Hypoxia down-regulates endostatin production by human microvascular endothelial cells and pericytes

Endostatin is a potent anti-angiogenic factor derived from the C-terminal r egion of collagen XVIII and is implicated in the regulation of physiologica l and pathological angiogenesis. In this study, reverse transcription-polym erase chain reaction analysis of poly(A)(+) RNA demonstrated the presence o f mRNA for collagen XVIII in human endothelial cells (EC) and pericytes, th e very constituents of microvessels wherein angiogenesis takes place. Enzym e immunoassay revealed that both cell types liberated endostatin into cultu re media and that the endostatin levels were decreased by hypoxia, the prin cipal cause of angiogenesis. Northern and Western blot analyses revealed th at while the collagen XVIII/endostatin mRNA levels were invariant between h ypoxic and normoxic conditions, the collagen XVIII protein levels in EC and pericytes decreased by hypoxia. Further, exogenously administered intact e ndostatin was significantly decreased when it was incubated with hypoxic co nditioned media of endothelial cells or pericytes, but not with normoxic me dia. The results suggest that the reduction of autocrine endostatin may tak e an active part in hypoxia-driven angiogenesis. (C) 2001 Academic Press.