Involvement of u-PA in the anti-apoptotic activity of TGFβ for vascular smooth muscle cells

Abstract

Previous studies suggest a role for the plasminogen or fibrinolytic system in the activation of latent-transforming growth β (L-TGFβ) into active TGFβ. In the present study, the anti-apoptotic activity of TGFβ on cultured vascular smooth muscle cells (SMC) isolated from the aorta of transgenic mice with single inactivation of genes encoding the tissue-type plasminogen activator (t-PA −/−), urokinase-type plasminogen activator (u-PA −/−), urokinase receptor (u-PAR −/−) or plasminogen (Plg −/−) genes was examined. Latent-TGFβ inhibited serum deprivation-induced apoptosis of SMC isolated from wild-type and t-PA −/− mice but failed to reduce apoptosis of SMC isolated from u-PA −/−, u-PAR −/− or Plg −/− mice. Active TGFβ, however, was able to inhibit serum deprivation-induced apoptosis of these 5 cell types, indicating that u-PA and/or plasmin were involved in the activation of L-TGFβ. The anti-apoptotic effect of L-TGFβ could not be evoked by addition of exogenous t-PA to u-PA −/− cells, but was revealed by addition of exogenous u-PA or plasmin. This effect was dependent on the catalytic activity of plasmin as revealed by the dose-dependent inhibition of aprotinin or epsilon aminocaproic acid (EACA). These results therefore indicate that, at least in vitro, u-PA-mediated plasmin, through the generation of active TGFβ from L-TGFβ, is required for the anti-apoptotic activity of TGFβ on SMC.