Inducible nitric oxide synthase modulates lipolysis in adipocytes

Abstract

The role of inducible nitric oxide synthase (iNOS) in the modulation of adipocyte lipolysis was investigated. Treatment of white and brown adipose cell lines and mouse adipose explants with a mixture of tumor necrosis factor-␣ , interferon-␥ , and lipopolysaccharide (LPS) doubled the lipolytic rate, and this was associated with marked induction of iNOS expression and nitric oxide (NO) production. iNOS inhibition by 1400W, aminoguanidine, or L-NIL pretreatment further increased the cytokine/LPS-mediated lipolysis by 30% ( P Ͻ 0.05) in cultured adipocytes and in adipose explants. However, this potentiating effect of iNOS inhibition was abolished in adipose explants isolated from iNOS knockout mice. Pharmacological inhibitors of adenylyl cyclase or protein kinase A reduced cytokine/LPS-induced lipolysis and also blunted the potentiating effect of iNOS inhibition on the lipolytic rate. Furthermore, addition of the antioxidants l -cystine and l -glutathione to cytokine/LPS-stimulated adipocytes mimicked the lipolytic effect of iNOS inhibition.In conclusion, inhibition of iNOS activity in adipocytes potentiates cytokine/LPS-induced lipolysis. This effect was fully reversed by adenylyl cyclase and protein kinase A inhibitors but was mimicked by cellular antioxidants. These data suggest that iNOS-mediated NO production counteracts cytokine/LPS-mediated lipolysis in adipocytes and that this feedback mechanism involves an oxidative process upstream of cAMP production in the signaling pathway. -Penfornis, P., and A. Marette. Major metabolic changes occur during sepsis as proinflammatory cytokines and endotoxins markedly affect energy metabolism in liver and peripheral tissues (reviewed in 1, 2). In vivo studies have shown that adipose tissue lipolysis is markedly increased in sepsis and other acute inflammatory settings, leading to an increased VLDL secretion and hepatic fatty acid synthesis. The lipolytic effect of cytokines and endotoxins can be reproduced in vitro using freshly isolated adipocytes or cultured adipose cell lines (3). Unlike ␤ -adrenergic agonists, which stimulate lipolysis within minutes through activation of the adenylyl cyclase/cAMP/protein kinase A (PKA) pathway, inflammatory cytokines such as tumor necrosis factor-␣ (TNF-␣ ) increase lipolysis only after long-term activation (hours) via activation of Ras-extracellular signal regulated kinase (ERK), which in turns promotes phosphorylation and activation of Hormone-sensitive lipase (HSL) and its translocation on cellular lipid droplets (3-6). TNF-␣ may also cause lipolysis through ERK-dependent inhibition of cyclic nucleotide phosphodiesterase 3B (PDE3B), increasing intracellular cAMP and PKA activity, leading to phosphorylation and decreased expression of perilipins (7-9). Perilipins are phosphoproteins located at the surface of the intracellular lipid droplets that have been proposed to act as a barrier to lipolysis (9-11).Sepsis is also associated with marked expression of inducible nitric oxide synthase (iNOS), a proinflammatory mediator i...

Cytokine-induced metabolic effects in human adipocytes are independent of endogenous nitric oxide

“…Surprisingly, glycerol release was markedly reduced in IFN-␥-and IL-1␤-administered cells compared with IL-1␤ alone. Based on studies in murine adipocyte models, including 3T3-L1, T37i, and adipose tissue explants from NOS 2 Ϫ/Ϫ knockout mice, iNOS-derived NO has been proposed as a negative feedback inhibitor containing excessive inflammation-induced lipoysis (34). In contrast, the lipolytic activity under inflammatory conditions appears to be NO independent in the present human adipocyte model.…”

“…*P Ͻ 0.01 compared with untreated controls. established (25,29,34,39). Obesity is increasingly recognized as an inflammatory condition (10,47), and human obesityrelated iNOS induction in adipose tissue has been proposed (14,15,43).…”

“…In contrast, diphenyliodonium (DPI)-mediated NOS blockade decreases both basal and dibutyryl cAMP-stimulated lipolysis (21). In LPS-and cytokine-challenged 3T3-L1 adipocytes, iNOS-derived NO was proposed as a negative lipolysis modulator (34). NOS inhibition resulted in impaired insulin-mediated glucose uptake in rat adipocytes and myocytes (41).…”

A comparative perspective on lipid storage in animals

“…Adipocytes react to infections through the activation of multiple inflammatory signal transduction cascades, and the secretion of potent inflammatory cytokines, such as interleukin 6 (IL6) and tumor necrosis factor a (TNFa) (Hotamisligil et al, 1993;Wellen and Hotamisligil, 2003). Interestingly, either bacterial infections or exposure to lipopolysaccharide (LPS) and/or cytokines can promote adipose tissue lipolysis and reduce TAG uptake by adipocytes (Feingold et al, 1994;Penfornis and Marette, 2005;Zu et al, 2009). Such a lipolytic response to bacterial infections is also present in flies (Dionne et al, 2006).…”

Effect of endothelial cell-based iNOS gene transfer on cavernosal eNOS expression and mouse erectile responses

“…A substrate analog inhibitor of NOS, L-NIL, has 14-28-fold greater selectivity for iNOS than for constitutive NOS isoforms. [8][9][10] NO production ([NO 2 À ]) and eNOS expression were measured in duplicate in three independent experiments.…”