Abnormal Regulation of Transforming Growth Factor-β Receptors on Vascular Smooth Muscle Cells From Spontaneously Hypertensive Rats by Angiotensin II

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Abstract
Abstract —The effects of angiotensin II (Ang II) on the expression and characteristics of transforming growth factor-β (TGF-β) receptors on vascular smooth muscle cells (VSMC) from Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR) were investigated. TGF-β–induced stimulation of DNA synthesis by VSMC from WKY rats was abolished with Ang II, whereas basal and TGF-β–stimulated DNA synthesis by VSMC from SHR was increased with Ang II. Ang II stimulated DNA synthesis by VSMC from WKY rats in the presence but not in the absence of neutralizing antibody to TGF-β 1 . Antibody to TGF-β 1 enhanced the stimulatory effect of Ang II on DNA synthesis by VSMC from SHR. Ang II increased the specific binding of TGF-β to VSMC from WKY rats by increasing both the expression of the lower-affinity of TGF-β receptors as well as the total number of TGF-β binding sites. In contrast, VSMC from SHR showed a higher affinity and number of TGF-β receptors in the absence of Ang II than did cells from WKY rats, and these parameters were not affected by Ang II. Ang II increased the expression of TGF-β type I receptor mRNA in VSMC from WKY rats but had no effect of TGF-β receptor type I or II mRNA in VSMC from SHR, which predominantly express the type II receptor. These results indicate that an increase in the expression of the TGF-β type I receptor by Ang II may facilitate the ability of endogenous TGF-β to counteract the stimulatory effect of Ang II on growth in VSMC from WKY rats, whereas endogenous TGF-β induced by Ang II cannot counteract the growth-promoting action of Ang II in VSMC from SHR. The abnormal regulation of TGF-β receptors by Ang II may be associated with the exaggerated growth of VSMC from SHR.