Abstract 12174: Inflammation-Dependent Hydroxyeicosatetraenoic Acids Dysregulate Macrophage Resolution Function

Abstract

Introduction and Hypothesis: Macrophage efferocytosis is a critical step in the resolution of inflammation. Dysregulated macrophage efferocytosis has been implicated in the pathogenesis of chronic inflammatory disorders including atherosclerosis and IBD. Nonetheless, the nature of possible dysregulating mechanisms remains incompletely understood. We reported that non-enzymatic lipid peroxidation and the mucosal levels of monohydroxylated PUFAs including 12- and 15-hydroxyeicosatetraenoic acid (HETE) correlated with disease in murine models of IBD. HETEs can form enzymatically and non-enzymatically and can signal through the leukotriene (LT) receptor BLT2. LTB4-BLT1/2 signaling can suppress macrophage efferocytosis capacity. We hypothesized that non-enzymatically derived mucosal HETEs correlate with disease in a murine Crohn’s disease (CD) model and in IBD patient biopsies; and that HETEs suppress murine and human macrophage efferocytosis capacity. Methods: We exploited the stereospecificity of enzymatic HETE formation to determine by chiral-LC-MS/MS the levels of non-enzymatically derived HETEs in intestine from a murine myeloid Cox2 knock-out model of Crohn’s disease (CD) and in human IBD patient biopsies. We assessed the effect of racemic HETEs on the efferocytosis capacity of murine BMDMs and human THP1 macrophages for apoptotic MPRO neutrophils. We performed proteomics using accurate mass LC-MS/MS followed by GO enrichment analysis. Results: Non-enzymatically derived mucosal 5-, 12-, and 15HETE were elevated with disease: a) by 3-4 fold in the murine CD model (p<0.01 to p<0.0001); and b) by 2-3 fold in ileal and colonic biopsies from areas of active inflammation in CD and ulcerative colitis patients compared to remission controls (p<0.05). Racemic HETEs suppressed efferocytosis of apoptotic neutrophils by murine (12- and 15-HETE: p<0.0001) and human (12-HETE: p<0.0001) macrophages. Racemic 12-HETE altered the proteome of efferocytic BMDM by inducing 200 proteins while silencing 200 more (<1% FDR), and by suppressing pathways associated with efferocytosis. Conclusion: Inflammation-dependent HETEs may suppress macrophage efferocytosis in chronic inflammatory disorders including IBD and atherosclerosis.