Dexamethasone inhibits Mycobacterium tuberculosis-induced glycolysis but preserves antimicrobial function in primary human macrophages.

Glucocorticoids (GC) are useful adjunctive host directed therapies (HDT) for sub-types of tuberculosis (TB). Macrophages play a central role in controlling Mycobacterium tuberculosis (Mtb) infection, relying on glycolytic reprogramming to support an effective host defence, yet the influence of GC on these important phagocytes is poorly understood. Here, we examined the impact of dexamethasone on metabolic and functional responses of primary human airway macrophages (AM) from bronchoalveolar lavage fluid and monocyte-derived macrophages (MDM). We found that dexamethasone significantly reduced basal and compensatory glycolysis in both AM and MDM, and decreased expression of the glycolytic enzyme PFKFB3. Oxidative metabolism was lower in dexamethasone AM but not MDM, indicating different specific metabolic sensitivity of macrophages. Dexamethasone also inhibited the glycolytic response to Mtb and reduced secretion of IL-1β, TNF, IL-6, IL-8, and IL-10. Dexamethasone-treated macrophages showed enhanced survival following Mtb infection and these cells had a significant reduction in bacterial burden. This antimicrobial effect was impaired when macrophages were pre-treated with bafilomycin A1, implicating that phagosomal acidification may at least in part mediate dexamethasone-induced bacterial control. Collectively, these findings demonstrate that dexamethasone reprograms human macrophage metabolism toward a less glycolytic state while preserving their ability to limit Mtb growth. These results may provide a basis for the clinical benefit of GC in some TB presentations and support the development of targeting GC therapies to macrophages, thereby mitigating inflammation without compromising host antimicrobial defence.