Candida albicans pathways that protect against organic peroxides and lipid peroxidation.
Human fungal pathogens must survive diverse reactive oxygen species (ROS) produced by host immune cells. ROS can oxidize a range of cellular molecules including proteins, lipids, and DNA. Formation of lipid radicals by ROS can be especially damaging, as it leads to a chain reaction of lipid peroxidation that causes widespread damage to the plasma membrane. Most previous studies on antioxidant pathways in fungal pathogens have been conducted with hydrogen peroxide, so the pathways used to combat organic peroxides and lipid peroxidation are not well understood. The most well-known peroxidase in Candida albicans, catalase, only acts on hydrogen peroxide. We therefore characterized a family of four glutathione peroxidases (GPxs) that were predicted to play an important role in reducing organic peroxides. One of the GPxs, Gpx3 is also known to activate the Cap1 transcription factor that plays the major role in inducing antioxidant genes in response to ROS. Surprisingly, we found that the only measurable role of the GPxs is activation of Cap1 and did not find a significant role for GPxs in the direct detoxification of peroxides. Furthermore, a CAP1 deletion mutant strain was highly sensitive to organic peroxides and oxidized lipids, indicating an important role for antioxidant genes upregulated by Cap1 in protecting cells from organic peroxides. We identified GLR1 (Glutathione reductase), a gene upregulated by Cap1, as important for protecting cells from oxidized lipids, implicating glutathione utilizing enzymes in the protection against lipid peroxidation. Furthermore, an RNA-sequencing study in C. albicans measuring the transcriptional response for exposure to an organic peroxide showed upregulation of antioxidant and protein damage pathways. Overall, our results identify novel mechanisms by which C. albicans responds to oxidative stress resistance which open new avenues for understanding how fungal pathogens resist ROS in the host. Overall design: We conducted RNA-sequencing to determine the transcriptional response of Candida albicans to the representative organic peroxide, tert-butyl hydroperoxide. For comparison, we also performed RNAseq with hydrogen peroxide. The strain used for this experiment is LLF100 which is a prototrophic, wild-type strain. The parental strain is SN152 which was derrived from SC5314. Cells were treated with 0.5mM t-BHP or H2O2 for 15 m (or no treatment for control samples), collected, and then submitted for RNAseq. Each condition was tested in triplicate.