Abstract Fri141: Effects of Cardiac-Specific EMRE Deletion on Complex I Activity in Ischemia/Reperfusion

Introduction: Previous studies have shown that inducible deletion of the mitochondrial Ca 2+ uniporter (MCU) or its regulatory protein EMRE in murine cardiac tissue impairs mitochondrial Ca 2+ uptake. Ca 2+ overload in ischemic mitochondria can contribute to permeability transition and tissue damage upon reperfusion. As expected, tamoxifen-induced deletion of EMRE is protective against ischemia/reperfusion (I/R) injury, but only acutely after induction. How this protection is lost over time with chronic EMRE deficiency despite persistent impaired mitochondrial Ca 2+ uptake is unknown. Research Question/Hypothesis: We hypothesize that chronic EMRE deficiency leads to dysfunction of complex I of the electron transport chain, which results in increased reactive oxygen species (ROS) production. Increased ROS may contribute to I/R injury despite reduced mitochondrial Ca 2+ overload. Methods: EMRE deletion was induced via tamoxifen injection in EMRE fl/fl aMHC-MerCreMer + mice 3 weeks (acute) or 3+ months (chronic) prior to experimentation. Hearts were cannulated on a Langendorff perfusion system and subjected to global ischemia, with rate pressure product (RPP) in the left ventricle measured at baseline, during ischemia, and upon reperfusion. Cardiac mitochondria were isolated, and ROS production and O 2 consumption rate (OCR) were assessed by Oroboros O2k. Results: Chronic EMRE loss did not improve RPP recovery post-I/R. Following ex vivo I/R, mitochondria from chronically EMRE-deficient mice showed decreased OCR and increased ROS (H 2 O 2 ) production rates compared to control mitochondria, suggesting reduced complex I activity and electron leak. In contrast, no differences in OCR or ROS production were observed in mitochondria from acutely EMRE-deficient mice. Conclusion: Complex I dysfunction, as indicated by decreased OCR and increased ROS production, manifests in isolated mitochondria with chronic and not acute EMRE deficiency. Hence, prolonged lack of mitochondrial Ca 2+ uptake potentially leads to functional decline of complex I. This maladaptive elevated ROS production during I/R could contribute to mitochondrial permeability transition, explaining decreasing cardio protection against I/R injury over time after EMRE deletion.