Attenuation of retinal endothelial cell migration and capillary morphogenesis in the absence of bcl-2

Apoptosis plays a critical role during development and in the maintenance of the vascular system. B-cell leukemia lymphoma 2 (bcl-2) protects endothelial cells (EC) from apoptosis in response to a variety of stimuli. Previous work from this laboratory demonstrated attenuation of postnatal retinal vascular development and retinal neovascularization during oxygen-induced ischemic retinopathy in bcl-2-deficient ([bcl-2.sup.-/-]) mice. To gain further insight into the function of bcl-2 in the endothelium, we isolated retinal EC from [bcl-2.sup.+/+] and [bcl.-2.sup.-/-] mice. Retinal EC lacking bcl-2 demonstrated reduced cell migration, tenascin-C expression, and adhesion to vitronectin and fibronectin. The [bcl-2.sup.-/-] retinal EC also failed to undergo capillary morphogenesis in Matrigel. In addition, using an ex vivo angiogenesis assay, we observed reduced sprouting from aortic rings grown in culture from [bcl-2.sup.-/-] mice compared with [bcl-2.sup.+/+] mice. Furthermore, reexpression of bcl-2 was sufficient to restore migration and capillary morphogenesis defects observed in [bcl-2.sup.-/-] retinal EC. Mechanistically, [bcl-2.sup.-/-] cells expressed significantly less endothelial nitric oxide synthase, an important downstream effecter of proangiogenic signaling. This may be attributed to increased oxidative stress in the absence of bcl-2. In fact, incubation of retinal EC or aortic rings from [bcl-2.sup.-/-] mice with the antioxidant N-acetylcysteine rescued their capillary morphogenesis and sprouting defects. Thus, bcl-2-mediated cellular functions play important roles not only in survival but also in proangiogenic phenotype of EC with a significant impact on vascular development and angiogenesis. angiogenesis; apoptosis; endothelial nitric oxide; oxidative stress