Death in the intestinal epithelium-basic biology and implications for inflammatory bowel disease

Expression of HIF1α in intestinal epithelium restricts arthritis inflammation by inhibiting RIPK3-induced cell death machinery

OBJECTIVES

To investigate the mechanism by which intestinal epithelial cell (IEC) death induces arthritis.

METHODS

IEC death was assessed by staining for necroptosis and apoptosis markers and fluorescence in situ hybridisation at different time points during collagen-induced arthritis (CIA). During the development of CIA, messenger RNA (mRNA) sequencing was performed, followed by Gene Ontology enrichment analysis of differentially expressed genes. Mice deficient for hypoxia-inducible factor 1α (Hif1a) in IECs (Hif1a ∆IEC) were generated and induced for arthritis. mRNA sequencing, chromatin immunoprecipitated (ChIP) DNA sequencing and ChIP-qualitative PCR were performed on IECs from Hif1a ∆IEC mice and littermate controls. Effects of HIF1α stabilisation by inhibition of prolyl hydroxylase domain-containing enzymes and treatment with the inhibitor of receptor-interacting protein kinase-3 (RIPK3) were tested in intestinal organoids and in CIA.

RESULTS

IEC underwent apoptotic and necroptotic cell death at the onset of arthritis, leading to impaired gut barrier function. HIF1α was identified as one of the most upregulated genes in IECs during the onset of arthritis. Deletion of Hif1a in IEC enhanced IEC necroptosis, triggered intestinal inflammation and exacerbated arthritis. HIF1α was found to be a key transcriptional repressor for the necroptosis-inducing factor RIPK3. Enhanced RIPK3 expression, indicating necroptosis, was also found in the intestinal epithelium of patients with new-onset rheumatoid arthritis. Therapeutic stabilisation of HIF1α as well as small-molecule-based RIPK3 inhibition rescued intestinal necroptosis in vitro and in vivo and suppressed the development of arthritis.

CONCLUSION

Our results identify IEC necroptosis as a critical link between the gut and the development of arthritis.

Cryptosporidium impacts epithelial turnover and is resistant to induced death of the host cell

Infection with the apicomplexan parasite Cryptosporidium is a leading cause of diarrheal disease. Cryptosporidiosis is of particular importance in infants and shows a strong association with malnutrition, both as a risk factor and as a consequence. Cryptosporidium invades and replicates within the small intestine epithelial cells. This is a highly dynamic tissue that is developmentally stratified along the villus axis. New cells emerge from a stem cell niche in the crypt and differentiate into mature epithelial cells while moving toward the villus tip, where they are ultimately shed. Here, we studied the impact of Cryptosporidium infection on this dynamic architecture. Tracing DNA synthesis in pulse-chase experiments in vivo, we quantified the genesis and migration of epithelial cells along the villus. We found proliferation and epithelial migration to be elevated in response to Cryptosporidium infection. Infection also resulted in significant cell loss documented by imaging and molecular assays. Consistent with these observations, single-cell RNA sequencing of infected intestines showed a gain of young and a loss of mature cells. Interestingly, enhanced epithelial cell loss was not a function of enhanced apoptosis of infected cells. To the contrary, Cryptosporidium-infected cells were less likely to be apoptotic than bystanders, and experiments in tissue culture demonstrated that infection provided enhanced resistance to chemically induced apoptosis to the host but not bystander cells. Overall, this study suggests that Cryptosporidium may modulate cell apoptosis and documents pronounced changes in tissue homeostasis due to parasite infection, which may contribute to its long-term impact on the developmental and nutritional state of children.

IMPORTANCE

The intestine must balance its roles in digestion and nutrient absorption with the maintenance of an effective barrier to colonization and breach by numerous potential pathogens. An important component of this balance is its constant turnover, which is modulated by a gain of cells due to proliferation and loss due to death or extrusion. Here, we report that Cryptosporidium infection changes the dynamics of this process increasing both gain and loss of enterocytes speeding up the villus elevator. This leads to a much more immature epithelium and a reduction of the number of those cells typically found toward the villus apex best equipped to take up key nutrients including carbohydrates and lipids. These changes in the cellular architecture and physiology of the small intestine may be linked to the profound association between cryptosporidiosis and malnutrition.

