Inflammatory bowel diseases (IBD), encompassing ulcerative colitis (UC), and Crohn’s disease (CD), are a group of disorders characterized by chronic, relapsing, and remitting, or progressive inflammation along the gastrointestinal tract. IBD is accompanied by massive infiltration of circulating leukocytes into the intestinal mucosa. Leukocytes such as neutrophils, monocytes, and T-cells are recruited to the affected site, exacerbating inflammation and causing tissue damage. Current treatments used to block inflammation in IBD include aminosalicylates, corticosteroids, immunosuppressants, and biologics. The first successful biologic, which revolutionized IBD treatment, targeted the pro-inflammatory cytokine, tumor necrosis factor alpha (TNFα). Infliximab, adalimumab, and other anti-TNF antibodies neutralize TNFα, preventing interactions with its receptors and reducing the inflammatory response. However, up to 40% of people with IBD become unresponsive to anti-TNFα therapy. Thus, more recent biologics have been designed to block leukocyte trafficking to the inflamed intestine by targeting integrins and adhesins. For example, natalizumab targets the α4 chain of integrin heterodimers, α4β1 and α4β7, on leukocytes. However, binding of α4β1 is associated with increased risk for developing progressive multifocal leukoencephalopathy, an often-fatal disease, and thus, it is not used to treat IBD. To target leukocyte infiltration without this life-threatening complication, vedolizumab was developed. Vedolizumab specifically targets the α4β7 integrin and was approved to treat IBD based on the presumption that it would block T-cell recruitment to the intestine. Though vedolizumab is an effective treatment for IBD, some studies suggest that it may not block T-cell recruitment to the intestine and its mechanism(s) of action remain unclear. Vedolizumab may reduce inflammation by blocking recruitment of T-cells, or pro-inflammatory monocytes and dendritic cells to the intestine, and/or vedolizumab may lead to changes in the programming of innate and acquired immune cells dampening down inflammation.

This study tested the hypothesis that Malt1 deficiency in macrophages contributes to dextran sodium sulfate (DSS)-induced intestinal inflammation in Malt1-deficient mice. In people, combined immunodeficiency caused by a homozygous mutation in the MALT1 gene is associated with increased susceptibility to bacterial infections and chronic inflammation, including severe inflammation along the gastrointestinal tract. The consequences of Malt1 deficiency have largely been attributed to its role in lymphocytes, but Malt1 is also expressed in macrophages, where it is activated downstream of TLR4 and dectin-1. The effect of Malt1 deficiency in murine macrophages and its contribution to DSS-induced colitis have not been investigated. Our objectives were to compare the susceptibility of Malt1 and Malt1 mice to DSS-induced colitis, to determine the contribution of macrophages to DSS-induced colitis in Malt1 mice, and to assess the effect of innate immune stimuli on Malt1 macrophage inflammatory responses. We found that Malt1 deficiency exacerbates DSS-induced colitis in mice, accompanied by higher levels of IL-1β, and that macrophages and IL-1 signaling contribute to pathology in Malt1 mice. Malt1 macrophages produce more IL-1β in response to either TLR4 or dectin-1 ligation, whereas inhibition of Malt1 proteolytic (paracaspase) activity blocked IL-1β production. TLR4 or dectin-1 stimulation induced Malt1 protein levels but decreased its paracaspase activity. Taken together, these data support the hypothesis that Malt1 macrophages contribute to increased susceptibility of Malt1 mice to DSS-induced colitis, which is dependent on IL-1 signaling. Increased IL-1β production by MALT1-deficient macrophages may also contribute to chronic inflammation in people deficient in MALT1.

