PFKFB3 Inhibits Fructose Metabolism in Pulmonary Microvascular Endothelial Cells

Pulmonary microvascular endothelial cells contribute to integrity of the lung gas exchange interface and they are highly glycolytic. While glucose and fructose represent discrete substrates available for glycolysis, pulmonary microvascular endothelial cells prefer glucose over fructose and the mechanisms involved in this selection are unknown. 6-Phosphofructo-2-kinase/fructose-2, 6-bisphosphatase 3 (PFKFB3) is an important glycolytic enzyme that drives glycolytic flux against negative feedback and links glycolytic and fructolytic pathways. We hypothesized that PFKFB3 inhibits fructose metabolism in pulmonary microvascular endothelial cells. We found that PFKFB3 knockout cells survive better than wild type cells in fructose-rich media, more so under hypoxia. Seahorse assays, lactate/glucose measurements, and stable isotope tracing showed that PFKFB3 inhibits fructose-hexokinase-mediated glycolysis and oxidative phosphorylation. Microarray analysis revealed that fructose upregulates PFKFB3 and PFKFB3 knockout cells increase fructose-specific glucose transporter 5 expression. Using conditional endothelial-specific PFKFB3 knockout mice, we demonstrated that endothelial PFKFB3 knockout increases lung tissue lactate production following fructose gavage. Lastly, we showed that pneumonia increases fructose in the bronchoalveolar lavage fluid in mechanically ventilated intensive care unit patients. Thus, PFKFB3 knockout increases glucose transporter 5 expression and the hexokinase-mediated fructose utilization in pulmonary microvascular endothelial cells that promotes their survival. Our findings indicate that PFKFB3 is a molecular switch that controls glucose versus fructose utilization in glycolysis and help to better understand lung endothelial cell metabolism during respiratory failure.