Role of H2O2and heme-containing O2 sensors in hypoxic regulation of tyrosine hydroxylase gene expression

Abstract

In the current study, we investigated links between O 2-regulated H 2 O 2 formation and the hypoxic induction of mRNA for tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine synthesis, in O 2-sensitive PC-12 cells. During exposure of PC-12 cells to 5% O 2, H 2 O 2 concentration decreased by 40% as measured with 2′,7′-dichlorofluorescein (DCF). Treatment with H 2 O 2 reduced TH mRNA during normoxia and prevented the induction of TH mRNA during hypoxia. Treatment with catalase or N-(2-mercaptopropionyl)-glycine, a reducing antioxidant agent that decreases H 2 O 2 concentration, also induced TH mRNA. Deferoxamine (DF), an iron chelator, failed to affect H 2 O 2 formation but induced TH mRNA in normoxia and hypoxia. CoCl 2 led to a decrease in H 2 O 2 at 20 h of treatment but induced TH mRNA during normoxia and hypoxia before it affected H 2 O 2. In conclusion, TH gene expression correlates inversely with H 2 O 2 formation. DF and Co 2+ seem to affect TH gene expression in the mechanism downstream from the H 2 O 2 formation rather than by interfering with the H 2 O 2-generating activity of the O 2 sensor.