This study tested the hypothesis that mucosa associated lymphoid tissue 1 (Malt1) deficiency causes osteoporosis in mice by increasing osteoclastogenesis and osteoclast activity. A patient with combined immunodeficiency (CID) caused by MALT1 deficiency had low bone mineral density resulting in multiple low impact fractures that was corrected by hematopoietic stem cell transplant (HSCT). We have reported that Malt1 deficient M s, another myeloid cell type, are hyper-responsive to inflammatory stimuli. Our objectives were to determine whether Malt1 deficient mice develop an osteoporosis-like phenotype and whether it was caused by Malt1 deficiency in osteoclasts. We found that Malt1 deficient mice had low bone volume by 12 weeks of age, which was primarily associated with reduced trabecular bone. Malt1 protein is expressed and active in osteoclasts and is induced by receptor activator of NF-B ligand (RANKL) in preosteoclasts. Malt1 deficiency did not impact osteoclast differentiation or activity in vitro. However, Malt1 deficient (Malt1 −/− ) mice had more osteoclasts in vivo and had lower levels of serum osteoprotegerin (OPG), an endogenous inhibitor of osteoclastogenesis. Inhibition of Malt1 activity in M s induced MCSF production, required for osteoclastogenesis, and decreased OPG production in response to inflammatory stimuli. In vitro, MCSF increased and OPG inhibited osteoclastogenesis, but effects were not enhanced in Malt1 deficient osteoclasts. These data support the hypothesis that Malt1 deficient mice develop an osteoporotic phenotype with increased osteoclastogenesis in vivo, but suggest that this is caused by inflammation rather than an effect of Malt1 deficiency in osteoclasts.

Background Crohn’s disease (CD) is a form of inflammatory bowel disease characterized by chronic inflammation along the gastrointestinal tract. We have described the SHIP-/- mouse model of CD-like intestinal inflammation. SHIP-/- mice develop spontaneous ileal inflammation that is characterized by villus hyperplasia and disorganization, edema, immune cell infiltration, ulceration, loss of goblet cells, and muscle wall thickening. SHIP deficiency in people with CD has been associated with a more severe and treatment-refractory disease. Interestingly, NOD2 gene variants, which are the most profound genetic associations for CD, are also associated with a more severe CD phenotype. Muramyl dipeptide (MDP) is a molecular associated microbial pattern, which activates the NOD2 signalling pathway. Recently, SHIP has been reported to play a role in the NOD2 pathway by disrupting the downstream interaction between RIPK2 and XIAP required for NOD2-mediated NFκB activation and pro-inflammatory cytokine production. Aims Based on this, we hypothesized that SHIP deficiency contributes to inflammation in CD by increasing NOD2-mediated pro-inflammatory cytokine production. Moreover, RIPK2 inhibitors will block intestinal inflammation caused by SHIP deficiency by blocking RIPK2-XIAP interactions required for NOD2 signalling and resultant pro-inflammatory cytokine production. To test this hypothesis, my aim was to determine the effect of RIPK2 inhibitors on the development of spontaneous intestinal inflammation in SHIP-/- mice. Methods 6 week-old SHIP-/- mice (and SHIP+/+ mice controls) were treated with RIPK2 inhibitors, FCG806791773 or Z1210264067, by intra-pertioneal injections every other day for 2 weeks and compared to SHIP-/- mice treated with 2% DMSO in PBS, as a vehicle control. On Day 14, distal ilea were harvested and gross pathology was assessed. Cross-sections of the ilea were H&E stained to evaluate histological damage based on villi architecture, edema, immune cell infiltration, ulceration, goblet cell loss, and muscle wall thickening. Results As expected, SHIP+/+ mice did not have gut pathology and their healthy gut phenotype was not affected by RIPK2 inhibitors. SHIP-/- mice had ileal inflammation that was evident in gross pathology and in H&E-stained tissue sections. Importantly, SHIP-/- mice treated with RIPK2 inhibitors, FCG806791773 or Z1210264067, had reduced gross pathology compared to vehicle control-treated mice. Z1210264067 treated SHIP-/- mice also had significantly lower histological damage compared to vehicle control-treated SHIP-/- mice. Conclusions RIPK2 inhibitors reduced gross and histopathology in SHIP-/- mice suggesting that RIPK2 inhibitors may be an effective treatment for people with CD, and may be particularly effective in people with CD, who harbor NOD2 risk variants and/or have low SHIP activity. Funding Agencies CCC, CIHR

