Redox signaling regulates commensal-mediated mucosal homeostasis and restitution and requires formyl peptide receptor 1

Mitochondria could be a potential key mediator linking the intestinal microbiota to depression

The intestinal microbiota has been reported to affect depression, a common mental condition with severe health-related consequences. However, what mediates the effect of the intestinal microbiota on depression has not been well elucidated. We summarize the roles of the mitochondria in eliciting beneficial effects on the gut microbiota to ameliorate symptoms of depression. It is well known that mitochondria play a key role in depression. An important pathogenic factor, namely inflammatory response, may adversely impact mitochondrial functionality to maintain cellular homeostasis. Dysfunction of mitochondria not only affects neuronal function but also reduces neuron cell numbers. We posit that the intestinal microbiota could affect neuronal mitochondrial function through short-chain fatty acids such as butyrate. Brain inflammatory processes could also be affected through the modulation of gut permeability and blood lipopolysaccharide levels. Aberrant mitochondria functionality coupled to adverse cellular homeostasis could be a key mediator for the effect of the intestinal microbiota on the progression of depression.

The gut-bone axis: how bacterial metabolites bridge the distance

The gut microbiome is a key regulator of bone health that affects postnatal skeletal development and skeletal involution. Alterations in microbiota composition and host responses to the microbiota contribute to pathological bone loss, while changes in microbiota composition that prevent, or reverse, bone loss may be achieved by nutritional supplements with prebiotics and probiotics. One mechanism whereby microbes influence organs of the body is through the production of metabolites that diffuse from the gut into the systemic circulation. Recently, short-chain fatty acids (SCFAs), which are generated by fermentation of complex carbohydrates, have emerged as key regulatory metabolites produced by the gut microbiota. This Review will focus on the effects of SCFAs on the musculoskeletal system and discuss the mechanisms whereby SCFAs regulate bone cells.

Interactions Between Commensal Bacteria and Enteric Neurons, via FPR1 Induction of ROS, Increase Gastrointestinal Motility in Mice

BACKGROUND & AIMS

Reduced gastrointestinal (GI) motility is a feature of disorders associated with intestinal dysbiosis and loss of beneficial microbes. It is not clear how consumption of beneficial commensal microbes, marketed as probiotics, affects the enteric nervous system (ENS). We studied the effects of the widely used probiotic and the commensal Lactobacillus rhamnosus GG (LGG) on ENS and GI motility in mice.

METHODS

Conventional and germ free C57B6 mice were gavaged with LGG and intestinal tissues were collected; changes in the enteric neuronal subtypes were assessed by real-time polymerase chain reaction, immunoblots, and immunostaining. Production of reactive oxygen species (ROS) in the jejunal myenteric plexi and phosphorylation (p) of mitogen-activated protein kinase 1 (MAPK1) in the enteric ganglia were assessed by immunoblots and immunostaining. Fluorescence in situ hybridization was performed on jejunal cryosections with probes to detect formyl peptide receptor 1 (FPR1). GI motility in conventional mice was assessed after daily gavage of LGG for 1 week.

RESULTS

Feeding of LGG to mice stimulated myenteric production of ROS, increased levels of phosphorylated MAPK1, and increased expression of choline acetyl transferase by neurons (P < .001). These effects were not observed in mice given N-acetyl cysteine (a ROS inhibitor) or LGGΩSpaC (an adhesion-mutant strain of LGG) or FPR1-knockout mice. Gavage of mice with LGG for 1 week significantly increased stool frequency, reduced total GI transit time, and increased contractions of ileal circular muscle strips in ex vivo experiments (P < .05).

CONCLUSIONS

Using mouse models, we found that LGG-mediated signaling in the ENS requires bacterial adhesion, redox mechanisms, and FPR1. This pathway might be activated to increase GI motility in patients.

Epithelial-microbial diplomacy: escalating border tensions drive inflammation in inflammatory bowel disease

Inflammatory bowel diseases (IBD) are chronic conditions of the gastrointestinal tract-the main site of host-microbial interaction in the body. Development of IBD is not due to a single event but rather is a multifactorial process where a patient’s genetic background, behavioral habits, and environmental exposures contribute to disease pathogenesis. IBD patients exhibit alterations to gut bacterial populations “dysbiosis” due to the inflammatory microenvironment, however whether this alteration of the gut microbiota precedes inflammation has not been confirmed. Emerging evidence has highlighted the important role of gut microbes in developing measured immune responses and modulating other host responses such as metabolism. Much of the work on the gut microbiota has been correlative and there is an increasing need to understand the intimate relationship between host and microbe. In this review, we highlight how commensal and pathogenic bacteria interact with host intestinal epithelial cells and explore how altered microenvironments impact these connections.

Control and dysregulation of redox signalling in the gastrointestinal tract

Redox signalling in the gastrointestinal mucosa is held in an intricate balance. Potent microbicidal mechanisms can be used by infiltrating immune cells, such as neutrophils, to protect compromised mucosae from microbial infection through the generation of reactive oxygen species. Unchecked, collateral damage to the surrounding tissue from neutrophil-derived reactive oxygen species can be detrimental; thus, maintenance and restitution of a breached intestinal mucosal barrier are paramount to host survival. Redox reactions and redox signalling have been studied for decades with a primary focus on contributions to disease processes. Within the past decade, an upsurge of exciting findings have implicated subtoxic levels of oxidative stress in processes such as maintenance of mucosal homeostasis, the control of protective inflammation and even regulation of tissue wound healing. Resident gut microbial communities have been shown to trigger redox signalling within the mucosa, which expresses similar but distinct enzymes to phagocytes. At the fulcrum of this delicate balance is the colonic mucosal epithelium, and emerging evidence suggests that precise control of redox signalling by these barrier-forming cells may dictate the outcome of an inflammatory event. This Review will address both the spectrum and intensity of redox activity pertaining to host-immune and host-microbiota crosstalk during homeostasis and disease processes in the gastrointestinal tract.

Lactococcus Lactis Subsp. cremoris Is an Efficacious Beneficial Bacterium that Limits Tissue Injury in the Intestine

The use of beneficial bacteria to promote health is widely practiced. However, experimental evidence corroborating the efficacy of bacteria promoted with such claims remains limited. We address this gap by identifying a beneficial bacterium that protects against tissue damage and injury-induced inflammation in the gut. We first employed the Drosophila animal model to screen for the capacity of candidate beneficial bacteria to protect the fly gut against injury. From this screen, we identified Lactococcus lactis subsp. cremoris as a bacterium that elicited potent cytoprotective activity. Then, in a murine model, we demonstrated that the same strain confers powerful cytoprotective influences against radiological damage, as well as anti-inflammatory activity in a gut colitis model. In summary, we demonstrate the positive salutary effects of a beneficial bacterium, namely, L. lactis subsp. cremoris on intestinal tissue and propose the use of this strain as a therapeutic to promote intestinal health.

