Background: Skeletal muscle mass is determined by the balance between protein synthesis and degradation. Mammalian target of rapamycin complex 1 (mTORC1) is a master regulator of protein translation and has been implicated in the control of muscle mass. Inactivation of mTORC1 by skeletal muscle-specific deletion of its obligatory component raptor results in smaller muscles and a lethal dystrophy. Moreover, raptor-deficient muscles are less oxidative through changes in the expression PGC-1α, a critical determinant of mitochondrial biogenesis. These results suggest that activation of mTORC1 might be beneficial to skeletal muscle by providing resistance to muscle atrophy and increasing oxidative function. Here, we tested this hypothesis by deletion of the mTORC1 inhibitor tuberous sclerosis complex (TSC) in muscle fibers.
Method: Skeletal muscles of mice with an acute or a permanent deletion of raptor or TSC1 were examined using histological, biochemical and molecular biological methods. Response of the muscles to changes in mechanical load and nerve input was investigated by ablation of synergistic muscles or by denervation .
Results: Genetic deletion or knockdown of raptor, causing inactivation of mTORC1, was sufficient to prevent muscle growth and enhance muscle atrophy. Conversely, short-term activation of mTORC1 by knockdown of TSC induced muscle fiber hypertrophy and atrophy-resistance upon denervation, in both fast tibialis anterior (TA) and slow soleus muscles. Surprisingly, however, sustained activation of mTORC1 by genetic deletion of Tsc1 caused muscle atrophy in all but soleus muscles. In contrast, oxidative capacity was increased in all muscles examined. Consistently, TSC1-deficient soleus muscle was atrophy-resistant whereas TA underwent normal atrophy upon denervation. Moreover, upon overloading, plantaris muscle did not display enhanced hypertrophy compared to controls. Biochemical analysis indicated that the atrophy response of muscles was based on the suppressed phosphorylation of PKB/Akt via feedback inhibition by mTORC1 and subsequent increased expression of the E3 ubiquitin ligases MuRF1 and atrogin-1/MAFbx. In contrast, expression of both E3 ligases was not increased in soleus muscle suggesting the presence of compensatory mechanisms in this muscle.
Conclusions: Our study shows that the mTORC1- and the PKB/Akt-FoxO pathways are tightly interconnected and differentially regulated depending on the muscle type. These results indicate that long-term activation of the mTORC1 signaling axis is not a therapeutic option to promote muscle growth because of its strong feedback induction of the E3 ubiquitin ligases involved in protein degradation.
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http://dx.doi.org/10.1186/2044-5040-3-6 | DOI Listing |
STAR Protoc
January 2025
Laboratory of Developmental Neurobiology, International Institute of Molecular Mechanisms and Machines, 02-247 Warsaw, Poland; Laboratory of Molecular and Cellular Neurobiology, International Institute of Molecular and Cell Biology in Warsaw, 02-109 Warsaw, Poland. Electronic address:
Mechanistic target of rapamycin complex 1 (mTorC1) activity plays a crucial role in brain development. Here, we present an approach for rapamycin microinjection into the habenula of larval zebrafish to achieve localized inhibition of the mTorC1 pathway and explore the role of mTorC1 in habenula function. We describe steps for performing microinjections and maintaining zebrafish larvae before and after the procedure.
View Article and Find Full Text PDFJ Biol Chem
January 2025
Institute for Biomedicine, Sahlgrenska Academy, Centre for Ageing and Health-AgeCap, University of Gothenburg, Sweden. Electronic address:
The mTOR (mechanistic target of rapamycin) signaling pathway appears central to the aging process as genetic or pharmacological inhibition of mTOR extends lifespan in most eukaryotes tested. While the regulation of protein synthesis by mTOR has been studied in great detail, its impact on protein misfolding and aggregation during stress and aging is less explored. In this study, we identified the mTOR signaling pathway and the linked SEA complex as central nodes of protein aggregation during heat stress and cellular aging, using Saccharomyces cerevisiae as a model organism.
View Article and Find Full Text PDFInt J Mol Sci
December 2024
Department of Pediatrics, McGovern Medical School UTHealth, Houston, TX 77030, USA.
Pseudoachondroplasia (PSACH), a severe dwarfing condition characterized by impaired skeletal growth and early joint degeneration, results from mutations in cartilage oligomeric matrix protein (COMP). These mutations disrupt normal protein folding, leading to the accumulation of misfolded COMP in chondrocytes. The MT-COMP mouse is a murine model of PSACH that expresses D469del human COMP in response to doxycycline and replicates the PSACH chondrocyte and clinical pathology.
View Article and Find Full Text PDFMolecules
December 2024
Xinjiang Key Laboratory of Biological Resources and Genetic Engineering, College of Life Science and Technology, Xinjiang University, Urumqi 830017, China.
Diabetic nephropathy (DN) is a common and serious complication of diabetes mellitus and a major cause of end-stage renal disease (ESRD). Renal fibrosis, which corresponds to excessive deposition of extracellular matrix and leads to scarring, is a characteristic feature of the various progressive stages of DN. It can trigger various pathological processes leading to the activation of autophagy, inflammatory responses and a vicious circle of oxidative stress and inflammation.
View Article and Find Full Text PDFMol Biol Rep
January 2025
Department of Pathology and Laboratory Medicine, Baylor Scott and White Medical Center, Baylor College of Medicine, Temple, TX, USA.
Background: Brain intraparenchymal schwannoma is a rare clinical entity, generally curable with adequate resection.
Methods And Results: We describe a case in a male patient first presenting at 19 months of age, the youngest reported age for this lesion. It also appears to be the first case connected to a germline TSC2 p.
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