Leptin upregulates CRAC channel expression in T lymphocytes (IRC2P.444)

Abstract

Abstract Obesity is a major health problem associated with systemic diseases whose pathogenesis has been linked to inflammation, but the underlying mechanisms are poorly understood. Leptin, an adipokine secreted by adipose tissue, is known to augment the antigen-dependent release of pro-inflammatory cytokines by T lymphocytes. Cytokine production is tightly regulated by cytoplasmic Ca2+ (Cac ) which is under the control of ion channels (Kv1.3, KCa3.1, calcium release activated Ca2+channel [CRAC, formed by Orai1 and Stim1]). We tested the hypothesis that ion channels contribute to the pro-inflammatory effects of leptin. CD3+ T cells isolated from healthy human donors were treated with 100-250 ng/ml leptin and ion channels’ gene expression was measured by RT-qPCR. Leptin induced a dose- and time-dependent increase in Orai1 expression up to 1.53 ± 0.21 (100 ng/ml) and 2.04 ± 0.40 folds (250 ng/ml, n=3) at 12 h. There was no significant difference in Stim1, Kv1.3 and KCa3.1 expression. CRAC channels are important for activation-mediated Ca2+ influx in T cells. Thus, we investigated whether Orai1 regulation by leptin affects Cac using a protocol that bypasses the T cell receptor and allows assessment of ion channel-dependent changes in Cac. Incubation with leptin-depleted serum reduced Ca2+ fluxes, while addition of 250 ng/ml of leptin to the leptin-free serum augmented Ca2+ fluxes. These findings suggest that leptin may promote hyperactivity of T cells via upregulation of ion channels.