A2 MUCUS DEFICIENCY IMPACTS INTESTINAL EPITHELIAL CELL PROLIFERATION INDEPENDENT OF THE MICROBIOTA

Background

Intestinal homeostasis is highly dependent on the proliferation and differentiation of intestinal epithelial cells (IEC). IEC arise from intestinal stem cells (ISCs) that reside at the bottom of intestinal crypts. Following proliferation, the IEC migrate up as transient amplifying (TA) cells, and differentiate into mature IEC subtypes. When this process is disrupted, it can lead to aberrant IEC proliferation and differentiation. Mucus production by secretory goblet cells is also crucial for intestinal homeostasis, as mucus separates the IEC from luminal microbiota. Surprisingly, mice lacking Muc2, the main protein component of mucus, display increased distal colonic IEC proliferation and crypt hyperplasia at baseline, suggesting a relationship between Muc2 production and IEC proliferation.

Aims

We investigated how mucus production impacts IEC proliferation and differentiation in the intestinal crypt.

Methods

We used wildtype (Muc2^+/+) and Muc2 deficient (Muc2^-/-) littermates to measure distal colon crypt length and IEC proliferation pattern via microscopy. Organoids were also derived from distal colons of Muc2^+/+ and Muc2^-/- mice, and quantified for size, density and proliferation for 7 days to test whether the hyper-proliferation phenotype was also seen in vitro, thus epithelial-intrinsic. Crypts and organoids were collected for RNA sequencing to examine changes in IEC proliferation pathways. Proliferation assessments were repeated in germ-free (GF) Muc2^+/+ and Muc2^-/- mice. Muc2^-/- mice were also cross-bred with Lgr5^{-EGFP-IRES-CreERT2} mice to investigate the contribution of ISCs to IEC hyperproliferation resulting from Muc2 deficiency.

Results

Significant crypt hyperplasia was observed in the distal colons of Muc2^-/- mice in concert with a > twofold increase in Ki67⁺ TA cells as compared to Muc2^+/+ mice. Similarly, Muc2^-/- organoids also displayed significantly greater size, density and an increased number of Ki67⁺ cells than Muc2^+/+ organoids. Hyperproliferation was also seen in GF mice and organoids, suggesting that mucus impacts IEC proliferation independent of the microbiome. Muc2^-/- Lgr5-EGFP⁺ mice showed no significant increase in numbers of Lgr5⁺ cells, indicating that Muc2 deficiency does not directly impact ISC number, but rather their proliferation and differentiation reflected in increased numbers of TA cells. RNA-sequencing results suggested that changes in lipid metabolism may underlie the increased IEC proliferation seen in Muc2^-/- mice.

Conclusions

Mucus not only promotes IEC homeostasis by separating luminal bacteria from the intestinal epithelium, but also intrinsically modifies IEC proliferation independent of the microbiota. Taken together, our results emphasize the importance of mucus in controlling gut health through mechanisms independent of its role in barrier function.

Funding Agencies

CCC, CIHRC.H.I.L.D Foundation

A40 IDENTIFYING NOVEL ROLES FOR TLR2 SIGNALING IN THE INTESTINAL EPITHELIUM USING ORGANOIDS

Background

Inflammatory bowel disease (IBD) is thought to result from an imbalance between protective and damaging immune responses to the resident microbiota and other luminal antigens. Increasing evidence suggests that toll-like-receptor (TLR)-mediated innate immune dysfunction contributes to the pathogenesis of IBD. Among the receptors in the TLR family, TLR2 and its signalling pathway appears to play an important protective role in the gastrointestinal (GI) tract. Notably, our group previously discovered that Tlr2 expression by nonhematopoietic cells played an important protective role in the Citrobacter rodentium model of infectious colitis.

Aims

To determine if intestinal epithelial cells (IECs) control Tlr2 dependent tissue protective responses, we sought to characterize the role of Tlr2 signalling in intestinal organoids. In addition, to better define the role of Tlr2 during C. rodentium infection, we developed a novel in vitro model of C. rodentium infection using organoid-derived monolayers.

Methods

Organoids were derived from the colonic tissue of wild type (C57BL/6J) and Tlr2 deficient (-/-) mice and then stimulated with Tlr2 agonists, and their responses were evaluated by qPCR, ELISA, Western blot and immunostaining. In addition, 2D monolayers were grown from organoids, and infected with C. rodentium to explore whether Tlr2 signaling regulates other protective IEC functions such as barrier proteins and cell death in response to noxious stimuli.

