Voltage Gated Calcium Channels Negatively Regulate Protective Immunity to Mycobacterium tuberculosis

Shashank Gupta,Rajiv Saxena,Rupak Singla,Nasir Salam,Krishnamurthy Natarajan,Khalid U Khayyam,Pawan Malhotra,Varsha Srivastava,Reshma Korde,Digamber Behera,Niyaz Ahmed

doi:10.1371/journal.pone.0005305

Shashank Gupta, Rajiv Saxena + Show 9 more

Open Access

https://doi.org/10.1371/journal.pone.0005305

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Journal: PloS one	Publication Date: Apr 23, 2009
Citations: 87	License type: CC BY 4.0

Affiliation: Jawaharlal Nehru University

Abstract

Mycobacterium tuberculosis modulates levels and activity of key intracellular second messengers to evade protective immune responses. Calcium release from voltage gated calcium channels (VGCC) regulates immune responses to pathogens. In this study, we investigated the roles of VGCC in regulating protective immunity to mycobacteria in vitro and in vivo. Inhibiting L-type or R-type VGCC in dendritic cells (DCs) either using antibodies or by siRNA increased calcium influx in an inositol 1,4,5-phosphate and calcium release calcium activated channel dependent mechanism that resulted in increased expression of genes favoring pro-inflammatory responses. Further, VGCC-blocked DCs activated T cells that in turn mediated killing of M. tuberculosis inside macrophages. Likewise, inhibiting VGCC in infected macrophages and PBMCs induced calcium influx, upregulated the expression of pro-inflammatory genes and resulted in enhanced killing of intracellular M. tuberculosis. Importantly, compared to healthy controls, PBMCs of tuberculosis patients expressed higher levels of both VGCC, which were significantly reduced following chemotherapy. Finally, blocking VGCC in vivo in M. tuberculosis infected mice using specific antibodies increased intracellular calcium and significantly reduced bacterial loads. These results indicate that L-type and R-type VGCC play a negative role in M. tuberculosis infection by regulating calcium mobilization in cells that determine protective immunity.

Highlights

Mycobacterium tuberculosis5 (M. tuberculosis) mediated mortality and morbidity continue to rise with the emergence of extremely-drug resistant bacteria, co-infection with HIV and variable efficacy of protection offered by M. bovis Bacillus Calmette-Guerin (BCG) vaccine [1,2]
As mycobacteria induced calcium influx was superior in GMCSF-dendritic cells (DCs) than in CFP10-DCs [23,24], to begin with looked at the roles of L-type and R-type Voltage Gated Calcium Channels (VGCC) to investigate their role in calcium mobilization and the effects thereof on immunity to and survival of mycobacteria
Our results clearly show that antibodies to both L-type and R-type VGCC showed binding to VGCC on CFP10-DCs and GM-CSF-DCs, while incubation with non-specific antibody showed insignificant binding

Summary

Introduction

Mycobacterium tuberculosis (M. tuberculosis) mediated mortality and morbidity continue to rise with the emergence of extremely-drug resistant bacteria, co-infection with HIV and variable efficacy of protection offered by M. bovis Bacillus Calmette-Guerin (BCG) vaccine [1,2]. Macrophages serve as long-term hosts for M. tuberculosis [4,5], M. tuberculosis, DCs are infected by M. tuberculosis and are crucial to initiate protective immune responses [8]. The initial response is the depletion of intracellular stores from the endoplasmic reticulum (ER) This is followed by the activation of store operated calcium channels that leads to a sustained increase in intracellular calcium concentrations [11]. This second phase of calcium influx is either via calcium release calcium activated (CRAC) channels or via Voltage Gated Calcium Channels (VGCC) or both [12]. Several intracellular proteins and adaptors show close associations with VGCC subunits and regulate various cellular processes [14]

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