Vascular smooth muscle cell hypertrophy vs. hyperplasia: Autocrine transforming growth factor-β, expression determines growth response to angiotensin II

Abstract

Recent observations in our laboratory suggest that angiotensin II (Ang II) is a bifunctional vascular smooth muscle cell (VSMC) growth modulator capable of inducing hypertrophy or inhibiting mitogen-stimulated DNA synthesis. Because transforming growth factor-β1 (TGFβ1) has similar bifunctional effects on VSMC growth, we hypothesized that autocrine production of TGFβ1, may mediate the growth modulatory effects of Ang II. Indeed, this study demonstrates that Ang II induces a severalfold increase in TGFβ1, mRNA levels within 4 h that is dependent on de novo protein synthesis and appears to be mediated by activation of protein kinase C (PKC). Ang II not only stimulates the synthesis of latent TGFβ1, but also promotes its conversion to the biologically active form as measured by bioassay. The coincubation of VSMCs with Ang II and control IgG has no significant mitogenic effect. However, the co-administration of Ang II and the unti-TGFβ1, antibody stimulates significantly DNA synthesis and cell proliferation. We conclude that: (a) Ang II induces increased TGFβ1, gene expression via a PKC dependent pathway involving de novo protein synthesis; (b) Ang II promotes the conversion of latent TGFβ1, to its biologically active form; (c) Ang II modulates VSMC growth by activating both proliferative and antiproliferative pathways; and (d) Autocrine active TGFβ1, appears to be an important determinant of VSMC growth by hypertrophy or hyperplasia.