Results

Stimulation of WT, but not Tlr2-/- mouse orgnaoids led to increased transcription of chemokine and cytokine genes Ccl20, Mcp-1, Cxcl1 and Tnf-α. This was accompanied by increased protein secretion through a NF-κB and p38 MAP kinase dependent mechanism. Interestingly, organoids derived from the distal colon displayed stronger Tlr2 responses than organoids from the proximal colon. During C. rodentium infection of monolayers, Tlr2 signaling had no effect on the distribution of tight junction proteins such as ZO-1 or Claudin3, however, Tlr2 did regulate levels of IEC apoptosis upon C. rodentium infection.

Conclusions

Our study demonstrates that colonic organoids express functional Tlr2, which upon stimulation, leads to pro-inflammatory responses as well as control over cell death. Our novel C. rodentium infection model enables us to further study the role of IEC in promoting host defense during bacterial infection. Futher work will examine how interactions with Tlr2 dependent cytokines (ie. IL-6, IL-22) impact IEC responses to C. rodentium.

Funding Agencies

CCC, CIHRCH.I.L.D

A1 USING HUMAN NEONATAL ORGANOIDS TO EXPLORE GUT-IMMUNE SYSTEM INTERACTIONS OF THE NEONATAL INTESTINE

Background

Necrotizing Enterocolitis (NEC) affects around 10% of preterm babies and is one of the leading causes of death for newborns. NEC is characterized by exaggerated inflammation of the intestinal mucosa, possibly triggered by aberrant exposure to gut microbes, leading to hypoxic conditions and the death of intestinal tissues. It has been hypothesized that NEC develops when the immature intestine (epithelium and immune system) is unable to properly balance these new microbial interactions. To date, NEC is poorly understood and due to the difficulty of modeling the human neonatal intestine, few therapeutic options are available.

Intestinal epithelial cells (IEC) are important players in promoting beneficial host-microbe interactions in the gut, being the primary barrier that separates the host’s mucosal immune system from luminal microbiota, as well as key players in mediating signaling between microbes and the host. Based on their location, IEC are also subject to injury associated with maladaptive immune responses against gut microbes. Many studies have shown that immune cells (such as T helper 17 cells) interact with IEC to promote gut health and function. These interactions include educating IEC on how to respond to, and fight pathogenic microbes, yet also remain tolerant to commensal microbes.

Aims

This project seeks to develop an in vitro human neonatal intestinal organoid model to study developmental changes in IEC and their functional interactions with neonatal Th17 cells.

Methods

3D organoids were established from human neonatal intestinal biopsies and then co-cultured with the supernatant of differentiated Th17 cells or with recombinant cytokines, IL-17 and IL-22. Changes in barrier function, cell proliferation, production of mucins and anti-microbial peptides (AMP) were analyzed by qPCR and immunostaining.

Results

Using 3D neonatal organoids we observed that the supernatants from neonatal Th17 cells (containing IL-17, IL-22 etc.) promoted the proliferation, differentiation and barrier function of the neonatal epithelium. By using specific recombinant cytokine (IL22, IL17) and neutralizing IL-22 antibodies in parallel, we demonstrated that the high levels of IL-22 produced by neonatal Th17 cells specifically induced proliferation of IEC, AMP and mucus production as compared to control media treated organoids, as shown by increases in Ki67, Reg3γ and Muc2 markers.

Conclusions

This experimental model mimicking the neonatal intestinal environment can be used to study interactions between neonatal IEC and immune cells. Our findings can provide clinically relevant information and clues to how developmental changes in the newborn intestine can influence susceptibility to NEC while demonstrating our development of a simple, yet accurate and clinically applicable model of the neonatal gut.

Funding Agencies

CAG, CIHRBCCHRI, CCC, C.H.I.L.D. Fdn

A9 SIALIC ACID METABOLISM PLAYS A KEY ROLE IN INTESTINAL FITNESS AND VIRULENCE OF AN ATTACHING/ EFFACING BACTERIAL PATHOGEN

Background

The gastrointestinal (GI) mucus barrier acts as an important interface between the host and luminal gut microbes, beyond its role in limiting direct contact between noxious luminal agents and the underlying intestinal epithelium. Mucus is comprised of highly glycosylated mucin proteins, modified by O-glycan side chains, formed by five sugar monomers, including sialic acid. Sialic acid frequently occupies the terminal position of O-glycans and can be cleaved by microbial sialidases. We hypothesize that upon entering their hosts, enteric pathogens, such as the attaching and effacing (A/E) family (EHEC, EPEC and Citrobacter rodentium) metabolically adapt to their intestinal environment, and express key virulence factors by sensing and metabolizing mucin sugars, such as sialic acid.