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Drosophila can be used as an animal model to screen for beneficial bacteria

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Lactococcus lactis subsp. cremoris elicited potent cytoprotection in the fly gut

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L. lactis cremoris elicited anti-inflammatory activity in a mouse colitis model

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L. lactis cremoris activated the cytoprotective Nrf2 pathway in flies and mice

Model Systems to Investigate NOX-Dependent Cell Migration and Invasiveness

There is mounting evidence indicating that reactive oxygen species (ROS) play a crucial role in cell migration and invasion. Our previous studies have demonstrated the NADPH oxidase (NOX) family of enzymes are a source of ROS in different cell types undergoing migration. Several NOX enzymes are induced or activated in processes including wound repair and maintenance of epithelial barriers, as well as in promoting metastatic cell migration and invasiveness. This chapter outlines three different in vitro assays used to examine how NOX enzymes are involved in cell motility: scratch-wound repair, Matrigel invasion, and migration from confluent cell monolayer boundaries created by cell culture inserts. The three methods provide a range of experimental approaches for delineating roles of NOX enzymes in cell migration through manipulation of the expression or activities of the endogenous or overexpressed oxidases.

Proteomic analysis of microbial induced redox-dependent intestinal signaling

Intestinal homeostasis is regulated in-part by reactive oxygen species (ROS) that are generated in the colonic mucosa following contact with certain lactobacilli. Mechanistically, ROS can modulate protein function through the oxidation of cysteine residues within proteins. Recent advances in cysteine labeling by the Isotope Coded Affinity Tags (ICATs) technique has facilitated the identification of cysteine thiol modifications in response to stimuli. Here, we used ICATs to map the redox protein network oxidized upon initial contact of the colonic mucosa with Lactobacillus rhamnosus GG (LGG). We detected significant LGG-specific redox changes in over 450 proteins, many of which are implicated to function in cellular processes such as endosomal trafficking, epithelial cell junctions, barrier integrity, and cytoskeleton maintenance and formation. We particularly noted the LGG-specific oxidation of Rac1, which is a pleiotropic regulator of many cellular processes. Together, these data reveal new insights into lactobacilli-induced and redox-dependent networks involved in intestinal homeostasis.

Role of gut microbiota in intestinal wound healing and barrier function

The mammalian intestine harbors a highly complex and abundant ensemble of bacteria that flourish in a nutrient-rich environment while profoundly influencing many aspects of host biology. The intestine coevolved with its resident microbes in a manner where the mucosa developed a barrier function to segregate the resident microbes from the rest of the body, and yet paradoxically, allowing integration of microbial signals for the host benefit. In this review, we provided a comprehensive overview of why the gut microbiota is key to the efficient development and maintenance of the intestinal barrier. We also highlighted how a destabilized equilibrium between gut microbiota and the host may eventuate in a wide range of intestinal diseases characterized by the disrupted intestinal barrier. Finally, the review delineated how microenvironmental changes in the injured mucosa result in an enrichment of a pro-regenerating consortium of bacteria, which augments mucosal wound repair and restoration of barrier functions.

Colonoscopic-Guided Pinch Biopsies in Mice as a Useful Model for Evaluating the Roles of Host and Luminal Factors in Colonic Inflammation

Colonic inflammation, a hallmark of inflammatory bowel disease, can be influenced by host intrinsic and extrinsic factors. There continues to be a need for models of colonic inflammation that can both provide insights into disease pathogenesis and be used to investigate potential therapies. Herein, we tested the utility of colonoscopic-guided pinch biopsies in mice for studying colonic inflammation and its treatment. Gene expression profiling of colonic wound beds after injury showed marked changes, including increased expression of genes important for the inflammatory response. Interestingly, many of these gene expression changes mimicked those alterations found in inflammatory bowel disease patients. Biopsy-induced inflammation was associated with increases in neutrophils, macrophages, and natural killer cells. Injury also led to elevated levels of sphingosine-1-phosphate (S1P), a bioactive lipid that is an important mediator of inflammation mainly through its receptor, S1P₁. Genetic deletion of S1P₁ in the endothelium did not alter the inflammatory response but led to increased colonic bleeding. Bacteria invaded into the wound beds, raising the possibility that microbes contributed to the observed changes in mucosal gene expression. In support of this, reducing bacterial abundance markedly attenuated the inflammatory response to wounding. Taken together, this study demonstrates the utility of the pinch biopsy model of colonic injury to elucidate the molecular underpinnings of colonic inflammation and its treatment.

Temporal Regulation of the Bacterial Metabolite Deoxycholate during Colonic Repair Is Critical for Crypt Regeneration

Colonic wound repair is an orchestrated process, beginning with barrier re-establishment and followed by wound channel formation and crypt regeneration. Elevated levels of prostaglandin E2 (PGE2) promote barrier re-establishment; however, we found that persistently elevated PGE2 hinders subsequent repair phases. The bacterial metabolite deoxycholate (DCA) promotes transition through repair phases via PGE2 regulation. During barrier re-establishment, DCA levels are locally diminished in the wound, allowing enhanced PGE2 production and barrier re-establishment. However, during transition to the wound channel formation phase, DCA levels increase to inhibit PGE2 production and promote crypt regeneration. Altering DCA levels via antibiotic treatment enhances PGE2 levels but impairs wound repair, which is rescued with DCA treatment. DCA acts via its receptor, farnesoid X receptor, to inhibit the enzyme cPLA2 required for PGE2 synthesis. Thus, colonic wound repair requires temporally regulated signals from microbial metabolites to coordinate host-associated signaling cascades. VIDEO ABSTRACT.

NADPH oxidases and ROS signaling in the gastrointestinal tract

Reactive oxygen species (ROS), initially categorized as toxic by-products of aerobic metabolism, have often been called a double-edged sword. ROS are considered indispensable when host defense and redox signaling is concerned and a threat in inflammatory or degenerative diseases. This generalization does not take in account the diversity of oxygen metabolites being generated, their physicochemical characteristics and their production by distinct enzymes in space and time. NOX/DUOX NADPH oxidases are the only enzymes solely dedicated to ROS production and the prime ROS producer for intracellular and intercellular communication due to their widespread expression and intricate regulation. Here we discuss new insights of how NADPH oxidases act via ROS as multifaceted regulators of the intestinal barrier in homeostasis, infectious disease and intestinal inflammation. A closer look at monogenic VEOIBD and commensals as ROS source supports the view of H₂O₂ as key beneficial messenger in the barrier ecosystem.

