Pharmacological inhibition of host pathways enhances macrophage killing of intracellular bacterial pathogens

After ingestion into macrophage phagosomes, some Bacterial pathogens such as Mycobacterium tuberculosis (Mtb) evade killing by preventing phagosome acidification and fusion of the phagosome with a lysosome. Mtb accumulates extracellular polyphosphate (polyP), and polyP inhibits macrophage phagosome acidification and Bacterial killing. In Dictyostelium discoideum, polyP also inhibits Bacterial killing, and we identified some proteins in D. discoideum that polyP requires to suppress the killing of ingested bacteria. Here, we find that pharmacological inhibition of human orthologues of the D. discoideum proteins, including P2Y1 receptors, mammalian Target of Rapamycin (mTOR), and inositol hexakisphosphate kinase, enhances the killing of Mtb, Legionella pneumophila, and Listeria monocytogenes by human macrophages. Mtb inhibits phagosome acidification, expression of the proinflammatory marker CD54, and Autophagy, and increases expression of the anti-inflammatory marker CD206. In Mtb-infected macrophages, the polyP-degrading enzyme polyphosphatase (ScPPX) and inhibitors reversed these effects, with ScPPX increasing CD54 expression more in female macrophages compared to male macrophages. In addition, Mtb inhibits Proteasome activity, and some, but not all, inhibitors reversed these effects. While the existence of a dedicated polyP signaling pathway remains uncertain, our findings suggest that pharmacological inhibition of select host proteins can restore macrophage function and enhances the killing of intracellular pathogens.

Host-directed therapies; Host-pathogen interactions; Intracellular pathogens; Macrophage signaling pathways; Polyphosphate signaling.