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) cells to form capillary-like structures, to examine the role of ionizing radiation in modulating the production of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinase-1 (TIMP-1). In particular, we irradiated both BRE cells and cocultures of BRE and SNB19 cells with a single dose of X-rays and then estimated the levels of MMP-2, MMP-9 and TIMP-1. Gelatin 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 MMP-2 and MMP-9 were markedly higher in irradiated cocultures at 72 hr after irradiation than in untreated cocultures. Northern blot analysis also demonstrated 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, but 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 nonirradiated cocultures, but these capillary networks fail to form in endothelial cells in irradiated cocultures. These findings establish that radiation differentially affects the production of MMP-2, MMP-9 and TIMP-1 during glial-endothelial morphogenesis and suggest mechanisms by which microvessels in the CNS respond to radiation.