Hydrogen peroxide production by lactobacilli promotes epithelial restitution during colitis

Inflammatory bowel disease (IBD) is a multifactorial chronic inflammatory disease of the gastrointestinal tract, characterized by cycles of acute flares, recovery and remission phases. Treatments for accelerating tissue restitution and prolonging remission are scarce, but altering the microbiota composition to promote intestinal homeostasis is considered a safe, economic and promising approach. Although probiotic bacteria have not yet fulfilled fully their promise in clinical trials, understanding the mechanism of how they exert beneficial effects will permit devising improved therapeutic strategies. Here we probe if one of the defining features of lactobacilli, the ability to generate nanomolar H2O2, contributes to their beneficial role in colitis. H2O2 generation by wild type L. johnsonii was modified by either deleting or overexpressing the enzymatic H2O2 source(s) followed by orally administering the bacteria before and during DSS colitis. Boosting luminal H2O2 concentrations within a physiological range accelerated recovery from colitis, while significantly exceeding this H2O2 level triggered bacteraemia. This study supports a role for increasing H2O2 within the physiological range at the epithelial barrier, independently of the enzymatic source and/or delivery mechanism, for inducing recovery and remission in IBD.

Interleukin-4 and interleukin-13 increase NADPH oxidase 1-related proliferation of human colon cancer cells

Human colon cancers express higher levels of NADPH oxidase 1 [NOX1] than adjacent normal epithelium. It has been suggested that reactive oxygen species [ROS] derived from NOX1 contribute to DNA damage and neoplastic transformation in the colon, particularly during chronic inflammatory stress. However, the mechanism(s) underlying increased NOX1 expression in malignant tumors or chronic inflammatory states involving the intestine are poorly characterized. We examined the effects of two pro-inflammatory cytokines, IL-4 and IL-13, on the regulation of NOX1. NOX1 expression was increased 4- to 5-fold in a time- and concentration-dependent manner by both cytokines in human colon cancer cell lines when a functional Type II IL-4 receptor was present. Increased NOX1 transcription following IL-4/IL-13 exposure was mediated by JAK1/STAT6 signaling, was associated with a ROS-related inhibition of protein tyrosine phosphatase activity, and was dependent upon activation and specific binding of GATA3 to the NOX1 promoter. NOX1-mediated ROS production increased cell cycle progression through S-phase leading to a significant increase in cellular proliferation. Evaluation of twenty pairs of surgically-resected colon cancers and their associated uninvolved adjacent colonic epithelium demonstrated a significant increase in the active form of NOX1, NOX1-L, in tumors compared to normal tissues, and a significant correlation between the expression levels of NOX1 and the Type II IL-4 receptor in tumor and the uninvolved colon. These studies imply that NOX1 expression, mediated by IL-4/IL-13, could contribute to an oxidant milieu capable of supporting the initiation or progression of colonic cancer, suggesting a role for NOX1 as a therapeutic target.

Bone Remodeling and the Microbiome

Exposed surfaces of mammals are colonized with 100 trillion indigenous bacteria, fungi, and viruses, creating a diverse ecosystem known as the microbiome. The gastrointestinal tract harbors the greatest numbers of these microorganisms, which regulate human nutrition, metabolism, and immune system function. Moreover, the intestinal microbiota contains pro- and anti-inflammatory products that modulate immune responses and may play a role in maintaining gut barrier function. Therefore, the community composition of the microbiota has profound effects on the immune status of the host and impacts the development and/or progression of inflammatory diseases. Accordingly, numerous studies have shown differences in the microbiota of patients with and without a given inflammatory condition. There is now strong evidence that the gut microbiome regulates bone homeostasis in health and disease, and that prebiotic and probiotics protect against bone loss. Herein, the evidence supporting the role of the microbiota and the effects of prebiotic and probiotics will be reviewed.

Annexin A1: Uncovering the Many Talents of an Old Protein

Annexin A1 (ANXA1) has long been classed as an anti-inflammatory protein due to its control over leukocyte-mediated immune responses. However, it is now recognized that ANXA1 has widespread effects beyond the immune system with implications in maintaining the homeostatic environment within the entire body due to its ability to affect cellular signalling, hormonal secretion, foetal development, the aging process and development of disease. In this review, we aim to provide a global overview of the role of ANXA1 covering aspects of peripheral and central inflammation, immune repair and endocrine control with focus on the prognostic, diagnostic and therapeutic potential of the molecule in cancer, neurodegeneration and inflammatory-based disorders.

Serum Amyloid A1 Is an Epithelial Prorestitutive Factor

Several proteins endogenously produced during the process of intestinal wound healing have demonstrated prorestitutive properties. The presence of serum amyloid A1 (SAA1), an acute-phase reactant, within inflamed tissues, where it exerts chemotaxis of phagocytes, is well recognized; however, a putative role in intestinal wound repair has not been described. Herein, we show that SAA1 induces intestinal epithelial cell migration, spreading, and attachment through a formyl peptide receptor 2-dependent mechanism. Induction of the prorestitutive phenotype is concentration and time dependent and is associated with epithelial reactive oxygen species production and alterations in p130 Crk-associated substrate staining. In addition, using a murine model of wound recovery, we provide evidence that SAA1 is dynamically and temporally regulated, and that the elaboration of SAA1 within the wound microenvironment correlates with the influx of SAA1/CD11b coexpressing immune cells and increases in cytokines known to induce SAA expression. Overall, the present work demonstrates an important role for SAA in epithelial wound recovery and provides evidence for a physiological role in the wound environment.

Alternative use of Bacillus subtilis spores: protection against environmental oxidative stress in human normal keratinocytes

Inorganic trivalent arsenic is a major environmental pollutant and exposure to human results in many pathologies, including keratosis and carcinoma. Here, we analyzed the effects of B. subtilis spores on human normal keratinocytes in the presence of sodium arsenite oxidative stress. Pre-treatment of cells with spores before inducing oxidative stress was able to keep normal levels of intracellular ROS, GSH and lipid peroxidation, as well as to inhibit the activation of the MAPK cascade. Moreover, spores showed a positive effect on cell proliferation, probably due to their binding on the cell surface and the activation of intracellular catalases. We found that spores exert their protective effect by the nuclear translocation of Nrf-2, involved in the activation of stress response genes. This, in turn, resulted in a protective effect against sodium arsenite stress injury, as oxidative stress markers were reported to physiological levels when cells were stressed before incubating them with spores. Therefore, B. subtilis spores can be considered as a new agent to counteract oxidative stress on normal human keratinocytes.

