Involvement of a cGMP-dependent Pathway in the Natriuretic Peptide-mediated Hormone-sensitive Lipase Phosphorylation in Human Adipocytes

Abstract

Our previous studies have demonstrated that natriuretic peptides (NPs), peptide hormones with natriuretic, diuretic, and vasodilating properties, exert a potent control on the lipolysis in human adipocytes via the activation of the type A guanylyl cyclase receptor (1, 2). In the current study we investigated the intracellular mechanisms involved in the NP-stimulated lipolytic effect in human preadipocytes and adipocytes. We demonstrate that the atrial NP (ANP)-induced lipolysis in human adipocytes was associated with an enhanced serine phosphorylation of the hormone-sensitive lipase (HSL). Both ANP-mediated lipolysis and HSL phosphorylation were inhibited in the presence of increasing concentrations of the guanylyl cyclase inhibitor LY-83583. ANP did not modulate the activity of the cAMP-dependent protein kinase (PKA). Moreover, H-89, a PKA inhibitor, did not affect the ANP-induced lipolysis. On primary cultures of human preadipocytes, the ANP-mediated lipolytic effect was dependent on the differentiation process. On differentiated human preadipocytes, ANPmediated lipolysis, associated with an increased phosphorylation of HSL and of perilipin A, was strongly decreased by treatment with the inhibitor of the cGMPdependent protein kinase I (cGKI), Rp-8-pCPT-cGMPS. Thus, ANP-induced lipolysis in human adipocytes is a cGMP-dependent pathway that induces the phosphorylation of HSL and perilipin A via the activation of cGKI. The present study shows that lipolysis in human adipocytes can be controlled by an independent cGKI-mediated signaling as well as by the classical cAMP/PKA pathway.Natriuretic peptides (NPs) 1 are a family of polypeptide hormones (atrial NP (ANP), brain NP, and C-type NP) that regulate blood pressure, natriuresis, diuresis, together with renin and aldosterone release by direct effects on the kidney, the adrenal glands, and the systemic vasculature (3-5). NPs signaling operates through two groups of cell surface receptors: the guanylyl cyclase (GC) receptors named GC-A and GC-B (6, 7) and the clearance receptor or type C NP receptor (NPr-C) without intrinsic GC activity (8 -10). The cGMP produced after the activation of GC-coupled receptors has multiple effectors within the cell, including the families of cGMPdependent protein kinases (cGK), cGMP-stimulated/cGMPinhibited phosphodiesterases (PDEs), cGMP-gated cation channels, and, in some cases, cAMP-dependent protein kinase A (PKA) (11,12).In addition to their renal, adrenal, and vascular effects, NPs may affect the metabolism of human adipocytes. In previous studies, we have demonstrated that ANP and brain NP, but not C-type NP, are potent stimulators of human fat cell lipolysis (1, 2). Clinical studies have validated their action in vivo (13,14). However, the intracellular pathway involved in the NP-stimulated lipolytic effect still remained to be characterized. Former studies on human adipocytes have shown the essential role of cAMP in the modulation of the lipolytic pathway. Indeed, the main lipolytic regulators in human fat cells, i.e. catech...

An Unsuspected Metabolic Role for Atrial Natriuretic Peptides

“…This was confirmed using the cGMP analogue inhibitor of cGK-I, 8-pCPT-cGMPS, which inhibited both HSL phosphorylation/activation and lipolysis. 5 This finding in isolated human fat cells confirms early data from a rat cell-free system where the phosphorylation of HSL by PKG was reported. 83,84 Recent studies have shown a role for the MAP-kinases in the control of lipolysis by TNF-␣ in human fat cells.…”

“…In contrast, NPs activate a 3Ј, 5Ј-cyclic guanosine monophosphate (cGMP)-dependent pathway that is completely independent from the cAMP-dependent pathway. 5 The NPs may represent a promising new pathway contributing to the control of lipid mobilization in humans in physiological and pathological conditions. The introductory section summarizes the role of circulating NEFAs and the regulation of lipolysis and lipid mobilizing pathways.…”

Association between High Molecular Weight Adiponectin Levels and Metabolic Parameters

“…In our study, simple and multiple regression analyses showed that the HMW adiponectin level correlated with BNP levels. NTproBNP is an inactive surrogate marker of BNP and there is evidence that natriuretic peptides have a direct lipid-mobilizing effect 27,28) . This suggests a causal relationship between BNP and adiponectin; however, further investigations are needed to elucidate a mechanistic link between BNP and adiponectin.…”

Adipose tissue gene expression in obese subjects during low-fat and high-fat hypocaloric diets

“…The slight decrease in phosphodiesterase 3B mRNA levels observed in the present study could favour an increase in fat cell cAMP levels and thus enhance lipolysis. However, the decreased levels of hormonesensitive lipase and natriuretic peptide type A receptor (which mediates cyclic GMP-dependent activation of lipolysis in human adipocytes [45]) mRNAs indicate a decreased lipolytic capacity. In addition, the expression of hormone-sensitive lipase is reportedly decreased following weight loss programmes [46,47].…”