Abstract
Leptin is an adipokine that is thought to be important in many inflammatory diseases, and is known to influence the function of several leukocyte types. However, no clear consensus is present regarding the responsiveness of neutrophils for this adipokine. In this study a 2D DIGE proteomics approach was used as an unbiased approach to identify leptin-induced effects on neutrophils. Additionally chemotaxis and survival experiments were performed to reproduce results from literature showing putative effects of leptin on these neutrophil responses. Leptin did not induce any significant changes in the proteome provided leptin was added at physiologically relevant concentrations (250 ng). Our leptin batches were biologically active as they induced proliferation in LeptinR expressing Ba/F3 cells. At high concentrations (25000 ng) leptin induced a change in neutrophil proteome. Seventeen differently regulated spots were identified of which twelve could be characterized by mass spectrometry. Two of these identified proteins, SerpinB1 and p40 phox, were chosen for further analysis but leptin-induced expression analyzed by western blot were highly variable. Additionally leptin also induced neutrophil survival at these high concentrations. No leptin-induced chemotaxis of human neutrophils was detected at any concentration. In conclusion, physiological concentrations of leptin do not affect neutrophils. High leptin concentrations induced survival and changes in the neutrophils proteome, but this was most likely mediated by an indirect effect. However, it cannot be ruled out that the effects were mediated by a yet not-identified leptin receptor on human neutrophils.
Highlights
Leptin is an adipokine involved in the control of energy intake and in immunity [1]
Ottonello et al have shown that Leptin is chemotactic for human neutrophils with a maximum migration at a concentration of 50 ng/ml [16,17]
In marked contrast to these studies that were mainly based on association between leptin and indicators of disease in obesity, surprisingly little is known regarding the leptin receptor on neutrophils and the functional responsiveness of these cells to this adipokine
Summary
Leptin is an adipokine involved in the control of energy intake and in immunity [1]. It is a protein which has structural similarities with pro-inflammatory cytokines such as IL-6, IL-12 and granulocyte colony-stimulating factor (G-CSF) [1]. The leptin receptor can be expressed in six alternatively spliced forms [1]. From these six receptors variants the OBRb receptor is the main signaling receptor [1,2]. Leptin has been shown to be important for the induction of inflammation in murine models of influenza infection and cigarette smoke exposure [6,7]. Data obtained in humans demonstrate an association between leptin concentrations and inflammation in tuberculosis patients [8]
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