Vitamin D Inhibits Monocyte/macrophage Pro-inflammatory Cytokine Production by Targeting Mitogen-Activated Protein Kinase Phosphatase-1

Abstract

Vitamin D deficiency has been linked to severity of various allergic diseases. However, the mechanisms of vitamin D-mediated inhibition of inflammation remain poorly understood. In this study, we investigated the inhibitory effects of physiologic levels of vitamin D on lipopolysaccharide (LPS)-stimulated immune responses. Peripheral blood mononuclear cells (PBMC) from normal and asthmatic subjects, and murine bone marrow-derived macrophages (BMM) were pre-incubated with 1,25(OH)2D3 or 25(OH)D3, followed by LPS stimulation. p38 phosphorylation was detected by flow cytometry and Western Blotting. mRNA expression was analyzed by real-time PCR. Vitamin D receptor (VDR) binding and histone acetylation at vitamin D response element in the murine mitogen-activated protein kinase phosphatase-1 (MKP-1) promoter were detected by Chromatin Immunoprecipitation. Physiologic concentrations of 1,25(OH)2D3, and 25(OH)D3 inhibited LPS induced p38 phosphorylation and IL-6 production in normal subjects by 78% (p<0.01, n=4) and 77% (p<0.01, n=4) respectively. 1,25(OH)2D3 inhibited LPS induced p38 phosphorylation in asthmatic subjects by 57% (p<0.01, n=5). No inhibition of LPS induced p38 phosphorylation was found at 15ng/ml of 25(OH)D3. 1,25(OH)2D3 significantly up-regulated the expression of MKP-1 mRNA in adherent PBMC which consisted mainly of monocytes (2.2±0.2 fold, p<0.01, n=5) and BMM (2.6 ± 0.2 fold, p<0.01, n=3), increased binding of VDR (3.7±0.4 fold, p<0.05, n=3) and histone H4 acetylation (6.26±0.04 fold, p<0.05, n=3) at MKP-1 promoter. In BMM from MKP1-/- mice, the inhibition of LPS-induced p38 phosphorylation by vitamin D was completely abolished. This study demonstrates that up-regulation of MKP-1 by vitamin D inhibits LPS-induced p38 activation and cytokine production in monocytes/macrophages.