A5 A MOUSE MODEL TO UNRAVEL THE PATHOPHYSIOLOGICAL LINK BETWEEN CROHN’S DISEASE AND TYPE-2 DIABETES-ASSOCIATED METABOLIC DISORDERS

Background

Crohn’s disease (CD), an idiopathic inflammatory bowel disease (IBD), has been recently shown to increase the risk of developing type 2 diabetes (T2D). Moreover, treatment with anti-diabetic drugs has a protective role in preventing the severity and course of CD progression. However, the pathophysiological basis of T2D development in CD remains unclear. Findings have highlighted the contribution of adipose tissue (AT) to the development of chronic inflammatory diseases and have identified parallels between T2D and CD that may provide hints to common mechanisms of disease pathogenesis. Typically, microbial dysbiosis, hyperpermeable intestinal barrier, and intra-abdominal AT accumulation are the common features of both diseases, yet how the interplay of these factors contribute to pathogenesis is not known. Therefore, common pathogenic paradigms underlying both T2D and CD have led us to hypothesize that chronic intestinal inflammation serves as an initiator of AT dysfunction in CD, predisposing individuals to T2D. Further, the lack of appropriate animal models of CD with chronic intestinal inflammation that manifests accumulation of intra-abdominal AT, and extra-intestinal metabolic disorder as observed in CD and T2D patients has been a limitation.

Purpose

To develop a genetic mouse model to investigate if gut inflammation-mediated microbial dysbiosis and metabolic dysregulation of AT are at the nexus that cause T2D in CD.

Method

We developed a CD-mouse model, where we challenged Nod2-deficient mice (NOD2 being the strongest genetic risk factor contributing to CD) with a chronic inflammatory insult regime, using dextran sulfate sodium (cDSS) for 3 cycles. Subsequently, intraperitoneal insulin and oral glucose tolerance tests, metabolic caging, and MRI imaging of mice were performed. Changes in AT metabolism and microbial infiltration into AT were analyzed by quantitative real-time PCR (qRT-PCR) and/or immunohistochemistry (IHC).

Result(s)

Our new CD-mouse model revealed increased gut inflammation (TNF and type-I IFN) in Nod2-deficient mice compared to wild-type control mice post-cDSS. Surprisingly, Nod2-deficient mice gained body weight, which was at least in part accounted for by an increased intra-abdominal AT accumulation along with decreased AT fatty-acid metabolism (Cpt1a, Fabp4 expression) and AT browning (Ucp1, Cidea expression, and UCP-1 staining), reduced intestinal goblet cell numbers, increased gut bacterial infiltration within the fat, more insulin resistance and energy expenditure.

Conclusion(s)

This experimental mouse model mimicking CD-associated T2D will provide insights into how the microbiome-AT axis fuel chronic inflammation-mediated extra-intestinal metabolic disorder and immune dysregulation. Understanding these connections will be transformative, as it will help us devise novel therapeutic strategies to prevent T2D development in progressive CD patients.

Disclosure of Interest

None Declared

A23 INTESTINAL STEM CELL REGULATION BY THE BACTERIAL METABOLITE ADP-HEPTOSE VIA ACTIVATION OF THE ALPK1-TIFA SIGNALLING PATHWAY

NOT PUBLISHED AT AUTHOR’S REQUEST

A173 ELUCIDATING THE EFFECTS OF NOD2-MEDIATED SIGNALLING ON INTESTINAL RESIDENT-MEMORY T-CELL FORMATION AND FUNCTION

Background

Aberrant resident memory T-cell (TRM) responses have been associated with increased intestinal inflammation and Crohn’s disease (CD) pathology in humans. Intestinal TRM cells are not only important for maintaining the integrity of the intestinal epithelial barrier, but also for the rapid clearance of pathogens in the intestine during infection. Understanding the signals received by the intestinal immune system to generate TRM responses is paramount to elucidating treatments for CD. Genetic mutations in NOD2 are associated with the highest risk of CD development. As a host intracellular sensor of bacterial peptidoglycan, NOD2 is critical for initiating both innate and adaptive immune responses. Furthermore, work from our lab as well as those of our collaborators suggest that NOD2 deficiency reduces systemic memory B and T-cell responses. However, the role of NOD2 in establishing memory T-cell responses in the intestine remains unclear. This work will therefore establish the role of NOD2 signaling in initiating and maintaining optimal TRM responses to achieve intestinal homeostasis and resilience to intestinal inflammation.