The Postbiotic Properties of Butyrate in the Modulation of the Gut Microbiota: The Potential of Its Combination with Polyphenols and Dietary Fibers

The gut microbiota is a diverse bacterial community consisting of approximately 2000 species, predominantly from five phyla: Firmicutes, Bacteroidetes, Actinobacteria, Proteobacteria, and Verrucomicrobia. The microbiota's bacterial species create distinct compounds that impact the host's health, including well-known short-chain fatty acids. These are produced through the breakdown of dietary fibers and fermentation of undigested carbohydrates by the intestinal microbiota. The main short-chain fatty acids consist of acetate, propionate, and butyrate. The concentration of butyrate in mammalian intestines varies depending on the diet. Its main functions are use as an energy source, cell differentiation, reduction in the inflammatory process in the intestine, and defense against oxidative stress. It also plays an epigenetic role in histone deacetylases, thus helping to reduce the risk of colon cancer. Finally, butyrate affects the gut-brain axis by crossing the brain-blood barrier, making it crucial to determine the right concentrations for both local and peripheral effects. In recent years, there has been a significant amount of attention given to the role of dietary polyphenols and fibers in promoting human health. Polyphenols and dietary fibers both play crucial roles in protecting human health and can produce butyrate through gut microbiota fermentation. This paper aims to summarize information on the key summits related to the negative correlation between intestinal microbiota diversity and chronic diseases to guide future research on determining the specific activity of butyrate from polyphenols and dietary fibers that can carry out these vital functions.

In situ profiling reveals spatially metabolic injury in the initiation of polystyrene nanoplastic-derived intestinal epithelial injury in mice

Despite increasing concerns regarding the harmful effects of plastic-induced gut injury, mechanisms underlying the initiation of plastic-derived intestinal toxicity remain unelucidated. Here, mice were subjected to long-term exposure to polystyrene nanoplastics (PS-NPs) of varying sizes (80, 200, and 1000 nm) at doses relevant to human dietary exposure. PS-NPs exposure did not induce a significant inflammatory response, histopathological damage, or intestinal epithelial dysfunction in mice at a dosage of 0.5 mg/kg/day for 28 days. However, PS-NPs were detected in the mouse intestine, coupled with observed microstructural changes in enterocytes, including mild villous lodging, mitochondrial membrane rupture, and endoplasmic reticulum (ER) dysfunction, suggesting that intestinal-accumulating PS-NPs resulted in the onset of intestinal epithelial injury in mice. Mechanistically, intragastric PS-NPs induced gut microbiota dysbiosis and specific bacteria alterations, accompanied by abnormal metabolic fingerprinting in the plasma. Furthermore, integrated data from mass spectrometry imaging-based spatial metabolomics and metallomics revealed that PS-NPs exposure led to gut dysbiosis-associated host metabolic reprogramming and initiated intestinal injury. These findings provide novel insights into the critical gut microbial-host metabolic remodeling events vital to nanoplastic-derived-initiated intestinal injury.

Chronic spindle assembly checkpoint activation causes myelosuppression and gastrointestinal atrophy

Interference with microtubule dynamics in mitosis activates the spindle assembly checkpoint (SAC) to prevent chromosome segregation errors. The SAC induces mitotic arrest by inhibiting the anaphase-promoting complex (APC) via the mitotic checkpoint complex (MCC). The MCC component MAD2 neutralizes the critical APC cofactor, CDC20, preventing exit from mitosis. Extended mitotic arrest can promote mitochondrial apoptosis and caspase activation. However, the impact of mitotic cell death on tissue homeostasis in vivo is ill-defined. By conditional MAD2 overexpression, we observe that chronic SAC activation triggers bone marrow aplasia and intestinal atrophy in mice. While myelosuppression can be compensated for, gastrointestinal atrophy is detrimental. Remarkably, deletion of pro-apoptotic Bim/Bcl2l11 prevents gastrointestinal syndrome, while neither loss of Noxa/Pmaip or co-deletion of Bid and Puma/Bbc3 has such a protective effect, identifying BIM as rate-limiting apoptosis effector in mitotic cell death of the gastrointestinal epithelium. In contrast, only overexpression of anti-apoptotic BCL2, but none of the BH3-only protein deficiencies mentioned above, can mitigate myelosuppression. Our findings highlight tissue and cell-type-specific survival dependencies in response to SAC perturbation in vivo.

