A caspase-dependent pathway is involved in Wnt/β-catenin signaling promoted apoptosis in Bacillus Calmette-Guerin infected RAW264.7 macrophages

Int J Mol Sci. 2014 Mar 21;15(3):5045-62. doi: 10.3390/ijms15035045.

Abstract

Apoptosis of alveolar macrophages following Mycobacterium tuberculosis infection have been demonstrated to play a central role in the pathogenesis of tuberculosis. In the present study, we found that Wnt/β-catenin signaling possesses the potential to promote macrophage apoptosis in response to mycobacterial infection. In agreement with other findings, an activation Wnt/β-catenin signaling was observed in murine macrophage RAW264.7 cells upon Mycobacterium bovis Bacillus Calmette-Guerin (BCG) infection at a multiple-of-infection of 10, which was accompanied with up-regulation of pro-inflammatory cytokines TNF-α and IL-6 production. However, the BCG-induced TNF-α and IL-6 secretion could be significantly reduced when the cells were exposed to a canonical Wnt signaling ligand, Wnt3a. Importantly, the activation of Wnt/β-catenin signaling was able to further promote apoptosis in BCG-infected RAW264.7 cells in part by a mitochondria-dependent apoptosis pathway. Immunoblotting analysis further demonstrated that Wnt/β-catenin signaling-induced cell apoptosis partly through a caspase-dependent apoptosis mechanism by down-regulation of anti-apoptotic protein Mcl-1, and up-regulation of pro-apoptotic proteins Bax and cleaved-caspase-3, as well as enhancement of caspase-3 activity in BCG-infected RAW264.7 cells. These data may imply an underlying mechanism of alveolar macrophages in response to mycobacterial infection, by which the pathogen induces Wnt/β-catenin signaling activation, which in turn represses mycobacterium-trigged inflammatory responses and promotes mycobacteria-infected cell apoptosis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis*
  • Caspase 3 / metabolism
  • Caspases / metabolism*
  • Cell Line
  • Flow Cytometry
  • Host-Pathogen Interactions
  • Immunoblotting
  • Interleukin-6 / metabolism
  • Macrophages / metabolism*
  • Macrophages / microbiology
  • Macrophages / ultrastructure
  • Membrane Potential, Mitochondrial
  • Mice
  • Microscopy, Electron, Scanning
  • Microscopy, Electron, Transmission
  • Mycobacterium bovis / physiology
  • Myeloid Cell Leukemia Sequence 1 Protein / metabolism
  • Signal Transduction*
  • Tumor Necrosis Factor-alpha / metabolism
  • Wnt Signaling Pathway*
  • bcl-2-Associated X Protein / metabolism
  • beta Catenin / metabolism*

Substances

  • Bax protein, mouse
  • Interleukin-6
  • Mcl1 protein, mouse
  • Myeloid Cell Leukemia Sequence 1 Protein
  • Tumor Necrosis Factor-alpha
  • bcl-2-Associated X Protein
  • beta Catenin
  • Caspase 3
  • Caspases