The biphasic effects of oxidized-low density lipoprotein on the vasculogenic function of endothelial progenitor cells

Late-outgrowth endothelial progenitor cells (EPCs) are stress-resistant and responsible for reparative functions in the cardiovascular system. Oxidized-LDL (oxLDL) plays a critical role in cardiovascular disease pathogenesis. However, it is largely unknown what the impacts of oxLDL are on late-outgrowth EPCs. This study aimed to investigate the concentration- related effects of oxLDL on EPC functions and related angiogenesis, in vitro and in vivo. In this study, early and late-outgrowth EPCs were generated from circulating human mononuclear cells. oxLDL may regulate EPC vasculogenic function via the lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1). Lower concentrations (5 μg/mL) of oxLDL can potentiate EPC tube formation in vitro and in vivo by activating eNOS mechanisms, which are mediated by p38 MAPK- and SAPK/JNK-related pathways. Higher concentrations of oxLDL (10-50 μg/mL) impaired EPC function via the activation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase pathways and consequent inhibition of eNOS activity, which could be reversed by anti-oxidants (diphenylene iodonium and apocynin) and gp91^phox siRNA. In conclusion, oxLDL has concentration-dependent biphasic effects on human late-outgrowth EPC tube formation in vitro and in vivo.