It is well established that physiological generation of low levels of ROS act as critical second messengers in multiple signaling pathways. These include the regulatory networks that control growth and differentiation in disparate biological systems, including the gut of many metazoans. However, the molecular mechanism of ROS production within the intestine is unknown. Recent reports have shown that the ROS‐generating enzyme NADPH oxidase 1 (Nox1) is highly expressed by colon epithelia. We report that Lactobacillus spp. are potent inducers of endogenous ROS generation, and of ROS‐dependent cellular proliferation within intestines of two metazoan models, namely the fruitfly Drosophila melanogaster, and the mouse. Moreover, we show that these induced responses are diminished in mice or Drosophila that are selectively deficient for Nox1 within intestinal epithelial cells. Together, these results implicate Nox1 in epithelial cell homeostasis and reveal a novel mechanism for the maintenance of intestinal tissue structure.

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N-formyl peptide receptors (FPRs) are critical regulators of host defense in phagocytes and are also expressed in epithelia. FPR signaling and function have been extensively studied in phagocytes, yet their functional biology in epithelia is poorly understood. We describe a novel intestinal epithelial FPR signaling pathway that is activated by an endogenous FPR ligand, annexin A1 (ANXA1), and its cleavage product Ac2-26, which mediate activation of ROS by an epithelial NADPH oxidase, NOX1. We show that epithelial cell migration was regulated by this signaling cascade through oxidative inactivation of the regulatory phosphatases PTEN and PTP-PEST, with consequent activation of focal adhesion kinase (FAK) and paxillin. In vivo studies using intestinal epithelial specific Nox1 -/-IEC and AnxA1 -/-mice demonstrated defects in intestinal mucosal wound repair, while systemic administration of ANXA1 promoted wound recovery in a NOX1-dependent fashion. Additionally, increased ANXA1 expression was observed in the intestinal epithelium and infiltrating leukocytes in the mucosa of ulcerative colitis patients compared with normal intestinal mucosa. Our findings delineate a novel epithelial FPR1/NOX1-dependent redox signaling pathway that promotes mucosal wound repair.

The mammalian intestine houses a complex microbial community, which influences normal epithelial growth and development, and is integral to the repair of damaged intestinal mucosa1–3. Restitution of injured mucosa involves the recruitment of immune cells, epithelial migration and proliferation4,5. Although microenvironmental alterations have been described in wound healing6, a role for extrinsic influences, such as members of the microbiota, has not been reported. Here, we show that a distinct subpopulation of the normal mucosal-associated gut microbiota expands and preferentially colonizes sites of damaged murine mucosa in response to local environmental cues. Our results demonstrate that formyl peptide receptor 1 (FPR1) and neutrophilic NADPH oxidase (NOX2) are required for the rapid depletion of microenvironmental oxygen and compensatory responses, resulting in a dramatic enrichment of an anaerobic bacterial consortium. Furthermore, the dominant member of this wound-mucosa-associated microbiota, Akkermansia muciniphila (an anaerobic, mucinophilic gut symbiont7,8), stimulated proliferation and migration of enterocytes adjacent to the colonic wounds in a process involving FPR1 and intestinal epithelial-cell-specific NOX1-dependent redox signalling. These findings thus demonstrate how wound microenvironments induce the rapid emergence of ‘probiont’ species that contribute to enhanced repair of mucosal wounds. Such microorganisms could be exploited as potential therapeutics.

The mammalian gut microbiota is essential for normal intestinal development, renewal and repair. Injury to the intestinal mucosa can occur with infection, surgical trauma, and in idiopathic inflammatory bowel disease. Repair of mucosal injury, termed restitution, as well as restoration of intestinal homeostasis involves induced and coordinated proliferation and migration of intestinal epithelial cells. N-formyl peptide receptors (FPRs) are widely expressed pattern recognition receptors that can specifically bind and induce responses to host derived and bacterial peptides and small molecules. Here we report that specific members of the gut microbiota stimulate FPR1 on intestinal epithelial cells to generate reactive oxygen species via enterocyte NADPH oxidase NOX1, causing rapid phosphorylation of Focal Adhesion Kinase (FAK) and ERK MAPK. These events stimulate migration and proliferation of enterocytes adjacent to colonic wounds. Together, these findings identify a novel role of FPR1 as pattern recognition receptors for perceiving the enteric microbiota that promotes repair of mucosal wounds via generation of ROS from the enterocyte NOX1.