Purpose

It is the main objective of this project to determine whether NOD2-mediated signalling affects:

1. Antigen-specific T-cell priming in vivo

2. Bona fide intestinal T_RM generation

3. Bona fide intestinal T_RM function

Method

To address the effects of NOD2-signalling on intestinal T-cell priming in vivo, wildtype (WT) mice were adoptively transferred 50,000 naïve LCMV-specific (SMARTA) CD4⁺ T-cells. Mice were subsequently infected with LCMV-Armstrong in the presence or absence of the NOD2 agonist; MDP. 5-days following infection, the numbers and percentage of LCMV-specific T-cells in the mesenteric lymph nodes and spleen were examined. To examine the effects of NOD2 on intestinal T_RM generation, littermate WT and NOD2 KO mice were infected with LCMV-Armstrong. Thirty-six-days following infection, the percentage and number of LCMV-specific CD4⁺ T-cells were profiled in the small and large intestinal lamina-propria by means of gp_66-77 class-II MHC-tetramer staining. In another set of experiments, littermate WT and NOD2 KO mice were re-infected with LCMV-C13 30-days following LCMV-Armstrong immunization, and the interferon-response in the small intestine was profiled by quantitative PCR to assess the effect of NOD2-deficiency on antigen recall responses.

Result(s)

NOD2-stimulation by means of MDP injection increased the percentage and number of adoptively transferred SMARTA CD4⁺ T-cells in the mesenteric lymph nodes upon LCMV infection. Furthermore, NOD2-deficiency did not alter intestinal LCMV-specific CD4⁺ T_RM seeding in the small and large intestinal lamina propria 36 days after infection. However, in vivo antigen recall experiments showed a decreased intestinal IFN response in NOD2 KO mice.

Conclusion(s)

Our findings reveal a potential role of NOD2 in the intestinal CD4⁺ T-cell priming and subsequent Ag-specific memory response.

Disclosure of Interest

None Declared

A22 USING INTESTINAL ORGANOIDS TO CHARACTERIZE THE NAIP-NLRC4 INFLAMMASOME RESPONSE IN THE INTESTINAL EPITHELIUM

Background

The NAIP-NLRC4 inflammasome is an important innate defence mechanism in intestinal epithelial cells (IECs) that protects the gut from invasive pathogens. NAIP-NLRC4 activation triggers pyroptotic cell death, releases active interleukin (IL)-18, and promotes the expulsion of infected enterocytes. Dysregulated inflammasomes result in exaggerated inflammation of the intestinal mucosa which is characterisitic of inflammatory bowel disease (IBD). There is increasing evidence that inflammasomes in IEC behave differently than in immune cells. However, a majority of inflammasome pathway characterization is studied immune cells. In addition, NAIP-NLRC4 activity in macrophages has been shown to be important for regulating the expression of nitric oxide (Nos2). The potential transcriptomic impact of NAIP-NLRC4 activity in IECs has yet to be explored.

Purpose

We will use intestinal orgnaoids to systematically characterize the NAIP-NLRC4 inflammasome pathway and identify the transcriptomic impact of NAIP-NLRC4 activity in IECs. To better define the role of NAIP-NLRC4 activity during a physiological infection, we have developed a novel ex vivo model of Shigella infection in 3D organoids.

Method

Organoids were derived from the ileal crypts of wild type (WT) and Nlrc4^-/-, Casp1^-/-, Pycard^-/-, or Tlr5^-/- mice and stimulated with Pam3CSk4, LPS, or flagellin. Inflammasome activation was assessed by Western blot (WB) and propidium iodide uptake. WT and Nlrc4^-/- organoids were infected with WT or a non-invasive Shigella mutant and the inflammasome response was evaluated by WB and a colony forming unit assay. WT and Nlrc4^-/- organoids were stimulated with flagellin and gene expression was assessed by RT-qPCR.

Result(s)

Basolateral organoid stimulation with bacterial ligands revealed a novel response of IECs to bacterial flagellin that results in pyroptosis and IL-18 processing. Basolateral internalization of flagellin occurred in a TLR5-independent manner. Inflammasome activation by flagellin was fully abrogated in Nlrc4^-/- and Casp1^-/- organoids while only IL-18 processing was affected in Pycard^-/- organoids. Infection with only WT Shigella induced inflammasome activation in an NLRC4-dependent manner. Interestingly, flagellin stimulation of WT but not Nlrc4^-/- organoids led to increased expression of Nos2. Furthermore, Nlrc4^-/- organoids had significantly lower expression levels of cytokine genes Ccl20, Cxcl1, and Tnf following inflammasome activation.

