Role of Cathepsins in Mycobacterium tuberculosis Survival in Human Macrophages.

David Pires,Olivier Neyrolles,Joana Marques,João Palma Pombo,Elsa Anes,Paulo Bettencourt,Nuno Carmo,Geanncarlo Lugo-Villarino

doi:10.1038/srep32247

Abstract

Cathepsins are proteolytic enzymes that function in the endocytic pathway, especially in lysosomes, where they contribute directly to pathogen killing or indirectly, by their involvement in the antigen presentation pathways. Mycobacterium tuberculosis (MTB) is a facultative intracellular pathogen that survives inside the macrophage phagosomes by inhibiting their maturation to phagolysosomes and thus avoiding a low pH and protease-rich environment. We previously showed that mycobacterial inhibition of the proinflammatory transcription factor NF-κB results in impaired delivery of lysosomal enzymes to phagosomes and reduced pathogen killing. Here, we elucidate how MTB also controls cathepsins and their inhibitors, cystatins, at the level of gene expression and proteolytic activity. MTB induced a general down-regulation of cathepsin expression in infected cells, and inhibited IFNγ-mediated increase of cathepsin mRNA. We further show that a decrease in cathepsins B, S and L favours bacterial survival within human primary macrophages. A siRNA knockdown screen of a large set of cathepsins revealed that almost half of these enzymes have a role in pathogen killing, while only cathepsin F coincided with MTB resilience. Overall, we show that cathepsins are important for the control of MTB infection, and as a response, it manipulates their expression and activity to favour its intracellular survival.

Highlights

Tuberculosis (TB) remains a worldwide health problem with 8 million new cases diagnosed and more than 1 million deaths per year, as reported by the World Health Organization[1]
We previously showed that a direct consequence of mycobacteria inhibition of nuclear factor- κB (NF-κB) activity is the impairment of the delivery of lysosomal enzymes to phagosomes, which results in reduced pathogen killing[14]
In order to determine the role of cathepsins and their natural inhibitors during mycobacterial infection, we started by performing qRTPCR transcriptomic analysis of cathepsins and cystatins expressed in macrophages at early stages of infection

Summary

Introduction

Tuberculosis (TB) remains a worldwide health problem with 8 million new cases diagnosed and more than 1 million deaths per year, as reported by the World Health Organization[1]. One of the first encounters of the immune system with the pathogen begins in the lungs where macrophages internalize the bacteria[2] These cells are usually able to destroy bacteria upon phagocytosis and exposure to oxidative stress at an early stage, and subsequent acidification of the bacteria-containing phagosome upon fusion with late endosomes and lysosomes; there, the bacteria still encounter a toxic environment characterized mainly by the activity of proteolytic and lipolytic enzymes[3]. These events will lead to pathogen destruction and processing of its antigens to be presented to lymphocytes through the class II antigen presentation machinery. This was associated with a concomitant decrease in cathepsin protein levels and enzymatic activity, favouring an increased intracellular survival of the pathogen

Methods

Results

Conclusion