Autophagy supportsCandida glabratasurvival during phagocytosis

Andreas Roetzer,Christoph Schã¼Ller,Pavel Kovarik,Nina Gratz

doi:10.1111/j.1462-5822.2009.01391.x

Abstract

The opportunistic human fungal pathogen Candida glabrata is confronted with phagocytic cells of the host defence system. Survival of internalized cells is thought to contribute to successful dissemination. We investigated the reaction of engulfed C. glabrata cells using fluorescent protein fusions of the transcription factors CgYap1 and CgMig1 and catalase CgCta1. The expression level and peroxisomal localization of catalase was used to monitor the metabolic and stress status of internalized C. glabrata cells. These reporters revealed that the phagocytosed C. glabrata cells were exposed to transient oxidative stress and starved for carbon source. Cells trapped within macrophages increased their peroxisome numbers indicating a metabolic switch. Prolonged phagocytosis caused a pexophagy-mediated decline in peroxisome numbers. Autophagy, and in particular pexophagy, contributed to survival of C. glabrata during engulfment. Mutants lacking CgATG11 or CgATG17, genes required for pexophagy and non-selective autophagy, respectively, displayed reduced survival rates. Furthermore, both CgAtg11 and CgAtg17 contribute to survival, since the double mutant was highly sensitive to engulfment. Inhibition of peroxisome formation by deletion of CgPEX3 partially restored viability of CgATG11 deletion mutants during engulfment. This suggests that peroxisome formation and maintenance might sequester resources required for optimal survival. Mobilization of intracellular resources via autophagy is an important virulence factor that supports the viability of C. glabrata in the phagosomal compartment of infected innate immune cells.

Highlights

Candida glabrata belongs to the diverse group of human fungal pathogens and is phylogenetically closely related to Saccharomyces cerevisiae (Kaur et al, 2005, MarcetHouben and Gabaldon, 2009)
We found that C. glabrata cells engulfed by mouse macrophages experience a mild oxidative stress and sustained carbon starvation
To find out the regulatory pattern of the C. glabrata catalase, we assayed its activity in crude protein extracts from cells grown either on glucose or on a non-fermentable carbon source

Summary

Introduction

Candida glabrata belongs to the diverse group of human fungal pathogens and is phylogenetically closely related to Saccharomyces cerevisiae (Kaur et al, 2005, MarcetHouben and Gabaldon, 2009). The high similarity of C. glabrata to S. cerevisiae suggests that for fungi, relatively small genetic changes may be sufficient for adaptation to a pathogenic lifestyle (Dujon et al, 2004). C. glabrata has to evade or survive attacks of the cell-mediated immune system (Nicola et al, 2008). Candida albicans destroys macrophages by hyphal outgrowth. C. glabrata engulfed by macrophages do not undergo morphological transitions such as C. albicans (Leberer et al, 2001). An open question concerns how C. glabrata is coping with cells of the immune system, such as macrophages

Results

Discussion

Conclusion