Double-negative B cells and DNASE1L3 colocalise with microbiota in gut-associated lymphoid tissue

Intestinal homeostasis is maintained by the response of gut-associated lymphoid tissue to bacteria transported across the follicle associated epithelium into the subepithelial dome. The initial response to antigens and how bacteria are handled is incompletely understood. By iterative application of spatial transcriptomics and multiplexed single-cell technologies, we identify that the double negative 2 subset of B cells, previously associated with autoimmune diseases, is present in the subepithelial dome in health. We show that in this location double negative 2 B cells interact with dendritic cells co-expressing the lupus autoantigens DNASE1L3 and C1q and microbicides. We observe that in humans, but not in mice, dendritic cells expressing DNASE1L3 are associated with sampled bacteria but not DNA derived from apoptotic cells. We propose that fundamental features of autoimmune diseases are microbiota-associated, interacting components of normal intestinal immunity.

The shared circulating diagnostic biomarkers and molecular mechanisms of systemic lupus erythematosus and inflammatory bowel disease

Background

Systemic lupus erythematosus (SLE) is a multi-organ chronic autoimmune disease. Inflammatory bowel disease (IBD) is a common chronic inflammatory disease of the gastrointestinal tract. Previous studies have shown that SLE and IBD share common pathogenic pathways and genetic susceptibility, but the specific pathogenic mechanisms remain unclear.

Methods

The datasets of SLE and IBD were downloaded from the Gene Expression Omnibus (GEO). Differentially expressed genes (DEGs) were identified using the Limma package. Weighted gene coexpression network analysis (WGCNA) was used to determine co-expression modules related to SLE and IBD. Pathway enrichment was performed using Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis for co-driver genes. Using the Least AbsoluteShrinkage and Selection Operator (Lasso) regressionand Support Vector Machine-Recursive Feature Elimination (SVM-RFE), common diagnostic markers for both diseases were further evaluated. Then, we utilizedthe CIBERSORT method to assess the abundance of immune cell infiltration. Finally,we used the single-cell analysis to obtain the location of common diagnostic markers.

Results

71 common driver genes were identified in the SLE and IBD cohorts based on the DEGs and module genes. KEGG and GO enrichment results showed that these genes were closely associated with positive regulation of programmed cell death and inflammatory responses. By using LASSO regression and SVM, five hub genes (KLRF1, GZMK, KLRB1, CD40LG, and IL-7R) were ultimately determined as common diagnostic markers for SLE and IBD. ROC curve analysis also showed good diagnostic performance. The outcomes of immune cell infiltration demonstrated that SLE and IBD shared almost identical immune infiltration patterns. Furthermore, the majority of the hub genes were commonly expressed in NK cells by single-cell analysis.

Conclusion

This study demonstrates that SLE and IBD share common diagnostic markers and pathogenic pathways. In addition, SLE and IBD show similar immune cellinfiltration microenvironments which provides newperspectives for future treatment.

