Hypoxia decreases mitochondrial ROS production in cells

Area of Science:

• Cellular Biology
• Biochemistry
• Hypoxia Research

Background:

• Mitochondrial reactive oxygen species (ROS) production is often reported to increase during acute hypoxia.
• The role of ROS in cellular responses to hypoxia, particularly HIF1α stabilization, remains incompletely understood.

Purpose of the Study:

• To re-examine the effect of acute hypoxia on cellular ROS production.
• To investigate the contribution of different ROS-producing sites to hypoxia-induced responses, including HIF1α stabilization.

Main Methods:

• Amplex Ultrared/horseradish peroxidase assay and diacetyldichlorofluorescein assay to measure hydrogen peroxide (H2O2) release.
• Assessment of ROS production from mitochondrial complex I (site I_Q), complex III (site III_Qo), and cytosolic NADH oxidases (NOX).
• HIF1α reporter cell line to evaluate the impact of ROS production on HIF1α expression.

Main Results:

• Acute hypoxia decreased H2O2 release from HEK293 cells, with no change in H2O2 degradation capacity.
• ROS production rates from mitochondrial sites I_Q, III_Qo, and cytosolic NOX were similarly reduced by acute hypoxia.
• Suppression of ROS production from sites I_Q, III_Qo, or NOX decreased HIF1α expression, similar to previous findings for site III_Qo.

Conclusions:

• Increased mitochondrial ROS production does not drive the HIF1α response to acute hypoxia.
• Cytosolic H2O2 derived from sites I_Q, III_Qo, and NOX is necessary for HIF1α stabilization by other signals.