Effects of exogenous homocysteine on cellular proliferation and extracellular matrix production in cultured rat mesangial cells

Homocysteine (HCY) is a thiol-containing amino acid produced as a result of the demethylation of methionine. It has been proved that elevated HCY is associated with a high risk of arteriosclerotic cardiovascular disease. Although hyperhomocysteinaemia is observed frequently in patients with end-stage renal disease, its role in the process of glomerulosclerosis is not clear. This study investigated the effects of exogenous HCY on proliferation, phenotype change and extracellular matrix production in rat mesangial cells (MCs). The results revealed that DNA synthesis in MCs, measured by the [H-3]-thymidine uptake, did not increase significantly when the cells were treated with HCY at concentrations of 5 x 10(-5), 5 x 10(-4) or 1 x 10(-3) mol/L, even though thymidine incorporation in MCs increased two- to fourfold using 20% fetal calf serum-RPMI medium or platelet-derived growth factor (20 ng/mL). A dose-dependent increase in thymidine incorporation in vascular smooth muscle cells was also found when these cells were treated with HCY at similar concentrations (P < 0.01). The cell cycle was not changed when MCs were stimulated by HCY at different doses (5 x 10(-5), 5 x 10(-4) and 1 x 10(-3) mol/L) or at different time points (24, 48 and 72 h). Additionally, increased extracellular signal-regulated kinase was observed in MCs induced by PDGF (10 ng/mL), but not by HCY (0.5 mmol/L) for 2-60 min. alpha -Smooth muscle actin, detected using Western blot analysis, was not changed when MCs were exposed to 0.5 mmol/L HCY for 6, 12, 18, 24 and 36 h. Fibronectin and laminin, which are detected in the supernatant of cultured MCs by inhibition enzyme-linked immunosorbent assay, were not changed when MCs were exposed to HCY (5 x 10(-4) mol/L) for 2, 4, 6 or 8 days. These results suggest that HCY has no effect on proliferation, phenotype change or extracellular matrix production in MCs. This indicates that HCY may not be a key factor contributing to the process of glomerulosclerosis.