Angiotensin II Stimulates Collagen Synthesis in Human Vascular Smooth Muscle Cells

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Abstract
—Angiotensin II is an established regulator of vascular tone and smooth muscle cell (SMC) growth. However, there are little data about its effect on collagen synthesis by SMCs and none regarding the mechanism of such an effect. We studied the effect of angiotensin II on collagen production by human arterial SMCs, using uptake of [3H]proline into collagenase-digestible proteins, and by ribonuclease protection assay for mRNA encoding the proα1 chain of type I collagen, the major collagen in arteries. This revealed a dose-dependent increase in relative collagen synthesis rate and a dose-dependent increase in proα1(I) collagen mRNA abundance, with the half-maximal effect at 1.7 nmol/L. Angiotensin II–stimulated collagen expression was associated with a 6-fold increase in transforming growth factor-β (TGF-β) production and was inhibited by a neutralizing antibody to TGF-β. Both collagen production and TGF-β release were inhibited by the AT1-specific antagonist, losartan, but not by the AT2receptor antagonist, PD123319. To determined if tyrosine phosphorylation was functionally linked to collagen synthesis, we studied the effect of 2 mechanistically distinct inhibitors of tyrosine kinase, genistein, and tyrphostin A25. These inhibitors abrogated angiotensin II–mediated procollagen mRNA expression and angiotensin II–mediated TGF-β production, whereas the inactive homolog tyrphostin A1 had no effect. We conclude that angiotensin II stimulates collagen production in human arterial SMCs via the AT1receptor and an autocrine loop of TGF-β, induction of which requires tyrosine phosphorylation.

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