Organic Solute Transporter α-β Protects Ileal Enterocytes From Bile Acid-Induced Injury

BACKGROUND & AIMS

Ileal bile acid absorption is mediated by uptake via the apical sodium-dependent bile acid transporter (ASBT), and export via the basolateral heteromeric organic solute transporter α-β (OSTα-OSTβ). In this study, we investigated the cytotoxic effects of enterocyte bile acid stasis in Ostα-/- mice, including the temporal relationship between intestinal injury and initiation of the enterohepatic circulation of bile acids.

METHODS

Ileal tissue morphometry, histology, markers of cell proliferation, gene, and protein expression were analyzed in male and female wild-type and Ostα-/- mice at postnatal days 5, 10, 15, 20, and 30. Ostα-/-Asbt-/- mice were generated and analyzed. Bile acid activation of intestinal Nrf2-activated pathways was investigated in Drosophila.

RESULTS

As early as day 5, Ostα-/- mice showed significantly increased ileal weight per length, decreased villus height, and increased epithelial cell proliferation. This correlated with premature expression of the Asbt and induction of bile acid-activated farnesoid X receptor target genes in neonatal Ostα-/- mice. Expression of reduced nicotinamide adenine dinucleotide phosphate oxidase-1 and Nrf2-anti-oxidant responsive genes were increased significantly in neonatal Ostα-/- mice at these postnatal time points. Bile acids also activated Nrf2 in Drosophila enterocytes and enterocyte-specific knockdown of Nrf2 increased sensitivity of flies to bile acid-induced toxicity. Inactivation of the Asbt prevented the changes in ileal morphology and induction of anti-oxidant response genes in Ostα-/- mice.

CONCLUSIONS

Early in postnatal development, loss of Ostα leads to bile acid accumulation, oxidative stress, and a restitution response in ileum. In addition to its essential role in maintaining bile acid homeostasis, Ostα-Ostβ functions to protect the ileal epithelium against bile acid-induced injury. NCBI Gene Expression Omnibus: GSE99579.

Probiotics or pro-healers: the role of beneficial bacteria in tissue repair

Probiotics are beneficial microorganisms, known to exert numerous positive effects on human health, primarily in the battle against pathogens. Probiotics have been associated with improved healing of intestinal ulcers, and healing of infected cutaneous wounds. This article reviews the latest findings on probiotics related to their pro-healing properties on gut epithelium and skin. Proven mechanisms by which probiotic bacteria exert their beneficial effects include direct killing of pathogens, competitive displacement of pathogenic bacteria, reinforcement of epithelial barrier, induction of fibroblasts, and epithelial cells' migration and function. Beneficial immunomodulatory effects of probiotics relate to modulation and activation of intraepithelial lymphocytes, natural killer cells, and macrophages through induced production of cytokines. Systemic effects of beneficial bacteria and link between gut microbiota, immune system, and cutaneous health through gut-brain-skin axes are discussed as well. In light of growing antibiotic resistance of pathogens, antibiotic use is becoming less effective in treating cutaneous and systemic infections. This review points to a new perspective and therapeutic potential of beneficial probiotic species as a safe alternative approach for treatment of patients affected by wound healing disorders and cutaneous infections.

Bioengineering Bacterially Derived Immunomodulants: A Therapeutic Approach to Inflammatory Bowel Disease

Bacterial enteric pathogens have evolved efficient mechanisms to suppress mammalian inflammatory and immunoregulatory pathways. By exploiting the evolutionary relationship between the gut and pathogenic bacteria, we have developed a potential mucosal therapeutic. Our findings suggest that engineered preparations of the Salmonella acetyltransferase, AvrA, suppress acute inflammatory responses such as those observed in inflammatory bowel disease (IBD). We created 125 nm diameter cross-linked protein nanoparticles directly from AvrA and carrier protein to deliver AvrA in the absence of Salmonella. AvrA nanoparticles are internalized in vitro and in vivo into barrier epithelial and lamina propria monocytic cells. AvrA nanoparticles inhibit inflammatory signaling and confer cytoprotection in vitro, and in murine colitis models, we observe decreased clinical and histological indices of inflammation. Thus, we have combined naturally evolved immunomodulatory proteins with modern bioengineering to produce AvrA nanoparticles, a potential treatment for IBD.

Annexin A1: shifting the balance towards resolution and repair

Epithelial barriers play an important role in regulating mucosal homeostasis. Upon injury, the epithelium and immune cells orchestrate repair mechanisms that re-establish homeostasis. This process is highly regulated by protein and lipid mediators such as Annexin A1 (ANXA1). In this review, we focus on the pro-repair properties of ANXA1.

ROS in gastrointestinal inflammation: Rescue Or Sabotage?

The intestine is composed of many distinct cell types that respond to commensal microbiota or pathogens with immune tolerance and proinflammatory signals respectively. ROS produced by mucosa-resident cells or by newly recruited innate immune cells are essential for antimicrobial responses and regulation of signalling pathways including processes involved in wound healing. Impaired ROS production due to inactivating patient variants in genes encoding NADPH oxidases as ROS source has been associated with Crohn's disease and pancolitis, whereas overproduction of ROS due to up-regulation of oxidases or altered mitochondrial function was linked to ileitis and ulcerative colitis. Here, we discuss recent advances in our understanding of how maintaining a redox balance is crucial to preserve gut homeostasis.

LINKED ARTICLES

This article is part of a themed section on Redox Biology and Oxidative Stress in Health and Disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.12/issuetoc.

