Mitochondrial Energetics and Ca2⁺-Activated ATPase in Obstructive Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is the most common genetic disease of the myocardium associated to mutations in sarcomeric genes, but the link between genotype and phenotype remains poorly understood. Magnetic resonance spectroscopy studies have demonstrated impaired cardiac energetics in patients with HCM, and altered mitochondria were described in biopsies, but little is known about possible perturbations of mitochondrial function and adenosine triphosphate (ATP) production/consumption. The aim of this study was to investigate possible abnormalities in mitochondrial enzymes generating/scavenging reactive oxygen species, and changes in the Ca²⁺-activated ATPases in myocardial tissue from patients with obstructive HCM undergoing surgical myectomy compared to unused donor hearts (CTRL). Methods and Results: Both the amount and activity of mitochondrial Complex I (nicotinamide adenine dinucleotide -reduced form, NADH, dehydrogenase) were upregulated in HCM vs. CTRL, whilst the activity of Complex V (ATP synthase) was not reduced and ATP levels were significantly higher in HCM vs. CTRL. Antioxidant Mn-activated superoxide dismutase (SOD2) and (m)-aconitase activities were increased in HCM vs. CTRL. The Cu/Zn-activated superoxide dismutase (SOD1) amount and mtDNA copy number were unaltered in HCM. Total Ca²⁺-activated ATPase activity and absolute amount were not different HCM vs. CTRL, but the ratio between ATPase sarcoplasmic/endoplasmic reticulum Ca2+ transporting type 2 (ATP2A2) and type 1 (ATP2A1), ATP2A2/ATP2A1, was increased in HCM in favor of the slow isoform (ATP2A2). Conclusion: HCM is characterized by mitochondrial Complex I hyperactivity and preserved Ca^2+-activated ATPase activity with a partial switch towards slow ATP2A2. This data may give insight into the abnormal cellular energetics observed in HCM cardiomyopathy but other studies would need to be performed to confirm the observations described here.