Elucidating the Physiological Role of Mitochondrial ETC Supercomplexes in the Heart

Abstract

BackgroundFor a long time, mitochondrial electron transport chain (ETC) complexes was thought to function as separate entities. However, studies conducted in the past decade revealed that individual ETC complexes can assemble to form supramolecular structures known as supercomplexes (SCs). The SCs, particularly respirasome are composed of the ETC complexes I, III and IV in various stoichiometry. The respirasome is considered to play an important role in facilitating electron transport, reducing ROS production, and maintaining structural integrity of individual ETC complexes. Despite extensive studies on the molecular identity, the physiological role of SCs in cells, particularly, in high energy‐consuming organs such as the heart and brain remain unknown. These studies seek to determine whether disassembly of SCs affects the cardiac function in rats.MethodsHearts isolated from Sprague Dawley rats (275–325g) were perfused with Krebs Henseleit solution (KHS) via the Langendorff‐perfusion model. Experimental groups were as follows: (i) perfusion for 40 min with KHS, (ii) perfusion for 20 min with KHS and 20 min with rotenone (an inducer of SC dissociation) (n=8), (iii) perfusion for 60 min with KHS (n=4), (iv) perfusion for 20 min with KHS followed by 20 min perfusion with rotenone and 20 min with KHS (washout, no rotenone) (n=6). In control groups (i) and (iii), ethanol was as a vehicle in concentration used for rotenone groups [(ii) and (iv)]. In addition, we compared SC levels in mitochondria isolated from non‐perfused hearts (v), and hearts perfused with KHS (vi) containing no vehicle (ethanol) with those in i–iv groups. Cardiac function was monitored throughout the entire perfusion period. At the end of each protocol, the mitochondria were isolated for analysis of SCs, permeability transition pore opening, respiration rates and ROS production.ResultsCardiac function between rats perfused with KHS (vi) and ethanol (i and iii) had no significant difference, though rotenone perfused rats (ii and iv) had a significant reduction (< 40%) in cardiac function. Mitochondrial respiration data shows a significant reduction in complex I oxygen consumption rate in rotenone perfused (ii and iv) rats. Analysis of SCs by blue native PAGE displayed a significant reduction in SC levels in both ethanol (i and iii) and rotenone (ii and iv) perfused rats in comparison to hearts perfused with KHS (vi) alone. No significant differences in SC levels were found between the ethanol (i and iii) and rotenone (ii and iv) perfused groups.ConclusionOur data demonstrate lack of causal relationship link between mitochondrial ETC SCs and cardiac function in rats.Support or Funding InformationSupported by the NIGMS NIH grants SC1GM128210 and R25GM061838This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.