Mitochondrial hyperpolarization during chronic complex I inhibition is sustained by low activity of complex II, III, IV and V

Abstract

The mitochondrial oxidative phosphorylation (OXPHOS) system consists of four electron transport chain (ETC) complexes (CI-CIV) and the FoF1-ATP synthase (CV), which sustain ATP generation via chemiosmotic coupling. The latter requires an inward-directed proton-motive force (PMF) across the mitochondrial inner membrane (MIM) consisting of a proton (ΔpH) and electrical charge (Δψ) gradient. CI actively participates in sustaining these gradients via trans-MIM proton pumping. Enigmatically, at the cellular level genetic or inhibitor-induced CI dysfunction has been associated with Δψ depolarization or hyperpolarization. The cellular mechanism of the latter is still incompletely understood. Here we demonstrate that chronic (24h) CI inhibition in HEK293 cells induces a proton-based Δψ hyperpolarization in HEK293 cells without triggering reverse-mode action of CV or the adenine nucleotide translocase (ANT). Hyperpolarization was associated with low levels of CII-driven O2 consumption and prevented by co-inhibition of CII, CIII or CIV activity. In contrast, chronic CIII inhibition triggered CV reverse-mode action and induced Δψ depolarization. CI- and CIII-inhibition similarly reduced free matrix ATP levels and increased the cell's dependence on extracellular glucose to maintain cytosolic free ATP. Our findings support a model in which Δψ hyperpolarization in CI-inhibited cells results from low activity of CII, CIII and CIV, combined with reduced forward action of CV and ANT.

Benzo[a]pyrene-induced nitric oxide production acts as a survival signal targeting mitochondrial membrane potential

“…This therefore clearly indicated that DWm was a target of endogenous NO in our cell model. It is worth noting that mitochondrial hyperpolarization has been related to alterations of the oxidative phosphorylation, evidenced by a decrease in cell respiration (Forkink et al, 2014), with concomitant stimulation of glycolysis in order to maintain ATP production (Sánchez-Cenizo et al, 2010). A similar link between reduced mitochondrial activity and shift toward glycolysis due to NO has been previously reported, for example in ovarian cancer cells (Caneba et al, 2014;Chang et al, 2015).…”

Metabolic Characterization of Intact Cells Reveals Intracellular Amyloid Beta but Not Its Precursor Protein to Reduce Mitochondrial Respiration

“…Indeed, this coincidence could be due to respiratory control, which intrinsically reduces respiration during mitochondrial hyperpolarization to prevent excessive ROS production [40–42]. Alternatively, it was shown that CI inhibition in HEK293 cells results in a hyperpolarization of mitochondrial membrane potential [43]. Thus, it might be cell-specific characteristics, indicating a defect in complex I respiration in APP-overexpressing cells.…”

Warm-preconditioning protects against acute heat-induced respiratory dysfunction and delays bleaching in a symbiotic sea anemone

“…In the absence of increased CCO activity (to sustain adequate rates of Cyt c oxidation in a less oxidative environment), higher NQO activity could result in the progressive over-reduction of the CoQ pool as well as an altered IMM polarisation state (Abele et al, 2007). These phenomena are common features of heat-or hypoxia-induced stress and, in addition to inhibiting ATP synthesis (Bagkos et al, 2014;Forkink et al, 2014), they promote superoxide generation through mETC III activity, ubiquinol autoxidation and/or NQO dysfunction (Boveris and Chance, 1973;Turrens and Boveris, 1980;Miwa and Brand, 2003;Yin et al, 2010). However, we observed no corresponding increases in host SOD activity, suggesting that (a) no O 2 − -driven oxidative challenge arose, and/or (b) constitutive SOD abundance was sufficiently protective.…”