Skeletal muscle-specific ablation of raptor, but not of rictor, causes metabolic changes and results in muscle dystrophy.
Level 5 - mechanism / opinion, no new human data
Preclinical animal model study (mouse knockout experiment)
PubMed 19046572 · doi:10.1016/j.cmet.2008.10.002
What was done
Investigated the distinct roles of mTORC1 and mTORC2 in skeletal muscle by generating muscle-specific knockout mouse models deficient in either raptor (mTORC1 component) or rictor (mTORC2 component) and evaluating survival, muscle phenotype, oxidative capacity, glycogen storage, and biochemical signaling pathways.
What was found
The abstract reports no numerical data. Raptor-deficient muscles displayed progressive muscle dystrophy, impaired oxidative capacity, elevated glycogen stores, and shortened survival despite expressing structural markers of oxidative fibers. Biochemically, raptor deletion resulted in loss of mTORC1 target activation, downregulation of mitochondrial biogenesis genes including PGC1alpha, and hyperactivation of PKB/Akt. In contrast, rictor-deficient muscles were phenotypically indistinguishable from wild-type controls, and PKB/Akt activation did not require mTORC2.
Why it matters
This work identifies mTORC1 as an essential regulator of muscle oxidative metabolism, mitochondrial gene expression, and structural maintenance, demonstrating functional divergence between mTORC1 and mTORC2 in skeletal muscle biology.
Limits
The study was performed entirely in mouse genetic models without human verification. The abstract omits sample sizes, quantitative effect sizes, statistical significance values, and specific survival durations.
Cited by
- supports Absence of mTORC1 in skeletal muscle causes muscle withering and wasting.