1,25-Dihydroxyvitamin D3suppresses high glucose-induced angiotensinogen expression in kidney cells by blocking the NF-κB pathway

Abstract

The renin-angiotensin system (RAS) is a major mediator of renal injury in diabetic nephropathy. Our previous studies demonstrated that 1,25-dihydroxyvitamin D₃[1,25(OH)₂D₃] plays a renoprotective role by suppressing the RAS, with renin and angiotensinogen (AGT) as the main targets. The mechanism whereby 1,25(OH)₂D₃transcriptionally suppresses renin gene expression has been elucidated; however, how vitamin D regulates AGT remains unknown. Exposure of mesangial cells or podocytes to high glucose (HG; 30 mM) markedly stimulated AGT expression. In mesangial cells, the stimulation was inhibited by 1,25(OH)₂D₃(20 nM) or NF-κB inhibitor BAY 11–7082, suggesting the involvement of NF- κB in HG-induced AGT expression and the interaction between 1,25(OH)₂D₃and NF-κB in the regulation. Plasmid pNF-κB-Luc luciferase reporter assays showed that 1,25(OH)₂D₃blocked HG-induced NF-κB activity. EMSA and ChIP assays demonstrated increased p65/p50 binding to a NF-κB binding site at −1734 in the AGT gene promoter upon high glucose stimulation, and the binding was disrupted by 1,25(OH)₂D₃treatment. Overexpression of p65/p50 overcame 1,25(OH)₂D₃suppression, and mutation of this NF-κB binding site blunted 1,25(OH)₂D₃suppression of the promoter activity. In mice lacking the vitamin D receptor, AGT mRNA expression in the kidney was markedly increased compared with wild-type mice, and AGT induction in diabetic mice was suppressed by treatment with a vitamin D analog. These data indicate that 1,25(OH)₂D₃suppresses hyperglycemia-induced AGT expression by blocking NF-κB-mediated pathway.