Toward a predictive understanding of epithelial cell death

Epithelial cell death is highly prevalent during development and tissue homeostasis. While we have a rather good understanding of the molecular regulators of programmed cell death, especially for apoptosis, we still fail to predict when, where, how many and which specific cells will die in a tissue. This likely relies on the much more complex picture of apoptosis regulation in a tissular and epithelial context, which entails cell autonomous but also non-cell autonomous factors, diverse feedback and multiple layers of regulation of the commitment to apoptosis. In this review, we illustrate this complexity of epithelial apoptosis regulation by describing these different layers of control, all demonstrating that local cell death probability is a complex emerging feature. We first focus on non-cell autonomous factors that can locally modulate the rate of cell death, including cell competition, mechanical input and geometry as well as systemic effects. We then describe the multiple feedback mechanisms generated by cell death itself. We also outline the multiple layers of regulation of epithelial cell death, including the coordination of extrusion and regulation occurring downstream of effector caspases. Eventually, we propose a roadmap to reach a more predictive understanding of cell death regulation in an epithelial context.

Non-professional efferocytosis of Salmonella-infected intestinal epithelial cells in the neonatal host

The intestinal epithelium is the first line of defense against enteric pathogens. Removal of infected cells by exfoliation prevents mucosal translocation and systemic infection in the adult host, but is less commonly observed in the neonatal intestine. Instead, here, we describe non-professional efferocytosis of Salmonella-infected enterocytes by neighboring epithelial cells in the neonatal intestine. Intestinal epithelial stem cell organoid cocultures of neonatal and adult cell monolayers with damaged enterocytes replicated this observation, confirmed the age-dependent ability of intestinal epithelial cells for efferocytosis, and identified the involvement of the "eat-me" signals and adaptors phosphatidylserine and C1q as well as the "eat-me" receptors integrin-αv (CD51) and CD36 in cellular uptake. Consistent with this, massive epithelial cell membrane protrusions and CD36 accumulation at the contact site with apoptotic cells were observed in the infected neonatal host in vivo. Efferocytosis of infected small intestinal enterocytes by neighboring epithelial cells may represent a previously unrecognized mechanism of neonatal antimicrobial host defense to maintain barrier integrity.

Luminol-conjugated cyclodextrin biological nanoparticles for the treatment of severe burn-induced intestinal barrier disruption

Background

The breakdown of intestinal barrier integrity occurs after severe burn injury and is responsible for the subsequent reactions of inflammation and oxidative stress. A new protective strategy for the intestinal barrier is urgently needed due to the limitations of the traditional methods. Recently, the application of nanoparticles has become one of the promising therapies for many inflammation-related diseases or oxidative damage. Herein, we developed a new anti-inflammatory and antioxidant nanoparticle named luminol-conjugated cyclodextrin (LCD) and aimed to evaluate its protective effects in severe burn-induced intestinal injury.

Methods

First, LCD nanoparticles, engineered with covalent conjugation between luminol and β-cyclodextrin (β-CD), were synthesized and examined. Then a mouse burn model was successfully established before the mouse body weight, intestinal histopathological manifestation, permeability, tight junction (TJ) expression and pro-inflammatory cytokines were determined in different groups. The proliferation, apoptosis, migration and reactive oxygen species (ROS) of intestinal epithelial cells (IECs) were assessed. Intraepithelial lymphocytes (IELs) were isolated and cultured for analysis by flow cytometry.

Results

LCD nanoparticle treatment significantly relieved the symptoms of burn-induced intestinal injury in the mouse model, including body weight loss and intestinal permeability abnormalities. Moreover, LCD nanoparticles remarkably recovered the mechanical barrier of the intestine after severe burn, renewed TJ structures, promoted IEC proliferation and migration, and inhibited IEC apoptosis. Mechanistically, LCD nanoparticles dramatically alleviated pro-inflammation factors (tumor necrosis factor-α, IL-17A) and ROS accumulation, which could be highly involved in intestinal barrier disruption. Furthermore, an increase in IL-17A and the proportion of IL-17A+Vγ4+ γδ T subtype cells was also observed in vitro in LPS-treated Vγ4+ γδ T cells, but the use of LCD nanoparticles suppressed this increase.

Conclusions

Taken together, these findings demonstrate that LCD nanoparticles have the protective ability to ameliorate intestinal barrier disruption and provide a therapeutic intervention for burn-induced intestinal injury.

