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.

Salmonellae are bacterial pathogens that have evolved sophisticated strategies to evade host immune defenses. These strategies include the secretion of effector proteins into mammalian cells so as to subvert innate immune and apoptotic signaling pathways, thereby allowing Salmonella to avoid elimination. Here, we show that the secreted Salmonella typhimurium effector protein AvrA possesses acetyltransferase activity toward specific mitogen-activated protein kinase kinases (MAPKKs) and potently inhibits c-Jun N-terminal kinase (JNK) and NF-kappaB signaling pathways in both transgenic Drosophila and murine models. Furthermore, we show that AvrA dampens the proapoptotic innate immune response to Salmonella at the mouse intestinal mucosa. This activity is consistent with the natural history of Salmonella in mammalian hosts, where the bacteria elicit transient inflammation but do not destroy epithelial cells. Our findings suggest that targeting JNK signaling to dampen apoptosis may be a conserved strategy for intracellular pathogens.

The resident prokaryotic microflora of the mammalian intestine influences diverse homeostatic functions of the gut, including regulation of cellular growth and immune responses; however, it is unknown how commensal prokaryotic organisms mechanistically influence eukaryotic signaling networks. We have shown that bacterial coculture with intestinal epithelial cells modulates ubiquitin-mediated degradation of important signaling intermediates, including b-catenin and the NF-jB inhibitor IjB-a. Ubiquitination of these proteins as well as others is catalyzed by the SCF bTrCP ubiquitin ligase, which itself requires regulated modification of the cullin-1 subunit by the ubiquitin-like protein NEDD8. Here we show that epithelia contacted by enteric commensal bacteria in vitro and in vivo rapidly generate reactive oxygen species (ROS). Bacterially induced ROS causes oxidative inactivation of the catalytic cysteine residue of Ubc12, the NEDD8-conjugating enzyme, resulting in complete but transient loss of cullin-1 neddylation and consequent effects on NF-jB and b-catenin signaling. Our results demonstrate that commensal bacteria directly modulate a critical control point of the ubiquitin-proteasome system, and suggest how enteric commensal bacterial flora influences the regulatory pathways of the mammalian intestinal epithelia.

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.

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Monodisperse silica‐coated manganese oxide nanoparticles (NPs) with a diameter of ∼35 nm are synthesized and are aminated through silanization. The amine‐functionalized core–shell NPs enable the covalent conjugation of a fluorescent dye, Rhodamine B isothiocyanate (RBITC), and folate (FA) onto their surface. The formed Mn3O4@SiO2(RBITC)–FA core–shell nanocomposites are water‐dispersible, stable, and biocompatible when the Mn concentration is below 50 µg mL−1 as confirmed by a cytotoxicity assay. Relaxivity measurements show that the core–shell NPs have a T1 relaxivity (r1) of 0.50 mM−1 s−1 on the 0.5 T scanner and 0.47 mM−1 s−1 on the 3.0 T scanner, suggesting the possibility of using the particles as a T1 contrast agent. Combined flow cytometry, confocal microscopy, and magnetic resonance imaging studies show that the Mn3O4@SiO2(RBITC)–FA nanocomposites can specifically target cancer cells overexpressing FA receptors (FARs). Findings from this study suggest that the silica‐coated Mn3O4 core–shell NPs could be used as a platform for bimodal imaging (both magnetic resonance and fluorescence) in various biological systems.

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.

Flagellin, the primary component of bacterial flagella, is a potent activator of toll-like receptor 5 (TLR5) signaling and is a major proinflammatory determinant of enteropathogenic Salmonella. In accordance with this, we report here that aflagellate Salmonella mutants are impaired in their ability to up-regulate proinflammatory and anti-apoptotic effector molecules in murine models of salmonellosis and that these mutants elicit markedly reduced early mucosal inflammation relative to their isogenic parent strains. Conversely, aflagellate bacteria were more potent activators of epithelial caspases and subsequent apoptosis. These phenomena correlated with a delayed but markedly exacerbated mucosal inflammation at the later stages of infection as well as elevated extra-intestinal and systemic bacterial load, culminating in a more severe clinical outcome. Systemic administration of exogenous flagellin primarily reversed the deleterious effects of in vivo Salmonella infection. These observations indicate that in Salmonella infection, flagellin plays a dominant role in activation of not only innate immunity but also anti-apoptotic processes in epithelial cells. These latter TLR-mediated responses that delay epithelial apoptosis may be as critical to mucosal defense as the classic acute inflammatory response. This notion is consistent with the emerging paradigm that specific TLR ligands may have a fundamental cytoprotective effect during inflammatory stress.