Phosphodiesterase-5A and neutral endopeptidase activities in human adipocytes do not control atrial natriuretic peptide-mediated lipolysis

BACKGROUND AND PURPOSE: Atrial natriuretic peptide (ANP) stimulates lipolysis in human adipocyte through a cGMP signalling pathway, the regulation of which is poorly known. Since phosphodiesterases (PDE) and neutral endopeptidase (NEP) play a major role in the regulation of the biological effects of natriuretic peptides in the cardiovascular and renal systems, we investigated whether these mechanisms could regulate cGMP signalling and ANP-mediated lipolysis in human adipocytes. EXPERIMENTAL APPROACH: The presence of cGMP-specific PDE and NEP in differentiated pre-adipocytes and in mature adipocytes was evaluated by real-time qPCR and Western blot. The effect of non-selective and selective inhibition of these enzymes on ANP-mediated cGMP signalling and lipolysis was determined in isolated mature adipocytes. KEY RESULTS: PDE-5A was expressed in both pre-adipocytes and adipocytes. PDE-5A mRNA and protein levels decreased as pre-adipocytes differentiated (10 days). PDE-5A is rapidly activated in response to ANP stimulation and lowers intracellular cGMP levels. Its selective inhibition by sildenafil partly prevented the decline in cGMP levels. However, no changes in baseline- and ANP-mediated lipolysis were observed under PDE-5 blockade using various inhibitors. In addition, NEP mRNA and protein levels gradually increased during the time-course of pre-adipocyte differentiation. Thiorphan, a selective NEP inhibitor, completely abolished NEP activity in human adipocyte membranes but did not modify ANP-mediated lipolysis. CONCLUSIONS AND IMPLICATIONS: Functional PDE-5A and NEP activities were present in human adipocytes, however these enzymes did not play a major role in the regulation of ANP-mediated lipolysis.