Studio del secretoma muscolare durante l’invecchiamento

Mitochondrial dysfunction is a recognized contributor to the pathogenesis of sarcopenia and aging. Tezze et al. (2017) showed that in adult mice acute muscle-specific blocks of fusion, throw the deletion of mitochondrial protein optic atrophy 1 (OPA1), induce a profound muscle loss, systemic inflammatory response, and precocious epithelial senescence that culminates with animal death. Mitochondrial dysfunction, caused by Opa1 ablation, triggers a dramatic increase in muscle fibroblast growth factor 21 (FGF21) expression and secretion from the skeletal muscle tissue. Impressively, the double muscle-specific ablation of Opa1/Fgf21 reverted completely the aging phenotype and prevented precocious death in mice. Importantly, the block of fission (Drp1 ko) or the concomitant block of fusion and fission (Drp1/Opa1 ko) showed higher FGF21 levels but not the precocious aging phenotype and the precocious death. Interestingly, sterile inflammation is visible in the iOpa1 mKO mice but not in the iDrp1 mKO and iOpa1/Drp1 DKO mice, suggesting that these pathways may contribute to the early aging phenotype observed in the iOpa1 mKO mice. This latter exhibited an elevated level of pro-inflammatory cytokines, particularly IL-6, specifically produced in skeletal muscle, which was mitigated by the double deletion in iFgf21-Opa1 m2KO mice. These observations support the concept that FGF21 needs the presence of other factors to elicit the precocious senescence phenotype of OPA1 KO mice. Investigating whether skeletal muscle contribute to inflammatory processes in OPA1 KO mice, we generated double Tamoxifen-inducible muscle-specific Opa1/IL-6 knockout mice (iOpa1-il-6 mDKO). Interestingly, we observed that muscle-specific deletion of IL-6 leads to increased survival in transgenic animals, attenuates systemic inflammation, and reduces cellular senescence. These findings suggest that muscle can directly influence senescence and systemic inflammation (inflammaging) through IL-6, during aging and sarcopenia. To identify other factors that, synergistically with Fgf21, induce premature senescence in Opa1 KO mice, we generated a novel mouse model by crossing inducible muscle-specific Opa1 knockout mice with floxed MetRS* knock-in mice. The latter expresses a mutant methionyl-tRNA synthetase that allows the incorporation of azidonorleucine (ANL), a non-canonical amino acid, in place of methionine in muscle proteins. This amino acid can be conjugated to different affinity tags and the labeled proteins can be identified by tandem mass spectrometry (MS/MS) both in the circulation and in the target tissue. To streamline the in vivo model, we opted to collect proteins tagged with ANL secreted by muscles into the extracellular fluids (EFs) for MS/MS analysis. Numerous studies have shown that while most serum-detectable proteins can be identified in EFs, proteins present in tissues are often difficult to detect in serum. This highlights the potential of EFs as a highly effective and efficient approach for identifying novel secreted factors