Does cAMP‐signaling regulate atrogenes expression in skeletal muscle upon motor denervation? (1162.9)

Abstract

Recent studies have focusing on the role of cAMP‐signaling in modulating the protein degradation via de ubiquitin‐proteasome pathway during muscle wasting. Decreases in this proteolytic system during chronic muscle disuse are thought to prevent the excessive loss of muscle mass. However, the intracellular pathways that elicit this response are elusive. In turn, this study was performed to shed light on the molecular mechanisms involved in this process. For this, C57/BL6 male mice (~30g) were anesthetized and submitted to motor denervation (DEN) by unilateral sciatic nerve section. After 3, 7 and 14 days, tibialis anterior muscles were harvested to examine: mRNA and protein levels of atrophy‐related genes (i.e atrogenes; MuRF1 and atrogin‐1) and different components of cAMP‐signaling, including muscle cAMP levels, the PKA activity (estimated by phospho‐PKA substrates) and the phospho‐CREB and mRNA levels of Sik1, a CREB‐target gene. Sham‐operated and denervated animals were treated with either saline or clenbuterol (CB, 3mg/kg/day; s.c.) during 14 days. The loss of muscle mass induced by DEN started on 7th day (13%) and reached 34% at 14 days after DEN. Skeletal muscles from 3‐days denervated mice showed an increase in the gene expression of atrogin‐1 (243%) and MuRF1 (553%). However, after the 7th day of DEN, atrogenes expression was normalized. This effect was associated with an increase of muscle cAMP content (25% in relation to innervated muscles), phospho‐PKA substrates (~2.2 fold), Sik1 mRNA expression (~5.2 fold) and phospho‐CREB (~4 fold) content. Furthermore, CB treatment for 3 days increased muscle cAMP content (16%) and blunted the up‐regulation of both atrogin‐1 and MuRF1 mRNAs. These results suggest the existence of an adaptive mechanism responsible to restrain the activation of atrogenes during motor denervation that seems to be mediated by activation of cAMP/PKA/CREB signaling.Grant Funding Source: FAPESP (2012/05697‐7; 2012/24524‐6)