Inflammatory bowel disease (IBD) is a chronic inflammatory disorder characterized by alternating periods of remission and relapse. Current therapeutic options for maintaining long-term remission are limited, and no established animal model exists for evaluating relapse. We hypothesized that enhancing interleukin-10 (IL-10) production in intestinal macrophages could serve as a novel therapeutic strategy. Through the screening of a library of natural compounds derived from medicinal herbs, we identified berberine as a promising IL-10 enhancer. This study aimed to develop an experimental relapse model and elucidate the mechanism through which berberine promotes IL-10 production. Male C57BL/6 mice were subjected to two cycles of dextran sulfate sodium (DSS) treatment to induce colitis relapse. Bone marrow-derived macrophages (BMDMs) were treated with berberine before LPS stimulation, and IL-10 levels were measured. Drug affinity responsive target stability (DARTS) analysis was used to identify berberine-binding proteins. Berberine increased IL-10 expression in the colons of treated mice and suppressed colitis relapse when it was administered during the recovery phase. Additionally, berberine promoted colonic mucosal wound repair in vivo. In vitro, berberine enhanced LPS-induced IL-10 secretion by BMDMs. DARTS analysis revealed fatty acid synthase (FASN) as a direct berberine-binding protein. The FASN inhibitor cerulenin and Fasn knockdown both attenuated berberine-induced IL-10 production, suggesting a FASN-dependent augmentation pathway. These findings indicate that berberine suppresses colitis relapse by enhancing IL-10 production in macrophages via FASN binding. Our study highlights the increase in IL-10 levels through FASN as a promising strategy for maintaining remission in patients with IBD.

Neutrophils (PMN), the first immune cells recruited to site of mucosal injury, are critical for wound healing, but too little or too many neutrophils perturb mucosal repair resulting in chronic, poorly healing wounds, as seen in individuals with chronic inflammatory bowel disease (IBD). Despite the clinical significance of dysregulated PMN intestinal influx, many details underlying temporal regulation of PMN recruitment that maintain the balance between inflammation and repair remain unknown. Leukotriene B4 (LTB4), a potent chemoattractant binding the high-affinity receptor BLT1 on PMNs, is a well-established regulator of neutrophil recruitment. We recently demonstrated that BLT1 is also expressed on colonic epithelium, where epithelial BLT1-LTB4 signaling is critical for resolution of colonic mucosal wounds. While is it known that LTB4 is derived from arachidonic acid (AA) by the successive action of the enzyme 5-lipoxygenase (5-LO), and the terminal enzyme LTA4 hydrolase (LTA4H), the precise source of LTA4H and its role in mucosal wound repair is unknown. Using RNAscope in situ hybridization assay, we found that intestinal epithelial cells (IEC) adjoining mucosal wounds significantly upregulate Lta4h as early as 1hour post-injury. Single-cell RNA sequencing confirmed upregulation of Lta4h in murine colonic wounds, and colonoids from ulcerative colitis (UC) patients showed higher LTA4H expression than healthy controls, indicating that both injury and inflammation enhance epithelial LTA4H. To understand the role of epithelial LTA4H in resolution of mucosal injury, we generated mice selectively lacking LTA4H in IEC (Lta4hΔIEC). In vivo pinch biopsy-based colonoscopy revealed a significantly impaired wound healing in Lta4hΔIEC mice compared to controls. We are now investigating how epithelial LTA4H modulates PMN and monocyte recruitment to the wounds. In order to recapitulate a physiologically relevant microenvironment for our studies, we performed experiments under hypoxic conditions as observed in the gut, especially during inflammation. We observed that injury mediated hypoxia in mucosal wounds induce Lta4h expression in IECs via hypoxia-inducible factor (HIF) signaling. Our in-vitro data indicates that Lta4h and hypoxia inducible factors (Hif-1α and Hif-2α) are significantly upregulated under hypoxic conditions in primary mouse colonoids. Finally, we find that hypoxia driven LTA4H expression in IECs leads to increased LTB4 production. Overall, these findings demonstrate that upon mucosal injury, hypoxia mediated stabilization of HIFs in IEC regulate epithelial LTA4H expression and thereby LTB4 production to promote resolution of colonic mucosal injury. Our findings highlight a novel pro-repair function of LTA4H-LTB4 signaling during mucosal wound healing that’s perturbed in pathological conditions such as ulcerative colitis.

