1,25‑Dihydroxyvitamin D regulates macrophage polarization and ameliorates experimental inflammatory bowel disease by suppressing miR-125b

Abstract

Macrophages are highly plastic cells. Depending on stimulation, macrophages rapidly polarize to functionally distinct phenotypes that are involved in the pathogenesis of inflammatory bowel disease (IBD). 1,25‑Dihydroxyvitamin D (1,25(OH)₂D₃) has immunomodulatory activity, and 1,25(OH)₂D₃ deficiency is correlated with autoimmune diseases, especially IBD. This study aimed to explore whether 1,25(OH)₂D₃ modulates macrophage polarization in inflammation. Peripheral blood mononuclear cells and colitis mice were treated with 1,25(OH)₂D₃. Macrophages were transfected with siRNA-vitamin D receptor (VDR) or miR-125b mimic or inhibitor, and 1,25(OH)₂D₃-pretreated colitis mice were injected with a miR-125b agomir. The distribution of macrophage subsets and macrophage subtype characteristics was analyzed. As expected, 1,25(OH)₂D₃ transformed lipopolysaccharide-induced M1 macrophages to the M2 subset, downregulated tumor necrosis factor-α and interleukin (IL)-6 expression and interferon regulatory factor 5 (IRF5) phosphorylation, and upregulated IL-10, arginase-1, VDR, and IRF4 expression. SiRNA-VDR and miR-125b mimic significantly impaired 1,25(OH)₂D₃ activity. In colitis mice, 1,25(OH)₂D₃ pretreatment ameliorated disease activity, converted M1 macrophages to the M2 subtype, suppressed IRF5 phosphorylation, and increased IRF4 expression in lamina propria mononuclear cells (LPMC). miR-125b agomir injections reversed 1,25(OH)₂D₃ action. Collectively, the results demonstrate that 1,25(OH)₂D₃ downregulates miR-125b expression and promotes M1 macrophage polarization to the M2 subtype. 1,25(OH)₂D₃ pretreatment ameliorated colitis by restoring the LPMC macrophage subtype balance.

Keywords: 1,25(OH)(2)D(3); Colitis; IBD; Macrophage; miR-125b.