Arachidonic acid modulates fluconazole-induced responses in Candida albicans biofilms

Candida albicans is a human commensal, which causes opportunistic infections with high morbidity and mortality and is characterised by the production of resistant biofilms. Polyunsaturated fatty acids, such as arachidonic acid, can increase azole susceptibility of C. albicans biofilms significantly. However, the underlining mechanism is not known. We investigated the effect of arachidonic acid on known fluconazole resistance mechanisms namely, overexpression of ERG11, increased ergosterol content, oxidative stress resistance, as well as expression and activity of the efflux pump, Cdr1p. Upregulation of ERG11 was observed in biofilms exposed to fluconazole. However, this was reversed in the presence of arachidonic acid, even in the presence of fluconazole. Furthermore, arachidonic acid downregulated the fluconazole-induced oxidative stress response of C. albicans. Previous transcriptome data indicated a significant increase in CDR1 expression during early biofilm formation in the presence of arachidonic acid. However, we found that efflux activity was reduced in the presence of arachidonic acid, which indicates the loss of function of the membrane-associated protein. This contradictory phenomenon was further investigated by determining the effect of arachidonic acid on the localisation and phosphorylation of Cdr1p (ProteomeXchange identifier PXD070958). Our results show that the presence of arachidonic acid may cause mislocalisation and changes in the phosphorylation of Cdr1p; all of which could impact its activity. These results demonstrate that multiple mechanisms are potentially involved in the arachidonic acid-induced increased fluconazole susceptibility and allows for further exploration of lipid-mediated modulation of antifungal responses.