Mitochondrial Reactive Oxygen Species Regulate Immune Responses of Macrophages to Aspergillus fumigatus.

Remi Hatinguais,Arnab Pradhan,Elena Shekhova,Adilia Warris,Alistair J P Brown,Gordon D Brown

doi:10.3389/fimmu.2021.641495

Remi Hatinguais, Arnab Pradhan + Show 4 more

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https://doi.org/10.3389/fimmu.2021.641495

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Abstract

Reactive Oxygen Species (ROS) are highly reactive molecules that can induce oxidative stress. For instance, the oxidative burst of immune cells is well known for its ability to inhibit the growth of invading pathogens. However, ROS also mediate redox signalling, which is important for the regulation of antimicrobial immunity. Here, we report a crucial role of mitochondrial ROS (mitoROS) in antifungal responses of macrophages. We show that mitoROS production rises in murine macrophages exposed to swollen conidia of the fungal pathogen Aspergillus fumigatus compared to untreated macrophages, or those treated with resting conidia. Furthermore, the exposure of macrophages to swollen conidia increases the activity of complex II of the respiratory chain and raises mitochondrial membrane potential. These alterations in mitochondria of infected macrophages suggest that mitoROS are produced via reverse electron transport (RET). Significantly, preventing mitoROS generation via RET by treatment with rotenone, or a suppressor of site IQ electron leak, S1QEL1.1, lowers the production of pro-inflammatory cytokines TNF-α and IL-1β in macrophages exposed to swollen conidia of A. fumigatus. Rotenone and S1QEL1.1 also reduces the fungicidal activity of macrophages against swollen conidia. Moreover, we have established that elevated recruitment of NADPH oxidase 2 (NOX2, also called gp91phox) to the phagosomal membrane occurs prior to the increase in mitoROS generation. Using macrophages from gp91phox-/- mice, we have further demonstrated that NOX2 is required to regulate cytokine secretion by RET-associated mitoROS in response to infection with swollen conidia. Taken together, these observations demonstrate the importance of RET-mediated mitoROS production in macrophages infected with A. fumigatus.

Highlights

Aspergillus fumigatus is a ubiquitous fungus that causes a wide range of illnesses, from allergic reactions to life-threatening invasive aspergillosis [1]
The mitochondrial inhibitor rotenone is known to prevent mitochondrial reactive oxygen species (ROS) (mitoROS) generation during reverse electron transport (RET) [13, 37, 38] (Figure 1F), and we tested the effect of treating bone marrow-derived macrophages (BMDM) with rotenone before exposure to swollen conidia
This study addresses how mitoROS levels in macrophages orchestrate antimicrobial responses against the major fungal pathogen A. fumigatus

Summary

Introduction

Aspergillus fumigatus is a ubiquitous fungus that causes a wide range of illnesses, from allergic reactions to life-threatening invasive aspergillosis [1]. The lack of NADPH oxidase (NOX)-derived reactive oxygen species (ROS) in CGD phagocytes results in the defective oxidative killing of pathogens [3]. Besides being crucial for intracellular oxidative killing, ROS can orchestrate inflammatory processes in response to microbial pathogens including fungi [5,6,7]. Changes in ROS levels are often a consequence of metabolic remodelling in activated immune cells. Together these changes in cellular metabolism and redox homeostasis can initiate, as well as resolve, inflammatory responses [8,9,10,11,12]. A growing number of investigations have shown that tuning the production of specific inflammatory mediators, cytokines, correlates directly with metabolic re-programming and altered ROS production [9, 11]

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