Remodeling pathway control of mitochondrial respiratory capacity by temperature in mouse heart: electron flow through the Q-junction in permeabilized fibers

Abstract

Fuel substrate supply and oxidative phosphorylation are key determinants of muscle performance. Numerous studies of mammalian mitochondria are carried out (i) with substrate supply that limits electron flow, and (ii) far below physiological temperature. To analyze potentially implicated biases, we studied mitochondrial respiratory control in permeabilized mouse myocardial fibers using high-resolution respirometry. The capacity of oxidative phosphorylation at 37 °C was nearly two-fold higher when fueled by physiological substrate combinations reconstituting tricarboxylic acid cycle function, compared with electron flow measured separately through NADH to Complex I or succinate to Complex II. The relative contribution of the NADH pathway to physiological respiratory capacity increased with a decrease in temperature from 37 to 25 °C. The apparent excess capacity of cytochrome c oxidase above physiological pathway capacity increased sharply under hypothermia due to limitation by NADH-linked dehydrogenases. This mechanism of mitochondrial respiratory control in the hypothermic mammalian heart is comparable to the pattern in ectotherm species, pointing towards NADH-linked mt-matrix dehydrogenases and the phosphorylation system rather than electron transfer complexes as the primary drivers of thermal sensitivity at low temperature. Delineating the link between stress and remodeling of oxidative phosphorylation is important for understanding metabolic perturbations in disease evolution and cardiac protection.

Permeabilised skeletal muscle reveals mitochondrial deficiency in malignant hyperthermia-susceptible individuals

“…Permeabilized muscle allows interplay between the mitochondria, SR and RyR1, which we believe is crucial to accurately assess the biological effects of MH. Furthermore, the oxygen uptake assay in the mouse study was conducted at 22 °C whereas we used a physiological 37 °C for our experiments: assay temperature significantly impacts OXPHOS capacity 27 .…”

Effects of mitonuclear combination and thermal acclimation on the energetic phenotype

“…Alternatively, this maximal COX activity could reflect a higher excess capacity; a well‐known phenomenon in ectotherms (Blier, Lemieux, & Pichaud, 2014). The excess capacity of the COX has been associated with higher O 2 affinity, regulation of reactive oxygen species and preservation of the oxidized state of upstream electron transport chain complexes (Gnaiger, Lassnig, Kuznetsov, Rieger, & Margreiter, 1998; Lemieux, Blier, & Gnaiger, 2017). A significantly superior COX enzymatic activity in cybrid has been previously observed in punctual sampling in a natural sympatric and allopatric environment with C. eos wild type (Angers, Chapdelaine et al, 2018; Deremiens et al, 2015).…”

Impairment of mitochondrial respiratory function as an early biomarker of apoptosis induced by growth factor removal

“…4C) does not contradict this conclusion, but provides evidence of a significant excess CIV capacity with respect to the S-pathway. The corresponding CIV threshold increases as the S/NS flux control ratio declines 43 . Since the S/NS flux control ratio was as low as 0.6 ( Fig.…”

“…Cytochrome c oxidase (Complex IV; CIV) is the terminal enzyme in the mitochondrial electron transfer system. Measurement of the enzyme activity of this single step in the pathway of oxygen consumption constitutes a key element in OXPHOS analysis 43 To gain insight into the possible mechanisms underlying the reduction of respiratory capacity in IL-3 starved 32D cells, we tested the hypothesis that the change in mitochondrial respiration was caused by a general decrease in mitochondrial content or by a switch from aerobic to glycolytic pathways. In specific tumors, a mitochondrial injury causing an increased dependence on glycolysis for ATP production is well documented (Warburg effect, see reviews [35][36][37][38][39] ).…”

“…When Complex IV is in excess, pathway flux does not decrease proportionally to inhibition of CIV activity due to a threshold effect. In most types of mitochondria, CIV is in excess of electron transfer pathway capacity, even at maximal upstream electron supply by the convergent NS-pathway 42,43 . In macrophage cells the apparent excess CIV capacity, (CIV-NS)/NS, is 0.46 44 .…”