CHARACTERISTICS AND EXPRESSION OF TRANSFORMING GROWTH-FACTOR-BETA RECEPTOR SUBTYPES ON VASCULAR SMOOTH-MUSCLE CELLS FROM SPONTANEOUSLY HYPERTENSIVE RATS

Objective: To investigate the characteristics and expression of transforming growth factor (TGF)-beta receptor subtypes on vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. Methods: The effects of TGF-beta(1) on DNA synthesis were evaluated by [H-3]-thymidine incorporation into quiescent VSMC plated at high (5 x 10(4) cells/cm(2)) or low (5 x 10(3) cells/cm(2)) cell density. Specific binding of TGF-beta to VSMC was assessed by incubation of the cells with [I-125]-TGF-beta(1). Affinity labelling of receptor subtypes was achieved by exposure of the cells to [I-125]-TGF-beta(1) and cross-linking with disuccimidyl suberate. Results: VSMC from SHR displayed a biphasic DNA synthesis response to TGF-beta 1 at high cell density, with DNA synthesis stimulated by low concentrations of TGF-beta(1) but not by high concentrations, whereas at low cell density there was a small increase in DNA synthesis in response to TGF-beta(1). TGF-beta 1 inhibited DNA synthesis in VSMC from WKY rats at both high and low cell densities. Binding assays revealed that VSMC from SHR had a larger number of TGF-beta receptors and a higher affinity for TGF-beta at high and at low cell densities. The affinity labelling with [I-125]-TGF-beta(1) revealed the presence of receptor subtypes with relative molecular masses of 280-300, 85, 70, 60 and 50x10(3) on vascular smooth muscle cells from both rat strains at high cell density. The abundance of the 85 x 10(3) molecular mass receptor subtype was greater in VSMC from SHR. The 85 x 10(3) molecular mass receptor subtype was not detected on VSMC from either strain at low cell density. Conclusion: The present results suggest a different expression of TGF-beta receptor subtypes on VSMC from SHR and WKY rats. These differences may account for the exaggerated proliferative response of VSMC from SHR to TGF-beta.