Abstract

A hallmark of pulmonary tuberculosis is formation of macrophage-rich granulomas. These may restrict Mycobacterium tuberculosis (Mtb) growth, or progress to central necrosis and cavitation, facilitating pathogen growth. To determine factors leading to Mtb proliferation and host cell death, we used live cell imaging to track Mtb infection outcomes in individual primary human macrophages. Internalization of Mtb aggregates caused macrophage death, and phagocytosis of large aggregates was more cytotoxic than multiple small aggregates containing similar numbers of bacilli. Macrophage death did not result in clearance of Mtb. Rather, it led to accelerated intracellular Mtb growth regardless of prior activation or macrophage type. In contrast, bacillary replication was controlled in live phagocytes. Mtb grew as a clump in dead cells, and macrophages which internalized dead infected cells were very likely to die themselves, leading to a cell death cascade. This demonstrates how pathogen virulence can be achieved through numbers and aggregation states.

Article and author information

Author details

  1. Deeqa Mahamed

    KwaZulu-Natal Research Institute for TB-HIV, Durban, South Africa
    Competing interests
    The authors declare that no competing interests exist.
  2. Mikael Boulle

    KwaZulu-Natal Research Institute for TB-HIV, Durban, South Africa
    Competing interests
    The authors declare that no competing interests exist.
  3. Yashica Ganga

    KwaZulu-Natal Research Institute for TB-HIV, Durban, South Africa
    Competing interests
    The authors declare that no competing interests exist.
  4. Chanelle Mc Arthur

    KwaZulu-Natal Research Institute for TB-HIV, Durban, South Africa
    Competing interests
    The authors declare that no competing interests exist.
  5. Steven Skroch

    KwaZulu-Natal Research Institute for TB-HIV, Durban, South Africa
    Competing interests
    The authors declare that no competing interests exist.
  6. Lance Oom

    KwaZulu-Natal Research Institute for TB-HIV, Durban, South Africa
    Competing interests
    The authors declare that no competing interests exist.
  7. Oana Catinas

    KwaZulu-Natal Research Institute for TB-HIV, Durban, South Africa
    Competing interests
    The authors declare that no competing interests exist.
  8. Kelly Pillay

    KwaZulu-Natal Research Institute for TB-HIV, Durban, South Africa
    Competing interests
    The authors declare that no competing interests exist.
  9. Myshnee Naicker

    KwaZulu-Natal Research Institute for TB-HIV, Durban, South Africa
    Competing interests
    The authors declare that no competing interests exist.
  10. Sanisha Rampersad

    KwaZulu-Natal Research Institute for TB-HIV, Durban, South Africa
    Competing interests
    The authors declare that no competing interests exist.
  11. Colisile Mathonsi

    KwaZulu-Natal Research Institute for TB-HIV, Durban, South Africa
    Competing interests
    The authors declare that no competing interests exist.
  12. Jessica Hunter

    KwaZulu-Natal Research Institute for TB-HIV, Durban, South Africa
    Competing interests
    The authors declare that no competing interests exist.
  13. Gopalkrishna Sreejit

    KwaZulu-Natal Research Institute for TB-HIV, Durban, South Africa
    Competing interests
    The authors declare that no competing interests exist.
  14. Alexander S Pym

    KwaZulu-Natal Research Institute for TB-HIV, Durban, South Africa
    Competing interests
    The authors declare that no competing interests exist.
  15. Gila Lustig

    KwaZulu-Natal Research Institute for TB-HIV, Durban, South Africa
    Competing interests
    The authors declare that no competing interests exist.
  16. Alex Sigal

    KwaZulu-Natal Research Institute for TB-HIV, Durban, South Africa
    For correspondence
    alexander.sigal@gmail.com
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0001-8571-2004

Funding

Bill and Melinda Gates Foundation (OPP1116944)

  • Alex Sigal

Human Frontier Science Program (CDA00050/2013-C)

  • Alex Sigal

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

Reviewing Editor

  1. Larry Schlesinger

Ethics

Human subjects: Blood was obtained from adult healthy volunteers after written informed consent (University of KwaZulu-Natal Institutional Review Board approval BE022/13). Alveolar macrophages were obtained from bronchoalveolar lavage as part of an indicated diagnostic procedure after written informed consent (University of KwaZulu-Natal Institutional Review Board approval BE037/12).

Version history

  1. Received: October 1, 2016
  2. Accepted: January 27, 2017
  3. Accepted Manuscript published: January 28, 2017 (version 1)
  4. Version of Record published: February 21, 2017 (version 2)
  5. Version of Record updated: May 5, 2017 (version 3)

Copyright

© 2017, Mahamed et al.

This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.

Metrics

  • 9,196
    views
  • 1,574
    downloads
  • 91
    citations

Views, downloads and citations are aggregated across all versions of this paper published by eLife.

Download links

A two-part list of links to download the article, or parts of the article, in various formats.

Downloads (link to download the article as PDF)

Open citations (links to open the citations from this article in various online reference manager services)

Cite this article (links to download the citations from this article in formats compatible with various reference manager tools)

  1. Deeqa Mahamed
  2. Mikael Boulle
  3. Yashica Ganga
  4. Chanelle Mc Arthur
  5. Steven Skroch
  6. Lance Oom
  7. Oana Catinas
  8. Kelly Pillay
  9. Myshnee Naicker
  10. Sanisha Rampersad
  11. Colisile Mathonsi
  12. Jessica Hunter
  13. Gopalkrishna Sreejit
  14. Alexander S Pym
  15. Gila Lustig
  16. Alex Sigal
(2017)
Intracellular growth of Mycobacterium tuberculosis after macrophage cell death leads to serial killing of host cells
eLife 6:e22028.
https://doi.org/10.7554/eLife.22028

Share this article

https://doi.org/10.7554/eLife.22028

Further reading

    1. Cell Biology
    2. Computational and Systems Biology
    Trine Line Hauge Okholm, Andreas Bjerregaard Kamstrup ... Christian Kroun Damgaard
    Research Article

    Circular RNAs represent a class of endogenous RNAs that regulate gene expression and influence cell biological decisions with implications for the pathogenesis of several diseases. Here, we disclose a novel gene-regulatory role of circHIPK3 by combining analyses of large genomics datasets and mechanistic cell biological follow-up experiments. Using time-course depletion of circHIPK3 and specific candidate RNA-binding proteins, we identify several perturbed genes by RNA sequencing analyses. Expression-coupled motif analyses identify an 11-mer motif within circHIPK3, which also becomes enriched in genes that are downregulated upon circHIPK3 depletion. By mining eCLIP datasets and combined with RNA immunoprecipitation assays, we demonstrate that the 11-mer motif constitutes a strong binding site for IGF2BP2 in bladder cancer cell lines. Our results suggest that circHIPK3 can sequester IGF2BP2 as a competing endogenous RNA (ceRNA), leading to target mRNA stabilization. As an example of a circHIPK3-regulated gene, we focus on the STAT3 mRNA as a specific substrate of IGF2BP2 and validate that manipulation of circHIPK3 regulates IGF2BP2-STAT3 mRNA binding and, thereby, STAT3 mRNA levels. Surprisingly, absolute copy number quantifications demonstrate that IGF2BP2 outnumbers circHIPK3 by orders of magnitude, which is inconsistent with a simple 1:1 ceRNA hypothesis. Instead, we show that circHIPK3 can nucleate multiple copies of IGF2BP2, potentially via phase separation, to produce IGF2BP2 condensates. Our results support a model where a few cellular circHIPK3 molecules can induce IGF2BP2 condensation, thereby regulating key factors for cell proliferation.