Leptin modulates dose‐dependently the metabolic and cytolytic activities of NK‐92 cells

Abstract

Leptin, a hormone-cytokine produced primarily in the adipose tissue, has pleiotropic effects on many biological systems and in several cell types, including immune cells. Hyperleptinemia is associated with immune dysfunction and carcinogenesis. Natural killer (NK) cells are critical mediators of anti-tumor immunity, and leptin receptor deficiency in mice leads to impaired NK function. It was thus decided to explore the in vitro effects of leptin on human NK cell function. NK-92 cells were cultured during 48 h with different leptin concentrations [absence, 10 (physiological), 100 (obesity), or 200 ng/ml (pharmacology)]. Their metabolic activity was assessed using the resazurin test. NK-92 cell cytotoxicity and intracellular IFN-γ production were analyzed by flow cytometry. NK-92 cell mRNA and protein expression levels of cytotoxic effectors were determined by RT-qPCR and Western blot. In our conditions, leptin exerted a dose-dependent stimulatory effect on NK-92 cell metabolic activity. In addition, high leptin concentrations enhanced NK-92 cell cytotoxicity against K562-EGFP and MDA-MB-231-EGFP target cells and inversely reduced cytotoxicity against the MCF-7-EGFP target. At 100 ng/ml, leptin up-regulated both NK cell granzyme B and TRAIL protein expressions and concomitantly down-regulated perforin expression without affecting Fas-L expression. In response to PMA/ionomycin stimulation, the proportion of IFN-γ expressing NK-92 cells increased with 100 and 200 ng/ml of leptin. In conclusion, leptin concentration, at obesity level, variably increased NK-92 cell metabolic activity and modulated NK cell cytotoxicity according to the target cells. The underlying mechanisms are partly due to an up-regulation of TRAIL and IFN-γ expression and a down-regulation of perforin.

Diet-Induced Obesity Is Associated with an Impaired NK Cell Function and an Increased Colon Cancer Incidence

“…Several former studies had already demonstrated that leptin influences NK cell cytotoxicity using different cell types as target cells [15, 24, 28–30]. Until now, no data existed about a leptin-mediated regulation on cytotoxic effects of NK cells against colon tumor cells.…”

“…However, all these studies were performed using the human myelogenous leukemia line K652 or the murine lymphoma cell line YAC-1 as target cells but not on colon cancer cell lines. Therefore, the conflicting results of the leptin effect on the lytic activity of NK cells may result from the use of different tumor target cells for cytotoxicity assays as it was already demonstrated by Lamas et al [30]. …”

Enhancement of Lytic Activity by Leptin Is Independent From Lipid Rafts in Murine Primary Splenocytes

“…Furthermore, NK cell enriched fraction lytic activity is quite proportional to effector cell amount with 13% and 31% in respectively 25:1 and 50:1 (effector:target cell) ratios. Previous studies were conducted on NK‐92 cell line versus K562, MDA‐MB‐231, and MCF‐7 cells (Lamas et al, ). Indeed, NK‐92 cell lytic activity reached already respectively 14%, 23%, and 20% with the same amount of target cells (5,000 cells/well).…”

“…The number of dead CFSE‐labelled target cells was determined by analyzing CFSE and PI double‐positive cells (emission at 509 and 625 nm, respectively) by flow cytometry. As reported previously (Allegra et al, ; Lamas et al, ), the percent of lytic activity was calculated with the following equation: …”

Immunological and Translational Aspects of NK Cell-Based Antitumor Immunotherapies

“…The stimulation of NK cells with cluster of differentiation 3 (CD3)-secreted cytokines resulted in a retardation of the growth of melanoma and breast tumors in mice with severe combined immunodeficiency (SCID). In a study by Lamas et al, it was demonstrated that leptin, a hormone–cytokine produced primarily by the adipose tissue, increased NK-92 cell metabolic activity and modulated NK cell cytotoxicity toward cancer cells due to an upregulated TNF-related apoptosis-inducing ligand (TRAIL) and IFN-γ expression (48). Another attractive cytokine candidate that was shown to enhance in vitro and in vivo NK cell-mediated cytotoxicity and cytokine production is IL-15 (49, 50).…”