Aims

Investigate the role of sialic acid in regulating the fitness and virulence strategies of the A/E pathogen C. rodentium within the GI environment.

Methods

C57Bl/6 mice were orally infected with either wildtype (WT) or mutant strains of C. rodentium to study bacterial pathogenicity in vivo. Sialic acid was localized in mouse colonic tissue sections through lectin staining, and quantified in mouse feces and mucus scrapings using a commercial kit. Protein secretion by C. rodentium, in the presence or absence of sialic acid was analyzed by SDS-PAGE and mass spectrometry. Intestinal epithelial cell lines were infected with enteropathogenic E. coli (EPEC) or C. rodentium to examine bacterial adherence.

Results

Sialic acid was expressed widely in the GI tracts of mice, primarily in the colonic mucus layer and by intestinal goblet cells. Both EPEC and C. rodentium were found to take up and metabolize sialic acid through the transporter NanT. A C. rodentium strain deficient in sialic acid uptake ( ΔnanT) was dramatically impaired in colonizing the intestines of mice and was rapidly cleared. Sialic acid also impacted C. rodentium’s virulence by inducing the secretion of two key virulence factors, which significantly enhanced the pathogen’s adhesion to intestinal epithelial cells. Moreover, sialic acid increased C. rodentium’s ability to degrade mucus, due to the increased production of these two secreted virulence factors.

Conclusions

We demonstrate that sialic acid, a mucin-derived sugar, is an essential nutrient for A/E pathogens to thrive and expand within their host’s intestines. Moreover, sialic acid enhances pathogen virulence by inducing secretion of two important virulence factors, which increase adhesion to the epithelium and promote the degradation of mucus.

Funding Agencies

CCC, CIHRCH.I.L.D. Fdn

A30 DIFFERENCES BETWEEN HUMAN AND MOUSE INTESTINAL EPITHELIAL CELLS IN THEIR INNATE IMMUNE RESPONSES TO BACTERIAL AND HOST STIMULI

Background

Intestinal epithelial cells (IEC) reside in close contact with the gut microbiota. It is thus important that IEC are hypo-responsive to bacterial products to prevent maladaptive inflammatory responses in the gut, such as those seen in Inflammatory bowel diseases (IBD). This suppression of innate immune signaling in IEC is in part due to their strong expression of Single Ig IL1 related receptor (SIGIRR), a negative regulator of interleukin (IL)-1 and toll-like receptor (TLR) signaling. IL37, a newly recognized anti-inflammatory cytokine has been shown to strongly inhibit innate signaling in cells by binding to, and signaling through SIGIRR, leading to suppression of various forms of inflammation in mice. Few studies have looked at the function of IL-37/SIGIRR in IEC and their potential use to balance inflammatory responses. Notably, while many groups have studied IEC immune response in vitro, using transformed IEC lines, our focus is on primary-derived IEC which more accurately reflect in vivo responses.

Aims

To characterize IEC intrinsic and species-specific immune responses elicited by bacteria and host products as well as the role of IL37/SIGIRR in regulating this innate signaling.

Methods

We used organoid to study the innate immune responses of primary IEC derived from human or mouse colon (colonoids). After stimulation with inflammatory stimuli (IL1β, FliC and LPS), qPCR, ELISA, Milliplex Multiplex Assay and Western blot were used to determine modification in signalling pathway and cytokine/chemokine secretion.

Results

Using colonoids derived from healthy donors, we demonstrated that unlike transformed cell lines or mouse IEC, human IEC respond only to the bacterial product FliC, and not to LPS or IL1β. We further characterized human colonoid innate immune responses and despite significant inter-individual variability upon FliC stimulation, all organoids released several chemokines (IL8, CXCL1, CXCL2, CCL2 and CCL20). We showed for the first time that IL37 attenuated these innate immune responses through inhibition of intracellular signaling pathways (p38 and NFkB). Using colonoids derived from wildtype and Sigirr deficient mice, we found that mice IEC were responsive to IL1b and FliC and that the suppressive effects of IL37 were Sigirr dependent.

Conclusions

Our results show that human IEC show variability among individuals in the magnitude of their innate immune responses, and these responses differ from those obtained from transformed cells and primary mouse IEC. For the first time, we show that IL37 suppresses IEC innate immune responses, through its ability to signal through Sigirr. Further investigations will assess the ability of IL37 to control inflammation of IEC derived from IBD patients, as a potential therapeutic to promote gut health.

