Ischemic N-Acetylneuraminic Acid Release Impairs Mitochondrial Hexokinases II and Autophagy in Cardiomyocytes

Background: Elevated levels of circulating N-acetylneuraminic acid (Neu5Ac) is considered as an independent risk factor for coronary artery diseases. This study aims to find the potential impact of free Neu5Ac on cardiomyocyte injury. Methods: The impact of free Neu5Ac on mitochondrial hexokinases II (HK-II) and autophagy was investigated in primary cardiomyocytes and the mouse heart subjected to hypoxic insult. Findings: Hypoxia activated neuraminidase-1(Neu-1) to induce sialic acid release in cardiomyocytes. Free Neu5Ac bound to HK-II and impaired mitochondrial function, leading to cell apoptosis. Nutrient deprivation elicits autophagy for cell salvage. HK-II binds and inactivates mTOR. However, Neu5Ac disrupted the binding and impaired autophagic response by reactivating mTOR, evidenced by impaired autophagic flux with increased p62 expression and reduced ratio of LC3-II/LC3-I. Impaired mitochondrial HK-II and autophagy were also observed in isoproterenol-induced ischemic heart of mice. By inhibiting neuraminidase, anti-influenza drugs oseltamivir and zanamivir reduced sialic acid release with improved mitochondrial HK-II and autophagy, resultantly rescuing cardiomyocytes survival from ischemic injury. Interpretation: Myocardial ischemia activates neuraminidase, and the released Neu5Ac acts as a mediator to impair cardiomyocytes. These findings establish a previously unrecognized role of Neu5Ac in cardiac ischemic injury and suggest the potential of neuraminidase inhibition in cardiomyocytes. Funding: This work was supported in part by the National Science Fund of China for Distinguished Young Scholars, Major Research Plan of the National Science Foundation of China, and National Natural Science Foundation of China.   Declaration of Interest: The authors declare no conflicts of interest that pertain to this work. Ethical Approval: All animal experiments were carried out according to the National Institutes of Health Guide for the Care and Use of Laboratory Animals and the procedures were approved by the Animal Care and Use Committee of China Pharmaceutical University.