1,25 dihydroxyvitamin D amplifies type a natriuretic peptide receptor expression and activity in target cells

1,25 dihydroxyvitamin D (VD) has been shown to exert a number of beneficial effects on cardiovascular function, including reduction in BP and inhibition of cardiac hypertrophy. In an effort to identify a possible mechanistic link between VD and these salutary effects, the role of VD in controlling the activity and expression of the type A natriuretic peptide receptor (NPR-A), a receptor that signals reductions in BP and suppression of cellular growth in the myocardium and vascular wall, was investigated. VD, as well as the nonhypercalcemic analogue RO-25-6760, increased NPR-A-dependent cyclic guanosine monophosphate production and NPR-A gene expression in cultured rat aortic smooth muscle cells. The increase in NPR-A expression was associated with an increase in NPR-A gene promoter activity that was critically dependent on the presence of a functional VD receptor response element located approximately 495 bp upstream from the transcription start site of the gene. This element was associated with the VD receptor/retinoid X receptor complex in vitro. Mutation of this element resulted in complete elimination of the VD-dependent induction of the NPR-A gene promoter but did not affect osmotic stimulation of the promoter. Treatment of rats with RO-25-6760 for 7 d increased the atrial natriuretic peptide-dependent excretion of sodium and cyclic guanosine monophosphate without affecting mean arterial BP or plasma calcium levels. This was associated with a twofold increase in NPR-A mRNA levels in the inner medulla. Amplification of NPR-A activity represents a plausible mechanism to account for at least some of the beneficial effects that VD exerts on cardiovascular function.