Author + information
- Lv Ping,
- Zhiyong Yin and
- Yan Li
The purpose of this study is to investigate whether nicotinamide riboside(NR), a newly discovered NAD+ precursor occurring in milk, could reduce myocardial ischemia-reperfusion injury by regulating autophagy and its mechanisms.
We utilized an in vivo mouse model of myocardial I/R injury and an in vitro adult mouse cardiomyocytes model of hypoxia/reoxygenation (H/R) injury. In vivo experiments, six groups were divided:1) control group;2) I/R group;3) I/R+NR group;4) I/R+NR+Ad-shSirt3 group;5) I/R+NR+Ad-shPGC-1α group;6) I/R+NR+ overexpressing P53 group. In vitro study, six groups were also divided:1) control group;2) H/R group;3) H/R+NR group;4) H/R+NR+Ad-shSirt3 group;5) H/R+NR+ Ad-shPGC-1α group;6) H/R+NR+ overexpressing P53 group. The cardiac function was evaluated with echocardiography, myocardial infarct size with Evan's Blue-triphenyltetrazolium chloride (TTC) double staining, myocardial apoptosis with TUNEL staining, autophagosome with electron transmission microscopy and proteins with western blot.
Compared with control group, I/R injury could significantly reduce the left ventricular ejection fractions (LVEF) and increase myocardial infarction size as well as myocardial apoptosis index and the accumulation of excessive autophagosome. Besides, it reduced the expression of proteins related to mitochondrial biogenesis like PGC-1α, Tfam and NRF1, but increased the level of autophagy markers such as LC3, P62, Beclin1, Atg5/7. However, adding NR could alleviate the myocardial I/R injury measured above. And NR could increase the level of PGC-1α, Tfam and NRF1 but decreased the level of LC3, P62, Beclin1, Atg5/7. By inhibiting Sirtuin3, the above roles of NR were abrogated, which suggested that the protective roles of NR depended on Sirtuin3. Additionally, the roles of NR were also weakened by PGC-1αinterference except the expression of autophagy markers and Sirtuin3, which showed that NR may alleviate the myocardial I/R injury via Sirt3-PGC-1α pathway. Interestingly, by overexpressing P53, similar results with PGC-1α interference were observed but the expression of PGC-1α, Tfam, NRF1 and Sirtuin3, which pointed out that NR may reduce autophagy via Sirt3-P53 pathway to alleviate the myocardial I/R injury. In accordance with in vivo experiments, in vitro results indicated that NR could reduce myocardial apoptosis index and the accumulation of excessive autophagosome, which were increased by H/R injury. Also, NR increased the expression of PGC-1α, Tfam and NRF1 via Sirt3-PGC-1α pathway, but decreased the expression of LC3, P62, Beclin1, Atg5/7 via Sirt3-P53 pathway.
These results for the first time demonstrated that NR could alleviate the myocardial ischemia/reperfusion injury. The underlying mechanism was improving the mitochondrial biogenesis via Sirt3-PGC-1α pathway and reducing the accumulation of excessive autophagosome via Sirt3-P53 pathway. This study provided important evidence for the potential clinical practice of NR in myocardial protection.