Interrogation of the glycolytic axis in pulmonary arterial hypertension models and how modifying these can lead to potential therapeutic options.
IntroductionPulmonary arterial hypertension (PAH) describes diseases characterized by increased pulmonary vessel pressures that lead to right ventricular failure and death if left untreated. Dysregulated metabolic function has been reported in endothelial cells from PAH patients. Healthy endothelial cells can rapidly shift from quiescence to proliferative and apoptotic states, partly due to a greater utilization of glycolysis for ATP production, rather than the slower oxidative phosphorylation more commonly relied on by other cell types. However, in PAH patients, pulmonary artery endothelial cells demonstrate an even greater shift towards glycolytic ATP production. This phenomenon, which was first described in cancer as the Warburg effect, is an adaptation for optimizing both energy production and biosynthetic processes for maximum proliferative potential. Hypothesis and MethodsWe hypothesize that targeting the PKM2 axis in endothelial cells may shift the balance to favor oxidative phosphorylation, in effect reversing the Warburg effect; and that this would have beneficial effects in cell and rodent models of PAH. To this end we have tested TEPP-46, an allosteric PKM2 activator that stabilizes the tetrameric form, blocking its translocation into the nucleus and increasing canonical enzymatic activity, in blood outgrowth endothelial cells (BOECs) and in a rat Sugen-hypoxia model. ResultsTEPP-46 treatment reduced levels of nuclear PKM2 (the homodimer form which promotes anabolic effects and proliferation). Cytoplasmic levels of PKM2 and levels of PKM1 were unaffected. Exposure to TEPP-46 lowered levels of polypyrimidine tract-binding protein 1 (PTPB1), which controls alternative splicing of the PKM gene to promote PKM2 expression; and reduced LDHA, which converts pyruvate to lactate, preventing its utilization for oxidative phosphorylation. In the Sugen-hypoxia rat model, administration of TEPP-46 significantly ameliorated the elevated right ventricular systolic pressures, reduced the loss of body weight and increased survival. The increased muscularization of the smaller blood arteries and arterioles in the lungs of rats due to Sugen-hypoxia were also improved by concurrent administration of TEPP-46. ConclusionWe have shown that TEPP-46 treatment reduces nuclear PKM2 and represses PKM2-driven gene expression, with the functional effect of ameliorating the Sugen-hypoxia phenotype. This suggests that antagonizing the Warburg effect may offer a novel therapeutic avenue for PAH.