Inhibition of Candida parapsilosis Fatty Acid Synthase (Fas2) Induces Mitochondrial Cell Death in Serum

Abstract

We have recently observed that a fatty acid auxotrophic mutant (fatty acid synthase, Fas2Δ/Δ) of the emerging human pathogenic yeast Candida parapsilosis dies after incubation in various media including serum. In the present study we describe the mechanism for cell death induced by serum and glucose containing media. We show that Fas2Δ/Δ yeast cells are profoundly susceptible to glucose leading us to propose that yeast cells lacking fatty acids exhibit uncontrolled metabolism in response to glucose. We demonstrate that incubation of Fas2Δ/Δ yeast cells with serum leads to cell death, and this process can be prevented with inhibition of protein or DNA synthesis, indicating that newly synthesized cellular components are detrimental to the mutant cells. Furthermore, we have found that cell death is mediated by mitochondria. Suppression of electron transport enzymes using inhibitors such as cyanide or azide prevents ROS overproduction and Fas2Δ/Δ yeast cell death. Additionally, deletion of mitochondrial DNA, which encodes several subunits for enzymes of the electron transport chain, significantly reduces serum-induced Fas2Δ/Δ yeast cell death. Therefore, our results show that serum and glucose media induce Fas2Δ/Δ yeast cell death by triggering unbalanced metabolism, which is regulated by mitochondria. To our knowledge, this is the first study to critically define a link between cytosolic fatty acid synthesis and mitochondrial function in response to serum stress in C. parapsilosis.

Author Summary

Candida parapsilosis is a human opportunistic pathogen associated with significant morbidity and mortality, especially in immunocompromised individuals such as premature, low-birthweight neonates. Our prior studies have indicated that C. parapsilosis effectively utilizes fatty acids/lipids for growth and virulence. We now show that inhibition of the fatty acid synthase (Fas2) results in a hypersensitivity to serum, indicating that yeast cell survival and replication in serum medium or in vivo is dependent on Fas2. Serum hypersensitivity of Fas2-inhibited yeast cells is due to mitochondrial mediated dysregulation of metabolism. Thus, we conclude that Fas2 is candidate antifungal target to combat disseminated fungal infections.