Conclusion(s)

Our study demonstrates an integral role for epithelial NAIP-NLRC4 inflammasomes in the response to bacterial flagellin and Shigella infection. We have uncovered a novel response of IECs to basolateral flagellin stimulation and revealed that NAIP-NLRC4 is important for the transcriptional regulation of inflammatory genes. Further work will examine how NAIP-NLRC4 activation controls inflammation and epithelial integrity by analyzing the NLRC4-dependent transcriptome and the effects on cell proliferation, differentiation, and barrier integrity.

Please acknowledge all funding agencies by checking the applicable boxes below

CCC, CIHR

Disclosure of Interest

None Declared

Modeling-Enabled Characterization of Novel NLRX1 Ligands

Nucleotide-binding domain and leucine-rich repeat containing (NLR) family are intracellular sentinels of cytosolic homeostasis that orchestrate immune and inflammatory responses in infectious and immune-mediated diseases. NLRX1 is a mitochondrial-associated NOD-like receptor involved in the modulation of immune and metabolic responses. This study utilizes molecular docking approaches to investigate the structure of NLRX1 and experimentally assesses binding to naturally occurring compounds from several natural product and lipid databases. Screening of compound libraries predicts targeting of NLRX1 by conjugated trienes, polyketides, prenol lipids, sterol lipids, and coenzyme A-containing fatty acids for activating the NLRX1 pathway. The ligands of NLRX1 were identified by docking punicic acid (PUA), eleostearic acid (ESA), and docosahexaenoic acid (DHA) to the C-terminal fragment of the human NLRX1 (cNLRX1). Their binding and that of positive control RNA to cNLRX1 were experimentally determined by surface plasmon resonance (SPR) spectroscopy. In addition, the ligand binding sites of cNLRX1 were predicted in silico and validated experimentally. Target mutagenesis studies demonstrate that mutation of 4 critical residues ASP677, PHE680, PHE681, and GLU684 to alanine resulted in diminished affinity of PUA, ESA, and DHA to NLRX1. Consistent with the regulatory actions of NLRX1 on the NF-κB pathway, treatment of bone marrow derived macrophages (BMDM)s with PUA and DHA suppressed NF-κB activity in a NLRX1 dependent mechanism. In addition, a series of pre-clinical efficacy studies were performed using a mouse model of dextran sodium sulfate (DSS)-induced colitis. Our findings showed that the regulatory function of PUA on colitis is NLRX1 dependent. Thus, we identified novel small molecules that bind to NLRX1 and exert anti-inflammatory actions.

Loss of NLRX1 results in increased intestinal pathology and T cell responses in mice with inflammatory bowel disease (HUM1P.312)

NLRX1 is a mitochondrial-associated NOD-like receptor that modulates antiviral immunity, cellular stress, autophagy, and reactive oxygen species (ROS). The role of NLRX1 in inflammatory bowel disease remains unknown. This study aimed to characterize NLRX1-mediated mechanisms of protection from IBD. We investigated the ability of NLRX1 to modulate gut pathology, inflammation and immunity by using DSS and CD4+CD45RBhigh transfer colitis models. Colons, spleens, and mesenteric lymph nodes were excised for characterizing immune cell subsets, histological analyses, cytokine and autophagy expression, NF-κB activity, and ROS production. The loss of NLRX1 increased severity of disease and colonic histopathology in both models of IBD. Colons of NLRX1-/- mice had significantly increased epithelial ulceration and leukocyte infiltration in the DSS model, while recipients of NLRX1-/- CD4+ T cells had increased leukocytic infiltration, proliferation, fibrosis, and crypt abscessation in both colon and ileum. The loss of NLRX1 increased numbers of Th1, Th17, and Treg in the spleen, increased colonic NF-κB activity, upregulation of IL-17, IFNγ and TNF-α production, and increased ROS production. NLRX1 ameliorates intestinal pathology during IBD by acting as an internal thermostat that modulates the balance of effector versus regulatory CD4+ T cell responses, and suppressing colonic NF-κB activity, inflammatory cytokine expression, ROS production, and autophagy.