Electrochemical reverse engineering: A systems-level tool to probe the redox-based molecular communication of biology

The intestine is the site of digestion and forms a critical interface between the host and the outside world. This interface is composed of host epithelium and a complex microbiota which is "connected" through an extensive web of chemical and biological interactions that determine the balance between health and disease for the host. This biology and the associated chemical dialogues occur within a context of a steep oxygen gradient that provides the driving force for a variety of reduction and oxidation (redox) reactions. While some redox couples (e.g., catecholics) can spontaneously exchange electrons, many others are kinetically "insulated" (e.g., biothiols) allowing the biology to set and control their redox states far from equilibrium. It is well known that within cells, such non-equilibrated redox couples are poised to transfer electrons to perform reactions essential to immune defense (e.g., transfer from NADH to O₂ for reactive oxygen species, ROS, generation) and protection from such oxidative stresses (e.g., glutathione-based reduction of ROS). More recently, it has been recognized that some of these redox-active species (e.g., H₂O₂) cross membranes and diffuse into the extracellular environment including lumen to transmit redox information that is received by atomically-specific receptors (e.g., cysteine-based sulfur switches) that regulate biological functions. Thus, redox has emerged as an important modality in the chemical signaling that occurs in the intestine and there have been emerging efforts to develop the experimental tools needed to probe this modality. We suggest that electrochemistry provides a unique tool to experimentally probe redox interactions at a systems level. Importantly, electrochemistry offers the potential to enlist the extensive theories established in signal processing in an effort to "reverse engineer" the molecular communication occurring in this complex biological system. Here, we review our efforts to develop this electrochemical tool for in vitro redox-probing.

Redox signaling mediated by the gut microbiota

The microbiota that inhabits the mammalian intestine can influence a range of physiological functions, including the modulation of immune responses, enhancement epithelial barrier function, and the stimulation of cell proliferation. While the mechanisms by which commensal prokaryotes stimulate immune signaling networks are well-characterized, less is known about the mechanistic control over homeostatic pathways within tissues. Recent reports by our research group have demonstrated that contact between the gut epithelia and some groups of enteric commensal bacteria prompts the rapid generation of reactive oxygen species (ROS) within host cells. Whereas the bacterial-induced production of ROS in phagocytes in response to ligand binding to Formyl Peptide Receptors (FPRs) and ensuing activation of NADPH oxidase 2 (Nox2) is a well-defined mechanism, ROS generated by other cell types such as intestinal epithelia in response to microbial signals via FPRs and the NADPH oxidase 1 (Nox1) is less appreciated. Importantly, enzymatically generated ROS have been shown to function as second messengers in many signal transduction pathways via the transient oxidative activity on sensor proteins bearing oxidant-sensitive thiol groups. Examples of redox sensitive proteins include tyrosine phosphatases that serve as regulators of MAPK pathways, focal adhesion kinase, as well as components involved NF-kB activation. Here, we review the leading edge discoveries gleaned from investigations that focus on microbial-induced generation of ROS and their functional effects on host physiology. These studies identify the functional molecular elements and mechanistic events that mediate the established effects of the normal microbiota on intestinal physiology.

Redox signaling in the gastrointestinal tract

Redox signaling regulates physiological self-renewal, proliferation, migration and differentiation in gastrointestinal epithelium by modulating Wnt/β-catenin and Notch signaling pathways mainly through NADPH oxidases (NOXs). In the intestine, intracellular and extracellular thiol redox status modulates the proliferative potential of epithelial cells. Furthermore, commensal bacteria contribute to intestine epithelial homeostasis through NOX1- and dual oxidase 2-derived reactive oxygen species (ROS). The loss of redox homeostasis is involved in the pathogenesis and development of a wide diversity of gastrointestinal disorders, such as Barrett's esophagus, esophageal adenocarcinoma, peptic ulcer, gastric cancer, ischemic intestinal injury, celiac disease, inflammatory bowel disease and colorectal cancer. The overproduction of superoxide anion together with inactivation of superoxide dismutase are involved in the pathogenesis of Barrett's esophagus and its transformation to adenocarcinoma. In Helicobacter pylori-induced peptic ulcer, oxidative stress derived from the leukocyte infiltrate and NOX1 aggravates mucosal damage, especially in HspB+ strains that downregulate Nrf2. In celiac disease, oxidative stress mediates most of the cytotoxic effects induced by gluten peptides and increases transglutaminase levels, whereas nitrosative stress contributes to the impairment of tight junctions. Progression of inflammatory bowel disease relies on the balance between pro-inflammatory redox-sensitive pathways, such as NLRP3 inflammasome and NF-κB, and the adaptive up-regulation of Mn superoxide dismutase and glutathione peroxidase 2. In colorectal cancer, redox signaling exhibits two Janus faces: On the one hand, NOX1 up-regulation and derived hydrogen peroxide enhance Wnt/β-catenin and Notch proliferating pathways; on the other hand, ROS may disrupt tumor progression through different pro-apoptotic mechanisms. In conclusion, redox signaling plays a critical role in the physiology and pathophysiology of gastrointestinal tract.

Pathogen control at the intestinal mucosa - H2O2 to the rescue

Intestinal infections are a global challenge, connected to malnutrition and inadequate hygiene in developing countries, and to expanding antibiotic resistance in developed countries. In general, a healthy host is capable of fighting off gut pathogens or at least to recover from infections quickly. The underlying protective mechanism, termed colonization resistance, is provided by indigenous commensal communities (microbiota) that are shaped and aided by the host's epithelial and innate immune system. Commensal-pathogen interactions are governed by competition for a suitable niche for replication and stable colonization, nutrient availability, species-specific alterations of the metabolic environment, changes in oxygen tension and release of chemicals and proteinaceous toxins (bacteriocins). This protective intestinal milieu is further reinforced by antimicrobial factors and chemicals secreted by the epithelial barrier, by dendritic cell sensing and by homeostasis between T-cell subsets (Treg/Th17) in the lamina propria. The 3 players (host-microbiota-pathogen) communicate via direct interactions or secreted factors. Our recent manuscript illustrates that reactive oxygen species (ROS) are an integral part of colonization resistance and should be considered an interkingdom antivirulence strategy.

Thiophene bridged hydrocyanine – a new fluorogenic ROS probe

In this report, we present a new hydrocyanine analog, termed as thiophene-bridged hydrocyanine (TBHC), which has its double bonds replaced with a bisthiophene, is 8.06-fold more stable to auto-oxidation than hydro-Cy5 and significantly better in cell culture.

