Apoptotic Pathways Are Inhibited by Leptin Receptor Activation in Neutrophils

Abstract

Leptin regulates food intake as well as metabolic, endocrine, and immune functions. It exerts proliferative and antiapoptotic activities in a variety of cell types, including T cells. Leptin also stimulates macrophages and neutrophils, and its production is increased during inflammation. In this study, we demonstrate that human neutrophils express leptin surface receptors under in vitro and in vivo conditions, and that leptin delays apoptosis of mature neutrophils in vitro. The antiapoptotic effects of leptin were concentration dependent and blocked by an anti-leptin receptor mAb. The efficacy of leptin to block neutrophil apoptosis was similar to G-CSF. Using pharmacological inhibitors, we obtained evidence that leptin initiates a signaling cascade involving PI3K- and MAPK-dependent pathways in neutrophils. Moreover, leptin delayed the cleavage of Bid and Bax, the mitochondrial release of cytochrome c and second mitochondria-derived activator of caspase, as well as the activation of both caspase-8 and caspase-3 in these cells. Taken together, leptin is a survival cytokine for human neutrophils, a finding with potential pathologic relevance in inflammatory diseases.

Involvement of leptin signaling in the survival and maturation of bone marrow‐derived dendritic cells

“…Therefore, in addition to our finding of reduced DC yield in db/db BM cultures, these results argue for a physiological role for leptin signaling in DC generation. Our observations of increased apoptosis of db/db DC support the notion that leptin signaling acts as a pro-survival factor in immune cells [13,27]. Although the exact molecular mechanism involved remains to be elucidated, the skewed balance of Bcl-2 family genes towards upregulated expression of the pro-apoptotic member Bim and down-regulation of the anti-apoptotic Bcl-2 suggests a potential role of leptin signaling in modulating Bcl-2 family proteins.…”

Neutrophil apoptosis mediated by nicotinic acid receptors (GPR109A)

“…Mature blood neutrophils were isolated from peripheral blood of healthy donors by Ficoll-Hypaque centrifugation. 11,15,35,36 Briefly, peripheral blood mononuclear cells were separated by centrifugation on Ficoll-Hypaque (Seromed-Fakola AG, Basel, Switzerland). The lower phase, mainly granulocytes and erythrocytes, was treated with erythrocyte lysis solution (155 mmol/l NH 4 Cl, 10 mmol/l KHCO 3 , and 0.1 mmol/l EDTA, pH 7.3).…”

“…Cell death was assessed by uptake of 1 mM ethidium bromide and flow cytometric analysis (FACSCalibur). 11,15,35,36 To determine whether cell death was apoptosis, DNA fragmentation and redistribution of PS were measured. 11,15,35,36 Immunoprecipitation.…”

“…11,15,35,36 To determine whether cell death was apoptosis, DNA fragmentation and redistribution of PS were measured. 11,15,35,36 Immunoprecipitation. Neutrophils (5 Â 10 6 ) were lysed in a buffer containing 0.2% Nonidet P-40, and protein samples were immunoprecipitated with 2 mg of anti-14-3-3 Ab followed by precipitation with A-Sepharose.…”

“…Gel electrophoresis and immunoblotting were performed as described previously. 11,15,16,35,36 Briefly, after electrotransfer of the separated proteins, the filters were incubated overnight with anti-caspase-3 Ab, anti-Mcl-1 mAb, or anti-phospho-Bad Abs (all 1/1000) at 41C in TBS/0.1% Tween 20/5% nonfat dry milk. For loading controls, stripped filters were incubated with anti-GAPDH mAb (1/2000) or anti-Bad Ab (1/1000).…”