Glutaminolysis Boosts Cardiac Performance Under High Workload via Enhancement of Mitochondrial GSH

Introduction: Glutamine, the most abundant non-essential amino acids in circulation, serves as an important energy source in proliferating cells. Previous evidence has indicated that glutamine is not a primary carbon source for the tricarboxylic acid cycle in cardiomyocytes under physiological workload. However, current clinical studies reveal that impaired glutaminolysis is associated with heart failure and an increased risk of cardiovascular events. Hypothesis: We hypothesized that impaired glutaminolysis would compromise cardiac function, especially under conditions of increased workload. Methods: We analyzed cardiac structure and function in a mouse model with cardiac-specific knockdown of glutaminase (GLS), a key enzyme of glutaminolysis. Cardiac reserve was assessed by isoproterenol stress echocardiography. We performed transcriptomic, 13 C isotopic labeling, and reactive oxygen species emission analyses to investigate the underlying mechanism. Results: GLS deficiency impaired cardiac reserve and exercise capacity in mice, but had no discernible effects on cardiac structure or function under baseline condition. Inhibition of glutaminolysis in pressure-overloaded hearts further exacerbated cardiac dysfunction, indicating the critical role of glutaminolysis in cardiomyocytes under high workload. Mechanistically, glutaminolysis maintained cardiomyocyte function by balancing intracellular redox status through the production of glutathione (GSH), particularly in mitochondria. Inhibition of glutaminolysis decreased both cytosolic and mitochondrial GSH levels, resulting in compromised cell contraction in isolated cardiomyocytes under high workload. Additionally, heterologous expression of an engineered mitochondrial GSH biosynthetic enzyme increased mitochondrial GSH levels and enhanced cardiac reserve in GLS knockout mice. Conclusions: Our findings establish the previously unrecognized role of glutaminolysis in cardiomyocytes, maintaining cardiac reserve via upregulating mitochondrial GSH levels. This suggests that targeting glutaminolysis is a potential strategy for improving cardiac reserve and managing cardiac diseases.