Brahma-related gene 1 (Brg1) epigenetically regulates CAM activation during hypoxic pulmonary hypertension

Establishment of an inflammatory milieu following elevated leukocyte adhesion to the vascular endothelium, which is mediated by transcriptional activation of cell adhesion molecules (CAMs), contributes to the pathogenesis of chronic hypoxia-induced pulmonary hypertension (HPH). The epigenetic switch that dictates CAM transactivation in response to hypoxia in endothelial cells leading up to HPH is not fully appreciated. We report here that brahma-related gene 1 (Brg1) and brahma (Brm), two catalytic components of the mammalian chromatin remodelling complex, were induced in cultured endothelial cells challenged with hypoxia in vitro as well as in pulmonary arteries in an animal model of HPH. Over-expression of Brg1/Brm enhanced, while the depletion of Brg1/Brm attenuated, CAM transactivation and adhesion of leukocytes. Endothelial-specific deletion of Brg1/Brm ameliorated vascular inflammation and HPH in mice. Chromatin immunoprecipitation (ChIP) and re-ChIP assays revealed that hypoxia up-regulated the occupancies of Brg1 and Brm on CAM promoters in a nuclear factor B (NF-B) -dependent manner. Finally, Brg1 and Brm activated CAM transcription by altering the chromatin structure surrounding the CAM promoters. Our data suggest that Brg1 provides the crucial epigenetic link to hypoxia-induced CAM induction and leukocyte adhesion that engenders endothelial malfunction and pathogenesis of HPH. As such, targeting Brg1 in endothelial cells may yield promising strategies in the intervention and/or prevention of HPH.