Role of polyunsaturated fatty acids during infection of Caenorhabditis elegans
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Date
2023
Authors
Mokoena, Nthabiseng Zelda
Journal Title
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Publisher
University of the Free State
Abstract
During polymicrobial infection, interactions between different microbial species can alter host responses and/or microbial virulence and pathogenesis, often complicating patient treatment and resolution of infection. Polyunsaturated fatty acids (PUFAs) are not only crucial for normal function in mammalian systems, but are also proposed to act as endogenous antimicrobial molecules. Thus, we adopted Caenorhabditis elegans to mimic the Pseudomonas aeruginosa and Candida albicans polymicrobial infections found in humans. We determined the influence of arachidonic acid (AA) and eicosopentaenoic acid (EPA) supplementation on mono- and polymicrobial infection, fatty acid (FA) composition and egg retention of the nematodes, as well as on expression of FA metabolic genes. Supplementation with either AA or EPA in mono- and polymicrobial infections resulted in changes in FA profiles and PUFA biosynthesis pathway. We discovered that the degree of egg retention elicited by C. albicans and P. aeruginosa varied, with C. elegans exposed to both C. albicans and P. aeruginosa showing the highest level of egg retention compared to nematodes infected by either C. albicans or P. aeruginosa alone. Interestingly, the AA supplemented infected nematodes showed an increased level of egg retention, while EPA supplemented infected nematodes showed a significant decrease. Using the C. elegans model, we determined the effects of AA and EPA supplementation on the survival of nematodes with mono- and polymicrobial infection. We showed that the survival of the infected nematodes was influenced by PUFA-supplementation. EPA supplementation effectively reduced C. albicans virulence and inhibited hyphal formation, thus leading to a partial rescue of pathogen susceptibility.
However, this was not the case for P. aeruginosa infections. In fact, EPA supplemented nematodes infected with P. aeruginosa were more susceptible. Notably hyphal formation is an important component of Candida pathogenesis in mammals. Furthermore, polymicrobial infection resulted in synergistic virulence. However, C. albicans did not produce any hyphae in the co-infection of either AA, EPA supplemented or unsupplemented nematodes, this suggests that the increase in pathogenesis may be associated with increased P. aeruginosa pathogenesis. To further test the role of EPA in hyphal formation of C. albicans, we hypothesised that cytochrome P450 (CYP450) metabolises EPA to 17,18-epoxyeicosatetraenoic acid (17,18-EpETE), inhibiting C. albicans hyphal formation. We showed that 17,18-EpETE inhibits C. albicans hyphal formation in vitro and in vivo in C. elegans and that inhibitors of mammalian EPA-metabolising CYP450 enzymes, 17-octadecynoic acid (17-ODYA) and 6-(2-propargyloxyphenyl) hexanoic acid (PPOH) restored C. albicans hyphal formation in vivo. Lastly, the role of EPA on the physiology of C. elegans as well as C. albicans in vivo was investigated using gene expression analyses. Among the up-regulated genes, we observed several genes with potential roles in lipid metabolism, hyphal formation, detoxification, stress response and immune response. For instance, we observed an up-regulation of several involved in the synthesis of FAs, including fat-3, fat-4, fat-6, cyp-29A2 and cyp-37A1. Other up-regulated genes were those involved in immune response, such as cyp-37B1, daf-16, fipr-22, ilys-2, lys-5, lys-6, spp-12 and fat-3. Interestingly common genes involved in hyphal formation, such as CAS5, CRZ1, CTA4, ERG11, FCR1, SNQ2, TAC1, TEC1, YOR1 and ZCF3 were also up-regulated. Overall, the benefits of EPA supplementation may be two-fold, by inhibiting virulence factors of C. albicans and stimulating the immune response of the host. Thus, PUFA supplementation might be useful in the treatment of infections in patients caused by C. albicans and P. aeruginosa.
Description
Thesis (Ph.D.(Microbiology))--University of the Free State, 2023