Essential Role of Bone Marrow Fibroblast Growth Factor-2 in the Effect of Estradiol on Reendothelialization and Endothelial Progenitor Cell Mobilization

Abstract

17␤-Estradiol (E 2 ) accelerates reendothelialization and increases the number of circulating endothelial progenitor cells (EPCs), but whether fibroblast growth factor-2 (FGF2) is involved in these processesEndothelium, uniquely positioned at the interface between the blood and the vessel wall, plays a crucial role in the physiology of circulation by performing multiple functions.1 It is involved in the regulation of coagulation, leukocyte adhesion in inflammation, transvascular flux of cells, liquids and solutes, vessel tone, and vascular smooth muscle growth. Endothelium also constitutes a target for the sex hormone 17␤-estradiol (E 2 ). In a series of experimental models, E 2 has been reported to promote endothelial regrowth after endothelial denudation in rats 2 and mice.3-5 These effects are known to be mediated through the estrogen receptor ␣ 3 and endothelial nitricoxide synthase. 4 Several growth factors could be involved in this process. Among them, in vitro models suggest that fibroblast growth factor-2 (FGF2) may be a key partner of E 2 . 6,7 Moreover, both FGF2 and FGF receptor 1 are expressed in regenerating endothelial cells in a model of rat carotid injury, 8 and FGF2 is an important mitogenic and angiogenic factor that stimulates endothelial cell growth, migration, and reendothelialization. 9 FGF2 expression is complex because at least four isoforms (18, 22, 22.5, and 24 kd) in humans and three (18, 21, and 22 kd) in mice are synthesized, not through the classic mechanism of

Estradiol accelerates endothelial healing through the retrograde commitment of uninjured endothelium

“…Third, platelets are abundant in the deendothelialized area (9,26) and release factors that can directly (32) or indirectly (27) contribute to accelerate reendothelialization. Indeed, we previously reported that BM FGF-2 is absolutely required in the accelerative effect of E 2 in reendothelialization, whereas extra-BM FGF-2 is dispensable (15), suggesting that FGF-2 is a key mediator of the E 2 action at the level of the BM. The en face analysis by EFCM does not suggest that BM-derived cells contribute substantially as cobblestones of the regenerated endothelial pavement, at least not in the repair process in the models used in the present study, in which the injury is limited to 4 mm and reendothelialization is completed after 1 wk.…”

“…However, whereas the number of GFP-positive cells in the Regen was about 4% and very abundant in the adventitia, no GFP-positive cells could be detected in the media (Ref. 15 and not shown).…”

“…Even though the perivascular carotid model has been used in several published studies (8,15,41,45), no systematic comparison with the endovascular injury has yet been reported, although both models behave similarly in terms of accelerated endothelial healing by 17␤-estradiol (E 2 ) estimated 3 days postinjury by Evans blue staining (8).…”

“…As an alternative method, we more recently proposed a model of perivascular electric injury of the carotid artery (9), based on a femoral artery injury model developed by Carmeliet and colleagues (10). Even though the perivascular carotid model has been used in several published studies (8,15,41,45), no systematic comparison with the endovascular injury has yet been reported, although both models behave similarly in terms of accelerated endothelial healing by 17␤-estradiol (E 2 ) estimated 3 days postinjury by Evans blue staining (8).Indeed, it is now clear that the physiological and pathophysiological role of E 2 is not limited to reproductive organs but involves many other tissues, in particular those belonging to the cardiovascular system. In particular, E 2 exerts several beneficial effects at the level of the endothelium; it promotes endothelial nitric oxide (eNO) production and prevents VCAM-1 expression and endothelial apoptosis (4, 28).…”

Estrogen Receptor α Expression in Both Endothelium and Hematopoietic Cells Is Required for the Accelerative Effect of Estradiol on Reendothelialization

“…15,28 However, most of these experiments showed a correlation between EPC increase and acceleration of reendothelialization rather than a causative relationship. 29 To further characterize the relationship between BM-derived cells and the regenerating endothelial cell monolayer, we grafted GFP-BM to wild-type mice and found that only a few GFP-positive cells (3% to 4% of intima cells) were present at the level of the regenerated endothelial cell monolayer, irrespective of the E2 treatment. Noteworthy, they were no longer detectable 30 days postinjury, indicating that these cells did not incorporate into the regenerated endothelium.…”