The mechanism of long-term low-dose asymmetric dimethylarginine inducing transforming growth factor-β expression in endothelial cells

Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase (NOS) inhibitor, accumulates in plasma during chronic kidney disease (CKD). High plasma levels of ADMA can increase transforming growth factor-beta (TGF-beta) expression, related to renal fibrosis, but the precise molecular mechanism is not explicit. The present study was designed to determine the mechanism through which long-term low-dose ADMA induces TGF-beta expression in endothelial cells and to investigate the molecular mechanism of its action. Human umbilical vein endothelial cells (HUVECs) were exposed to low-dose ADMA (5 and 10 mu mol/l) for 7 passages and TGF-beta expression was determined. Human renal glomerular endothelial cells (HRGECs) were exposed to high-dose ADMA (100 mu mol/l) which were used to clarify the molecular mechanism. The results showed that long-term low-dose ADMA (5 and 10 mu mol/l) increases TGF-beta production in both mRNA and protein levels in HUVECs in a time-dependent manner. We confirmed that exogenous ADMA (100 mu mol/l) significantly enhanced stress fiber formation in HRGECs and upregulated TGF-beta expression. Such effects of ADMA in HRGECs were inhibited by pre-treatment with actin depolymerizing agent, actin stabilizing agent, p38 MAPK inhibitor and NADPH oxidase inhibitor. In addition, we demonstrated that ADMA (100 mu mol/l) significantly activated nuclear factor-kappa B (NF-kappa B) in HRGECs, which was markedly attenuated by actin depolymerizing agent, actin stabilizing agent, p38 MAPK inhibitor and NADPH oxidase inhibitor. In brief, the present study demonstrated that long-term low-dose ADMA induces TGF-beta expression in endothelial cells at both the gene