ODP201 Fyn regulates sarcopenia via autophagy

Sarcopenia is an important element that impairs daily activity. Sarcopenia is also linked to insulin resistance, and the number of diabetic patients also presenting sarcopenia is increasing. In recent years, autophagy has been identified as one of the novel mechanisms associated with sarcopenia. We previously reported that Fyn not only participates in the metabolic syndrome but also that autophagy-regulating sarcopenia was decreased in muscle specific Fyn transgenic mice through STAT3 regulation (Cell metabolism 2010, Cell Rep. 2012). More recently, we revealed Fyn-dependent STAT3 phosphorylation by IL6, which is involved in chronic inflammation and metabolic syndrome, using mouse C2C12 myotube cells expressing shRNA for Fyn. Furthermore, using WT mice with both the denervated and the hind limb suspension (HS) that promotes disuse atrophy by suspending the hind limb, not only both Fyn and IL6 gene expressions were increased but the expression and phosphorylation levels of STAT3 were also augmented, while the autophagic activity was decreased. To confirm those regulations are Fyn dependent, we took advantage of Fyn null mice (FynKO) with HS. Compare to WT mice with HS, all the muscles of FynKO were resistant for the loss of muscle mass induced by HS. The expressions of bothatrogin-1 and muRF-1,the key muscle specific E3 ubiquitin ligases as well as the markers for sarcopenia, were not changed in the muscles of FynKO with HS. Moreover, the STAT3 phosphorylation on tyrosine 705 was decreased in the muscle of FynKO compared to WT mice after hind limb suspension, while expression levels of STAT3 were not changed. IL-6mRNA expression levels were increased in the HS muscle of control mice, but were not changed in FynKO HS muscle. Finally, the autophagic activity, examined by both LC3-2 protein levels after intraperitoneal administration of colchicine andSQSTM1/p62 immunofluorescence in muscles, was retained in FynKO after HS. These results strongly suggest that Fyn is involved not only in the metabolic syndrome but also in the pathogenesis of sarcopenia, and may lead to a better understanding of the pathology of sarcopenia-associated obesity and the development of therapeutic methods. Presentation: No date and time listed