Reduction in Acetylation of Superoxide Dismutase 2 in Skeletal Muscle Improves Exercise Capacity in Mice With Heart Failure.

Background: Skeletal muscle abnormalities, including mitochondrial dysfunction, play a crucial role in decreasing exercise capacity in patients with heart failure (HF). Although enhanced reactive oxygen species (ROS) production in skeletal muscle mitochondria has been implicated in skeletal muscle abnormalities, the underlying mechanisms have not been fully elucidated to date. Superoxide dismutase 2 (SOD2), an antioxidant enzyme present in mitochondria, is modified by acetylation, which reduces its activity. The aim of this study was to clarify whether reducing SOD2 acetylation by sirtuins 3 (SIRT3) activation improves skeletal muscle mitochondrial function and exercise capacity in HF model mice.

Methods: Myocardial infarction (MI) by ligation of the coronary artery or sham surgery was performed in male C57BL/6 J mice. Two weeks after surgery, these mice were treated with either the SIRT3 activator Honokiol (5 mg/kg body weight/day, i.p.) or vehicle. After 2 weeks of treatment, exercise capacity was evaluated by the treadmill test. Gastrocnemius muscle samples collected from the mice were used to measure mitochondrial function, as well as the levels of SIRT3, acetylated SOD2, and ROS production. Finally, the effect of adeno-associated virus serotype 9 (AAV9)-mediated overexpression of SIRT3 in the skeletal muscle on the exercise capacity of MI mice was investigated.

Results: MI mice showed decreased cardiac function and skeletal muscle weight, but Honokiol did not affect these. Exercise capacity was significantly decreased in MI mice compared with sham mice by 24.9%, and Honokiol treatment improved the exercise capacity of MI mice by 40.4% (p < 0.05). The mitochondrial oxygen consumption rate was impaired in MI mice, but was improved by Honokiol treatment. SIRT3 expression was decreased by 26.8%, and SOD2 acetylation was increased by 36.9% in the skeletal muscle of MI mice compared with sham (p < 0.05), and Honokiol treatment resulted in complete recovery of these levels (p < 0.05). Consistent with SOD2 acetylation, ROS production in the skeletal muscle was increased in MI mice and was ameliorated by Honokiol (p < 0.05). SIRT3 expression was increased in MI + AAV9-SIRT3 mice compared with MI + AAV9-Control mice. The overexpression of SIRT3 improved exercise capacity without altering cardiac function.

Conclusions: The SIRT3 activator Honokiol improved exercise capacity in MI model mice with HF, by improving mitochondrial function in skeletal muscle through the reduction of SOD2 acetylation. SIRT3 activation may thus be a novel therapeutic target for improving exercise capacity in patients with HF.