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The neuromuscular junction is a focal point of mTORC1 signaling in sarcopenia [TSCmKO data set].

ABSTRACT: Purpose: Sustained muscle fiber-specific mTORC1 activity, through deletion of the mTORC1 upstream inhibitor Tsc1, drives progressive muscle wasting and weakness reminiscent of sarcopenia. We aimed to characterise gene expression changes coinciding with the development of sarcopenia-like features in TSCmKO mice. Methods: Extensorum digitorum longus (EDL) muscles from 3- (weak phenotype) and 9-month-old (severe phenotype) TSCmKO and littermate control mice (Tsc1 floxed, HSA-Cre negative) treated with either vehicle or rapamycin (8 mg.kg.min-1) for 3 days were processed and sequenced. Results: The principal component analysis showed two major gene expression patterns. The first pattern represents an aging-like pattern with gene expression remaining stable between 3 and 9 months in wild type mice, but changing between 3 and 9 months in TSCmKO mice. The second pattern seems to represent early alterations in TSCmKO mice compared to WT, which subside between 3 and 9 months in TSCmKO. Importantly, when comparing changes in the gene expression in TSCmKO mice with natural aging gene expression profiles, there was a significant overrepresentation of commonly increasing and decreasing genes and an underrepresentation of oppositely regulated genes. Likewise, many of the top enriched GO terms for natural aging gene expression profiles were also enriched for genes changing the expression in the premature aging TSCmKO mice. 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.

ORGANISM(S): Mus musculus

PROVIDER: GSE139213 | GEO | 2020/06/19

REPOSITORIES: GEO

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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: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.

Project description:Abstract Background: The prevalence of sarcopenia is increasing and effective interventions are required to prevent or reverse age-related muscle loss. However it is often challenging expensive and time-consuming to develop and test the effectiveness of such interventions. Furthermore translational animal models that adequately mimic underlying physiological pathways are scarce. Strong predictors for the incidence of sarcopenia include a sedentary life-style and malnutrition. Therefore our objective was to investigate the translational value of three potential mouse models for sarcopenia namely partial immobilized caloric restricted (CR) and a combination (immobilized & CR) model. Methods: C57BL/6J mice were calorically restricted (-40%) and/or one hindleg was immobilized for two weeks to induce loss of muscle mass and function. Muscle mass function and diameter and distribution of slow (type 1) and fast ( type 2) myofibers were compared to those of young control (4 months) and old reference mice (21 months). Transcriptome analysis of quadriceps muscle was performed to identify underlying pathways and were compared with those being expressed in aged human vastus lateralis muscle-biopsies using a meta-analysis of five different human studies. Results: Caloric restriction induced overall loss of lean body mass (-15% p<0.001) whereas immobilization decreased muscle strength (-28% p<0.001) and muscle mass of hindleg muscles specifically (on average -25% p<0.001). The proportion of slow myofibers increased with aging in mice (+5% p<0.05) and this was not recapitulated by the CR and/or immobilization models. The diameter of fast myofibers decreased with aging (-7% p<0.05) and this was mimicked by all models. Transcriptome analysis revealed that the combination of CR and immobilization recapitulated more pathways characteristic for human muscle-aging (73%) than naturally aged (21 months old) mice (45%). These pathways included critical pathways relevant for protein synthesis/ breakdown (mitochondrial) metabolism neurology and the vascular system. Conclusions: The combination model exhibits loss of both muscle mass (due to CR) and function (due to immobilization) and has a remarkable similarity with pathways underlying human sarcopenia. Our results demonstrate that naturally aging up to 21 months in mice only partially recapitulates the human pathology with fewer overlapping pathways than the combination model. These findings underline that external factors such as sedentary behavior and malnutrition are key elements of a translational mouse model and favor the combination model as a rapid model for testing the treatments against sarcopenia.