Abstract 5424: Hypoxia Induces the Histone Demethylase Jmjd3 and Epigenetically Reprograms Endothelial Progenitor Cells

Abstract

Endothelial progenitor cells (EPCs) contribute to vascular repair and postnatal neovascularisation. Cell therapy using EPCs improved neovascularisation and functional recovery after ischemia. However, it has been extensively debated whether EPCs can differentiate into endothelial cells and the mechanisms of EPC differentiation are poorly understood. Endothelial differentiation requires the expression of endothelial marker genes, which are silenced by chromatin dependent repressive mechanisms such as histone H3 lysine 27 trimethylation (H3K27me3) in non-endothelial cells. We observed that induction of hind limb ischemia increased the expression of Jmjd3, which was shown to demethylate H3K27me3 thereby removing repressive histone marks. Therefore, we examined whether EPC might be reprogrammed by hypoxic/ischemic injury through epigenetic pathways. We report here that Jmjd3 was induced when EPCs were exposed to hypoxia for more than 24 hours. Hypoxia additionally stimulated the nuclear translocation of Jmjd3 in EPC as shown by immunostaining (12.0±3.2% in normoxia, 68.5±3.6% in hypoxia, Jmjd3 positive nuclei/whole nuclei). Increased expression and nuclear translocation of Jmjd3 after hypoxic stimulation was associated with a reduction of global H3K27m3. Additionally, chromatin immunoprecipitation showed that the promoter of eNOS and KDR, which is transcriptionally silenced by high levels of H3K27me3 in early EPC under normoxic conditions, is activated by hypoxia. Hypoxia induced a down-regulation of H3K27me3 (0.045±0.017% input in normoxia and 0.024±0.010% input in hypoxia at the eNOS promoter, 0.197±0.067% input in normoxia and 0.126±0.030% input in hypoxia at the KDR promoter) and increased the ratio of active versus repressive chromatin marks at the eNOS and KDR promoter. Consistently, eNOS and KDR mRNA levels in EPC were increased after hypoxia. In summary, these data demonstrate that hypoxia-induced up-regulation and translocation of the histone demethylase Jmjd3 is associated with a reduction of repressive histone marks at the promoter of endothelial genes. These findings indicate that hypoxia may epigenetically modulate endothelial commitment.