NAD⁺ or β-Hydroxybutyrate Each Protects Against Tachypacing-induced Metabolic Remodeling Through Regulation of Mitophagy in HL-1 Cardiomyocytes

Atrial fibrillation is associated with metabolic remodeling and mitochondrial dysfunction, leading to impaired energy production, oxidative stress, and structural changes. Targeting metabolic pathways may therefore provide therapeutic benefit. We previously showed that nicotinamide adenine dinucleotide and beta-hydroxybutyrate protect against pacing-induced contractile dysfunction, but their effects on mitochondrial and metabolic remodeling remain unclear. In this study, atrial cardiomyocytes were subjected to rapid electrical stimulation to mimic atrial fibrillation-related stress. Cells were treated with nicotinamide adenine dinucleotide, beta- hydroxybutyrate, or control. Metabolic changes were evaluated by transcriptomic analysis, protein expression, and imaging of pathways related to fatty acid oxidation, glycolysis, and lipid accumulation. Glycolytic activity was assessed by measuring glucose consumption and lactate production, and mitochondrial function was determined by high-resolution respirometry. Markers of mitophagy and NLRP3 inflammasome activation were also examined. Tachypacing-induced metabolic remodeling is characterized by reduced fatty acid oxidation and fatty acid oxidation-linked mitochondrial respiration, increased glycolysis, oxidative stress, and lipid droplet accumulation, impaired mitophagy, and activation of NLRP3-related inflammatory signaling. Treatment with nicotinamide adenine dinucleotide or beta-hydroxybutyrate attenuated many of these changes and partially restored mitochondrial respiratory capacity and metabolic balance. Notably, knockdown of mitophagy-related proteins (mitofusin 2, PTEN-induced kinase 1, and Parkin) caused contractile dysfunction and diminished the protective effects of both treatments on cardiomyocyte contractile function, suggesting that mitophagy may mediate the functional benefits of these compounds. These findings indicate that mitochondrial and metabolic remodeling are closely associated with tachypacing-induced cellular dysfunction and mitophagy and suggest that metabolic interventions may help preserve cardiomyocyte function partially by preserving mitophagy.