Effects of radiation on the levels of MMP-2, MMP-9 and TIMP-1 during morphogenic glial-endothelial cell interactions

Radiation-induced damage to the central nervous system (CNS) is believed to target glial or endothelial cells or both, although the pathophysiology of the process is poorly understood. We therefore used a coculture system, in which glioblastoma SNB19 cells induced bovine retinal endothelial (BRE) ce lls to form capillary-like structures, to examine the role of ionizing radi ation in modulating the production of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinase-1 (TIMP-1). In particular, we irradi ated both BRE cells and cocultures of BRE and SNB19 cells with a single dos e of X-rays and then estimated the levels of MMP-2, MMP-9 and TIMP-1. Gelat in zymography revealed a continuous increase in the levels of MMP-2 and MMP -9 during capillary-like structure formation. Of note, the levels of both M MP-2 and MMP-9 were markedly higher in irradiated cocultures at 72 hr after irradiation than in untreated cocultures. Northern blot analysis also demo nstrated an increased expression of MMP-9 mRNA in the irradiated cocultures . In addition, TIMP-1 mRNA and protein levels increased up to 48 hr in both irradiated and nonirradiated BRE cells and in nonirradiated cocultures, bu t there was a significant decrease in the TIMP-1 mRNA and protein levels in irradiated cocultures. It takes about 72 hr for capillaries to form in non irradiated cocultures, but these capillary networks fail to form in endothe lial cells in irradiated cocultures, These findings establish that radiatio n differentially affects the production of MMP-2, MMP-9 and TIMP-1 during g lial-endothelial morphogenesis and suggest mechanisms by which microvessels in the CNS respond to radiation. (C) 2000 Wiley-Liss, Inc.