2009 Southern Regional Meeting Abstracts

Purpose of Study: Cardiac hormone atrial natriuretic peptide (ANP) plays a pivotal role in maintaining cardiovascular homeostasis and preventing cardiac remodeling. The binding of ANP to guanylyl cyclase/natriuretic peptide receptor-A (GC-A/NPRA) produces second messenger cGMP, which activates downstream signaling and biological effects of ANP/NPRA including vasorelaxation, antimitogenic, and cardiac anti-hypertrophic effects. The present study was aimed at gaining insight into the function of all-trans retinoic acid (ATRA) involving transcription factor Ets-1 in the regulation of Npr1 (coding for GC-A/NPRA) gene transcription and expression, which is an important regulator of ANP-dependent signaling in pathophysiology of hypertension and cardiovascular disorders.
Methods Used: Npr1 gene promoter- reporter deletion constructs were transiently transfected in cultured rat thoracic aortic smooth muscle cells (RTASMCs) using Lipofectamine-2000 and transcriptional activity was measured by dual luciferase assay. To determine the effect of all-trans retinoic acid (ATRA) signaling on NPRA expression, electrophoretic mobility shift assay, RT-PCR, and cGMP assays were performed.
Summary of Results: Promoter deletion analysis and luciferase assays demonstrated that ATRA enhances Npr1 promoter activity by more than 6- fold in a dose-dependent manner and induced NPRA mRNA levels by 4-fold in a time-dependent manner. The effect of ATRA is mimicked by TTNPB, a RA receptor agonist, which increased Npr1 gene transcription. ATRA also increased Ets-1 expression and enhanced its in vitro binding to Npr1 promoter as confirmed by gel shift assay. ATRA enhanced NPRA protein expression, its guanylyl cyclase activity, and ANP-dependent intracellular accumulation of second messenger cGMP.
Conclusions: The results demonstrate that retinoic acid signaling enhances Npr1 gene transcription and expression. The identification of retinoid signaling as a regulator of Npr1 gene transcription and protein expression will have important implications in cardiovascular regulation and prevention of cardiac hypertrophy and remodeling.