Background: Primary immune deficiencies are often accompanied by intestinal inflammation. A patient with severe combined immunodeficiency and dramatic inflammation along the gastrointestinal tract was diagnosed with a homozygous mutation in MALT1. Malt1 acts both as a scaffolding protein and a protease. The consequences of MALT1 immunodeficiency have largely been attributed to its role in lymphocytes. However, macrophages play an important role in gut inflammation and Malt1 is activated in macrophages downstream of toll-like receptor 4 and dectin-1. The effect of MALT1 deficiency in macrophages and its contribution to gut inflammation has not been investigated. Aims: We hypothesized that Malt1 deficiency in murine macrophages increases susceptibility to DSS-induced colitis by increasing pro-inflammatory cytokine production. To address this hypothesis, we will determine: 1) whether Malt1 deficient mice are more susceptible to DSS-induced intestinal inflammation than wild type mice, and 2) the role of Malt1 expression and activity in pro-inflammatory macrophage responses. Methods: Malt1+/+ and Malt1 -/-mice were subjected to DSS-induced colitis and sacrificed for histology, immunohistochemistry, and tissue cytokine analyses by ELISA. Malt1 +/+ or Malt1

Background Intestinal epithelial cells may actively regulate homeostasis by recognizing and responding to extracellular signals. One of these cell types, tuft cells, has been proposed to have a role in secretion, absorption, and reception. However, their role in the intestine has not been fully characterized. We have found that tuft cells express the SH2 domain-containing inositol 5’-phosphatase (SHIP), which was formerly thought to be restricted to hematopoietic cells. SHIP negatively regulates PI3K-mediated cell growth, proliferation, and activation. Tuft cells secrete IL-25, which activates group 2 innate lymphoid cells (ILC2s), leading to type 2 immune responses. Tuft cells may contribute to inflammation in the intestine by increasing ILC2 numbers and/or activation, leading to type II inflammation. Aims My hypothesis is that SHIP inhibits tuft cell responses to innate immune stimuli by limiting PI3K activation. Moreover, SHIP deficiency will increase tuft cell responses to commensal microbes, causing ILC2-mediated type II inflammation. To investigate the role of SHIP in tuft cell responses in vivo, I will use a tuft cell-specific SHIP deficient mouse in the dextran sodium sulfate (DSS)-induced colitis model. Methods We created a mouse deficient in SHIP only in intestinal tuft cells (Fabpcre x SHIPfl/fl) to investigate the impact of SHIP deficiency in tuft cells on responses to luminal microbes. Tuft cell-specific SHIP deficient mice (8-week-old) and their wild type littermates were subjected to DSS-induced colitis for 7 days. Clinical disease activity was monitored daily and gross pathology, including total colon length, was examined at the experimental endpoint. The concentrations of pro-inflammatory type I and type II cytokines were assessed in colonic tissue homogenates via ELISA. Results During DSS-induced colitis, mice with SHIP deficient tuft cells had increased disease activity compared to their wild type littermates, particularly evident in their weight loss. Mice with SHIP deficient tuft cells also had significantly shorter colons than their wild type littermates. IL-25 concentrations (produced by tuft cells) were increased in full thickness colon homogenates from mice with SHIP deficient tuft cells. In contrast, pro-inflammatory cytokines IL-1β, IL-6, and TNF did not differ between genotypes. Thus, increased tuft cell activity due to SHIP deficiency correlated with increased disease severity during DSS-induced colitis. Conclusions SHIP deficiency in intestinal tuft cells leads to increased tuft cell activity and exacerbated colitis during DSS treatment. Tuft cells may contribute to inflammation via IL-25 production, leading to increased type II inflammation by ILC2s. In future studies, we will target IL-25 in this model to determine whether increased tuft cell IL-25 production plays a causal role in disease exacerbation. Funding Agencies NSERC