Fatty acid metabolism in Saccharomyces cerevisiae and effects of fatty acid metabolites on neutrophil functio

In the presence of arachidonic acid (AA), Saccharomyces cerevisiae produces prostaglandin E2 (PGE2). S. cerevisiae and its metabolites may be consumed in products manufactured using the yeast (e.g. beer). Neutrophils are immune cells present in the gastrointestinal (GI) tract during inflammation. As a lipid-signaling molecule, PGE2 can potentially modify neutrophil functions and exacerbate pre-existing inflammation. As neutrophil migration is a hallmark of inflammation, we investigated the impact of PGE2 on neutrophil chemotaxis. Chemotaxis assays were performed on neutrophils isolated from human whole blood using the chemotactic agents f-Met-Leu-Phe (fMLP) or interleukin-8 (IL-8). Neutrophil chemotaxis was concentration dependent as it was enhanced 3.5-fold at low concentrations of PGE2 (0.1 nM-10 nM) and reduced 3.0-fold at higher concentrations of PGE2 (100 nM).;The biochemical pathway utilized by S. cerevisiae to produce PGE2 is unknown. Identifying enzymes that metabolize AA may direct approaches to reduce the impact that yeast PGE2 may have on neutrophils. S. cerevisiae does not have genes homologous to those involved in mammalian AA metabolism. We employed RNAseq transcriptome sequencing to study the lipid biosynthetic pathway in S. cerevisiae and observed 1248 genes upregulated in yeast that were cultured in the presence of AA relative to yeast that were cultured without AA. Notably, genes that mediate beta-oxidation of fatty acids (Pot1, Pox1, Faa1 and Faa2) were upregulated up to 2.3-fold.;The results demonstrate that low concentrations of PGE2 enhance neutrophil chemotaxis that is mediated by fMLP or IL-8, suggesting that PGE 2 may aid in recruiting neutrophils from regions that are distant to a site of inflammation. Once a higher concentration of PGE2 is encountered by neutrophils, neutrophils may halt their migration and engage effector functions such as phagocytosis and superoxide production. Increased expression of genes involved with fatty acid metabolism points to enzymes that may utilize AA to produce PGE2 in S. cerevisiae. Experiments testing PGE2 levels in knock-out strains of yeast will identify genes involved in PGE2 production. Results of this study have implications to reduce potential off-target effects caused by yeast PGE 2 in consumables.