Suppression of Protective Responses upon Activation of L-Type Voltage Gated Calcium Channel in Macrophages during Mycobacterium bovis BCG Infection

PLoS One. 2016 Oct 10;11(10):e0163845. doi: 10.1371/journal.pone.0163845. eCollection 2016.

Abstract

The prevalence of Mycobacterium tuberculosis (M. tb) strains eliciting drug resistance has necessitated the need for understanding the complexities of host pathogen interactions. The regulation of calcium homeostasis by Voltage Gated Calcium Channel (VGCCs) upon M. tb infection has recently assumed importance in this area. We previously showed a suppressor role of VGCC during M. tb infections and recently reported the mechanisms of its regulation by M. tb. Here in this report, we further characterize the role of VGCC in mediating defence responses of macrophages during mycobacterial infection. We report that activation of VGCC during infection synergistically downmodulates the generation of oxidative burst (ROS) by macrophages. This attenuation of ROS is regulated in a manner which is dependent on Toll like Receptor (TLR) and also on the route of calcium influx, Protein Kinase C (PKC) and by Mitogen Activation Protein Kinase (MAPK) pathways. VGCC activation during infection increases cell survival and downmodulates autophagy. Concomitantly, pro-inflammatory responses such as IL-12 and IFN-γ secretion and the levels of their receptors on cell surface are inhibited. Finally, the ability of phagosomes to fuse with lysosomes in M. bovis BCG and M. tb H37Rv infected macrophages is also compromised when VGCC activation occurs during infection. The results point towards a well-orchestrated strategy adopted by mycobacteria to supress protective responses mounted by the host. This begins with the increase in the surface levels of VGCCs by mycobacteria and their antigens by well-controlled and regulated mechanisms. Subsequent activation of the upregulated VGCC following tweaking of calcium levels by molecular sensors in turn mediates suppressor responses and prepare the macrophages for long term persistent infection.

MeSH terms

  • Animals
  • Calcium Channels, L-Type / immunology*
  • Calcium Signaling / immunology*
  • Cell Line, Tumor
  • Female
  • Humans
  • Interferon-gamma / immunology
  • Interleukin-12 / immunology
  • Macrophages / immunology*
  • Male
  • Mice
  • Mice, Inbred BALB C
  • Mycobacterium Infections / immunology*
  • Mycobacterium bovis / immunology*
  • Reactive Oxygen Species / immunology

Substances

  • Calcium Channels, L-Type
  • IFNG protein, human
  • IFNG protein, mouse
  • Reactive Oxygen Species
  • Interleukin-12
  • Interferon-gamma

Grants and funding

The study was funded by grants from the Department of Biotechnology, Ministry of Science and Technology, Government of India to KN and YS. DS is a recipient of UGC-SRF. BKT is a recipient of UGC-DSK-PDF. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.