Glucocorticoids Induce an Opposite Metabolic Switch in Human Monocytes Contingent upon Their Polarization.

Background

Monocytes can commit to different phenotypes associated with specific features required in inflammation and homeostasis. Classical and alternative activation are two extremes of monocyte polarization and are both influenced by glucocorticoids (GCs).

Methods

Human monocytes were sorted from the blood of healthy individuals and activated with LPS or IL-4 and IL-13, either in the absence or presence of dexamethasone (Dex). Metabolic adjustments were analyzed using Seahorse stress tests, SCENITH, and RT-qPCR.

Results

LPS enhanced glycolysis and also, to a lesser extent, oxidative phosphorylation (OXPHOS), whereas addition of Dex induced a metabolic switch in favor of the latter. In contrast, activation of monocytes with IL-4 and IL-13 exclusively stimulated OXPHOS, which was suppressed by concomitant Dex treatment. The glycolytic function of monocytes matched alterations in gene expression of glucose transporters and metabolic enzymes, which were upregulated by LPS and inhibited by Dex via interference with the mTORC1 pathway but remained unaltered in response to IL-4 and IL-13. Although the dependency of classically and alternatively activated monocytes on OXPHOS and glucose usage markedly differed, modulation by GCs was limited to the latter polarization state.

Conclusions

Our findings unravel a highly selective regulation of human monocyte energy metabolism by different activating stimuli as well as by GCs.