Enhanced Mitochondrial Calcium Uptake Suppresses Atrial Fibrillation Associated With Metabolic Syndrome

Patients with metabolic syndrome (MetS) have an increased risk of atrial fibrillation (AF). Impaired Ca²⁺ homeostasis and mitochondrial dysfunction have emerged as an arrhythmogenic substrate in both patients and animal models of MetS. Whether impaired mitochondrial Ca²⁺ handling underlies AF associated with MetS remains poorly explored.

The aim of this study was to determine the initial mechanisms related to AF susceptibility and mitochondrial dysfunction encountered in metabolic cardiomyopathy.

A total of 161 mice and 34 patients were studied. Mitochondrial Ca²⁺ and mitochondrial Ca²⁺ uniporter complex (MCUC) were investigated in right atrial tissue of patients with (n = 18) or without (n = 16) MetS and of C57Bl/6J mice fed with a high-fat sucrose diet (HFS) for 2 (n = 42) or 12 (n = 39) weeks. Susceptibility to AF was evaluated in isolated sinoatrial tissue and in vivo in mice.

Increased expression of the MICUs subunits of the MCUC (1.00 ± 0.33 AU vs 1.29 ± 0.23 AU; P = 0.034) was associated with impaired mitochondrial Ca²⁺ uptake in patients (168.7 ± 31.3 nmol/min/mg vs 127.3 ± 18.4 nmol/min/mg; P = 0.026) and HFS mice (0.10 ± 0.04 ΔF/F0 × ms^-1 vs 0.06 ± 0.03 ΔF/F0 × ms^-1; P = 0.0086, and 0.15 ± 0.07 ΔF/F0 × ms^-1 vs 0.046 ± 0.03 ΔF/F0 × ms^-1; P = 0.0076 in 2- and 12-week HFS mice, respectively). HFS mice elicited a 70% increased susceptibility to AF. The MCUC agonist kaempferol restored MCUC activity in vitro and abolished the occurrence of AF in HFS mice.

Impaired MCUC activity and mitochondrial Ca²⁺ homeostasis from the early stage of metabolic cardiomyopathy in mice lead to AF. Given that similar defects in cardiac mitochondrial Ca²⁺ handling are present in MetS patients, the modulation of the MCUC activity represents an attractive antiarrhythmic strategy.