Ulcerative colitis (UC) is characterized by chronic mucosal inflammation, recurrent epithelial injury, and impaired colonic mucosal wound healing. While WNT/β-catenin dysregulation has been reported in UC, the mechanisms of such abnormalities remain unclear. To investigate epithelial intrinsic alterations associated with UC, we performed single-nucleus RNA-seq (snRNA-seq) and ATAC-seq (snATAC-seq) multiomics on human primary colonic epithelial cells (colonoids) from healthy donors and patients with inactive or active UC. Colonoids were cultured in a 3D matrix recapitulating crypt base cells or grown as 2D monolayers in differentiation medium to recapitulate luminal epithelial cells. Colonoids from active UC had a unique cell population with elevated CTNNB1 and reduced APC expression. Chromatin profiling identified enrichment of RUNX2 motifs in this UC-associated cell population. Active UC colonoids exhibited reduced OLFM4 expression in 3D and the differentiation marker VIL1 in 2D, suggesting impaired epithelial stem-cell maintenance and maturation. RUNX2 inhibition using CADD522 reduced β-catenin levels in 3D colonoids and restored VIL1 expression and junctional β-catenin localization in 2D cultures. These findings reveal an intrinsic defect in epithelial renewal in UC, driven in part by RUNX2-dependent WNT dysregulation. Our study identifies RUNX2 as a transcriptional regulator of epithelial stem cell function and WNT signaling in the inflamed human colon.

Polymorphonuclear neutrophils (PMNs) serve as frontline defenders against injury and infection, eliminating pathogens and initiating mucosal tissue repair. However, excessive PMN transepithelial migration (TEpM) contributes to chronic mucosal inflammatory disorders, including inflammatory bowel disease. PMN proinflammatory and pro-repair functions are regulated by incompletely defined signaling cascades involving kinases and phosphatases. Here, we determined how the protein tyrosine phosphatase CD45/PTPRC regulates PMN trafficking and effector functions in the gut. Pharmacologic inhibition of CD45 significantly reduced PMN colonic TEpM in vitro and in vivo and decreased intestinal PMN trafficking was observed in transgenic mice with PMN-specific deletion of Cd45 (MRP8-Cre;Cd45fl/fl). Beyond limiting TEpM, CD45 depletion impaired key antimicrobial functions, including degranulation and phagocytosis, indicating broader effects on PMN effector activity. Importantly, recovery from dextran sodium sulfate-induced colitis and biopsy-induced colonic wounding was delayed in MRP8-Cre;Cd45fl/fl mice, linking altered PMN function to defective mucosal healing. Mechanistically, CD45 depletion reduced surface expression of the β2 integrin CD11b/CD18 and inactivated the Src family kinase member Lyn. Together, these data highlight an important CD45/CD11b/Lyn signaling axis that regulates PMN trafficking and effector functions in the intestine and identify CD45 as a promising target for modulating PMN function to promote mucosal tissue repair.

The gastrointestinal epithelium depends on the apical junctional complex (AJC), composed of tight and adherens junctions, to regulate barrier function. Here, we identify the apical polarity protein Crumbs homolog 3 (CRB3) as an important regulator of AJC assembly and barrier function in intestinal epithelium. Using primary murine colonic epithelial cells (colonoids) from inducible, conditional Crb3-knockout (Crb3ERΔIEC) and control (Crb3fl/fl) mice, we show that CRB3 deficiency compromised barrier function that was associated with a hypercontractile perijunctional actomyosin network and impaired AJC assembly. Loss of CRB3 exacerbated proinflammatory cytokine-induced AJC remodeling, leading to increased intestinal permeability. Crb3ERΔIEC cells exhibited increased RhoA activity and junctional tension, which could be reversed by ROCK-II or myosin II inhibition, restoring junctional architecture. Mechanistically, CRB3A interacts with the actin cytoskeletal linker protein, Merlin (NF2) via its FERM-binding domain, and NF2 knockdown phenocopied CRB3 loss, suggesting their cooperative role in AJC assembly. These findings establish CRB3 and NF2 signaling as key regulators of perijunctional actomyosin contractility and AJC organization during both de novo junctional assembly and inflammation-induced remodeling. This work defines a CRB3- and NF2-dependent pathway by which epithelial cells regulate mechanical tension to coordinate barrier assembly during homeostasis and junctional remodeling under inflammatory stress.

