Abstract 541: Uncovering the Physiological Role of Mitochondrial Respiratory Supercomplexes in the Heart

Abstract

The assembly of mitochondrial electron transport chain (ETC) supercomplexes (SCs), particularly the respirasome containing complexes I, III, and IV have been shown to participate in facilitating electron transport, reducing ROS production and maintaining the structural integrity of individual ETC complexes. However, the physiological role of SCs in high energy demanding tissues such as the heart remains unknown. Here, we elucidated whether disassembly of SCs affects the cardiac function. Hearts isolated from adult male Sprague Dawley rats were perfused using a Langendorff-mode perfusion with Krebs-Henseleit solution (KHS) for the first 20 min (equilibration period) followed by perfusion in the following groups: (i) 40-min perfusion with KHS (n=4), (ii, iii) 20-min perfusion with rotenone (an inducer of SC dissociation) or vehicle (ethanol, n=8 for both), and (iv, v) 20-min perfusion with rotenone or vehicle followed by a 20-min perfusion with KHS without rotenone or vehicle (n=6 for both). 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, respiration rates, and ROS production. We found that cardiac function between rats perfused with KHS (i) and ethanol (i, iii) had no significant difference, though rotenone perfused rats (ii and iv) had a significant reduction (<40%) in cardiac function associated with reduced oxygen consumption rates in these groups. Furthermore, a significant increase in ROS production (ii) and permeability transition pore opening (iv) was observed when the hearts were perfused with rotenone with and without subsequent washout, respectively. Analysis of SCs by blue native PAGE displayed a significant reduction in SC levels in both ethanol (iii and v) and rotenone (ii and iv) perfused rats. Surprisingly, there were no differences in SC levels between the ethanol (iii and v) and rotenone (ii and iv) perfused groups. In addition, incubation of isolated intact mitochondria with ethanol and acetaldehyde did not demonstrate any direct effects of these compounds on ETC SC assembly. In conclusion, our data demonstrate a lack of an associative link between mitochondrial ETC SCs and cardiac function in rats.