Effects of wild-type (Trp72) and mutant (Arg72) apolipoprotein(a) kringle IV-10 on the proliferation of human arterial smooth muscle cells

Objective To assess the atherogenicity of lipoprotein( a), the effect of the heterogeneity of lysine. binding of apolipoprotein ( a) [apo ( a)], a plasminogen-like glycoprotein component on the proliferation of human arterial smooth muscle cells (SMCs). Methods Both wild type (wt) Trp72 and mutant (mut) Trp72-->Arg forms of apo(a) kringle IV-10 were expressed by employing a GST-gene fusion system into E coli. The proliferation of SMCs was determined by flow cytometry and MTT colorimetry. Enzyme-linked immunosorbent assay ( ELISA) assay was used to detect the active form of transforming growth factor beta(1) (TGF-beta(1)). Results Apo(a) wt-kringle IV-10 that has lysine binding properties possessed a growth-stimulating activity to SMCs on a dose-dependence manner by stimulating cells in the G(1)/G(0) phase of cell cycle to S and G(2)/M phase, and reduced significantly the amounts of endogenous active TGF-beta(1) in culture when compared with the control medium and the GST group (2. 4 +/- 0. 5 vs 8. 6 +/- 1. 6 and 9. 1 +/- 1. 7 ng/ml, P<0.01). The growth-stimulating effect of apo(a) mut-kringle IV-10 deficient in lysine binding was negligible. Conclusions Apo(a) induces SMCs growth by inhibiting the activation of latent TGF-beta(1), an activity that may involve the ability of apo(a) kringle IV-10 to bind lysine. The mitogenic effect of apo(a) wt-kringle IV-10 on SMCs might play an active role in the atherogenic function of lipoprotein(a).