RESUMO
Leptin is a cytokine, produced mainly by mature adipocytes, that regulates the central nervous system, mainly to suppress appetite and stimulate energy expenditure. Leptin also regulates the immune response by controlling activation of immunomodulatory cells, including eosinophils. While emerging as immune regulatory cells with roles in adipose tissue homeostasis, eosinophils have a well-established ability to synthesize pro-inflammatory molecules such as lipid mediators, a key event in several inflammatory pathologies. Here, we investigated the impact and mechanisms involved in leptin-driven activation of eicosanoid-synthesizing machinery within eosinophils. Direct in vitro activation of human or mouse eosinophils with leptin elicited synthesis of lipoxygenase as well as cyclooxygenase products. Displaying selectivity, leptin triggered synthesis of LTC4 and PGD2, but not PGE2, in parallel to dose-dependent induction of lipid body/lipid droplets biogenesis. While dependent on PI3K activation, leptin-driven eosinophil activation was also sensitive to pertussis toxin, indicating the involvement of G-protein coupled receptors on leptin effects. Leptin-induced lipid body-driven LTC4 synthesis appeared to be mediated through autocrine activation of G-coupled CCR3 receptors by eosinophil-derived CCL5, inasmuch as leptin was able to trigger rapid CCL5 secretion, and neutralizing anti-RANTES or anti-CCR3 antibodies blocked lipid body assembly and LTC4 synthesis induced by leptin. Remarkably, autocrine activation of PGD2 G-coupled receptors DP1 and DP2 also contributes to leptin-elicited lipid body-driven LTC4 synthesis by eosinophils in a PGD2-dependent fashion. Blockade of leptin-induced PGD2 autocrine/paracrine activity by a specific synthesis inhibitor or DP1 and DP2 receptor antagonists, inhibited both lipid body biogenesis and LTC4 synthesis induced by leptin stimulation within eosinophils. In addition, CCL5-driven CCR3 activation appears to precede PGD2 receptor activation within eosinophils, since neutralizing anti-CCL5 or anti-CCR3 antibodies inhibited leptin-induced PGD2 secretion, while it failed to alter PGD2-induced LTC4 synthesis. Altogether, sequential activation of CCR3 and then PGD2 receptors by autocrine ligands in response to leptin stimulation of eosinophils culminates with eosinophil activation, characterized here by assembly of lipidic cytoplasmic platforms synthesis and secretion of the pleiotropic lipid mediators, PGD2, and LTC4.
Assuntos
Eosinófilos/imunologia , Leptina/metabolismo , Leucotrieno C4/biossíntese , Receptores CCR3/metabolismo , Receptores Imunológicos/metabolismo , Receptores de Prostaglandina/metabolismo , Animais , Células Cultivadas , Quimiocina CCL5/antagonistas & inibidores , Quimiocina CCL5/metabolismo , Eosinófilos/citologia , Eosinófilos/efeitos dos fármacos , Eosinófilos/metabolismo , Feminino , Humanos , Hidantoínas/farmacologia , Oxirredutases Intramoleculares/antagonistas & inibidores , Oxirredutases Intramoleculares/metabolismo , Leptina/imunologia , Leucotrieno C4/imunologia , Gotículas Lipídicas/imunologia , Gotículas Lipídicas/metabolismo , Masculino , Camundongos , Camundongos Endogâmicos BALB C , Piperidinas/farmacologia , Cultura Primária de Células , Prostaglandina D2/metabolismo , Receptores CCR3/antagonistas & inibidores , Receptores CCR3/imunologia , Receptores Imunológicos/antagonistas & inibidores , Receptores Imunológicos/imunologia , Receptores de Prostaglandina/antagonistas & inibidores , Receptores de Prostaglandina/imunologia , Proteínas Recombinantes/imunologia , Proteínas Recombinantes/metabolismoRESUMO
Leukotriene C(4) is an important mediator in the development of inflammatory reactions and ischaemia. Previous studies have shown that leukotriene C(4) is able to modulate the function of dendritic cells (DCs) and induce their chemotaxis from skin to lymph node. In this study, we decided to evaluate the modulation exerted by leukotriene C(4) on DCs, depending on their status of activation. We showed for the first time that leukotriene C(4) stimulates endocytosis both in immature and lipopolysaccharide (LPS) -activated DCs. Moreover, it suppressed the interleukin-12p70 (IL-12p70) release, but induces the secretion of IL-23 by DCs activated with LPS and promotes the expansion of T helper type 17 (Th17) lymphocytes. Furthermore, blocking the release of IL-23 reduced the percentages of CD4(+) T cells producing IL-17 in a mixed lymphocyte reaction. Ours results suggest that leukotriene C(4) interferes with the complete maturation of inflammatory DCs in terms of phenotype and antigen uptake, while favouring the release of IL-23, the main cytokine involved in the maintenance of the Th17 profile.