Funding Agencies

CAG, CIHRMSFHR

A21 ULCERATIVE COLITIS-ASSOCIATED E. COLI PATHOBIONTS POTENTIATE COLITIS IN SUSCEPTIBEL HOSTS

Background

Ulcerative colitis (UC) is a chronic inflammatory condition linked to intestinal microbial dysbiosis, including the expansion of E. coli strains related to extra-intestinal pathogenic E. coli. These “pathobionts” exhibit pathogenic properties, but their potential to promote UC is unclear due to the lack of relevant animal models.

Aims

We explored the potential to establish a mouse model of GI infection by the UC-associated E. coli strain p19A, as well as characterize the pathogenic features of p19A.

Methods

We used a representative UC pathobiont strain (p19A), and mice lacking single immunoglobulin and toll-interleukin 1 receptor domain (SIGIRR), a deficiency increasing susceptibility to gut infections. Vancomycin-pretreated Sigirr-/- mice were subsequently gavaged with the control E. coli DH10B (a derivative of commensal strain K-12) or p19A. One day after infection, mice were exposed to 2.5% dextran sodium sulfate (DSS) in their drinking water for another 4 days.

Results

Strain p19A was found to adhere to the cecal mucosa of Sigirr-/- mice, causing modest inflammation. Moreover, it dramatically worsened DSS-induced colitis. This potentiation was attenuated using a p19A strain lacking α-hemolysin genes, or when we targeted pathobiont adherence using a p19A strain lacking the adhesin FimH, or following treatment with FimH antagonists.

Conclusions

Thus, UC pathobionts adhere to the intestinal mucosa, and worsen the course of colitis in susceptible hosts in a manner dependent on specific virulence factors, including α-hemolysin and FimH.

Funding Agencies

CCC, CIHR

A46 THE INFLAMMATORY CASPASES COORDINATE MUCOSAL RESTRICTION OF SALMONELLA THROUGH THE EPITHELIAL-INTRINSIC INFLAMMASOME AND IL-22 DRIVEN MUCIN SECRETION

Background

Intestinal epithelial cells (IECs) are located at the interface between the gut lumen and the underlying mucosal defense system. Here, they play a central role in the coordination of intestinal homeostasis, tempering pro-inflammatory responses but remaining rapidly responsive to noxious stimuli such as enteric pathogens. One early response mechanism by which IECs engage in immune defense is through the activation of the inflammasome which mobilizes the inflammatory caspases; caspase-1 and -11.

Aims

Here, we investigated the role of the inflammasome in overall mucosal defense against the enteric pathogen Salmonella enterica serovar Typhimurium.

Methods

Streptomycin-pretreated C57BL/6 (wildtype), Casp1/11 deficient (−/−), Casp1−/− and Casp11−/− mice were orally infected with Salmonella and burdens determined in intestinal tissues at 18h post infection (p.i.).

Results

Increased pathogen loads were observed for all caspase-deficient mice compared to wildtype, which correlated with increased IEC intracellular Salmonella burdens. Interestingly, despite increased bacterial loads, pathology scores for all inflammatory caspase mice were decreased, especially with regard to ‘IEC damage’ and ‘goblet cell loss’.

To determine if the increased burdens were due to the loss of IEC-intrinsic inflammasomes, enteroid monolayers were derived and infected with Salmonella. This revealed significantly increased intracellular burdens in caspase-deficient monolayers as compared to wildtype, in concert with a marked decrease in IEC shedding and cell death. Peak inflammatory caspase activity was displayed in shedding wildtype IECs, suggesting the IEC-intrinsic inflammasome restricts Salmonella infection through infected IEC expulsion.

The role of inflammasome signaling in acute mucosal defense was also examined. Wildtype tissue demonstrated a dramatic increase in mucus thickness (as evaluated by Muc2 immunostaining) and antimicrobial Reg3γ and β lectin transcript levels compared to caspase-deficient mice. Mucin release and Reg3 induction has been previously linked to IL-22, therefore we measured IL-22 expression and observed increased secretion in infected wildtype mice compared to Casp1/11−/−. This correlated with increased cecal infiltration of IL-22 producing ILC3 and NK T-cells. When infected mice were treated with IL-22 neutralizing antibody, this increased Salmonella burdens and decreased infection-induced mucus secretion, while no differences were observed in Casp1/11−/− treated with neutralizing antibody or isotype control.

Conclusions

Therefore the intestinal epithelium utilizes inflammasome signaling to coordinate multiple layers of innate defense at the gut mucosal surface to ultimately restrict enteric pathogen infections and their systemic spread.

