Homocysteine stimulates MAP kinase in bovine aortic smooth muscle cells

Background. Hyperhomocysteinemia is recognized as a risk factor for atheros clerotic disease. However; the mechanism of homocysteine effects on smooth muscle cell proliferation, which is a hallmark of atherosclerosis. is unkno wn. The object of this study was to test the effects of homocysteine on smo oth muscle cell proliferation, and to examine the mitogen-activated protein (MAP) kinases, extracellular signal-regulated protein kinase 1 and 2, that are known to be involved in cell proliferation. Methods. For the proliferation study, bovine aortic smooth muscle cells (BA SMC, 10, 000/well) were allowed to grow for 2 days before 2 mmol/L D,L-homo cysteine was added for 2, 4, 6, and 8 days to simulate the clinical hyperho mocysteinemic condition. For the MAP kinase study, quiescent BASMC were exp osed to 2 mmol/L D,L-homocysteine for 1.5, 5, 10, 20, 30, and 60 minutes, a nd the active forms of MAP Kinase were detected with Western immunoblotting . The degree of phosphorylation of MAP Kinase was determined by densitometr y. Results. D,L-homocysteine stimulated BASMC proliferation by 20% by day 8. M AP Kinase phosphorylation was activated as much as sixfold by D,L-homocyste ine, with a peak at 30 minutes. PD98059, an inhibitor of MAP kinase Phospho rylation, inhibited the homocysteine-induced MAP Kinase phosphorylation and attenuated the increase in BASMC proliferation. Conclusions. These data are consistent with the hypothesis that D,L-homocys teine stimulation of BASMC proliferation involves MAP kinase activation.