Effect of AT 2 Receptor on Expression of AT 1 and TGF-β Receptors in VSMCs from SHR

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Abstract
We recently reported that overexpression of the angiotensin II type 2 (AT 2 ) receptor downregulates the AT 1a receptor through the bradykinin/NO pathway in a ligand-independent manner in vascular smooth muscle cells (VSMCs). In the present study, we investigated the effect of AT 2 receptor overexpression on the expression of the AT 1a receptor and transforming growth factor-β (TGF-β) receptor subtypes in VSMCs from spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY). Transfection of the AT 2 receptor gene downregulated expression of the AT 1a receptor in VSMCs from WKY, but did not affect expression of the AT 1a receptor in VSMCs from SHR. Transfection of the AT 2 receptor abolished DNA synthesis in response to angiotensin II in VSMCs from WKY; in VSMCs from SHR, basal DNA synthesis was suppressed, but DNA synthesis in response to Ang II was not altered. The NO substrate l -arginine augmented downregulation of the AT 1a receptor in VSMCs from WKY, whereas it did not affect expression of the AT 1a receptor in VSMCs from SHR. In response to AT 2 receptor transfection, expression of TGF-β type I receptor mRNA was suppressed significantly in VSMCs from WKY, whereas expression of TGF-β type I receptor was not altered in VSMCs from SHR. These results suggest that the AT 2 receptor downregulates AT 1a and TGF-β type I receptors in normal VSMCs, but not in SHR-derived VSMCs. The lack of downregulation of the AT 1a receptor may contribute, in part, to the exaggerated growth of VSMCs from SHR.