Oxidized low density lipoprotein impairs endothelial progenitor cell function by downregulation of E-selectin and integrin αvβ5

https://doi.org/10.1016/j.bbrc.2008.06.066Get rights and content

Abstract

Background

Oxidized low density lipoprotein (oxLDL) has been shown to induce apoptosis and senescence of endothelial progenitor cells (EPC). In the present study, we hypothesized that even sub-apoptotic concentrations of oxLDL impair the angiogenic potential of EPC and investigated if this effect is mediated by affecting adhesion and incorporation.

Methods

A co-culture system of human microvascular endothelial cells and EPC was used to study the effect of sub-apoptotic concentrations of native (nLDL) and oxLDL on cell–cell interaction. The expression and the functional role of angiogenic adhesion molecules and integrins was monitored by FACS and neutralizing assay, respectively.

Results

We observed an inhibition of tube formation and impairment of EPC integration into the vascular network of mature endothelial cells by oxLDL. In contrast, nLDL did not affect angiogenic properties of EPC. Incubation of EPC with sub-apoptotic oxLDL concentrations significantly decreased E-selectin and integrin αvβ5 expression (37.6% positive events vs. 71.5% and 24.3% vs. 49.9% compared to control culture media without oxLDL). Interestingly, expression of αvβ3, VE-cadherin and CD31 remained unchanged. Blocking of E-selectin and integrin αvβ5 by neutralizing antibody effectively inhibited adhesion of EPC to differentiated endothelial cells (56.5% and 41.9% of control; p < 0.001).

Conclusion

In conclusion, oxidative alteration of LDL impairs angiogenic properties of EPC at sub-apoptotic levels by downregulation of E-selectin and integrin αvβ5, both substantial mediators of EPC-endothelial cell interaction.

Section snippets

Materials and methods

Cell culture. Peripheral blood mononuclear cells were isolated from buffy coats of human donors by density gradient centrifugation with Histopaque®-1077 (Sigma) as previously described [11]. Briefly, cells were plated on culture dishes coated with human fibronectin (Sigma) and maintained in EC basal medium-2 (EBM-2) (Clonetics) supplemented with endothelial growth medium SingleQuots and 5% fetal bovine serum (FBS; Sigma). After 4 days in culture, adherent cells were passaged and maintained in

Prevention of vascular structure formation by oxLDL

Applying a co-culture system on growth factor-reduced Matrigel®, VEGF acted as a strong promoter of capillary-like tubuli formation where EPC worked in concert with differentiated EC (HMEC) to form vessel-like structures (Fig. 1A). While the addition of nLDL had no effect on the organization of the co-culture system (data not shown), oxLDL in sub-apoptotic concentrations impaired network formation at 50 μg/ml (Fig. 1B) and totally inhibited formation of capillary-like network-like structures at

Discussion

In the present study, we investigated mechanisms responsible for the impaired angiogenic potential of EPC induced by oxLDL. Sub-apoptotic concentrations of oxLDL inhibited tube formation and impaired the integration of EPC into the vascular network of differentiated EC, an effect that was not seen when treated with nLDL. A possible mechanism for the observed impaired functional properties is the reduced expression of E-selectin and integrin αvβ5 on EPC by oxLDL as both molecules are relevant

Acknowledgments

Supported in part by the Swiss National Foundation (No. 3200B0-114100 to C.K.), the Swiss Heart Foundation to C.K. and the University of Bern, Switzerland (Grant-in-aid to C.K.).

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