ADP-dependent glucokinase (ADPGK) is not critical for the activation of human macrophages by LPS

Abstract

Background: Activated immune cells show an enhanced glucose metabolism, suggesting that the inhibition of this pathway selective in immune cells could be a potential approach to combat inflammatory diseases. We studied here whether ADP-dependent glucokinase (ADPGK), a glucose-phosphorylating enzyme predominantly expressed in immune cells, could be a suitable target for the inhibition of macrophage activation. Methods: The regulation and role of ADPGK in human primary macrophages differentiated from blood monocytes was studied using Real-time quantitative PCR (RT-qPCR), gene silencing, whole-cell MALDI-mass spectrometry (MS) imaging as well as immune-based and enzymatic medium analyzes. Results: The expression of ADPGK was induced in response to the activation of toll-like receptors (TLRs). The most robust effect was observed with the TLR4 ligand Lipopolysaccharide (LPS) leading to an approximately 4-fold increase of ADPGK RNA levels. For this induction, the activation of p38 MAPK and IKKε was important. Silencing of ADPGK expression using siRNAs had neither an effect on LPS-induced expression and release of proinflammatory cytokines nor on cellular ATP levels and lactate production. Untargeted metabolic cell profiling by whole-cell MALDI-MS imaging did not reveal any metabolic regulations after ADPGK down-regulation suggesting no specific metabolic pathway involvement. Conclusions: ADPGK neither catalyzes a rate-limiting step of glucose metabolism in LPS-activated macrophages nor is required for the proinflammatory phenotype of these cells in vitro. Our data do not indicate that ADPGK inhibition could be a pharmacological approach to modulate immunometabolism.