DNA demethylation regulates the expression of miR-210 in neural progenitor cells subjected to hypoxia

Several studies have identified a set of hypoxia-regulated microRNAs, among which is miR-210, whose expression is highly induced by hypoxia in various cancer cell lines. Recent studies have highlighted the importance of miR-210 and its transcriptional regulation by the transcription factor hypoxia-inducible factor-1 (HIF-1). We report here that the expression of miR-210 was highly induced in neural progenitor cells (NPCs) subjected to hypoxia. Specifically, treating hypoxic NPCs with the DNA demethylating agent 5-aza-2'-deoxycytidine significantly increased the expression of miR-210, even under normoxia; however, the activity of hypoxia-inducible factor-1 was unaffected. Further analysis of the miR-210 sequence revealed that it is embedded in a CpG island. Bisulfite sequencing of the miR-210 CpG island from NPCs grown under hypoxic conditions showed 24% CpG methylation in NPCs exposed to 20% O2, 18% in NPCs exposed to 3% O2, and 12% in NPCs exposed to 0.3% O2. In addition, the activity of DNA methyltransferases (DNMTs) in NPCs decreased after exposure to hypoxia. Specifically, the expression of DNMT3b decreased significantly after exposure to 0.3% O2. Thus, these results demonstrate that DNA demethylation regulates miR-210 expression in NPCs under both normoxia and hypoxia.