[Microbiota-intestinal stem cells dialog: a key element for intestinal regeneration]

The most abundant and well-studied microbiota on the human body resides in the intestinal tract. Its impact extends the limits of the mucosal interface as it plays an essential role in systemic functions such as development of the immune system. At the level of the intestine, commensal microbes play important metabolic functions and promote the integrity of the mucosal barrier. Moreover, a large number of studies points to a role of the microbiota in intestinal regeneration both under homeostatic conditions and after epithelial damage. As intestinal regeneration is sustained by highly proliferative intestinal stem cells (ISCs), these observations raise the question of a direct impact of commensals on the activity of these cells. Key mediators of the dialog between microbes and the epithelium are the immune cells residing in the gut. Consistently, both innate lymphoid cells and macrophages activated by microbial stimuli have been shown to promote ISCs proliferation by secreting cytokines. More direct routes of communication have been described recently, either through the binding of bacterial ligands to Pattern Recognition Receptors expressed in ISCs, or through the sensing by ISCs of bacterial metabolites. In this review, we explore this stem cell-microbiota dialog and its impact on gut homeostasis.

Cellular ROS imaging with hydro-Cy3 dye is strongly influenced by mitochondrial membrane potential

BACKGROUND

Hydrocyanines are widely used as fluorogenic probes to monitor reactive oxygen species (ROS) generation in cells. Their brightness, stability to autoxidation and photobleaching, large signal change upon oxidation, pH independence and red/near infrared emission are particularly attractive for imaging ROS in live tissue.

METHODS

Using confocal fluorescence microscopy we have examined an interference of mitochondrial membrane potential (ΔΨm) with fluorescence intensity and localisation of a commercial hydro-Cy3 probe in respiring and non-respiring colon carcinoma HCT116 cells.

RESULTS

We found that the oxidised (fluorescent) form of hydro-Cy3 is highly homologous to the common ΔΨm-sensitive probe JC-1, which accumulates and aggregates only in 'energised' negatively charged mitochondrial matrix. Therefore, hydro-Cy3 oxidised by hydroxyl and superoxide radicals tends to accumulate in mitochondrial matrix, but dissipates and loses brightness as soon as ΔΨm is compromised. Experiments with mitochondrial inhibitor oligomycin and uncoupler FCCP, as well as a common ROS producer paraquat demonstrated that signals of the oxidised hydro-Cy3 probe rapidly and strongly decrease upon mitochondrial depolarisation, regardless of the rate of cellular ROS production.

CONCLUSIONS

While analysing ROS-derived fluorescence of commercial hydrocyanine probes, an accurate control of ΔΨm is required.

GENERAL SIGNIFICANCE

If not accounted for, non-specific effect of mitochondrial polarisation state on the behaviour of oxidised hydrocyanines can cause artefacts and data misinterpretation in ROS studies.

The G-protein coupled chemoattractant receptor FPR2 promotes malignant phenotype of human colon cancer cells

The G-protein coupled chemoattractant receptor formylpeptide receptor-2 (FPR2 in human, Fpr2 in mice) is expressed by mouse colon epithelial cells and plays a critical role in mediating mucosal homeostasis and inflammatory responses. However, the biological role of FPR2 in human colon is unclear. Our investigation revealed that a considerable number of human colon cancer cell lines expressed FPR2 and its ligands promoted cell migration and proliferation. Human colon cancer cell lines expressing high levels of FPR2 also formed more rapidly growing tumors in immunocompromised mice as compared with cell lines expressing lower levels of FPR2. Knocking down of FPR2 from colon cancer cell lines highly expressing FPR2 reduced their tumorigenicity. Clinically, FPR2 is more highly expressed in progressive colon cancer, associated with poorer patient prognosis. These results suggest that FPR2 can be high-jacked by colon cancer cells for their growth advantage, thus becoming a potential target for therapeutic development.

The Influence of the Gut Microbiota on Host Physiology: In Pursuit of Mechanisms

The results generated from the NIH funded Human Microbiome Project (HMP) are necessarily tied to the overall mission of the agency, which is to foster scientific discoveries as a basis for protecting and improving health. The investment in the HMP phase 1 accomplished many of its goals including the preliminary characterization of the human microbiome and the identification of links between microbiome diversity and disease states. Going forward, the next step in these studies must involve the identification of the functional molecular elements that mediate the positive influence of a eubiotic microbiome on health and disease. This review will focus on recent advances describing mechanistic events in the intestine elicited by the microbiome. These include symbiotic bacteria-induced activation of redox-dependent cell signaling, the bacterial production of short chain fatty acids and ensuing cellular responses, and the secretion of bacteriocins by bacteria that have anti-microbial activities against potential pathogens.

Peroxiredoxin 6 (Prdx6) supports NADPH oxidase1 (Nox1)-based superoxide generation and cell migration

Nox1 is an abundant source of reactive oxygen species (ROS) in colon epithelium recently shown to function in wound healing and epithelial homeostasis. We identified Peroxiredoxin 6 (Prdx6) as a novel binding partner of Nox activator 1 (Noxa1) in yeast two-hybrid screening experiments using the Noxa1 SH3 domain as bait. Prdx6 is a unique member of the Prdx antioxidant enzyme family exhibiting both glutathione peroxidase and phospholipase A2 activities. We confirmed this interaction in cells overexpressing both proteins, showing Prdx6 binds to and stabilizes wild type Noxa1, but not the SH3 domain mutant form, Noxa1 W436R. We demonstrated in several cell models that Prdx6 knockdown suppresses Nox1 activity, whereas enhanced Prdx6 expression supports higher Nox1-derived superoxide production. Both peroxidase- and lipase-deficient mutant forms of Prdx6 (Prdx6 C47S and S32A, respectively) failed to bind to or stabilize Nox1 components or support Nox1-mediated superoxide generation. Furthermore, the transition-state substrate analogue inhibitor of Prdx6 phospholipase A2 activity (MJ-33) was shown to suppress Nox1 activity, suggesting Nox1 activity is regulated by the phospholipase activity of Prdx6. Finally, wild type Prdx6, but not lipase or peroxidase mutant forms, supports Nox1-mediated cell migration in the HCT-116 colon epithelial cell model of wound closure. These findings highlight a novel pathway in which this antioxidant enzyme positively regulates an oxidant-generating system to support cell migration and wound healing.

The potential role of some phytochemicals in recognition of mitochondrial damage-associated molecular patterns

Mitochondria are the source of damage-associated molecular patterns (DAMPs). DAMPs modulate responses to stress and trauma in animals, influencing the onset of many diseases. Dietary phytochemicals, which target various cellular molecules, are potential modulators of immunological status. In this review the existence of the possible impact of some plant-derived compounds with proven anti-cancer and anti-inflammatory properties (isothiocyanates and curcumin) on DAMPs recognition is highlighted. Special consideration is given to the mtDNA recognizing Toll-like receptor 9 and formyl peptide receptors. In the context of the phytochemicals action, the role of these receptors in epithelial homeostasis is also discussed.

