The role of oxygen on the interaction of Candida albicans with intestinal epithelial cells

The opportunistic fungal pathogen Candida albicans frequently occurs as commensal in the gastrointestinal tract of humans. While it is known that intestinal epithelial cells are highly sensitive to ischemia-reperfusion (IR) injury, the exact role of oxygen for IR-mediated fungal translocation has however not been addressed so far. Thus, the aim of this study was to investigate C. albicans-enterocyte interactions in dependence of oxygen availability. Enterocytes were able to maintain barrier function across a range of oxygen concentrations. Their susceptibility to C. albicans infection was however significantly influenced by oxygen: The shift from low to high oxygen enhanced susceptibility to infection, likely mediated by increased intracellular oxidative stress and alterations of tight junctions facilitating increased invasion of the fungus. In contrast, low oxygen concentrations and especially hypoxic shock were associated with less damage and partially retained barrier function. Additionally, fungal translocation was reduced after hypoxic shock. HIF-1α contributed to the protective effect, independent of the antimicrobial cathelicidin LL-37. Furthermore, peracute hypoxic preconditioning, compared to enterocytes constantly cultured at low oxygen, led to enhanced adhesion but reduced invasion and reduced hyphal growth of C. albicans, suggesting that oxygen-mediated changes of enterocytes also directly influence the fungus. Fungal adaptation to oxygen availability contributes to these interactions, as a C. albicans TYE7 deletion mutant showed oxygen-dependent alterations in virulence. Finally, this study provides evidence that the early stages of the infection process determine the fate of enterocytes during their interaction with C. albicans in an oxygen-dependent manner. In summary, this study demonstrates that oxygen availability significantly influences the interaction between C. albicans and the intestinal barrier by affecting both host cells and pathogen.