Mechanism by Which Inflammation and Oxidative Stress Induce Mineralocorticoid Receptor Gene Expression in Aging Vascular Smooth Muscle Cells

Background: Vascular MR (mineralocorticoid receptor) expression increases with age driving aging-associated vascular stiffness and hypertension. MR has two isoforms (1α and 1β) with distinct 5'-untranslated and promoter sequences (P1 and P2), but the gene regulatory mechanisms remain unknown. We investigated mechanisms driving MR gene transcriptional regulation in aging human smooth muscle cells (SMC).

Methods: MR was quantified in aortic tissue and primary human aortic SMC (HASMC) comparing adult and aged donors and adult HASMC treated with H₂O₂, to induce aging. Predicted transcription factor (TF) binding sites in the MR gene were validated using chromatin immunoprecipitations and reporter assays. The impact of TF inhibitors on MR isoforms and fibrosis target gene expression was examined.

Results: Expression of both MR mRNA isoforms increased with donor age or H₂O₂ treatment in HASMCs. HIF1α (hypoxia-inducible factor) and the inflammatory TF NFκB (nuclear factor kappa B) both increased with age in HASMCs and are predicted to bind MR promoters. H₂O₂ induced HIF1α and NFκB expression and DNA binding of HIF1α to the MR P1 promoter and of NFκB to both MR promoters in HASMCs. HIF1α inhibition decreased MR-1α isoform expression while NFκB inhibition decreased both MR isoforms. HIF1α, NFκB, and MR inhibition decreased the expression of a SMC-MR target gene implicated in vascular fibrosis. In human aortic tissues, expression of HIF1α and NFκB each positively correlated with donor age and MR expression (P<0.0001).

Conclusions: These data implicate the inflammatory TF, NFκB, and oxidative stress-induced TF, HIF1α, in regulating SMC MR transcription in aging HASMCs, which drives aging-related vascular stiffness and cardiovascular disease.