Effects of treadmill exercise on mitochondrial fusion and fission in the hippocampus of APP/PS1 mice

Mitochondrial dysfunction is widely recognized as an early event in the pathogenesis of Alzheimer's disease (AD). Defects in mitochondrial fusion and fission have been proposed to lead to learning and memory impairments in AD. The current study aimed to investigate whether exercise-improved learning and memory were associated with improves in mitochondrial function by increased mitochondrial fusion and decreased mitochondrial fission. APP/PS1 transgenic mice were divided into transgenic sedentary (ADC, n = 15) and transgenic exercise (ADE, n = 15) groups. Wild-type mice were also separated into sedentary (WTC, n = 15) and exercise (WTE, n = 15) groups. The WTE and ADE mice were subjected to treadmill exercise for 12 weeks. In this study, learning and memory were significantly decreased in ADC mice compared with those in WTC mice, whereas exercise improved learning and memory in APP/PS1 transgenic mice. Meanwhile, ADC mice displayed defective mitochondrial function as evidenced by a significant increase in swollen mitochondria and vacuoles, loss of mitochondrial cristae, and decreased ATP levels, as well as an imbalance in mitochondrial fusion and fission as evidenced by significantly increased Drp1 and Mff and decreased Mfn1, Mfn2, and Opa1 in the hippocampus. Interestingly, exercise mitigated mitochondrial dysfunction as evidenced by a significant reduction in swollen mitochondria and vacuoles and increased mitochondrial cristae and ATP levels in ADE mice. Coincidentally, exercise promoted the balance of mitochondrial fusion and fission as evidenced by a significantly decreased Drp1 and Mff and increased Mfn1, Mfn2, and Opa1 in the hippocampus. These findings suggest that treadmill exercise efficiently enhances learning and memory in AD by improving mitochondrial dysfunction in APP/PS1 transgenic mice.