Objective: To investigate whether oxidized low-density lipoprotein (oxLDL) affects the survival and activity of endothelial progenitor cell (EPC) and whether the effects are mediated by lectin-like oxidized low-density lipoprotein receptor (LOX-1).
Methods: CD34+ cells isolated from human umbilical blood were cultured in endothelial cell growth medium-2 (EGM-2). After 14 days of culture, some EPCs were stimulated with 10, 25, 50 microg/ml of oxLDL for 48 hours; some were preincubated with LOX-1 mAb, a blocking antibody of LOX-1, for 24 hours, then exposed to 50 microg/ml oxLDL for 48 hours; others without any further treatment were used as control. The survival of EPC and the ability of adhesion, migration, and tube formation were examined. The levels of LOX-1 protein and mRNA expression were also assayed.
Results: Incubation with oxLDL at concentrations of 25 microg/ml or higher resulted in a dose-dependent increase of EPC apoptosis [25 microg/ml: (15.8 +/- 1.1.0%, 50 microg/ml: (18.8 +/- 2.0)% versus control: (9.0 +/- 1.2)%; P < 0.05]. Treated with oxLDL led to a significantly reduced migratry rate [25 microg/ml: (5.7 +/- 1.0)%, 50 microg/ml: (5.1 +/- 0.8)% versus control: (9.5 +/- 0.8)%; P < 0.05]. EPC treated with oxLDL showed a dose-dependent reduction of adhesion to fibronectin (25 Kg/ml: 33 +/- 2, 50 microg/ml: 30 +/- 3 versus control: 37 +/- 5; P < 0.05). Treatment with oxLDL impaired the in vitro vasculogenesis ability of EPCs. The total length of the tube structures in each photograph was decreased [25 microg/ml: (2.9 +/- 0.5) mm, 50 microg/ml: (1.8 +/- 0.5) mm versus control: (5.0 +/- 0.6) mm; P < 0.05]. The tube structure was severely disrupted, resulting in an incomplete and sparse tube network. However, all the detrimental effects on EPC were attenuated by pretreatment of EPC with LOX-1 mAb. In addition, Western blot analysis revealed that oxLDL increased LOX-1 protein expression from 100% to (172 +/- 8)% at a dose of 50 microg/ml. Furthermore, oxLDL caused an increase in LOX-1 mRNA expression from 100% to (174 +/- 39)% at a dose of 50 microig/ml.
Conclusion: OxLDL can directly inhibit EPC survival and activity and these effects are mediated by its receptor, LOX-1.