L-theanine attenuates H2O2-induced inflammation and apoptosis in IPEC-J2 cells via inhibiting p38 MAPK signaling pathway

This study investigated the protective effects of L-theanine on hydrogen peroxide (H2O2)-induced intestinal barrier dysfunction in IPEC-J2 cells. Results showed that L-theanine reduced H2O2-induced IPEC-J2 cells inflammation and apoptosis, and decreased protein phosphorylation levels of p38 mitogen-activated protein kinase (p38 MAPK) and nuclear factor kappa-B (NF-κB). The p38 MAPK inhibitor (SB203580) decreased oxidative stress, the protein expression of phosphorylation of p38 MAPK and NF-κB, the H2O2-induced increase in mRNA expression of pro-apoptotic and pro-inflammatory related genes expression and secretion, and tight junction protein related genes expression, which was similar to the effect of L-theanine. In conclusion, L-theanine inhibited H2O2-induced oxidative damage and inflammatory reaction, eliminated apoptosis, and protected intestinal epithelial barrier damage by inhibiting the activation of p38 MAPK signaling pathway.

Submucosal Injection of the RNA Oligonucleotide GUT-1 in Active Ulcerative Colitis Patients: A Randomized, Double-Blind, Placebo-Controlled Phase 2a Induction Trial

BACKGROUND AND AIMS

Carbohydrate sulfotransferase 15 [CHST15] biosynthesizes sulphated matrix glycosaminoglycans and is implicated in intestinal inflammation and fibrosis. Here, we evaluate the efficacy and safety of the double-stranded RNA oligonucleotide GUT-1, a specific blocker of CHST15, as induction therapy in patients with ulcerative colitis [UC].

METHODS

In this randomized, double-blind, placebo-controlled, phase 2a study, we enrolled endoscopically active UC patients, refractory to conventional therapy, in five hospital centres across Germany. Patients were randomized 1:1:1 using a block randomized technique to receive a single dosing of 25 nM GUT-1, 250 nM GUT-1, or placebo by endoscopic submucosal injections. The primary outcome measure was improvement of endoscopic lesions at weeks 2 or 4. The secondary outcome measures included clinical and histological responses. Safety was assessed in all patients who received treatment.

RESULTS

Twenty-eight patients were screened, 24 were randomized, and 21 were evaluated. Endoscopic improvement at weeks 2 or 4 was achieved by 71.4% in the GUT-1 250 nM, 0% in the GUT-1 25 nM, and 28.6% in the placebo group. Clinical remission was shown by 57.1% in the GUT-1 250 nM, 0% in the GUT-1 25 nM, and 14.3% in the placebo groups. Histological improvement was shown by 42.9% in the GUT-1 250 nM, 0% in the GUT-1 25 nM, and 0% in the placebo groups. GUT-1 250 nM reduced CHST15 expression significantly and suppressed mucosal inflammation and fibrosis. GUT-1 application was well tolerated.

CONCLUSION

Single dosing by submucosal injection of GUT-1 repressed CHST15 mucosal expression and may represent a novel induction therapy by modulating tissue remodelling in UC.

Staying away from the breaking point: Probing the limits of epithelial cell elimination

Epithelial tissues are dramatically remodelled during embryogenesis and tissue homeostasis and yet need to maintain their sealing properties to sustain their barrier functions at any time. Part of these remodellings involve the elimination of a large proportion of cells through apoptosis. Cell extrusion, the remodelling steps leading to seamless dying cell expulsion, helps to maintain tissue cohesion. However, there is an intrinsic limit in the system that can only accommodate a certain proportion/rate of cell elimination as well as certain spatiotemporal distributions. What are then the critical conditions leading to epithelial rupture/tear/sealing defects upon cell elimination and which mechanisms ensure that such limits are never reached? In this short review, I document the conditions in which epithelial rupture has been observed, including in the contexts of epithelial cell death, and the mechanical parameters influencing tissue rupture, and review feedback mechanisms which help to keep the epithelia away from the breaking point.

