inhibitors would work at a cost of losing muscle mass is unclear, as most studies have been focusing on the role of mTORC1 specifically during hypertrophy. In order to answer this question we developed an inducible muscle specific knockout mouse model in which raptor can be ablated during adulthood to eliminate mTORC1 activity. We analysed the muscles after different time points and found that after 3 months the mice showed a fiber shift towards slower fiber types, a loss in oxidative capacity but only very few myopathic features. After 5 months the myopathic features became more apparent, however it did not largely affect the ex vivo muscle force. Surprisingly despite the myopathy we did not see a significant loss of muscle mass even after 5 months, that we hypothesised based on mTORC1s central role in protein synthesis. We assume that the myopathy after long-term mTORC1 inactivation is mostly a result of secondary effects through the loss of mitochondria, alterations in metabolism and in cytoskeletal components. In conclusion, during skeletal muscle maintenance mTORC1 is more essential for metabolic processes than it is for maintaining basal muscle mass.Maintaining skeletal muscle mass is of high importance as muscle atrophy like during sarcopenia or cachexia lead to a decrease in independence and a higher risk of morbidity and mortality. A leading compound in the treatment against ageing and cancer is rapamycin, an inhibitor of mechanistic target of rapamycin complex 1 (mTORC1). Whether the treatment with mTORC1 inhibitors would work at a cost of losing muscle mass is unclear, as most studies have been focusing on the role of mTORC1 specifically during hypertrophy. In order to answer this question we developed an inducible muscle specific knockout mouse model in which raptor can be ablated during adulthood to eliminate mTORC1 activity. We analysed the muscles after different time points and found that after 3 months the mice showed a fiber shift towards slower fiber types, a loss in oxidative capacity but only very few myopathic features. After 5 months the myopathic features became more apparent, however it did not largely affect the ex vivo muscle force. Surprisingly despite the myopathy we did not see a significant loss of muscle mass even after 5 months, that we hypothesised based on mTORC1s central role in protein synthesis. We assume that the myopathy after long-term mTORC1 inactivation is mostly a result of secondary effects through the loss of mitochondria, alterations in metabolism and in cytoskeletal components. In conclusion, during skeletal muscle maintenance mTORC1 is more essential for metabolic processes than it is for maintaining basal muscle mass.

INSTRUMENT(S): LTQ Orbitrap Elite

ORGANISM(S): Mus Musculus (mouse)

TISSUE(S): Muscle

SUBMITTER: Alexander Schmidt

LAB HEAD: Alexander Schmidt

PROVIDER: PXD013294 | Pride | 2019-10-14

REPOSITORIES: Pride

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Project description:Purpose: Despite demonstrating that the overall effect of long-term rapamycin-treatment is overwhelmingly positive in aging skeletal muscle, we observed muscle-specificity in the responsiveness to rapamycin, leading us to hypothesize that the primary drivers of age-related muscle loss and therefore effective intervention strategies may differ between muscles. To address this question and dissect the key signaling nodes associated with mTORC1-driven muscle aging, we created a comprehensive multi-muscle gene expression atlas in adult, sarcopenic and rapamycin-treated mice using RNA-seq. Methods: To examine the impact of long-term rapamycin treatment, male C57BL/6 mice were fed encapsulated rapamycin incorporated into a standardized AIN93M diet at 42 ppm (i.e. mg per kg of food), corresponding to a dose of ~4 mg·kg-1·day-1, from 15- to 30-months of age. This dose of rapamycin has been shown to extend lifespan maximally in male C57BL/6 mice. We performed RNA-seq on gastrocnemius (GAS), tibialis anterior (TA), triceps brachii (TRI) and soleus (SOL) muscles from each of six mice for 10m, 30m and 30mRM groups. The four muscle types were chosen to encompass fore- and hindlimb locations (e.g. TRI and GAS); slow and fast contraction properties (e.g. SOL and GAS); anterior and posterior positioning (e.g. TA and GAS) and the extent of protection by rapamycin (TA and TRI: protected; SOL: partiallly protected; GAS: not protected). Results: Age-related gene expression changes were remarkably consistent across the four different muscles, varying only in magnitude. Despite having the smallest age-related muscle loss of the four muscles, TA had the strongest age-related gene expression response which was associated with an increased reinnervation response. Despite the strong between-muscle commonality of age-related changes, gene expression responses to prolonged rapamycin treatment differed substantially between muscles. Rapamycin partially reversed many age-related changes in mRNA expression in the TA and TRI, but not in SOL or GAS muscle. Principle component analysis (PCA) showed that rapamycin had common 'anti-aging' effects on all muscles, while also exerting muscle-specific pro-aging effects on muscles not protected by rapamycin. Conclusions: Sustained, muscle fiber-specific mTORC1 activity drives sarcopenia-like gene expression programs, and the hyperactive mTORC1 seen in sarcopenic muscle may therefore contribute to sarcopenia.

Project description:<p>Severe myopathic events occur in 0.1-0.5% of patients taking statins. Although genetic association studies have identified some possibly associated gene loci, these have not been reproducible in additional studies with independent patient cohorts. A more reasonable explanation for susceptibility to statin-induced myopathy is the presence of rare pathogenic variants in genes important for skeletal muscle structure and function. In support of this, we have previously reported an increased incidence of pathogenic variants in genes causing metabolic myopathies in patients with statin-induced myopathy (<a href="https://www.ncbi.nlm.nih.gov/pubmed/16671104">Vladutiu et al.</a>,2006). We also reported a patient with statin myopathy who had an <i>RYR1</i> variant known to be causative of malignant hyperthermia susceptibility (MHS) (<a href="https://www.ncbi.nlm.nih.gov/pubmed/21795085">Vladutiu et al.</a>, 2011). There are a number of genes associated with metabolic myopathies triggered by various factors such as extreme exercise, fasting, extremes in temperature, viral infection and exposure to volatile anesthetics. In addition, many of the genes causing congenital myopathies, myofibrillar myopathies and muscular dystrophies have overlapping phenotypes with these genes. We propose that statins act as an additional trigger inducing myopathic symptoms and many patients with severe statin-induced myopathy have causative genetic variants within similar genes associated with MHS and congenital myopathy. We have analyzed the resultant data using a disease model in which rare pathogenic variants, possibly within multiple genes, are causative of statin-induced myopathy. In this study, we have identified potentially causative genetic variants in greater than 50% of the statin-induced myopathy cases and in particular, rare and possibly pathogenic in the RYR1 and CACNA1S genes were present in 25% of the patient samples studied. Vladutiu, G. D., Simmons, Z., Isackson, P.J., Tarnopolsky, M., Peltier, W.L., Barboi, A.C., Sripathi, N., Wortmann, R.L., Phillips, P.S., (<a href="https://www.ncbi.nlm.nih.gov/pubmed/16671104">2006</a>). "Genetic risk factors associated with lipid-lowering drug-induced myopathies." Muscle Nerve 34: 153-162. Vladutiu, G. D., Isackson, P.J., Kaufman, K., Harley, J.B., Cobb, B., Christopher-Stine, L., Wortmann, R.L, (<a href="https://www.ncbi.nlm.nih.gov/pubmed/21795085">2011</a>). "Genetic risk for malignant hyperthermia in non-anesthesia-induced myopathies." Mol Genet Metab 104: 167-173. </p>

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Proteomics analysis of 3 months induced RAmKO mice muscle

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