Funding Agencies

CCC, CIHR, NRCUBC

Use of diagnostic clusters to assess the economic consequences of rhinopharyngitis in children in Italy and France during the winter. Rhinitis Survey Group

To determine how practitioners diagnose rhinopharyngitis (RP), we conducted a longitudinal, multicenter study of a cohort of 900 children, collecting medical and economic data without interfering with usual medical practice during the winter of 1996-1997 in France and Italy. All ear, nose, and throat (ENT) infections were described clinically; data on the consumption of medical items (physician visits, drug treatment, hospitalization, physiotherapy, preventive treatment, laboratory tests, roentgenograms, and outpatient procedures) were collected to estimate the cost of caring for patients with RP. The mean age of the children was 28.0 months, and the ratio of males to females was approximately 5 to 4. Patients had had a mean 4.1 episodes of RP the previous year and 1.4 episodes of acute otitis media (AOM). There were no marked differences in the children's characteristics between France and Italy. During the winter of the study, this population experienced 4.26 episodes of ENT infection, of which 73.5% were documented at the study sites. Seven homogeneous groups of RP were found, 2 of them each representing <4% of the overall population. One group presented with otalgia, although the diagnosis of AOM was not recorded by the physician. In 4 groups, the presence of nasal discharge plus cough (without otalgia) was used to make the diagnosis. Medical item consumption varied by country and by group of RP, mainly in the prevailing choice of antibiotics. The difference in duration of treatment was not statistically significant. As a consequence, the costs of caring for patients with RP varied greatly, RP with AOM being the most costly. Last, prognostic factors for costly episodes of infectious ENT were identified. The population at risk included young children who had had AOM episodes during the previous winter, had a first episode of AOM before 6 months of age, had a history of AOM associated with effusion, or attended a community-based child care facility. Therefore, clinical trials aimed at demonstrating cost-effectiveness of prophylaxis should focus on this population.

Kinetics of specific salivary IgA responses in man after oral challenge by ribosomal immunostimulant

The kinetics of specific IgA mucosal responses was assessed in 12 healthy volunteers over 3 weeks of treatment by oral administration of an immunostimulant, Ribomunyl, composed of ribosomes from the four bacteria Streptococcus pyogenes, Streptococcus pneumoniae, Klebsiella pneumoniae and Haemophilus influenzae. The levels of IgA specific for these four bacteria increased after each immunization and, after the third week of treatment, were significantly higher than baseline day 0 values. This study demonstrates that oral ribosomal immunostimulation results in the production of specific salivary antibodies liable to recognize whole bacteria antigens, and therefore likely to confer protection. The kinetic analysis performed also demonstrates the rapidity of specific mucosal immune responses after oral stimulation in man, a feature still seldom explored.

[Pharmacologic study of the glucocorticoid activity of flunisolide compared with other steroids in the rat]

Flunisolide (FLU), beclomethasone dipropionate (BDP) and its pulmonary metabolites beclomethasone monopropionate (BMP) and beclomethasone (B) were studied in rat for: their relative binding affinity (RBA) for the 5 classes of steroid receptors, their in vitro glucocorticoid activity on rat thymocytes, their in vivo glucocorticoid activity by oral route. These compounds displayed a strong RBA for rat lung, thymus and liver glucocorticoid receptors (FLU > or = BMP > BDP > or = B). They were also shown to have a moderate RBA for both mineralocorticoid and progestin receptors, while being devoid of any binding to androgen and oestrogen receptors. On rat thymocytes FLU exhibited the highest glucocorticoid activity (FLU > B > or = BMP > BDP). In rat oral FLU displayed a strong glucocorticoid activity with a slight first-pass metabolism as opposed to what has been reported in human.

Investigation of gyrate atrophy using a cDNA clone for human ornithine aminotransferase

Gyrate atrophy of the choroid and retina is an autosomal recessive disease associated with reduced or absent ornithine aminotransferase (OAT) activity. To approach the defect in OAT at the molecular level, we have cloned a cDNA for the mRNA encoding the OAT precursor from human liver. The clone contains the complete coding region of 1317 nucleotides along with 44 nucleotides of 5' and 654 nucleotides of 3' untranslated sequences. When used to probe genomic DNA, the OAT cDNA did not detect any evidence of gene deletion or rearrangement in patients with gyrate atrophy. The cDNA hybridizes to a 2.15-kb RNA species in liver, fibroblasts, and lymphoblasts. The size and approximate amount of this mRNA is not altered in fibroblasts and/or lymphoblasts of seven gyrate atrophy patients who display a 25- to 100-fold reduction in OAT activity. Our results suggest the defect in these individuals may be caused by a subtle sequence alteration in the mRNA that does not affect its apparent size.