Sex steroid deficiency-associated bone loss is microbiota dependent and prevented by probiotics

A eubiotic microbiota influences many physiological processes in the metazoan host, including development and intestinal homeostasis. Here, we have shown that the intestinal microbiota modulates inflammatory responses caused by sex steroid deficiency, leading to trabecular bone loss. In murine models, sex steroid deficiency increased gut permeability, expanded Th17 cells, and upregulated the osteoclastogenic cytokines TNFα (TNF), RANKL, and IL-17 in the small intestine and the BM. In germ-free (GF) mice, sex steroid deficiency failed to increase osteoclastogenic cytokine production, stimulate bone resorption, and cause trabecular bone loss, demonstrating that the gut microbiota is central in sex steroid deficiency-induced trabecular bone loss. Furthermore, we demonstrated that twice-weekly treatment of sex steroid-deficient mice with the probiotics Lactobacillus rhamnosus GG (LGG) or the commercially available probiotic supplement VSL#3 reduces gut permeability, dampens intestinal and BM inflammation, and completely protects against bone loss. In contrast, supplementation with a nonprobiotic strain of E. coli or a mutant LGG was not protective. Together, these data highlight the role that the gut luminal microbiota and increased gut permeability play in triggering inflammatory pathways that are critical for inducing bone loss in sex steroid-deficient mice. Our data further suggest that probiotics that decrease gut permeability have potential as a therapeutic strategy for postmenopausal osteoporosis.

Role of nitrite, urate and pepsin in the gastroprotective effects of saliva

Dietary nitrate is now recognized as an alternative substrate for nitric oxide (•NO) production in the gut. This novel pathway implies the sequential reduction of nitrate to nitrite, •NO and other bioactive nitrogen oxides but the physiological relevance of these oxidants has remained elusive. We have previously shown that dietary nitrite fuels an hitherto unrecognized nitrating pathway at acidic gastric pH, through which pepsinogen is nitrated in the gastric mucosa, yielding a less active form of pepsin in vitro. Here, we demonstrate that pepsin is nitrated in vivo and explore the functional impact of protein nitration by means of peptic ulcer development. Upon administration of pentagastrin and human nitrite-rich saliva or sodium nitrite to rats, nitrated pepsin was detected in the animal's stomach by immunoprecipitation. •NO was measured in the gastric headspace before and after nitrite instillation by chemiluminescence. At the end of each procedure, the stomach's lesions, ranging from gastric erosions to haemorrhagic ulcers, were scored. Nitrite increased gastric •NO by 200-fold (p<0.05) and nitrated pepsin was detected both in the gastric juice and the mucosa (p<0.05). Exogenous urate, a scavenger of nitrogen dioxide radical, blunted •NO detection and inhibited pepsin nitration, suggesting an underlining free radical-dependent mechanism for nitration. Functionally, pepsin nitration prevented the development of gastric ulcers, as the lesions were only apparent when pepsin nitration was inhibited by urate. In sum, this work unravels a novel dietary-dependent nitrating pathway in which pepsin is nitrated and inactivated in the stomach, preventing the progression of gastric ulcers.

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The nitrate-nitrite-nitric oxide pathway promotes gastric protein nitration.

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Pepsin is nitrated by dietary nitrite through the production of ∙NO₂.

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Nitrated pepsin prevents the development of acute peptic ulcers.

The reduction of oxidative stress by nanocomposite Fullerol decreases mucositis severity and reverts leukopenia induced by Irinotecan

Irinotecan is a useful chemotherapeutic agent for the treatment of several solid tumors. However, this therapy is associated with side effects, including leukopenia and mucositis. Reactive oxygen species (ROS) activate inflammatory pathways and contribute to Irinotecan-induced mucositis. Fullerol is a nanocomposite with anti-oxidant properties that may reduce tissue damage after inflammatory stimuli. In this paper, the effects of Fullerol and mechanisms of protection were investigated in a model of Irinotecan-induced mucositis. Mucositis was induced by an injection of Irinotecan per 4 days in C57BL/6. Fullerol or a vehicle was injected every 12h. On day 7, the intestines were removed to evaluate histological changes, leukocyte influx, and the production of cytokines and ROS. Irinotecan therapy resulted in weight loss, an increased clinical score and intestinal injury. Treatment with Fullerol attenuated weight loss, decreased clinical score and intestinal damage. Irinotecan also induced increased ROS production in enterocytes, oxidative stress, IL-1β production, neutrophil and eosinophil influx in the ileum. Fullerol treatment decreased production of ROS in the enterocytes, oxidative stress, IL-1β production, neutrophil and eosinophil influx in the ileum. Irinotecan therapy also induced leukopenia in an ROS-dependent manner because leukopenia reverted in WT mice treated with Fullerol or Apocynin or in Gp91phox(-/-) mice. Mice treated with Irinotecan presented less melanoma tumor growth compared to the control group. Fullerol does not interfere in the anti-tumor action of Irinotecan. Fullerol has a great pharmacology potential to decreases the severity of mucositis and of leukopenia during chemotherapy treatment.

New development in studies of formyl-peptide receptors: critical roles in host defense

Formyl-peptide receptors are a family of 7 transmembrane domain, Gi-protein-coupled receptors that possess multiple functions in many pathophysiologic processes because of their expression in a variety of cell types and their capacity to interact with a variety of structurally diverse, chemotactic ligands. Accumulating evidence demonstrates that formyl-peptide receptors are critical mediators of myeloid cell trafficking in the sequential chemotaxis signal relays in microbial infection, inflammation, and immune responses. Formyl-peptide receptors are also involved in the development and progression of cancer. In addition, one of the formyl-peptide receptor family members, Fpr2, is expressed by normal mouse-colon epithelial cells, mediates cell responses to microbial chemotactic agonists, participates in mucosal development and repair, and protects against inflammation-associated tumorigenesis. These novel discoveries greatly expanded the current understanding of the role of formyl-peptide receptors in host defense and as potential molecular targets for the development of therapeutics.

The microenvironment of injured murine gut elicits a local pro-restitutive microbiota

The mammalian intestine houses a complex microbial community, which influences normal epithelial growth and development, and is integral to the repair of damaged intestinal mucosa(1-3). Restitution of injured mucosa involves the recruitment of immune cells, epithelial migration and proliferation(4,5). Although microenvironmental alterations have been described in wound healing(6), 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 symbiont(7,8)), 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.

