Divergent regulation of the vascular endothelial growth factor (VEGF) gene in hypoxic pulmonary vascular endothelial cell (EC) phenotypes

Endothelial cells from the rat pulmonary artery (PA) and pulmonary microvasculature (MV) are phenotypically distinct and often exhibit different responses to physiological and pathological stimuli. In the present study, we tested the hypothesis that regulation of hypoxia‐induced chromatin remodeling and VEGF expression differs between these cell populations. While hypoxia (2% oxygen) increased VEGF mRNA expression in PAECs, in MVECs, which have high level of normoxic VEGF expression, hypoxia caused a substantial decrease in VEGF mRNA. To determine if this difference in VEGF expression was accompanied by predictable differences in chromatin remodeling, we treated nuclei from normoxic and hypoxic ECs with micrococcal nuclease and used electrophoresis to separate the released DNA fragments into nucleosomes of increasing complexity. The total amount of DNA released from nuclei after micrococcal nuclease digestion was increased by hypoxia in PAECs and decreased in MVECs, possibly reflecting changes in the total number of active genes accessible to the nuclease. Southern blot analysis of DNA from PAECs using a probe for the VEGF promoter showed that hypoxia induced a shift in hybridization to the mono‐ and di‐nucleosome fractions. In contrast, hybridization intensity in MVEC samples decreased in all nucleosomal fractions without redistribution. These results indicate that lung EC phenotype‐dependent differences in hypoxia‐regulated VEGF expression are associated with differences in hypoxia‐induced chromatin remodeling. Supported by NIH.