Eliminating Legionella by inhibiting BCL-XL to induce macrophage apoptosis

Abstract

Human pathogenic Legionella replicate in alveolar macrophages and cause a potentially lethal form of pneumonia known as Legionnaires' disease1. Here, we have identified a host-directed therapeutic approach to eliminate intracellular Legionella infections. We demonstrate that the genetic deletion, or pharmacological inhibition, of the host cell pro-survival protein BCL-XL induces intrinsic apoptosis of macrophages infected with virulent Legionella strains, thereby abrogating Legionella replication. BCL-XL is essential for the survival of Legionella-infected macrophages due to bacterial inhibition of host-cell protein synthesis, resulting in reduced levels of the short-lived, related BCL-2 pro-survival family member, MCL-1. Consequently, a single dose of a BCL-XL-targeted BH3-mimetic therapy, or myeloid cell-restricted deletion of BCL-XL, limits Legionella replication and prevents lethal lung infections in mice. These results indicate that repurposing BH3-mimetic compounds, originally developed to induce cancer cell apoptosis, may have efficacy in treating Legionnaires' and other diseases caused by intracellular microbes.

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Figure 1: Loss of BCL-XL restricts Legionella burdens in macrophages by inducing host cell death.
Figure 2: Loss of BCL-XL causes intrinsic apoptosis of Legionella-infected macrophages.
Figure 3: Loss of MCL-1 due to Legionella-mediated inhibition of protein synthesis sensitizes cells to apoptosis following BCL-XL antagonism.
Figure 4: Legionella depends on BCL-XL to cause lung infections in mice.

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Acknowledgements

The authors thank members of the Monash Micro Imaging facility for their technical support, D. Newman (Monash University) for the statistical analysis, E. Latz (University of Bonn) for immortalized C57Bl/6 macrophages and D. Vaux, J. Silke, W. Alexander, S. Masters, L. Lindqvist and P. Bouillet (Walter and Eliza Hall Institute of Medical Research) for providing mice or reagents. This study was funded by grants and fellowships from the NHMRC (Canberra, Australia), programme grants 606788 (T.L. and E.L.H.) and 1016701 (A.S.), project grants 1024839 (T.N. and J.E.V.), 1051235 (S.P.G.) and 1009145 (L.O.R.), CDF1 fellowships 1052598 (J.E.V.) and 1020363 (A.S.), an NHMRC infrastructure grant, Independent Research Institutes Infrastructure Support Scheme grant 361646, the Victorian State Government (OIS grant) and the Leukemia and Lymphoma Society (SCOR grants 7413 and 7001-13).

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M.S., K.E.L., S.P.G., S.H., K.E.S., E.L.H., T.L., A.S., G.L., D.C.S.H., J.E.V. and T.N. designed the research and carried out analysis. M.S., K.E.L., G.A., S.H., A.V., J.E.V. and T.N. performed experiments. K.E.S. wrote ImageJ and Metamorph scripts. L.A.O.R. and K.M. generated knockout mice. R.S. and E.L.H. designed and generated GFP-expressing and mutant Legionella. G.L. and D.C.S.H. generated and analysed BH3 mimetic compounds. M.S., K.E.L., A.S., J.E.V. and T.N. wrote the manuscript.

Corresponding authors

Correspondence to James E. Vince or Thomas Naderer.

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Competing interests

The authors declare that S.P.G., L.A.O.R., A.S., G.L., D.S.C.H. and J.E.V. are employees of The Walter and Eliza Hall Medical Institute, which receives milestone payments from Genentech and AbbVie for the development of ABT-199 for cancer therapy.

Supplementary information

Supplementary Information

Supplementary Figures 1–5. (PDF 2978 kb)

Supplementary Video 1

Time-lapse video microscopy of L. pneumophila infected macrophages. (AVI 10681 kb)

Supplementary Video 2

Time-lapse video microscopy of ABT-737 treated macrophages infected with L. pneumophila. (AVI 8366 kb)

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Speir, M., Lawlor, K., Glaser, S. et al. Eliminating Legionella by inhibiting BCL-XL to induce macrophage apoptosis. Nat Microbiol 1, 15034 (2016). https://doi.org/10.1038/nmicrobiol.2015.34

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