Nod proteins link bacterial sensing and autophagy

Autophagy is one of the main cellular degradation systems in eukaryotes, responsible for the elimination of long-lived proteins and damaged organelles. Besides its well-documented role as a housekeeping mechanism, autophagy has recently caught the attention of groups working in the fields of microbiology and immunology, especially those working in innate immunity. In particular, the highly specific segregation and degradation of intracellular bacteria by the autophagic machinery was a matter of great interest. However, it was still unclear how the autophagy machinery could target intracellular bacteria with such specificity. We have recently analyzed the role of the intracellular peptidoglycan (PG) receptors Nod1 and Nod2 as a link between intracellular bacterial sensing and the induction of autophagy. Our results demonstrated that Nod2 recruits the critical autophagy protein ATG16L1 to the plasma membrane during bacterial invasion and that cells expressing mutations in these proteins--two of the most important associated with Crohn disease--autophagy is defective upon infection or stimulation with the bacterial peptidoglycan fragment MDP. Thus, our findings put together two genes previously reported as independent risk factors for the development of Crohn disease and open a venue in the study of new therapies to cure the disease.

Nucleotide oligomerization domains 1 and 2: regulation of expression and function in preadipocytes

Translocation of bacteria into the mesenteric fat during intestinal inflammation and the expression of functional TLR1-9 in murine preadipocytes and adipocytes suggest an active role for these cells in innate immunity. The present study focuses on nucleotide oligomerization domains 1 and 2 representing intracellular pattern recognition receptors that sense motifs derived from bacterial peptidoglycans. On mRNA level nucleotide oligomerization domain 1 was found to be constitutively expressed in the preadipocyte cell line 3T3L1 and in primary preadipocytes isolated from murine mesenteric fat, while nucleotide oligomerization domain 2 was only weakly expressed by these cells. Treatment with lactyl-tetra-diaminopimelic acid, muramyl dipeptide, LPS, IL-1beta, and TNF-alpha did not affect cellular nucleotide oligomerization domain 1 mRNA amounts. Except muramyl dipeptide, all factors significantly increased nucleotide oligomerization domain 2 mRNA in mesenteric fat preadipocytes after 4 h. However, specific stimulation of nucleotide oligomerization domain 1 induced IL-6 synthesis in preadipocytes from wild-type or TLR2/4-deficient mice. Confirming nucleotide oligomerization domain 1 specificity, transfection of nucleotide oligomerization domain 1-specific small interfering RNA significantly blocked the effect of lactyl-tetra-diaminopimelic acid on IL-6 production. With specific inhibitors and a NF-kappaB reporter plasmid, nucleotide oligomerization domain 1-mediated activation of NF-kappaB was shown to be responsible for the induction of IL-6 in preadipocytes. In addition, expression of functional nucleotide oligomerization domain 1 could be confirmed in primary human preadipocytes. In summary, we here identified preadipocytes as a novel cell population expressing nucleotide oligomerization domains 1 and 2. Not regulated on transcriptional level, nucleotide oligomerization domain 1 in preadipocytes serves as a sensor for bacterial degradation products and triggers proinflammatory effector responses. Thus, our results further strengthen the allocation of the mesenteric fat and especially of preadipocytes to the innate immune system.

[How can we give quick yet relevant nutritional advice in our daily medical practice?]

Within our diabetology Unit CHUV-PMU, the dietetic consultation is an integral part of the patients' management, for the majority of diabetic patients. The general practitioner offers very different perspectives. What are the possible modalities of ambulatory dietetic counselling? Are the numerous existing standardized documents really relevant? We bring a critical analysis on such documents, the use of which often engenders a feeling of failure for the patients and the health professionals. We suggest an intervention guide so that the nutritional education work undertaken in an ambulatory consultation may then lead to dietetic management.

Caspase-1 activation of lipid metabolic pathways in response to bacterial pore-forming toxins promotes cell survival

Many pathogenic organisms produce pore-forming toxins as virulence factors. Target cells however mount a response to such membrane damage. Here we show that toxin-induced membrane permeabilization leads to a decrease in cytoplasmic potassium, which promotes the formation of a multiprotein oligomeric innate immune complex, called the inflammasome, and the activation of caspase-1. Further, we find that when rendered proteolytic in this context caspase-1 induces the activation of the central regulators of membrane biogenesis, the Sterol Regulatory Element Binding Proteins (SREBPs), which in turn promote cell survival upon toxin challenge possibly by facilitating membrane repair. This study highlights that, in addition to its well-established role in triggering inflammation via the processing of the precursor forms of interleukins, caspase-1 has a broader role, in particular linking the intracellular ion composition to lipid metabolic pathways, membrane biogenesis, and survival.