Myocardial angiogenesis : aspects on endogenous determinants and effects of stimulation

Abstract

Background: Therapeutic angiogenesis using i.e. VEGF and FGF have shown beneficial effects, however, delivery routes and other modulating agents have not been thoroughly investigated. In this study the efficacy of adenovirus gene transfer was compared to plasmid gene transfer. The angiogenic effects of ephrinB2 were explored, as were the cardioprotective effects of erythropoietin and estrogen, with angiogenic effects in focus. Since hypoxia is the key regulator of angiogenesis, the studies were performed in an ischemic setting with a myocardial infarction model.

Results: Intramyocardial AdhVEGF-A165 transfer induced higher hVEGF-A protein expression than PhVEGF-A165 in rat myocardium (p<0.001). PhVEGF- A165 and AdhVEGF-A165 stimulated angiogenesis and improved left ventricular function to similar extent. AdhVEGFA165 induced more apoptotic cells (p<0.001) and higher ectopic expression of VEGF-A165 than PhVEGF-A165 gene transfer. Treatment with darbepoietin-alpha did not alter capillary density after myocardial infarction in a mouse myocardial infarction model. Cell proliferation was higher in the periinfarct area compared to the non infarcted area. Darbepoietin-alpha treatment gave a decreased cell proliferation (BrdU, p< 0.02) and apoptosis (TUNEL, p<0.005) with 30% in the periinfarct area. Darbepoietin-alpha and VEGF-A165 both induced angiogenic sprouting from cultured murine aortic rings.

The ephrin/Eph system was expressed in murine myocardium and altered as regards the ephrinB2/EphB4 expression after myocardial infarction (p<0.005). Modulation of ephrinB2 with fusion protein tended to increase mitosis, measured by BrdU incorporation in the periinfarct area, and also increased capillary density in the periinfarct area. EphrinB2 induced proliferation in human aortic endothelial cells (p<0.0005) and aortic ring sprouting (p<0.05) to a similar extent as VEGF-A165. In ERbetaKO mice the downregulation of ERalpha and the absence of functional ERbeta and in ERalphaKO the absence of functional ERalpha and the downregulation of ERbeta did not influence myocardial angiogenesis or arteriogenesis after myocardial infarction. In the periinfarct area of ERalphaKO mice the number of macrophages was lower compared to control (p<0.05).

Conclusions: AdhVEGF-A165 does not have any obvious superior angiogenic efficacy compared to PhVEGF-A165 but more side effects in a rat myocardial infarction model. Darbepoietin-alpha induces endothelial sprouting in a murine aortic ring culture, but in this model darbepoietin-alpha decreases cell proliferation and apoptosis in the periinfarct area with capillary and arteriolar densities unchanged. The ephrin/Eph system is present in the myocardium, and alters after myocardial infarction. EphrinB2 Fc tends to increase the mitotic activity and prevents a decrement in capillary density in the periinfarct area. Also ephrinB2 Fc induces endothelial cell proliferation in vitro, and stimulates angiogenic sprouting in an aortic ring model. mRNA expression of estrogen receptors are present in the myocardium. After myocardial infarction in ERbetaKO ERalpha mRNA and in ERalphaKO ERbeta mRNA are downregulated, without any influence on angiogenesis or arteriogenesis.