Neutrophil influx into the intestinal lumen is a critical response to infectious agents, but is also associated with severe intestinal damage observed in idiopathic inflammatory bowel disease. The chemoattractant hepoxilin A3, an eicosanoid secreted from intestinal epithelial cells by the apically restricted efflux pump multidrug resistance protein 2 (MRP2), mediates this neutrophil influx. Information about a possible counterbalance pathway that could signal the lack of or resolution of an apical inflammatory signal, however, has yet to be described. We now report a system with such hallmarks. Specifically, we identify endocannabinoids as the first known endogenous substrates of the apically restricted multidrug resistance transporter P-glycoprotein (P-gp) and reveal a mechanism, which we believe is novel, for endocannabinoid secretion into the intestinal lumen. Knockdown or inhibition of P-gp reduced luminal secretion levels of N-acyl ethanolamine-type endocannabinoids, which correlated with increased neutrophil transmigration in vitro and in vivo. Additionally, loss of CB2, the peripheral cannabinoid receptor, led to increased pathology and neutrophil influx in models of acute intestinal inflammation. These results define a key role for epithelial cells in balancing the constitutive secretion of antiinflammatory lipids with the stimulated secretion of proinflammatory lipids via surface efflux pumps in order to control neutrophil infiltration into the intestinal lumen and maintain homeostasis in the healthy intestine.

Enteroaggregative Escherichia coli (EAEC) causes diarrhea and intestinal inflammation worldwide. EAEC strains are characterized by the presence of aggregative adherence fimbriae (AAF), which play a key role in pathogenesis by mediating attachment to the intestinal mucosa and by triggering host inflammatory responses. Here, we identify the epithelial transmembrane mucin MUC1 as an intestinal host cell receptor for EAEC, demonstrating that AAF-mediated interactions between EAEC and MUC1 facilitate enhanced bacterial adhesion. We further demonstrate that EAEC infection also causes elevated expression of MUC1 in inflamed human intestinal tissues. Moreover, we find that MUC1 facilitates AAF-dependent migration of neutrophils across the epithelium in response to EAEC infection. Thus, we show for the first time a proinflammatory role for MUC1 in the host response to an intestinal pathogen. IMPORTANCE: EAEC is a clinically important intestinal pathogen that triggers intestinal inflammation and diarrheal illness via mechanisms that are not yet fully understood. Our findings provide new insight into how EAEC triggers host inflammation and underscores the pivotal role of AAFs-the principal adhesins of EAEC-in driving EAEC-associated disease. Most importantly, our findings add a new dimension to the signaling properties of the transmembrane mucin MUC1. Mostly studied for its role in various forms of cancer, MUC1 is widely regarded as playing an anti-inflammatory role in response to infection with bacterial pathogens in various tissues. However, the role of MUC1 during intestinal infections has not been previously explored, and our results describe the first report of MUC1 as a proinflammatory factor following intestinal infection.

Enterohaemorrhagic Escherichia coli (EHEC) colonizes the intestine and causes bloody diarrhoea and kidney failure by producing Shiga toxin. Upon binding intestinal cells, EHEC triggers a change in host cell shape, generating actin 'pedestals' beneath bound bacteria. To investigate the importance of pedestal formation to disease, we infected genetically engineered mice incapable of supporting pedestal formation by an EHEC-like mouse pathogen, or wild type mice with a mutant of that pathogen incapable of generating pedestals. We found that pedestal formation promotes attachment of bacteria to the intestinal mucosa and vastly increases the severity of Shiga toxin-mediated disease.