Ulcerative colitis (UC) is characterized by chronic mucosal inflammation, recurrent epithelial injury, and impaired colonic mucosal wound healing. While WNT/β-catenin dysregulation has been reported in UC, the mechanisms of such abnormalities remain unclear. To investigate epithelial intrinsic alterations associated with UC, we performed single-nucleus RNA-seq (snRNA-seq) and ATAC-seq (snATAC-seq) multiomics on human primary colonic epithelial cells (colonoids) from healthy donors and patients with inactive or active UC. Colonoids were cultured in a 3D matrix recapitulating crypt base cells or grown as 2D monolayers in differentiation medium to recapitulate luminal epithelial cells. Colonoids from active UC had a unique cell population with elevated CTNNB1 and reduced APC expression. Chromatin profiling identified enrichment of RUNX2 motifs in this UC-associated cell population. Active UC colonoids exhibited reduced OLFM4 expression in 3D and the differentiation marker VIL1 in 2D, suggesting impaired self-renewal and maturation. RUNX2 inhibition using CADD522 reduced β-catenin levels in 3D colonoids and restored VIL1 expression and junctional β-catenin localization in 2D cultures. These findings reveal an intrinsic defect in epithelial renewal in UC, driven in part by RUNX2-dependent WNT dysregulation. Our study identifies RUNX2 as a transcriptional regulator of epithelial stem cell function and WNT signaling in the inflamed human colon.

Desmosomes are adhesive cell contacts abundant in tissues exposed to mechanical strain, such as the stratified and simple epithelia of the epidermis and mucous membranes, as well as the myocardium. Besides their role in mechanical cell cohesion, desmosomes also modulate pathways important for tissue differentiation, wound healing and immune responses. Dysfunctional desmosomes, resulting from pathogenic variants in genes encoding desmosomal components, autoantibodies targeting desmosomal adhesion molecules or inflammation, cause the life-threatening diseases arrhythmogenic cardiomyopathy and pemphigus and contribute to the pathogenesis of inflammatory bowel diseases. The Alpine Desmosome Disease Meeting 2024 (ADDM 2024), held in Grainau, Germany in October 2024, connected international researchers from basic sciences with clinical experts from dermatology, cardiology, gastroenterology and surgery. The participants discussed recent advances, identified hot topics in desmosome biology and disease and provided new concepts for pathogenesis and treatment approaches.

Increased reactive oxygen species (ROS) levels are a hallmark of inflammatory bowel disease (IBD) and constitute a major mechanism of epithelial cell death. Approaches to broadly inhibit ROS have had limited efficacy in treating IBD. Here we show that lipid peroxidation contributes to the pathophysiology of IBD by promoting ferroptosis, an iron-dependent form of programmed cell death. Mechanistically, we provide evidence of heterocellular crosstalk between intestinal fibroblasts and epithelial cells. In IBD tissues and mouse models of chronic colitis, acyl-CoA synthetase long-chain family 4 (ACSL4) is overexpressed in fibroblasts. ACSL4 in fibroblasts reprograms lipid metabolism and mediates intestinal epithelial cell sensitivity to ferroptosis. In mouse models, overexpressing ACSL4 in fibroblasts results in increased intestinal epithelial ferroptosis and worsened colitis, while pharmacological inhibition or deletion of fibroblast ACSL4 ameliorates colitis. Our work provides a targeted approach to therapeutic antioxidant treatments for IBD. Acyl-CoA synthetase long-chain family 4 (ACSL4)-driven changes in lipid metabolism are shown to modulate the sensitivity of intestinal epithelial cells to ferroptosis, thereby exacerbating inflammatory bowel disease.

