Abstract 12789: Time-Dependent Changes in Mitochondrial Properties and Function in Dogs During Electrically Maintained Atrial Fibrillation

Abstract

Introduction: Atrial fibrillation (AF) causes atrial remodeling, leading to progressive resistance to therapy. Changes in cell metabolism likely contribute to remodeling; here, we studied the nature and time course of mitochondrial (MITO) changes during AF . Methods: Atrial cardiomyocytes were isolated from control dogs and dogs kept in AF for 24 hrs, 3 days, 1 and 3 wks by atrial tachypacing at 600 bpm (N=10/group). MITO were visualized with transmission electron microscopy. [Ca 2+ ] Mito (Rhod-2 AM), MITO ROS production (MitoSOX), membrane potential (αψ, JC-1), mPTP opening (TMRM) and FAD autofluorescence were measured via confocal microscope, NADH autofluorescence was determined under UV light. Protein expression was assayed by western blotting. Results: MITO elongation occurred following 24-hr and 3-day AF, while 3-week AF induced MITO fragmentation, rupture and shrinking (A). MITO fusion protein (MFN1) decreased from 3 days to 3 wks of AF and fission protein pDRP1ser-616 was increased at 1 and 3 wks of AF, potentially accounting for MITO fragmentation. [Ca 2+ ] Mito increased progressively with AF-time (B). MITO ROS production increased at 24 hr AF, and remained elevated from 3 days to 3 wks of AF (C). SOD2 was reduced after 3 days AF. NOX4 expression was increased at 3 wks AF. mPTP opening frequency and duration increased progressively during AF (D). AF increased JC-1 fluorescence, indicating depolarized αψ, beginning 24 hours after AF-onset (E). NADH increased by 15% at 24 hr AF, and then decreased progressively with AF-time (F). FAD was decreased during AF. Mitotempo (5-μM) reversed AF-induced atrial-cell I CaL downregulation (G) and reduced triggered activity (H). Conclusions: MITO are activated early during AF, but then show progressive changes likely due to ROS autotoxicity. MITO dysfunction and impaired bioenergetics may contribute to AF maintenance/ progress. MITO-targeted antioxidant intervention may have potential as a novel therapeutic approach for AF.