To our understanding, this is the first study to demonstrate that Rpost can regulate autophagy through the ALDH2/SIRT3/HIF1α signaling pathway and attenuates 4-HNE protecting the myocardium from I/R injury. Rpost is feasible and straightforward and is expected to be a more promising myocardial protection measure in clinical applications. Using this strategy, we observed a significant improvement in myocardial function after I/R injury in mice. In addition, our study demonstrated that Rpost could attenuate 4-HNE and regulate myocardial autophagy through the ALDH2/SIRT3/HIF1α pathway, reduce myocardial infarction area, and inhibit myocardial cell apoptosis. This study suggests that Rpost plays a vital role in cardiac protection after I/R injury.
Myocardial ischemia-reperfusion injury is widely used in the clinical treatment of cardiovascular diseases, such as aortic opening after cardiopulmonary bypass surgery and coronary artery stent implantation. Rpost can initiate the endogenous protective mechanism of the body by temporary ischemia-reperfusion of another organ before the onset of myocardial ischemia-reperfusion. Previous studies have shown that Rpost can reduce infarct size, protect myocardial function, and improve adverse cardiac remodeling in patients with MI[21, 22]. Furthermore, Rpost can improve the inflammatory response after cerebral ischemia and reduce cerebral hemorrhage and the risk of cerebral hemorrhage . As an exogenous intervention, Rpost is simple and easy to implement. It can improve the clinical prognosis of patients with myocardial infarction in various ways, but the specific mechanism of Rpost remains unclear. In this study, a mouse I/R model was constructed, and post-treatment was performed. It was found that Rpost can significantly reduce the area of myocardial infarction and myocardial cell apoptosis and protect heart function. However, when ALDH2 is deficient, the myocardial protection of Rpost disappears. In addition, we found that Rpost significantly promoted the expression of ALDH2 in the myocardium.
ALDH2 is an endogenous cardioprotective factor in the mitochondria and is involved in the pathophysiological processes of coronary heart disease, heart failure, cardiomyopathy, and several other diseases [24–26]. Ma et al. performed ischemia-reperfusion treatment in wild mice, ALDH2-overexpressed mice, and ALDH2-KO mice and found that the area of myocardial infarction in ALDH2-overexpressed mice was significantly decreased, whereas that in ALDH2-KO mice was increased . Our research shows that after I/R, ALDH2 expression was significantly decreased, and Rpost can significantly increase the expression of ALDH2. Furthermore, we found that Rpost upregulated the expression of ALDH2 and SIRT3. SIRT3 is mainly located in the mitochondria and can reduce oxidative stress damage and the area of myocardial infarction by activating the anti-oxidative stress signaling pathway, thereby protecting the myocardium from reperfusion injury . ALDH2 is a direct SIRT3 substrate, and its deacetylation increases acetaminophen toxic-metabolite binding and enzyme inactivation[20, 29]. Therefore, we believe that Rpost can reduce myocardial ischemia-reperfusion injury by promoting the expression of ALDH2/SIRT3, thereby exerting myocardial protection.
Myocardial ischemia-reperfusion injury stabilizes the transcription factor HIF1α, the primary regulator of the transcriptional response initiated by hypoxia, and HIF2α. ALDH2 can regulate mitochondrial fission and smooth muscle cell proliferation via the 4-HNE/HIF1α signal pathway[31, 32]. Thus, ALDH2 acts as an endogenous cardiac protective factor in the mitochondria and can exert myocardial protection by regulating autophagy . The results of this study prove that Rpost can regulate autophagy through the ALDH2/SIRT3/HIF1α pathway to exert myocardial protection, reduce myocardial ischemia-reperfusion injury and myocardial infarction area, inhibit myocardial cell apoptosis, and improve cardiac function,. In addition, we found that Rpost reduced myocardial inflammation after I/R.
Mitochondria are the main source of ROS in cells, and when ROS exceed their antioxidant capacity, they lead to fatty acid oxidation, a process known as lipid peroxidation. 4-HNE is the most abundant lipid peroxidation product and forms adducts with proteins, which affects its biological function and destroys intracellular homeostasis. The level of plasma 4-HNE was increased in patients with HF, which was negatively correlated with cardiac function. ALDH2 is a mitochondrial enzyme that metabolizes ethanol and toxic aldehydes, such as 4-HNE. In this study, we found for the first time that MI/RI leads to excessive 4-HNE levels in the mitochondria and has serious consequences in cardiac dysfunction after I/R. Conversely, Rpost can upregulate ALDH2 expression, clear excessive 4-HNE levels, protect the myocardium, and reduce ROS levels.
Notably, 40% of the East Asian population and 8% of the global population carry the ALDH2 mutation, which is caused by the replacement of glutamate with lysine at amino acid 487 and results in only 1 5% of the catalytic activity of the wild-type ALDH2[38–40]. Our present study indicates that Rpost can protect the myocardium from I/R damage through the ALDH2/SIRT3/HIF1α pathway and by decreasing 4-HNE levels. Furthermore, Rpost is highly operable, simple, easy to implement, and significant for clinical transformation. Therefore, it is expected to become a myocardial protection measure with more clinical application prospects.