Enhancement of Reactive Oxygen Species Production and Chlamydial Infection by the Mitochondrial Nod-like Family Member NLRX1

Ali A Abdul-Sater,Najwane Saïd-Sadier,Verissa M Lam,Bhavni Singh,Matthew A Pettengill,Fraser Soares,Ivan Tattoli,Simone Lipinski,Stephen E Girardin,Philip Rosenstiel,David M Ojcius

doi:10.1074/jbc.m110.137885

Abstract

Chlamydia trachomatis infections cause severe and irreversible damage that can lead to infertility and blindness in both males and females. Following infection of epithelial cells, Chlamydia induces production of reactive oxygen species (ROS). Unconventionally, Chlamydiae use ROS to their advantage by activating caspase-1, which contributes to chlamydial growth. NLRX1, a member of the Nod-like receptor family that translocates to the mitochondria, can augment ROS production from the mitochondria following Shigella flexneri infections. However, in general, ROS can also be produced by membrane-bound NADPH oxidases. Given the importance of ROS-induced caspase-1 activation in growth of the chlamydial vacuole, we investigated the sources of ROS production in epithelial cells following infection with C. trachomatis. In this study, we provide evidence that basal levels of ROS are generated during chlamydial infection by NADPH oxidase, but ROS levels, regardless of their source, are enhanced by an NLRX1-dependent mechanism. Significantly, the presence of NLRX1 is required for optimal chlamydial growth.

Highlights

Member of the intracellular Nod-like receptor (NLR) family that is localized in mitochondria, enhances reactive oxygen species (ROS) production induced by poly(I1⁄7C), TNF␣, and Shigella flexneri infection (5)
NLRX1 Overexpression Augments C. trachomatis-induced ROS Production—A recent study demonstrated that NLRX1, the only NLR family member that translocates to the mitochondria, enhances ROS production induced by cytokines and S. flexneri infection (5)
We confirmed by immunofluorescence microscopy that NLRX1 is overexpressed in HeLa cells and that it translocates to mitochondria (Fig. 1A)

Summary

Introduction

Member of the intracellular Nod-like receptor (NLR) family that is localized in mitochondria, enhances ROS production induced by poly(I1⁄7C), TNF␣, and Shigella flexneri infection (5). We measured ROS production in C. trachomatis-infected HeLa cells treated with Lipofectamine alone or transfected with empty vector or with NLRX1-FLAG. We demonstrated that NLRX1-overexpressing HeLa cells produced higher levels of ROS in response to C. trachomatis infection than those treated with Lipofectamine (control) or transfected with empty vector (Fig. 2A).

Results

Conclusion