The gastrointestinal epithelium serves as a critical barrier separating intestinal lumen contents from the underlying tissue environment. Structure and function of the apical junctional complex (AJC), comprising tight and adherens junctions, are essential for establishing and maintaining a polarized and functional epithelial barrier. In this study, we investigated mechanisms by which an apical polarity protein Crumbs homolog 3 (CRB3) regulates AJC assembly and barrier function in primary murine intestinal epithelial cells. Using primary colonic epithelial cells (colonoids) derived from inducible and conditional Crb3 knockdown (Crb3ERΔIEC) and control mice (Crb3fl/fl), we demonstrate that Crb3 loss leads to compromised epithelial barrier function that was associated with hypercontractile perijunctional actomyosin and defective assembly of the AJC. We identified CRB3 associates with the Band 4.1 family of cytoskeletal linker proteins, Merlin (NF2) via FERM (band4.1/ezrin/radixin/moesin) binding domain (FBD) of CRB3. Interestingly, NF2 knockdown in cultured intestinal epithelial cells phenocopied the effect of CRB3 deletion, supporting a coordinated role in AJC formation and barrier assembly. Moreover, increased active Rho was detected in assembling junctions of Crb3-null cells and inhibition of ROCKII and myosin II alleviated the hypercontractile phenotype, highlighting involvement of Rho/ROCK signaling. Additionally, increased vinculin localization at the AJC seen in Crb3-null epithelial cells indicates elevated tension at junctions. Our findings underscore the important role of Crb3 and NF2 in regulating contractility of the perijunctional actomyosin ring, mechanical tension at the AJC and barrier function via Rho/ROCK signaling during junctional assembly in intestinal epithelial cells.

BACKGROUND:Tissue repair and regeneration in the gastrointestinal system are crucial for maintaining homeostasis, with the process relying on intricate cellular interactions and affected by micro- and macro-nutrients. Iron, essential for various biological functions, plays a dual role in tissue healing by potentially causing oxidative damage and participating in anti-inflammatory mechanisms, underscoring its complex relationship with inflammation and tissue repair. OBJECTIVE:The study aimed to elucidate the role of low dietary iron in gastrointestinal tissue repair. METHODS:We utilized quantitative iron measurements to assess iron levels in inflamed regions of patients with ulcerative colitis and Crohn's disease. In addition, 3 mouse models of gastrointestinal injury/repair (dextran sulfate sodium-induced colitis, radiation injury, and wound biopsy) were used to assess the effects of low dietary iron on tissue repair. RESULTS:We found that levels of iron in inflamed regions of both patients with ulcerative colitis and Crohn's disease are elevated. Similarly, during gastrointestinal repair, iron levels were found to be heightened, specifically in intestinal epithelial cells across the 3 injury/repair models. Mice on a low-iron diet showed compromised tissue repair with reduced proliferation. In standard diet, epithelial cells and the stem cell compartment maintain adequate iron stores. However, during a period of iron deficiency, epithelial cells exhaust their iron reserves, whereas the stem cell compartments maintain their iron pools. During injury, when the stem compartment is disrupted, low iron levels impair proliferation and compromise repair mechanisms. CONCLUSIONS:Low dietary iron impairs intestinal repair through compromising the ability of epithelial cells to aid in intestinal proliferation.

Food allergy is a prevalent, potentially deadly disease caused by inadvertent sensitization to benign food antigens. Pathogenic Th2 cells are a major driver for disease, and allergen-specific immunotherapies (AIT) aim to increase the allergen threshold required to elicit severe allergic symptoms. However, the majority of AIT approaches require lengthy treatments and convey transient disease suppression, likely due to insufficient targeting of pathogenic Th2 responses. Here, the ability of allergen-encapsulating nanoparticles to directly suppress pathogenic Th2 responses and reactivity is investigated in a mouse model of food allergy. NPs associate with pro-tolerogenic antigen presenting cells, provoking accumulation of antigen-specific, functionally suppressive regulatory T cells in the small intestine lamina propria. Two intravenous doses of allergen encapsulated in poly(lactide-co-glycolide) nanoparticles (NPs) significantly reduces oral food challenge (OFC)-induced anaphylaxis. Importantly, NP treatment alters the fates of pathogenic allergen-specific Th2 cells, reprogramming these cells toward CD25 + FoxP3 + regulatory and CD73 + FR4 + anergic phenotypes. NP-mediated reductions in the frequency of effector cells in the gut and mast cell degranulation following OFC are also demonstrated. These studies reveal mechanisms by which an allergen-encapsulating NP therapy and, more broadly, allergen-specific immunotherapies, can rapidly attenuate allergic responses by targeting pathogenic Th2 cells.

