Paricalcitol Inhibits Renal Inflammation by Promoting Vitamin D Receptor–Mediated Sequestration of NF-κB Signaling

Abstract

Inflammation is a pathologic feature of a variety of chronic kidney diseases. Several lines of evidence suggest a potential anti-inflammatory role for vitamin D in chronic kidney disease, but the underlying mechanism remains unknown. Here, the effect of the synthetic vitamin D analogue paricalcitol on renal inflammation was investigated in a mouse model of obstructive nephropathy. Paricalcitol reduced infiltration of T cells and macrophages in the obstructed kidney. This inhibition of inflammatory cell infiltration was accompanied by a decreased expression of RANTES and TNF-alpha. Induction of RANTES was localized primarily to the tubular epithelium, underscoring a role for tubular cells in renal inflammation. In a human proximal tubular cell line (HKC-8), paricalcitol inhibited RANTES mRNA and protein expression and abolished the ability of tubular cells to recruit lymphocytes and monocytes after TNF-alpha stimulation. Although RANTES induction depended on NF-kappaB signaling, paricalcitol affected neither TNF-alpha-mediated IkappaB alpha phosphorylation and degradation nor p65 NF-kappaB activation and nuclear translocation. Instead, chromatin immunoprecipitation assay showed that paricalcitol abolished the binding of p65 to its cognate cis-acting element in the RANTES promoter. The vitamin D receptor (VDR) and p65 formed a complex in tubular cells after paricalcitol treatment, which inhibited the ability of p65 to trans-activate gene transcription. In vivo, paricalcitol did not block NF-kappaB nuclear translocation after obstructive injury but did increase the expression and nuclear distribution of VDR. These results suggest that paricalcitol inhibits renal inflammatory infiltration and RANTES expression by promoting VDR-mediated sequestration of NF-kappaB signaling.