Control of mitochondrial superoxide production by reverse electron transport at complex I

Abstract

The generation of mitochondrial superoxide (O2˙̄) by reverse electron transport (RET) at complex I causes oxidative damage in pathologies such as ischemia reperfusion injury, but also provides the precursor to H2O2 production in physiological mitochondrial redox signaling. Here, we quantified the factors that determine mitochondrial O2˙̄ production by RET in isolated heart mitochondria. Measuring mitochondrial H2O2 production at a range of proton-motive force (Δp) values and for several coenzyme Q (CoQ) and NADH pool redox states obtained with the uncoupler p-trifluoromethoxyphenylhydrazone, we show that O2˙̄ production by RET responds to changes in O2 concentration, the magnitude of Δp, and the redox states of the CoQ and NADH pools. Moreover, we determined how expressing the alternative oxidase from the tunicate Ciona intestinalis to oxidize the CoQ pool affected RET-mediated O2˙̄ production at complex I, underscoring the importance of the CoQ pool for mitochondrial O2˙̄ production by RET. An analysis of O2˙̄ production at complex I as a function of the thermodynamic forces driving RET at complex I revealed that many molecules that affect mitochondrial reactive oxygen species production do so by altering the overall thermodynamic driving forces of RET, rather than by directly acting on complex I. These findings clarify the factors controlling RET-mediated mitochondrial O2˙̄ production in both pathological and physiological conditions. We conclude that O2˙̄ production by RET is highly responsive to small changes in Δp and the CoQ redox state, indicating that complex I RET represents a major mode of mitochondrial redox signaling.

Nandrolone induces a stem cell-like phenotype in human hepatocarcinoma-derived cell line inhibiting mitochondrial respiratory activity

“…In addition to compromise the mitochondrial respiratory chain activity, inhibition of CxIII is well-known to enhance ROS production 35 . This appears to be due to accumulation of reactive radical intermediates, which are intrinsic to the catalytic cycle of the CxIII, and in addition to a phenomenon defined as "reverse electron transfer" that move reducing equivalents from ubiquinol back through the CxI, which becomes under this condition a further ROS generator 28,36 . Accordingly, we detected enhanced production of ROS, following nandrolone-treatment, traceable back to the mitochondrial compartment.…”

Respiratory chain signalling is essential for adaptive remodelling following cardiac ischaemia

“…AOX was previously demonstrated to blunt RET-induced ROS production under various conditions. 33,34,36,37 We therefore first tested whether the extent of acute I/R injury (infarct size) would be decreased in the post-ischaemic heart of mice with excellent cardiac AOX protein expression and catalytic AOX activity. 33 Using the open-chest in situ I/R model, 41 30 minutes of ischaemia were applied by occluding the left anterior descending (LAD) coronary artery followed by 2 hours of reperfusion in wild-type (WT) and AOX littermates.…”

Metabolic Reprogramming in Mitochondria of Myeloid Cells

“…One of major ROS production sites is through the electron leak at Complex I (CI) during the forward electron transport (FET) and the reverse electron transport (RET) [64]. A highly reduced pool of Q and a large membrane potential (proton gradient) trigger the reverse electron transport (RET) from over-reduced Q back to CI [64,65]. During RET, Q is over-reduced by electrons from Complex II (CII) and other sources such as GPS shunt.…”