Endothelial cell apoptosis in capillary network remodeling

Abstract

We hypothesized that the regulation of apoptosis is an important determinant of capillary network structure. Using human umbilical vein endothelial cells (HUVEC) in in vitro model systems of capillary tube formation, we initially documented that apoptosis is a prominent feature of network formation. Perturbations of integrin-matrix signaling by the administration of either colchicine or an anti-αvβ3 antibody resulted in the dissolution of the tubular network in association with increased apoptosis. The activation of the αvβ3 integrin induced increased expression of the anti-apoptotic gene bcl-2 and conferred resistance to the proapoptotic effect of TGF-β1. In contrast to the stable networks formed by HUVEC, bovine aortic endothelial cells (BAEC) exhibited a more dynamic process of network formation and spontaneous involution. The inhibition of BAEC apoptosis by stable transfection of bcl-2 prevented the involution of the network. We hypothesized that TGF-β1 present within the model system mediated network involution by inducing BAEC death. Indeed, blockade of TGF-β1 with neutralizing antibodies reduced BAEC apoptosis and preserved the network structure. As observed with HUVEC networks, stable BAEC networks formed during blockade of TGF-β1 were also dependent on the survival-promoting effects of matrix-integrin interactions. This study suggests that capillary network structure is determined by the balance of proapoptotic vs. anti-apoptotic signals mediated by the engagement of cytokine and integrin receptors within the milieu. J. Cell. Physiol. 178:359–370, 1999. © 1999 Wiley-Liss, Inc.