Regulation of Natriuretic Peptide Receptor A and B Expression by Transforming Growth Factor-/*! in Cultured Aortic Smooth Muscle Cells

Two types of natriuretic peptide receptors (NPR-A and NPR-B) are membrane guanylate cyclases whose relative expression varies in different tissues. Because natriuretic peptides have been shown to inhibit aortic smooth muscle proliferation, we investigated the regulation of NPR-A and NPR-B in these cells under different proliferative conditions. NPR subtype mRNA levels were measured by our newly developed quantitative reverse transcription-polymerase chain reaction assay using mutated NPR-A and NPR-B cRNA as internal standards. The functional impact of their expression was determined by atrial nutriuretic peptide (ANP)and C-type natriuretic peptide (CNP)-induced stimulation of cyclic GMP production. In the intact aorta, NPR-B mRNA levels were found to be 10-fold higher than those of NPR-A. This dominance was further amplified (1000-fold) in long-term cultures (10 to 15 passages) of aortic smooth muscle cells (ASMC). Higher cyclic GMP production with CNP than with ANP was observed in cultured ASMC from Wistar-Kyoto (WKY) rats. Similar stimulation by the two agonists was noted in spontaneously hypertensive rat (SHR) cells, paralleled by a The natriuretic peptide family consists of at least three members: atrial natriuretic peptide (ANP),brain natriuretic peptide (BNP),and C-type natriuretic peptide (CNP). Three types of receptors of this natriuretic peptide family have been identified and cloned. Natriuretic peptide receptor-C (NPR-C) is considered to have mainly a clearance function,while the other two, natriuretic peptide receptor-A (NPR-A) and natriuretic peptide receptor-B (NPR-B), also known as guanylate cyclase-A and guanylate cyclase-B, respectively,-" are believed to be biologically active binding sites possessing intrinsic particulate guanylate cyclase activity. Several studies have shown that NPR-A and NPR-B have different ligand selectivity. NPR-A mainly binds ANP and BNP, whereas NPR-B mainly binds CNP.-This differential selectivity suggests that they play distinct physiological roles. Suga et al recently reported that NPR-B is highly expressed in vascular smooth muscle and that CNP is synthesized in and secreted from endothelial cells in response to various secretaFrom the Centre de recherche, H6tel-Dieu de Montreal, University de Montreal (Quebec, Canada). Reprint requests to Dr Johanne Tremblay, Laboratory of Cellular Biology of Hypertension, Centre de recherche, Hotel-Dieu de Montreal, 3840, rue Saint-Urbain, Pavilion Jeanne-Mance, Montreal, Quebec, Canada H2W ITS. 10-fold increase in NPR-A mRNA levels and ANP stimulation of cyclic GMP in hypertensive cells. The present study also evaluated NPR-A and NPR-B mRNA control by transforming growth factor-/?, (TGF-/3,), an important regulator of cell proliferation that is overexpressed in SHR ASMC. TGF-0, decreased both NPR-A and NPR-B mRNA levels with a predominant effect in SHR cells at high cell density. This effect was paralleled by a fall in CNPand ANP-induced cyclic GMP levels after preincubation with TGF-/3,. Our study demonstrates the increase of NPR-B expression from contractile to proliferative phenotypes of ASMC and presents the first evidence of cytokine regulation of the two NPR subtypes at the mRNA level with the potential for an integrated role of these two systems in the control of vascular smooth muscle growth. (Hypertension. 1994;23[part 2]:908-913.)