Author + information
Myocardial infarction (MI) caused by coronary atherosclerosis or spasm takes an important role in the progression of cardiac hypertrophy, heart failure and arrhythmia. Notch signaling has been proved to be crucial for cell-to-cell interaction and involve in human development and diseases. Most importantly, mitochondrial dysfunction is linked with MI in which Notch1 has attracted more attention. However, Notch1's function on mitochondrial impairment in post-MI is poorly defined, no matter the role of mitochondrial fusion-associated protein 2 (Mfn2) in it. Moreover, whether melatonin potentiates Notch1/Mfn2 pathway in post-MI remains unclear. The present study was to investigate the effect of melatonin treatment on the Notch1/Mfn2 pathway in post-MI.
Small interfering RNA (siRNA, 20 μg per heart) against Notch1 or Mfn2 and Jagged1 were delivered via intramyocardial injection. 3 days later, MI was established by ligation of anterior descending branch. C57 mice were randomly assigned to the following experimental groups (n=10): (1) Sham; (2) MI; (3) Control; (4) NKD; (5) MKD; (6) Vehicle; (7) Jagged1; (8) Jagged1 + Control; (9) Jagged1+ MKD; (10) Mel: (10 mg/kg/day, 14 days before MI; 20 mg/kg/day, 2 days after MI) with MI; (11) Mel + Luz: (1 mg/kg/day, 14 days before MI; 2 mg/kg/day, 2 days after MI) with MI; (12) Vehicle + Control; (13) Mel + Control; (14) Mel + NKD; (15) Mel + MKD. Myocardial function, fibrosis, apoptosis, reactive oxygen species (ROS) and mitochondrial disorder were determined through echocardiography, masson-trichrome, caspase-3 kit, lucigenin-enhanced luminescence, transmission electron microscopy and ATP kit, respectively.
The genetic ablation of Notch1 or Mfn2 aggravated post-MI injury, along with worse mitochondrial damage and more ROS generation, when compared with control group (P<0.01). In contrast, Jagged1 improved mitochondrial structure and function, reduced ROS production, and attenuated post-MI injury (P<0.05). Interestingly, although Mfn2 expression was slightly regulated by Notch1 signaling in myocardium, Mfn2 deficiency was able to largely eliminate Jagged1's cardioprotection, evidenced by suppressed cardiac function, aggravated myocardial fibrosis, increased cell apoptosis, worsened mitochondrial impairment and enhanced oxidative stress (P<0.01). These reveal an indispensable role of Mfn2 in Notch1's protection against MI injury, perhaps by breaking the positive feedback loop of mitochondrial impairment and ROS production. Furthermore, melatonin activated Notch1 signaling and increased Mfn2 expression, all of which were reversed by luzindole (a nonselective antagonist of melatonin receptor) (P<0.05). Notably, melatonin attenuated post-MI injury in normal mice, but not in Notch1 or Mfn2 deficiency mice.
Melatonin attenuates post-MI injury through Notch1/Mfn2 pathway in a receptor-dependent manner, perhaps by blocking the vicious circle of mitochondrial impairment and ROS generation.
Key Words: Myocardial infarction; Mitochondria; Melatonin; Notch1; Mfn2; ROS