A dual role of lysophosphatidic acid type 2 receptor (LPAR2) in nonsteroidal anti-inflammatory drug-induced mouse enteropathy

Lysophosphatidic acid (LPA) is a bioactive phospholipid mediator that has been found to ameliorate nonsteroidal anti-inflammatory drug (NSAID)-induced gastric injury by acting on lysophosphatidic acid type 2 receptor (LPAR2). In this study, we investigated whether LPAR2 signaling was implicated in the development of NSAID-induced small intestinal injury (enteropathy), another major complication of NSAID use. Wild-type (WT) and Lpar2 deficient (Lpar2-/-) mice were treated with a single, large dose (20 or 30 mg/kg, i.g.) of indomethacin (IND). The mice were euthanized at 6 or 24 h after IND treatment. We showed that IND-induced mucosal enteropathy and neutrophil recruitment occurred much earlier (at 6 h after IND treatment) in Lpar2-/- mice compared to WT mice, but the tissue levels of inflammatory mediators (IL-1β, TNF-α, inducible COX-2, CAMP) remained at much lower levels. Administration of a selective LPAR2 agonist DBIBB (1, 10 mg/kg, i.g., twice at 24 h and 30 min before IND treatment) dose-dependently reduced mucosal injury and neutrophil activation in enteropathy, but it also enhanced IND-induced elevation of several proinflammatory chemokines and cytokines. By assessing caspase-3 activation, we found significantly increased intestinal apoptosis in IND-treated Lpar2-/- mice, but it was attenuated after DBIBB administration, especially in non-obese diabetic/severe combined immunodeficiency (NOD/SCID) mice. Finally, we showed that IND treatment reduced the plasma activity and expression of autotaxin (ATX), the main LPA-producing enzyme, and also reduced the intestinal expression of Lpar2 mRNA, which preceded the development of mucosal damage. We conclude that LPAR2 has a dual role in NSAID enteropathy, as it contributes to the maintenance of mucosal integrity after NSAID exposure, but also orchestrates the inflammatory responses associated with ulceration. Our study suggests that IND-induced inhibition of the ATX-LPAR2 axis is an early event in the pathogenesis of enteropathy.

Epigenetic modification of m6A methylation: Regulatory factors, functions and mechanism in inflammatory bowel disease

Although the exact cause of inflammatory bowel disease (IBD) is still unknown, there is a lot of evidence to support the notion that it results from a combination of environmental factors, immune system issues, gut microbial changes, and genetic susceptibility. In recent years, the role of epigenetics in the pathogenesis of IBD has drawn increasing attention. The regulation of IBD-related immunity, the preservation of the intestinal epithelial barrier, and autophagy are all significantly influenced by epigenetic factors. The most extensive epigenetic methylation modification of mammalian mRNA among them is N6-methyladenosine (m6A). It summarizes the general structure and function of the m6A regulating factors, as well as their complex effects on IBD by regulating the intestinal mucous barrier, intestine mucosal immunity, epidermal cell death, and intestinal microorganisms.This paper provides key insights for the future identification of potential new targets for the diagnosis and treatment of IBD.

Epithelial CRL4DCAF2 Is Critical for Maintaining Intestinal Homeostasis Against DSS-Induced Colitis by Regulating the Proliferation and Repair of Intestinal Epithelial Cells

BACKGROUND AND AIMS

Inflammatory bowel disease (IBD) is currently gaining an increasing global interest. Intestinal epithelial barrier dysfunction is crucial toward developing IBD; however, the underlying mechanisms are not yet elucidated. This study is aimed at elucidating the function of CRL4DCAF2, an E3 ligase, toward mediating intestinal homeostasis.

METHODS

Colon samples were collected from patients with IBD and healthy individuals to examine the expression of CRL4DCAF2. CRL4DCAF2 conditional knockdown in mouse intestinal epithelial cells (IECs) (DCAF2EKD) were constructed. DCAF2EKD and their littermate control (DCAF2EWT) were treated with dextran sodium sulfate (DSS) to induce acute colitis. Transcriptome analysis was performed on inflamed colon samples obtained from the mice. Cell cycle regulators were evaluated using real-time polymerase chain reaction (PCR), while tight junction and apoptosis proteins were examined via immunofluorescence and western blot.

