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. British Journal of Pharmacology (2007) 152 , 1102–1110; doi: 10.1038/sj.bjp.0707485 ; published online 1 October 2007