Background P-glycoprotein (P-gp) plays a critical role in protection of the intestinal epithelia by mediating efflux of drugs/xenobiotics from the intestinal mucosa into the gut lumen. Recent studies bring to light that P-gp also confers a critical link in communication between intestinal mucosal barrier function and the innate immune system. Yet, despite knowledge for over 10 years that P-gp plays a central role in gastrointestinal homeostasis, the precise molecular mechanism that controls its functional expression and regulation remains unclear. Here, we assessed how the intestinal microbiome drives P-gp expression and function. Results We have identified a “functional core” microbiome of the intestinal gut community, specifically genera within the Clostridia and Bacilli classes, that is necessary and sufficient for P-gp induction in the intestinal epithelium in mouse models. Metagenomic analysis of this core microbial community revealed that short-chain fatty acid and secondary bile acid production positively associate with P-gp expression. We have further shown these two classes of microbiota-derived metabolites synergistically upregulate P-gp expression and function in vitro and in vivo. Moreover, in patients suffering from ulcerative colitis (UC), we find diminished P-gp expression coupled to the reduction of epithelial-derived anti-inflammatory endocannabinoids and luminal content (e.g., microbes or their metabolites) with a reduced capability to induce P-gp expression. Conclusion Overall, by means of both in vitro and in vivo studies as well as human subject sample analysis, we identify a mechanistic link between cooperative functional outputs of the complex microbial community and modulation of P-gp, an epithelial component, that functions to suppress overactive inflammation to maintain intestinal homeostasis. Hence, our data support a new cross-talk paradigm in microbiome regulation of mucosal inflammation.

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Dysregulation of gut homeostasis may drive a variety of pathological conditions like inflammatory bowel disease (IBD). One of the first events associated with induction of a proinflammatory state is the recruitment of neutrophils to the intestinal lumen. Neutrophils play a critical role in the maintenance homeostasis by eliminating pathogens and contributing to mucosal healing for the resolution of inflammation. However, an excessive recruitment and accumulation of activated neutrophils in the intestine under pathological conditions, such as IBD, is associated with mucosal injury. While the basolateral release of interleukin-8 by intestinal epithelial cells stimulates the recruitment of neutrophils from the vasculature to the submucosa, secretion of the bioactive lipid hepoxilin A3 (HxA3) from the apical surface is required to draw neutrophils across the epithelial barrier. HxA3 is a potent neutrophil chemoattractant, derived from arachidonic acid by the 12/15-lipoxygenase (12/15-LO) pathway, that is secreted to the intestinal lumen by the multidrug resistance protein 2 (MRP2) to form a gradient required for neutrophil trans-epithelial migration (TEM). Previous research developed in our laboratory demonstrated that another multidrug resistance protein, P-glycoprotein (P-gp), was responsible for the apical secretion of endocannabinoids (eCBs) to the intestinal lumen. Moreover, these eCBs were shown to inhibit HxA3-driven neutrophil TEM. Given that neutrophil TEM is critical to the development of inflammatory pathology and that current therapies for IBD suffer from damaging sequelae and an inability to prevent relapses, the main goal of this project is to characterize the mechanisms by which cannabinoids (CB) modulate the TEM of neutrophils induced by HxA3 and to develop CB-based therapies to treat IBD. We used collagen-coated transwells to screen a panel of eCBs, phytocannabinoids (pCBs), and synthetic cannabinoids (SC) for their ability to inhibit HxA3-driven migration. These CB showed a different efficiency to inhibit neutrophil migration, with anandamide (100%), cannabidiol (90%), and AM1241 (90%), exhibiting the highest inhibition. Moreover, migration experiments using an agonist (CP55940) and an antagonist (SR144528) specific for the cannabinoid receptor 2 (CB2), revealed that although this receptor participates in the modulation of neutrophil TEM mediated by CB, there are other still unidentified receptors involved in this process. Finally, to understand the fine resolution decision-making process neutrophils formulate between activation and inhibitory signals, we are using a novel microfluidic device coupled to an on-demand chemotaxis gradient that allows us to interrogate neutrophil responses to various combinations of HxA3 and CB gradients. Together, our results will greatly help define neutrophil biology in health and disease and should allow us to uncover new therapeutic strategies for controlling intestinal inflammation. This research was funded by grant R01 DK109677 from National Institutes of Health This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.