Formyl peptide receptors at the interface of inflammation, angiogenesis and tumor growth

N-formyl peptide receptors (FPRs) belong to the family of pattern recognition receptors (PRRs) that regulate innate immune responses. Three FPRs have been identified in humans: FPR1-FPR3. FPR expression was initially described in immune cells and subsequently in non-hematopoietic cells and certain tissues. Besides their involvement in inflammatory disorders, FPRs have been implicated in the regulation of tissue repair and angiogenesis. Angiogenesis is not only a key component of pathogen defence during acute infection and of chronic inflammatory disorders, but also plays a critical role in wound healing and tissue regeneration. Moreover, pathologic uncontrolled angiogenesis is central for tumour growth, progression, and the formation of metastases. In this review, we summarise the evidence for a central role of FPRs at the intersection between inflammation, physiologic angiogenesis and pathologic neovascularisation linked to cancer. These findings provide insights into the potential clinical relevance of new treatment regimens involving FPR modulation.

Wound repair: role of immune-epithelial interactions

The epithelium serves as a highly selective barrier at mucosal surfaces. Upon injury, epithelial wound closure is orchestrated by a series of events that emanate from the epithelium itself as well as by the temporal recruitment of immune cells into the wound bed. Epithelial cells adjoining the wound flatten out, migrate, and proliferate to rapidly cover denuded surfaces and re-establish mucosal homeostasis. This process is highly regulated by proteins and lipids, proresolving mediators such as Annexin A1 protein and resolvins released into the epithelial milieu by the epithelium itself and infiltrating innate immune cells including neutrophils and macrophages. Failure to achieve these finely tuned processes is observed in chronic inflammatory diseases that are associated with non-healing wounds. An improved understanding of mechanisms that mediate repair is important in the development of therapeutics aimed to promote mucosal wound repair.

Lactobacilli Modulate Epithelial Cytoprotection through the Nrf2 Pathway

An optimal gut microbiota influences many beneficial processes in the metazoan host. However, the molecular mechanisms that mediate and function in symbiont-induced host responses have not yet been fully characterized. Here, we report that cellular ROS enzymatically generated in response to contact with lactobacilli in both mice and Drosophila has salutary effects against exogenous insults to the intestinal epithelium via the activation of Nrf2 responsive cytoprotective genes. These data show that the xenobiotic-inducible Nrf2 pathway participates as a signaling conduit between the prokaryotic symbiont and the eukaryotic host. Indeed, our data imply that the capacity of lactobacilli to induce redox signaling in epithelial cells is a highly conserved hormetic adaptation to impel cellular conditioning to exogenous biotic stimuli. These data also highlight the role the microbiota plays in eukaryotic cytoprotective pathways and may have significant implications in the characterization of a eubiotic microbiota.

The role of formylated peptides and formyl peptide receptor 1 in governing neutrophil function during acute inflammation

Neutrophil migration to sites of inflammation and the subsequent execution of multiple functions are designed to contain and kill invading pathogens. These highly regulated and orchestrated processes are controlled by interactions between numerous receptors and their cognate ligands. Unraveling and identifying those that are central to inflammatory processes may represent novel therapeutic targets for the treatment of neutrophil-dominant inflammatory disorders in which dysregulated neutrophil recruitment, function, and elimination serve to potentiate rather than resolve an initial inflammatory insult. The first G protein-coupled receptor to be described on human neutrophils, formyl peptide receptor 1 (FPR1), is one such receptor that plays a significant role in the execution of these functions through multiple intracellular signaling pathways. Recent work has highlighted important observations with regard to both receptor function and the importance and functional relevance of FPR1 in the pathogenesis of a range of both sterile and infective inflammatory conditions. In this review, we explore the multiple components of neutrophil migration and function in both health and disease, with a focus on the role of FPR1 in these processes. The current understanding of FPR1 structure, function, and signaling is examined, alongside discussion of the potential importance of FPR1 in inflammatory diseases suggesting that FPR1 is a key regulator of the inflammatory environment.

Annexin A1-containing extracellular vesicles and polymeric nanoparticles promote epithelial wound repair

Epithelial restitution is an essential process that is required to repair barrier function at mucosal surfaces following injury. Prolonged breaches in epithelial barrier function result in inflammation and further damage; therefore, a better understanding of the epithelial restitution process has potential for improving the development of therapeutics. In this work, we demonstrate that endogenous annexin A1 (ANXA1) is released as a component of extracellular vesicles (EVs) derived from intestinal epithelial cells, and these ANXA1-containing EVs activate wound repair circuits. Compared with healthy controls, patients with active inflammatory bowel disease had elevated levels of secreted ANXA1-containing EVs in sera, indicating that ANXA1-containing EVs are systemically distributed in response to the inflammatory process and could potentially serve as a biomarker of intestinal mucosal inflammation. Local intestinal delivery of an exogenous ANXA1 mimetic peptide (Ac2-26) encapsulated within targeted polymeric nanoparticles (Ac2-26 Col IV NPs) accelerated healing of murine colonic wounds after biopsy-induced injury. Moreover, one-time systemic administration of Ac2-26 Col IV NPs accelerated recovery following experimentally induced colitis. Together, our results suggest that local delivery of proresolving peptides encapsulated within nanoparticles may represent a potential therapeutic strategy for clinical situations characterized by chronic mucosal injury, such as is seen in patients with IBD.

Formyl peptide receptor as a novel therapeutic target for anxiety-related disorders

Formyl peptide receptors (FPR) belong to a family of sensors of the immune system that detect microbe-associated molecules and inform various cellular and sensorial mechanisms to the presence of pathogens in the host. Here we demonstrate that Fpr2/3-deficient mice show a distinct profile of behaviour characterised by reduced anxiety in the marble burying and light-dark box paradigms, increased exploratory behaviour in an open-field, together with superior performance on a novel object recognition test. Pharmacological blockade with a formyl peptide receptor antagonist, Boc2, in wild type mice reproduced most of the behavioural changes observed in the Fpr2/3^-/- mice, including a significant improvement in novel object discrimination and reduced anxiety in a light/dark shuttle test. These effects were associated with reduced FPR signalling in the gut as shown by the significant reduction in the levels of p-p38. Collectively, these findings suggest that homeostatic FPR signalling exerts a modulatory effect on anxiety-like behaviours. These findings thus suggest that therapies targeting FPRs may be a novel approach to ameliorate behavioural abnormalities present in neuropsychiatric disorders at the cognitive-emotional interface.