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Updated: May 10, 2025
Using a Bacterial Pathogen to Probe for Cellular and Organismic-level Host Responses
Published on: February 22, 2019
Pharmacological inhibition of host pathways enhances macrophage killing of intracellular bacterial pathogens
Ramesh Rijal1,2, Richard H Gomer2
1School of Biological, Environmental, and Earth Sciences, The University of Southern Mississippi, Hattiesburg, Mississippi, USA.
Abstract:
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.
Insights
Targeting specific macrophage proteins with drugs can enhance the killing of intracellular pathogens like Mycobacterium tuberculosis. This approach restores macrophage function against infections such as tuberculosis, Legionnaires
Area of Science:
- Immunology
- Microbiology
- Cell Biology
Background:
- Pathogenic bacteria like Mycobacterium tuberculosis (Mtb) evade macrophage killing by preventing phagosome acidification and fusion with lysosomes.
- Extracellular polyphosphate (polyP) accumulated by Mtb inhibits macrophage phagosome acidification and bacterial killing.
- Host proteins are involved in polyP's suppression of bacterial killing in Dictyostelium discoideum.
Purpose of the Study:
- To investigate if pharmacological inhibition of human orthologues of Dictyostelium discoideum proteins can enhance macrophage killing of intracellular pathogens.
- To determine the effect of inhibiting specific host proteins on Mtb-induced changes in macrophage function, including phagosome acidification, inflammatory markers, and autophagy.
Main Methods:
- Pharmacological inhibition of human orthologues of Dictyostelium discoideum proteins, including P2Y1 receptors, mammalian Target of Rapamycin (mTOR), and inositol hexakisphosphate kinase.
- Treatment of Mtb-infected human macrophages with polyP-degrading enzyme (ScPPX) and proteasome inhibitors.
- Assessment of bacterial killing, phagosome acidification, CD54 and CD206 expression, autophagy, and proteasome activity in treated macrophages.
Main Results:
- Inhibition of specific host proteins (P2Y1 receptors, mTOR, inositol hexakisphosphate kinase) enhanced the killing of Mtb, Legionella pneumophila, and Listeria monocytogenes by human macrophages.
- ScPPX and certain inhibitors reversed Mtb-induced inhibition of phagosome acidification, CD54 expression, and autophagy, and increased CD54 expression in female macrophages.
- Mtb's inhibition of proteasome activity was reversed by some, but not all, tested inhibitors.
Conclusions:
- Pharmacological inhibition of select host proteins can restore macrophage function and enhance the killing of intracellular pathogens.
- Targeting host factors involved in bacterial evasion mechanisms offers a potential therapeutic strategy against infections like tuberculosis, Legionnaires' disease, and listeriosis.
- The findings suggest potential therapeutic avenues by modulating host responses to intracellular bacterial infections.
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