HIF1α and NFκB Regulate Mineralocorticoid Receptor Gene Expression in Aging Human Vascular Smooth Muscle Cells

Abstract

BackgroundMineralocorticoid receptor (MR) activation drives aging‐associated cardiovascular diseases including hypertension, vascular stiffness and heart failure. Vascular MR expression increases with age and drives the aging phenotype but the mechanism of MR gene regulation is unknown. The MR has two mRNA isoforms (1α and 1β) that differ in only the 5’‐untranslated region (exon 1α or 1β) and in the promoter sequence (P1 or P2, respectively). Thus, we investigated the transcriptional mechanisms regulating MR gene expression in aging human smooth muscle cells (SMC).MethodsMR mRNA and protein expression were quantified in primary human aortic SMC (HASMC) and human aortic tissue comparing adult (average age 40s) and aged (average age 70s) male and female donors and comparing adult HASMC or Pac1 (rat SMC line) treated with H2O2 to induce aging. MR promoter activity was tested by luciferase reporter assays. In silico analysis of the MR promoters identified putative transcription factor (TF) binding sites and inhibitor studies and chromatin immunoprecipitations (ChIP) were performed to validate the predicted regulatory mechanisms.ResultsIncreased SMC donor age or H2O2 treatment were associated with significantly increased expression of both of the MR mRNA isoforms, MR protein level, and activity of both MR promoters in HASMCs. The hypoxia‐inducible TF, HIF1α, and the inflammatory TF, NFκB, were predicted in silico to bind to the MR promoters and found to increase significantly with age in HASMCs. HIF1α was induced by H2O2 in HASMCs and this was associated with significant enrichment of HIF1α binding specifically at a site in the 1a exon, near the MR P1 promoter. HIF1α inhibition attenuated expression specifically of the MR‐1α mRNA isoform resulting in decreased MR protein in HASMC. NFκB also increased with age in HASMCs and contributes to MR expression. In response to H2O2,NFκB binding is enriched at to two different binding sites, one each in the P1 and P2 promoters and NFκB inhibition decreased expression of both MR mRNA isoforms (1α and 1β) and MR protein in SMC. Finally, HIF1α and NFκB expression each positively correlated with donor age and with MR expression (p<0.0001) in human aortic tissue from males and females.ConclusionThe MR gene is regulated by the inflammatory transcription factor NFkB and by the hypoxia/oxidative stress‐induced TF HIF1α, to increase MR expression in SMC of the aging human vasculature. This molecular insight may explain enhanced MR activity in cardiovascular aging and could potentially contribute to other cardiovascular conditions driven by oxidative stress and inflammation.