Functional and Pharmacological Characterization of the Natriuretic Peptide-Dependent Lipolytic Pathway in Human Fat Cells

Abstract

A lipolytic pathway involving natriuretic peptides has recently been discovered in human fat cells. Its functional characteristics and the interactions of the atrial natriuretic peptide (ANP)-induced effects with adrenergic and insulin pathways were studied. Characterization of the action of ANP antagonists, i.e., A71915, anantin, S-28-Y (Ser-28-Tyr, a synthesized peptide), and HS-142-1 (a microbial polysaccharide), was performed. Lipolytic assays and intracellular cGMP and cAMP determinations were performed on isolated fat cells. Cell membranes were used for binding studies. At low concentrations ANP and isoproterenol [␤-adrenergic receptor (␤-AR) agonist] exerted additive lipolytic effects. The ␣ 2 -AR pathway did not interfere with that of ANP. Lipolytic effects of ANP were unaltered by a 2-h pretreatment of fat cells with insulin, whereas ␤-AR-induced lipolysis was reduced. Homologous desensitization occurred for ANP-dependent lipolytic pathways. Dendroapsis natriuretic peptide exhibited a similar maximal effect but a 10-fold higher lipolytic potency than ANP and mini-ANP (the shortest form of ANP). The antagonist A71915 exhibited competitive antagonistic properties with a pA 2 value of 7.51. Anantin displayed noncompetitive antagonism and exerted an inhibitory action on basal and ␤-adrenergic receptor-induced lipolytic response. S-28-Y exhibited antagonist potencies toward ANPinduced lipolysis and behaved as a partial lipolytic agonist with a lower pD 2 value (7.4 Ϯ 0.2) than ANP (9.4 Ϯ 0.3). HS-142-1 exerted the weakest antagonistic effects. The results demonstrate that ANP-dependent effects do not interfere with ␤-and ␣ 2 -adrenergic pathways in human fat cells. They are unaffected by insulin pretreatments of fat cells but undergo desensitization. In the search of potent and specific natriuretic peptide receptor-A antagonist, in the human fat cell, A71915 was the only reliable one found.Natriuretic peptides ANP, BNP, and C-type natriuretic peptide (NPs) are a family of peptides that exert potent diuretic, natriuretic, and vasodilator activities (Athanassopoulos and Dennis, 1991; Levin et al., 1998). They are synthesized as preprohormones in the mammalian heart, stored as prohormones, and then released into the plasma after cardiomyocyte stretch. ANP sequence comprises 28 amino acids with a Cys 7 -Cys 23 bridge, which enables binding to atrial natriuretic peptide receptors (NPRs) (Levin et al., 1998). ANP binds with high affinity to human fat cell membranes, and we have recently demonstrated that NPs are potent lipolytic agents in human and in nonhuman primate fat cells only (Sengenes et al., 2000(Sengenes et al., , 2002a. Among the members of the NP family, the relative order of lipolytic potencies is ANP Ͼ BNP Ͼ C-type natriuretic peptide. The lipolytic activity of ANP and BNP is mediated by specific fat cell-plasma membrane receptors (NPR-A) bearing a guanylyl cyclase activity. They operate via a cGMP-dependent pathway and independently of phosphodiesterase-3B inhibition (Sengenes et al., 2000)....

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

“…ANP and BNP bind preferentially to NPR-A receptors. We have previously demonstrated that the NPs, including ANP and BNP, also exert a potent control of human adipocyte lipolysis through the activation of the type A guanylyl cyclase receptor (Sengenès et al, 2000;Moro et al, 2004b). Lipolysis is mediated by a cGMP-dependent pathway that induces the phosphorylation of hormone-sensitive lipase and perilipin A (Sengenès et al, 2003).…”

An Unsuspected Metabolic Role for Atrial Natriuretic Peptides

“…This effect is unrelated to inhibition of the cGMP-inhibitable phosphodiesterase PDE-3B of the adipocytes. 3,82 In fact, although PDE-3B catalytic sites have a similar high affinity for cAMP and cGMP, the V max for cAMP is much higher (4 to 10ϫ) than for cGMP. ANP-induced lipolysis is associated with an increase in the serine phosphorylation of HSL in mature human adipocytes as well as in adipocyte precursors differentiated into adipocytes.…”

“…The physiological contribution of ANP, concomitantly with SNS, to the control of lipid mobilization is supported by these results. Because of the lack of a suitable NPR-A receptor antagonist, 82 it is difficult to determine the relative contributions of the 2 pathways in the physiological control of lipid mobilization. Other than ANP, it is impossible to propose another reliable candidate in the context of the biological factors released during exercise and that is known to exert lipolytic effects in human.…”

“…Insulin treatment of human fat cells has no effect on ANP-induced lipolytic response. 3,82,87 Because the antilipolytic effects of insulin are mediated by the reduction of intracellular cAMP levels initiated by PDE-3B activation, it is understandable why this hormone does not interfere with cGMP-dependent NP effects. Delineation of mechanisms involved in the downregulation of NP action merits attention.…”

Les peptides natriurétiques : Une nouvelle voie de régulation de la lipolyse chez l’homme

“…Cet effet est équivalent à celui de l'agoniste β-adrénergique de réfé-rence, l'isoprénaline. L'ANP, le BNP et le CNP (C-type natriuretic peptide) stimulent la lipolyse selon l'ordre de potentialité suivant: ANP>BNP>>CNP (Figure 2A) et que ce second messager n'intervient pas dans les mécanismes d'action de l'ANP [14]. Cette observation souligne que les effets lipolytiques des peptides natriurétiques ne sont pas modulables par la seule hormone douée de propriétés antilipolytiques.…”