Role of hydrogen peroxide in hypoxia-induced erythropoietin production

Abstract

The addition of exogenous H2O2 inhibited hypoxia-induced erythropoietin (Epo) production in the human hepatoma cell line HepG2. Likewise, elevation of endogenous H2O2 levels by the addition of menadione or the catalase inhibitor, aminotriazole, dose-dependently lowered Epo production. The inhibitory effect of exogenous H2O2 on Epo formation could be completely overcome by co-incubation with catalase. When GSH levels in HepG2 cells were lowered, Epo production was more susceptible to H2O2-induced inhibition, indicating that H2O2 might affect thiol groups in regulatory proteins. Endogenous production of H2O2 in HepG2 cells was dependent on the pericellular O2 tension, being lowest under conditions of hypoxia. Our results support the hypothesis that an H2O2-generating haem protein might be part of the O2 sensor that controls Epo production. High H2O2 levels under conditions of normoxia suppress, whereas lower levels in hypoxic cells allow epo gene expression.

Regulation of the gluconeogenic phosphoenolpyruvate carboxykinase and the glycolytic aldolase A gene expression by O2 in rat hepatocyte cultures. Involvement of hydrogen peroxide as mediator in the response to O2

“…latation whereas under hypoxia, when H202 production was low, vasoconstriction was observed [21]. The recent finding that the hypoxia-induced EPO production in HepG2 cells is inhibited by H202 [12] supports the idea that H202 could be a mediator of O2 signals.…”

“…The hypothesis that an NADPH-like oxidase is part of the 02 sensor is in line with results from this and earlier studies on the regulation of EPO and PCK induction, which had shown the participation of a heme protein [6,9,10]: the hypoxia-induced EPO production was modulated by inducers and inhibitors of a b-type cytochrome, the P-450 system [25], and it was sensitive to 02 but not cyanide [11] or dinitrophenol [10], which excludes respiratory chain type-b cytochromes. Moreover, the hypoxia-induced increases in EPO mRNA [12] and ALD A mRNA were inhibited and the glucagondependent induction of PCK mRNA was increased by H202 (Fig. 3).…”

“…The stimulatory H202 concentration of 50 /aM was chosen for further experiments. The optimal concentration of catalase was deduced from a previous study with HepG2 cells [12]: exposure of these cells to 100 p.g/ml catalase did not reduce cell viability.…”

“…Western blots with antibodies against the small subunit (22 kDa) and the cytosolic activation factor (47 kDa) of NADPH oxidase demonstrated the presence of an NADPH oxidase-like heme protein in HepG2 cells [I 1]. This was further substantiated by the finding that HepG2 cells produced H202 in response to 02 and that the hypoxia-induced EPO production could be inhibited by H202 [12]. It was the aim of the present study to investigate the role of H202 as possible mediator in the 02 sensing system of primary hepatocytes which causes the positive modulation by arterial 02 of the glucagon-dependent activation of the PCK gene and elicits the activation of the ALD A gene by venous 02.…”

Nitric Oxide Impairs Normoxic Degradation of HIF-1α by Inhibition of Prolyl Hydroxylases

“…Although fluorescent dyes, e.g., dihydrofluorescein, seem to indicate enhanced ROS generation in hypoxia (Chandel et al, 2000), other methods such as the detection of hydrogen peroxide using the chemiluminescent dye luminol suggest that ROS production is rather decreased in hypoxia (Fandrey et al, 1994;Vaux et al, 2001). If hypoxia favors increased ROS production and if a chemical reaction of NO with ROS occurs, then NO would antagonize the stabilizing effect of ROS on HIF-1␣ that has been postulated.…”