1,25-Dihydroxyvitamin D3Promotes High Glucose-Induced M1 Macrophage Switching to M2 via the VDR-PPARγSignaling Pathway

Abstract

Macrophages, especially their activation state, are closely related to the progression of diabetic nephropathy. Classically activated macrophages (M1) are proinflammatory effectors, while alternatively activated macrophages (M2) exhibit anti-inflammatory properties. 1,25-Dihydroxyvitamin D3has renoprotective roles that extend beyond the regulation of mineral metabolism, and PPARγ, a nuclear receptor, is essential for macrophage polarization. The present study investigates the effect of 1,25-dihydroxyvitamin D3on macrophage activation state and its underlying mechanism in RAW264.7 cells. We find that, under high glucose conditions, RAW264.7 macrophages tend to switch to the M1 phenotype, expressing higher iNOS and proinflammatory cytokines, including TNFαand IL-12. While 1,25-dihydroxyvitamin D3significantly inhibited M1 activation, it enhanced M2 macrophage activation; namely, it upregulated the expression of MR, Arg-1, and the anti-inflammatory cytokine IL-10 but downregulated the M1 markers. However, the above effects of 1,25-dihydroxyvitamin D3were abolished when the expression of VDR and PPARγwas inhibited by VDR siRNA and a PPARγantagonist. In addition, PPARγwas also decreased upon treatment with VDR siRNA. The above results demonstrate that active vitamin D promoted M1 phenotype switching to M2 via the VDR-PPARγpathway.