Neovascularization of Embryonic Rat Hearts Cultured in oculo Closely Mimics in utero Coronary Vessel Development

Abstract

Coronary neovascularization was studied following grafting of avascular hearts from gestation day-12 (E-12) rat embryos to the anterior eye chambers of adult rats. Volume densities (V_v) of vessels, myocytes, and the extracellular matrix (ECM) after 3–7, 14, 21, and 35 days in oculo were compared to V_v in hearts developing in utero at E-15, E-18, and E-20. The myocardium in both models exhibited similar vessel V_v and capillary developmental stages: (1) clustering of endothelial cells and red blood cells; (2) endothelial cell migration, and (3) tube formation/maturation. The V_v of myocytes increased while that of the ECM remained constant over time. Cross-species grafting utilizing species-specific antibodies determined that the majority, but not all, of the 10-day graft vasculature was of graft origin. Therefore, both de novo growth (vasculogenesis) and sprouting (angiogenesis) were occurring in oculo. Tracer molecules infused into host rats reached the outermost graft vessels only after 10 days in oculo, suggesting a functional link with the host circulation after this time. Thus, we have shown that both models exhibit similar: (1) vascular V_v; (2) shifts in V_v of nonvascular components; (3) stages of neovascularization, and (4) mechanisms of neovascularization. In conclusion, coronary neovascularization occurring in oculo closely mimics normal coronary vessel development.

Vasculogenesis of the embryonic heart: Origin of blood island‐like structures

“…The NRBCs residing in blood islands express Ter/119 antigen, whereas endothelial cells exhibited PECAM1 antigen. In addition to the previous TEM studies (Rongish et al, 1994;Ratajska and Fiejka, 1999), which claimed that red blood cells were accompanied by angioblasts/endothelial cells, we demonstrated that some of the NRBCs were located in areas where angioblasts were absent. These solitary (free) NRBCs were mostly positioned in the subendocardium.…”

“…Vessel development within the embryonic heart occurs via two processes: vasculogenesis and angiogenesis (Rongish et al, 1994;Risau, 1995Risau, , 1997. Vasculogenesis is the formation in situ of coronary vessels from endothelial cell progenitors (angioblasts) or angioblast migration to areas of vessel formation and their subsequent differentiation into vascular channels.…”

“…The first sings of vasculogenesis in heart development are blood island-like structures. This term was introduced due to the structures' morphological resemblance to the blood island of the yolk sac (Rongish et al, 1994). These structures assemble in clusters prior to their presumed coalescence and differentiation into vascular channels (Tomanek et al, 1996).…”

“…Blood island-like structures are located within the myocardial wall and the subepicardium of 10 and 11 dpc mice (Virá gh and Challice, 1981). They are encountered within 13 dpc rat hearts (Rongish et al, 1994;Ratajska and Fiejka, 1999). They are also found in the embryonic heart in later stages of development (until full term).…”

Multiple growth factors regulate coronary embryonic vasculogenesis

“…The first step in establishing a coronary vasculature involves the migration of angioblasts from the subepicardium into the myocardium, their differentiation into endothelial cells, and their assembly to form vascular tubes (Mikawa and Fischman, 1992;Poelmann et al, 1993;Rongish et al, 1994;Viragh et al, 1993). This process is termed vasculogenesis and also consists of fusion of the vascular tubes (a process reviewed by Drake and Little, 1999).…”