VASCULAR ENDOTHELIAL GROWTH-FACTOR MEDIATES REACTIVE ANGIOGENESIS IN THE POSTNATAL DEVELOPING BRAIN

Although chronic sublethal hypoxia has been shown to promote angiogene sis in the developing brain, the pathogenesis of this response is unkn own. We hypothesized that this response may be mediated in part by vas cular endothelial growth factor (VEGF). We reared newborn rats (P3) in a chamber with FIO2 of 9.5 +/- 1% (exposed, E). At P33, the animals w ere removed from the chamber and the blains prepared for immunohistoch emistry, mRNA extraction, or horseradish peroxidase (HRP) permeability studies. We also isolated beagle brain germinal matrix endothelial ce lls from PND 1 beagle pups and placed them in three-dimensional (3-D) coculture with PND 1 rat forebrain astrocytes. Cultures were grown for 6 days in 11% O-2 and compared to control 3-D cocultures. When compar ed to age-matched controls, the experimental rats had significantly in creased cortical vascular density (vessels/mm(2): 518 +/- 18 vs, 400 /- 15, P = 0.025). HRP studies demonstrated significantly increased pe rmeability in all cortical vessels examined in experimental rats compa red to controls. Compared to controls, VEGF mRNA from hypoxic pups was increased 2.3 times, and immunohistochemical studies of VEGF protein confirmed this finding. Similarly, when compared to controls, hypoxic cocultures of brain microvascular endothelial cells and astrocytes dem onstrated significant increase in tubelike structures representing in vitro angiogenesis. Additionally, astrocyte VEGF protein levels increa sed 4.4-fold in hypoxic compared to control astrocyte cultures and VEG F protein levels increased 1.7-fold in hypoxic compared to control coc ultures. Finally, addition of VEGF (10 ng/ml culture medium) to BBMEC alone in 3-D culture elicited not only significant proliferation (P = 0.001) but also increased tube formation. These data demonstrate that the developing brain responds to chronic sublethal hypoxia with increa ses in permeability and angiogenesis and suggest that VEGF mediates th is response. (C) 1997 Elsevier Science B.V.