Leptin-induced nitric oxide production in white adipocytes is mediated through PKA and MAP kinase activation

Abstract

Leptin injection increases plasma levels of nitrites and/or nitrates, an index of nitric oxide (NO) production. Because plasma levels of NO are correlated with fat mass and because adipose tissue is the main source of leptin, it seems that adipose tissue plays a major role in NO release induced by leptin. Adipocytes express both leptin receptors and nitric oxide synthase (NOS; including the endothelial isoform, NOS III, and the inducible isoform, NOS II). In this study, we have demonstrated that physiological concentrations of leptin stimulate NOS activity in adipocytes. This effect of leptin is abolished by 1) AG490, an inhibitor of Janus tyrosine kinase 2/signal transducer and activator of transcription 3; 2) U0126, an inhibitor of mitogen-activated protein kinase kinase/extracellular signal-regulated kinase (p42/p44 MAPK); and 3) N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide (H-89) or Rp diastereomer of adenosine 3',5'-cyclic phosphorothioate, two inhibitors of protein kinase A, but not by wortmannin, an inhibitor of phosphatidylinositol 3-kinase. Immunoblotting studies have shown that leptin fails to activate Akt but increases p42/p44 MAPK phosphorylation, an effect that is prevented by U0126 but not by H-89. Furthermore, leptin induces NOS III phosphorylation at Ser(1179) and Thr(497), but not when adipocytes are pretreated with H-89 or U0126. Finally, stimulation of adipocyte NOS activity by leptin is either unaltered when protein phosphatase 2A is inhibited by 1 nM okadaic acid or completely abolished when protein phosphatase 1 (PP1) activity is inhibited by 3 nM tautomycin, which supports a crucial role for PP1 in mediating this effect of leptin. On the whole, these experiments demonstrate that NOS activity is a novel target for leptin in adipocytes and that the leptin-induced NOS activity is at least in part the result of NOS III phosphorylations via both protein kinase A and p42/p44 MAPK activation. More generally, this study also leads to the hypothesis of NO as a potentially important factor for leptin signaling in adipocytes.

Role of nitric oxide and endothelium-derived hyperpolarizing factor (EDHF) in the regulation of blood pressure by leptin in lean and obese rats

“…Leptin stimulates NO production not only in the endothelium but also by other cell types including adipocytes (Mastronardi et al, 2002;Mehebik et al, 2005). We cannot estimate what part of leptin-induced NO originates from adipose tissue in our in vivo study.…”

Characterization ofl-arginine transport in adrenal cells: effect of ACTH

“…In this sense, upregulation of eNOS expression by db-cAMP has been demonstrated in cardiomyocytes (34) and in vascular endothelial cells (25), although PKAdependent phosphorylation and activation of eNOS was also shown in platelets and adipocytes (23,30). However, because the magnitude of the effect of ACTH on L-arginine uptake and nitrite production in Y1 cells was similar, we hypothesized that the observed increase in NO production is probably due to the stimulation of L-arginine uptake by ACTH.…”

Gene Expression Profiling of Adipose Tissues in Obesity Susceptible and Resistant Rats under a High Fat Diet

“…Thus, Tpm1 affects cell adhesion, and, thereby, cell shape during adipocyte differentiation [46]. Rat adipose tissue expresses two isoforms of Nos, the endothelial isoform (Nos III) and the inducible isoform (Nos II) [47]. NO increases mitochondrial biogenesis, oxidative metabolism, and ATP levels in several cell types [48,49].…”