PD_{n-3 DPA} Pathway Regulates Human Monocyte Differentiation and Macrophage Function

Macrophages are central in orchestrating the clearance of apoptotic cells and cellular debris during inflammation, with the mechanism(s) regulating this process remaining of interest. Herein, we found that the n-3 docosapentaenoic acid-derived protectin (PD_{n-3 DPA}) biosynthetic pathway regulated the differentiation of human monocytes, altering macrophage phenotype, efferocytosis, and bacterial phagocytosis. Using lipid mediator profiling, human primary cells and recombinant enzymes we found that human 15-lipoxygenases initiate the PD_{n-3 DPA} pathway catalyzing the formation of an allylic epoxide. The complete stereochemistry of this epoxide was determined using stereocontrolled total organic synthesis as 16S,17S-epoxy-7Z,10Z,12E,14E,19Z-docosapentaenoic acid (16S,17S-ePD_{n-3 DPA}). This intermediate was enzymatically converted by epoxide hydrolases to PD1_{n-3 DPA} and PD2_{n-3 DPA}, with epoxide hydrolase 2 converting 16S,17S-ePD_{n-3 DPA} to PD2_{n-3 DPA} in human monocytes. Taken together these results establish the PD_{n-3 DPA} biosynthetic pathway in human monocytes and macrophages and its role in regulating macrophage resolution responses.