The knowledge of the mechanisms regulating skeletal muscle mass is of great relevance, since the excessive loss of muscle mass associated with various clinical conditions can lead to serious health complications. Considering the evidences for the role of cyclic adenosine 3,5-monophosphate (cAMP) signaling in the inhibition of muscle proteolysis by catecholamines and beta2-adrenergic agonists, our laboratory studied the role of phosphodiesterase type 4 (PDE 4, most prevalent PDE isoform in skeletal muscles degrading cAMP) in the control of proteolytic systems. The treatment of diabetic rats (experimental model of muscle atrophy) with rolipram (PDE 4 inhibitor) for 3 days caused an increase in the cAMP levels, in both soleus and EDL skeletal muscles, followed by activation of PKA and EPAC1 signaling, as well as increase in the phosphorylation levels of AKT (Ser-473) and FoxO1 (Thr-24) and FoxO3 (Thr-32) transcription factors. Changes in the components of the proteolytic machinery involved in the release of sarcomeric proteins were also found, such as reduction in the caspase-3 and Bax expression (pro-apoptotic protein) and increase of Bcl-2 (pre-apoptotic protein) and calpastatin (calpain inhibitor). Biomarkers of ubiquitin-proteassome system (UPS) were also decreased, such as MurF-1, atrogin-1 and polyubiquitin conjugates. The treatment with rolipram inhibited the activities of caspase-3, calpain and proteasome, as well as avoided the loss of muscle mass in diabetic rats. These findings suggest that the antiproteolytic effect of rolipram on skeletal muscles may be related to the participation of PKA/CREB and EPAC/AKT/FoxO signaling pathways, inhibiting the proteases involved in the sarcomere derangement and the UPS. Studies have demonstrated that the cAMP signaling related to beta2-adrenergic agonists is able to inhibit autophagy in skeletal muscles; however, it is not known the effects of the cAMP increase on this proteolytic pathway achieved after the inhibition of PDE 4. Therefore, this project proposes to investigate the in vivo role of PDE 4 in the autophagy control in skeletal muscles of rats.
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