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:Protein-leucine supplement ingestion following strenuous endurance exercise accentuates skeletal-muscle protein synthesis and adaptive molecular responses, but the underlying transcriptome is uncharacterized. In a randomized single-blind triple-crossover design, 12 trained men completed 100 min of high-intensity cycling then ingested either 70/15/180/30g protein/leucine/carbohydrate/fat (15LEU), 23/5/180/30g (5LEU) or 0/0/274/30g (CON) beverages during the first 90 min of a 240-min recovery period. Vastus lateralis muscle samples (30 and 240-min post-exercise) underwent transcriptome analysis by microarray followed by bioinformatic analysis. Gene expression was regulated by Protein-leucine in a dose-dependent manner impacting the inflammatory response, muscle growth and development. At 30 min, 15LEU and 5LEU vs. CON activated transcriptome networks with geneset functions involving cell-cycle arrest (Z-score 2.0-2.7; P<0.01), leukocyte maturation (1.7; P=0.007), cell viability (2.4; P=0.005), promyogenic networks encompassing myocyte differentiation and myogenin (MYOD1, MYOG), and a proteinaceous extracellular matrix, adhesion, and development programme correlated with plasma lysine, arginine, tyrosine, taurine, glutamic acid, and asparagine concentrations. High protein-leucine dose (15LEU-5LEU) activated an IL1b-centered proinflammatory network and leukocyte migration, differentiation, and survival functions (2.0-2.6; <0.001). By 240 min, the protein-leucine transcriptome was anti-inflammatory and promyogenic (IL-6, NF-kÎ², SMAD, STAT3 network inhibition), with overrepresented functions including decreased leukocyte migration and connective tissue development (-1.8-2.4; P<0.01), increased apoptosis of myeloid and muscle cells (2.2-3.0; P<0.002) and cell metabolism (2.0-2.4; P<0.01). The analysis suggests protein-leucine ingestion modulates inflammatory-myogenic regenerative processes during skeletal muscle recovery from endurance exercise. Further cellular and translational research is warranted to validate amino acid-mediated myeloid and myocellular mechanisms within skeletal-muscle functional plasticity. Total RNA obtained from isolated skeletal muscles

Project description:Background. Skeletal muscle is a major target organ for ethanol induced perturbations with resultant sarcopenia in alcohol-related liver disease (ALD). Targeted studies show that in skeletal muscle, ethanol causes mitochondrial oxidative dysfunction and impaired mTORC1 signaling with consequent decreased protein synthesis and increased autophagy. However, complex interactions and pathway intersections involved in cellular adaptive and maladaptive responses are not well understood. Unlike hypotheses driven focused experiments, an integrated multiomics-experimental validation approach helps identify the global landscape of complex, interacting perturbations in the skeletal muscle. Methods. We used an integrated multiomics approach in a comprehensive array of models, including murine and human induced pluripotent stem cell-derived myotubes (hiPSCm), skeletal muscle from a mouse model of ALD (mALD), and human patients with alcohol-related cirrhosis (CIR) and controls (CON), to identify novel regulatory mechanisms of sarcopenia in ALD. We generated 13 untargeted datasets, including chromosomal conformation, RNA sequencing, proteomics, phosphoproteomics, acetylomics, and metabolomics and conducted a comprehensive analysis using upset plots and feature extraction-based approaches. The most altered molecular interactions were experimentally validated in different models using immunoblots, redox measurements, imaging methods, and measures of senescence associated molecular phenotype (SAMP). Redox ratio was reversed using mitochondrial targeted Lactobacillus brevis NADH oxidase (MitoLbNOX). Results. Enrichments in mitochondrial oxidative function, protein synthesis, and senescence pathways were identified. Multiomics analyses were consistent with the known effects of hypoxia inducible factor 1 (HIF1) that inhibits mitochondrial oxidative dysfunction and promotes skeletal muscle senescence. Pertubrations in genes in the nicotinamide dinucleotide-related pathways including sirtuin signaling, known regulators of senescence, was also noted with ethanol treatment. Experimentally, HIF1 protein was stabilized in myotubes and muscle tissue without cellular hypoxia. Mitochondrial electron transport chain protein expression was less in murine myotubes and hiPSCm with lower redox ratio, less expression of sirtuins, and increased acetylation of mitochondrial proteins. SAMP noted in multiple models in response to ethanol exposure and reversing redox ratio with MitoLbNOX prevented HIF1a stabilization and SAMP in murine myotubes. Conclusions. Our integrated multiomics analyses combined with complementary experimental validation, identify HIF1a stabilization with accelerated skeletal muscle post-mitotic senescence as novel mechanisms of sarcopenia in ALD, highlighting the complex interactions that result in mitochondrial dysfunction with persistent and progressive sarcopenia in ALD.

			Action	DRS
	NCT503_ex10.cnx	Other
	NCT503_ex11.cnx	Other
	NCT503_ex12.cnx	Other
	NCT503_ex13.cnx	Other
	NCT503_ex14.cnx	Other

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Serine synthesis pathway enzyme PHGDH is critical for muscle cell biomass, anabolic metabolism and mTORC1 signaling

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Serine synthesis pathway enzyme PHGDH is critical for muscle cell biomass, anabolic metabolism, and mTORC1 signaling.

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