KLF2 regulates eNOS uncoupling via Nrf2/HO-1 in endothelial cells under hypoxia and reoxygenation.

Kruppel-like factor 2 (KLF2) regulates endothelial functions by modulating endothelial nitric oxide synthase (eNOS)/nitric oxide (NO) pathway. Tetrahydrobiopterin (BH4) and S-glutathionylation of eNOS play essential roles in eNOS uncoupling and activation. However, the influence of KLF2 on eNOS uncoupling and the mechanism of eNOS activation still remain unknown. A hypoxia and reoxygenation (H/R) model of human umbilical vein endothelial cells (HUVECs) was utilized in this study. Cell viability and the eNOS uncoupling-related oxidative stress index were measured. The Nrf2 inhibitor ML385 and HO-1 siRNA were used to elucidate the mechanism of activation. The results show that overexpression of KLF2 increased the cell viability, reduced the lactate dehydrogenase leakage rate, downregulated the generation of O2•- and ONOO-, and increased NO levels and eNOS activity. Overexpression of KLF2 also increased the BH4/BH2 ratio and the GSH/GSSG ratio, thus significantly improving eNOS uncoupling in the H/R model. KLF2 has no regulatory effect on the upstream-associated proteins in eNOS activation. However, when combined with the Nrf2 inhibitor or HO-1 siRNA, the regulatory effect of KLF2 on eNOS uncoupling was strongly reduced. These results suggest that KLF2 could improve eNOS uncoupling via Nrf2/HO-1 in H/R-induced endothelial injury.