ANGIOSTATIC ROLE OF ASTROCYTES - SUPPRESSION OF VASCULAR ENDOTHELIAL-CELL GROWTH BY TGF-BETA AND OTHER INHIBITORY FACTOR(S)

Our previous in vivo analyses have suggested that astrocytes play a ke y role in retinal vascularization by inducing endothelial cell differe ntiation. Here we demonstrate that medium conditioned by cultured rat brain astrocytes (ACM) contains factors, including transforming growth factor-beta (TGF-beta), that inhibit endothelial cell growth. Serum-f ree medium conditioned for 1-3 days was tested on exponentially growin g bovine retinal microvascular endothelial, aortic endothelial, mink l ung epithelial CCL-64, and Swiss mouse 3T3 fibroblast cells. The growt h of all four cell types was inhibited in a dose-and time-dependent ma nner. CCL cells, which are used as a model for assaying TGF-beta activ ity, were more sensitive than the endothelial cells, suggesting that A CM contains TGF-beta. Moreover, acid treatment significantly increased the inhibitory activity of ACM, indicating that TGF-beta in ACM is pr edominantly in the latent form. Mouse fibroblasts, which are not affec ted by TGF-beta treatment under the same conditions, were also inhibit ed by ACM. This suggests that other inhibitory factors in addition to TGF-beta may be involved. Adsorption by an anti-TGF-beta polyclonal an tibody column substantially reduced but did not eliminate the inhibito ry activity of ACM for CCL and endothelial cells. Western blot analysi s of ACM and proteins eluted from the affinity column revealed a 25 kD a band that co-migrates with TGF-beta. Comparative densitometry of the 25 kDa bands on Western blot indicated that the amount of TGF-beta in ACM is not sufficient to account for the total growth-inhibitory acti vity. These experiments demonstrate directly that rat brain astrocytes express TGF-beta. They also indicate that astrocytes may produce othe r growth-inhibitory factor(s) yet to be identified. (C) 1995 Wiley-Lis s, Inc.