Glycolytic Stimulation Is Not a Requirement for M2 Macrophage Differentiation

Highlights

• M2 differentiation via the JAK-STAT6 pathway requires a threshold level of ATP

• Glycolysis is not required for M2 differentiation as long as OXPHOS remains intact

• When glycolysis is reduced, glutamine can fuel the Krebs cycle in M2 macrophages

• 2-DG impairs not only glycolysis, but all of the above

Summary

Enhanced glucose uptake and a switch to glycolysis are key traits of M1 macrophages, whereas enhanced fatty acid oxidation and oxidative phosphorylation are the main metabolic characteristics of M2 macrophages. Recent studies challenge this traditional view, indicating that glycolysis may also be critically important for M2 macrophage differentiation, based on experiments with 2-DG. Here we confirm the inhibitory effect of 2-DG on glycolysis, but also demonstrate that 2-DG impairs oxidative phosphorylation and significantly reduces ¹³C-labeled Krebs cycle metabolites and intracellular ATP levels. These metabolic derangements were associated with reduced JAK-STAT6 pathway activity and M2 differentiation marker expression. While glucose deprivation and glucose substitution with galactose effectively suppressed glycolytic activity, there was no effective suppression of oxidative phosphorylation, intracellular ATP levels, STAT6 phosphorylation, and M2 differentiation marker expression. These data indicate that glycolytic stimulation is not required for M2 macrophage differentiation as long as oxidative phosphorylation remains active.