MicroRNA 26a (miR-26a)/KLF4 and CREB-C/EBPβ regulate innate immune signaling, the polarization of macrophages and the trafficking of Mycobacterium tuberculosis to lysosomes during infection

PLoS Pathog. 2017 May 30;13(5):e1006410. doi: 10.1371/journal.ppat.1006410. eCollection 2017 May.

Abstract

For efficient clearance of Mycobacterium tuberculosis (Mtb), macrophages tilt towards M1 polarization leading to the activation of transcription factors associated with the production of antibacterial effector molecules such as nitric oxide (NO) and proinflammatory cytokines such as interleukin 1 β (IL-1β) and tumor necrosis factor α (TNF-α). At the same time, resolution of inflammation is associated with M2 polarization with increased production of arginase and cytokines such as IL-10. The transcriptional and post-transcriptional mechanisms that govern the balance between M1 and M2 polarization, and bacteria-containing processes such as autophagy and trafficking of Mtb to lysosomes, are incompletely understood. Here we report for the first time, that the transcription factor KLF4 is targeted by microRNA-26a (miR-26a). During Mtb infection, downregulation of miR-26a (observed both ex vivo and in vivo) facilitates upregulation of KLF4 which in turn favors increased arginase and decreased iNOS activity. We further demonstrate that KLF4 prevents trafficking of Mtb to lysosomes. The CREB-C/EBPβ signaling axis also favors M2 polarization. Downregulation of miR-26a and upregulation of C/ebpbeta were observed both in infected macrophages as well as in infected mice. Knockdown of C/ebpbeta repressed the expression of selected M2 markers such as Il10 and Irf4 in infected macrophages. The importance of these pathways is substantiated by observations that expression of miR-26a mimic or knockdown of Klf4 or Creb or C/ebpbeta, attenuated the survival of Mtb in macrophages. Taken together, our results attribute crucial roles for the miR-26a/KLF4 and CREB-C/EBPβsignaling pathways in regulating the survival of Mtb in macrophages. These studies expand our understanding of how Mtb hijacks host signaling pathways to survive in macrophages, and open up new exploratory avenues for host-targeted interventions.

MeSH terms

  • Animals
  • CCAAT-Enhancer-Binding Protein-beta / genetics
  • CCAAT-Enhancer-Binding Protein-beta / immunology*
  • CREB-Binding Protein / genetics
  • CREB-Binding Protein / immunology*
  • Cell Polarity
  • Humans
  • Kruppel-Like Factor 4
  • Kruppel-Like Transcription Factors / genetics
  • Kruppel-Like Transcription Factors / immunology*
  • Lysosomes / genetics
  • Lysosomes / immunology
  • Lysosomes / microbiology*
  • Macrophages / cytology
  • Macrophages / immunology*
  • Macrophages / microbiology
  • Mice
  • MicroRNAs / genetics
  • MicroRNAs / immunology*
  • Mycobacterium tuberculosis / immunology
  • Mycobacterium tuberculosis / physiology*
  • RAW 264.7 Cells
  • Signal Transduction
  • Tuberculosis / genetics
  • Tuberculosis / immunology*
  • Tuberculosis / microbiology
  • Tuberculosis / physiopathology

Substances

  • CCAAT-Enhancer-Binding Protein-beta
  • Cebpb protein, mouse
  • KLF4 protein, human
  • Klf4 protein, mouse
  • Kruppel-Like Factor 4
  • Kruppel-Like Transcription Factors
  • MicroRNAs
  • Mirn26 microRNA, mouse
  • CREB-Binding Protein
  • Crebbp protein, mouse

Grants and funding

This work was supported by a grant from the Department of Biotechnology, Government of India to JB (BT/PR3260/BRB/10/967/2011). MKum was supported by a fellow ship from the Council of Scientific and Industrial Research, Government of India (19-12/2010(1)EU-IV). SKS was supported by a fellowship from the University Grants Commission (20-6/2009(i)EU-IV). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.