The role of PI3K-Akt-mTOR axis in Warburg effect and its modification by specific protein kinase inhibitors in human and rat inflammatory macrophages.

ABSTRACT

The Warburg effect occurs both in cancer cells and in inflammatory macrophages. The aim of our work was to demonstrate the role of PI3K-Akt-mTOR axis in the Warburg effect in HL-60 derived, rat peritoneal and human blood macrophages and to investigate the potential of selected inhibitors of this pathway to antagonize it. M1 polarization in HL-60-derived and human blood monocyte-derived macrophages was supported by the increased expression of NOS2 and inflammatory cytokines. All M1 polarized and inflammatory macrophages investigated expressed higher levels of HIF-1α and NOS2, which were reduced by selected kinase inhibitors, supporting the role of PI3K-Akt-mTOR axis. Using Seahorse XF plates, we found that in HL-60-derived and human blood-derived macrophages, glucose loading reduced oxygen consumption (OCR) and increased glycolysis (ECAR) in M1 polarization, which was antagonized by selected kinase inhibitors and by dichloroacetate. In rat peritoneal macrophages, the changes in oxidative and glycolytic metabolism were less marked and the NOS2 inhibitor decreased OCR and increased ECAR. Non-mitochondrial oxygen consumption and ROS production were likely due to NADPH oxidase, expressed in each macrophage type, independently of PI3K-Akt-mTOR axis. Our results suggest that inflammation changed the metabolism in each macrophage model, but a clear relationship between polarization and Warburg effect was confirmed only after glucose loading in HL-60 and human blood derived macrophages. The effect of kinase inhibitors on Warburg effect was variable in different cell types, whereas dichloroacetate caused a shift toward oxidative metabolism. Our findings suggest that these originally anti-cancer inhibitors may also be candidates for anti-inflammatory therapy.