BACKGROUND & AIMS: CXADR-like membrane protein (CLMP) is structurally related to coxsackie and adenovirus receptor. Pathogenic variants in CLMP gene have been associated with congenital short bowel syndrome, implying a role for CLMP in intestinal development. However, the contribution of CLMP to regulating gut development and homeostasis is unknown. METHODS: In this study, we investigated CLMP function in the colonic epithelium using complementary in vivo and in vitro approaches, including mice with inducible intestinal epithelial cell (IEC)-specific deletion of CLMP (ClmpDIEC), intestinal organoids, IECs with overexpression, or loss of CLMP and RNA sequencing data from individuals with colorectal cancer. RESULTS: Loss of CLMP enhanced IEC proliferation and, conversely, CLMP overexpression reduced proliferation. Xenograft experiments revealed increased tumor growth in mice implanted with CLMP-deficient colonic tumor cells, and poor engraftment was observed with CLMP-overexpressing cells. ClmpDIEC mice showed exacerbated tumor burden in an azoxymethane and dextran sulfate sodium-induced colonic tumorigenesis model, and CLMP expression was reduced in human colorectal cancer samples. Mechanistic studies revealed that CLMP-dependent regulation of IEC proliferation is linked to signaling through mTOR-Akt-b-catenin pathways. CONCLUSIONS: These results reveal novel insights into CLMP function in the colonic epithelium, highlighting an important role in regulating IEC proliferation, suggesting tumor supin

Abstract Intestinal epithelium maintains gut homeostasis by protecting the underlying tissue compartments from harmful contents. Although it is suggested that epithelial barrier function compromise contributes to the pathogenesis of inflammatory bowel disease (IBD), the underlying mechanisms are not well understood. Claudins (CLDN) are tight junctions (TJ) proteins that determine epithelial barrier properties during homeostasis and whose expression is altered in IBD, thereby contributing to a leaky barrier. We recently identified the expression of an atypical CLDN family member, CLDN23, in the regulation of homeostatic intestinal epithelial barrier function. Analysis of the human colonic crypt-luminal axis revealed increased CLDN23 expression in differentiated intestinal epithelial cells (IEC) facing the lumen compared to the proliferative crypt-base IECs. Complementary cell biologic approaches using IEC-specific Cldn23 knockout mice (Cldn23ERΔIEC) and human colon cell lines revealed that CLDN23 strengthens epithelial barrier function. Mechanistically, CLDN23 promoted redistribution of barrier-forming CLDN3 and CLDN4 from the lateral membrane to the TJ through cis- and trans-interactions, resulting in narrowed CLDN3 and CLDN4 pore diameters. Since inflammation compromises the epithelial barrier and contributes to disease pathogenesis in IBD, we first examined CLDN23 expression in colonic mucosal tissue from IBD individuals. Immunofluorescence and RNA scope labeling revealed that CLDN23 expression was significantly decreased in colonic epithelial cells of IBD individuals. Furthermore, reduced CLDN23 expression was also detected in primary colonic epithelial cells (colonoids) from mice treated with pro-inflammatory cytokines TNFα and IFNγ compared to untreated colonoids. Barrier function assays of control Cldn23f/f and Cldn23ERΔIEC mice-derived colonoids treated with TNFα and IFNγ identified decreased transepithelial electrical resistance in colonoids lacking CLDN23 and treated with these pro-inflammatory cytokines. These findings suggest a protective role for CLDN23 in regulating barrier function under homeostatic and inflammatory conditions.