Abstract 1292: Osteopontin Mediates The Estradiol Effect On Endothelium Regrowth By Increasing The Capacity Of Bone Marrow-derived Cells To Adhere To Endothelial Cells
The improvement of the reendothelialization process could prevent atherosclerosis initiationand stent-induced neointima formation. We and others have demonstrated that estrogens (E2)accelerate the reendothelialization process through estrogen receptor α. However, the mechanisms involved are still poorly understood. In this work, we asked whether the multipotent protein osteopontin (OPN), which induces endothelial cells (EC) adhesion, proliferation and survival, was involved in E2 effect on reendothelialization. For this purpose, we compared the effect of E2 in wild type (OPN+/+) and OPN deficient (OPN−/−) mice. We demonstrated that OPN was required for the accelerative effect of E2 on endothelium regrowth. Moreover, we showed that E2 induced a 30% increase in EC proliferation in OPN+/+ mice but in OPN−/− mice, confirming that OPN is required for E2-mediated endothelium healing. Since E2 has been shown to act on endothelium regrowth through bone marrow (BM)-derived cells, we used a graft strategy and showed that OPN presence in the BM cells was absolutely required for the accelerative effect of E2. Since OPN was involved in adhesion processes, we hypothesized that OPN contribution in reendothelialization could be mediated through its capacity to induce a better adhesion of BM cells to the injured carotid in presence of E2. Indeed, we showed that E2 increased the adhesion of OPN using OPN+/+ and OPN−/− BM cells, that OPN was required for adhesion of these cells to EC (adhered BM cells numbering after 24h: 67 ± 44 OPN+/+ cells, 38 ± 24 OPN−/− cells and 50 ± 22 OPN−/− cells when human recombinant OPN (rOPN) was added, p<0.01). Furthermore, we showed that E2 action depended on OPN to increase adhesion of BM-derived cells on collagen I, a low-adhesive matrix for these cells compared to fibronectin. Indeed, E2 increased OPN expression in BM cells and OPN−/− BM cells showed an impaired adhesion on collagen I, which was reversed by addition of rOPN. Moreover, blocking anti-OPN antibody inhibited this E2-mediated effect. Altogether, our results suggest that E2 accelerates reendothelialization through OPN production by BM-derived cells, allowing them to adhere on the EC of the regenerating endothelium.