RESULTS

CRL4DCAF2 expression was significantly decreased in the inflamed IBD epithelium, and low expression of CRL4DCAF2 associated with high recurrence risk. Mice with DCAF2 specific knockout in IECs suffer from embryonic death. Multiple genes involved in cell proliferation, immune response, and gap junction were differentially expressed in inflamed colon from DCAF2EKD compared with DCAF2EWT. Furthermore, conditional downregulation of CRL4DCAF2 in the intestinal epithelium induced primarily epithelial damage, increased intestinal permeability, and diminished tight junction protein expression. In vivo and in vitro cell transfection experiments revealed that CRL4DCAF2 enhanced cell proliferation by promoting p21 ubiquitination and degradation, thereby inhibiting G2/M cell cycle. In addition, CRL4DCAF2 can also inhibit IEC apoptosis and promote cell autophagy.

CONCLUSIONS

CRL4DCAF2 downregulation in IECs promotes intestinal barrier dysfunction and inhibits IEC proliferation, thus making it more susceptible to inflammation.

Design and validation of a dual-fluorescence reporter system to monitor bacterial gene expression in the gut environment

Fluorescence-based reporter systems are valuable tools for studying gene expression dynamics in living cells. However, available strategies to follow gene expression in bacteria within their natural ecosystem that can be typically rich and complex are scarce. In this work, we designed a plasmid-based tool ensuring both the identification of a strain of interest in complex environments and the monitoring of gene expression through the combination of two distinct fluorescent proteins as reporter genes. The tool was validated in Escherichia coli to monitor the expression of eut genes involved in the catabolism of ethanolamine. We demonstrated that the constructed reporter strain gradually responds with a bimodal output to increasing ethanolamine concentrations during in vitro cultures. The reporter strain was next inoculated to mice, and flow cytometry was used to detect the reporter strain among the dense microbiota of intestinal samples and to analyze specifically the expression of eut genes. This novel dual-fluorescent reporter system would be helpful to evaluate transcriptional processes in bacteria within complex environments. KEY POINTS: • A reporter tool was developed to monitor bacterial gene expression in complex environments. • Ethanolamine utilization (eut) genes are expressed by commensal E. coli in the mouse gut. • Expression of eut genes follows a bimodal distribution.

Defects in microvillus crosslinking sensitize to colitis and inflammatory bowel disease

Intestinal epithelial cells are covered by the brush border, which consists of densely packed microvilli. The Intermicrovillar Adhesion Complex (IMAC) links the microvilli and is required for proper brush border organization. Whether microvillus crosslinking is involved in the intestinal barrier function or colitis is currently unknown. We investigate the role of microvillus crosslinking in colitis in mice with deletion of the IMAC component CDHR5. Electron microscopy shows pronounced brush border defects in CDHR5-deficient mice. The defects result in severe mucosal damage after exposure to the colitis-inducing agent DSS. DSS increases the permeability of the mucus layer and brings bacteria in direct contact with the disorganized brush border of CDHR5-deficient mice. This correlates with bacterial invasion into the epithelial cell layer which precedes epithelial apoptosis and inflammation. Single-cell RNA sequencing data of patients with ulcerative colitis reveals downregulation of CDHR5 in enterocytes of diseased areas. Our results provide experimental evidence that a combination of microvillus crosslinking defects with increased permeability of the mucus layer sensitizes to inflammatory bowel disease.

[Acetylcorynoline relieves 2, 4, 6-trinitrobenesulfonic acid-induced Crohn's disease-like colitis in mice by regulating intestinal epithelial cell apoptosis]

OBJECTIVE

To explore the effect of acetylcorynoline for relieving 2, 4, 6-trinitrobenzenesulfonic acid (TNBS)-induced Crohn's disease (CD)-like colitis in mice and explore the underlying mechanism.

METHODS

Male C57BL/6 mice were subjected to TNBS treatment to establish models of TNBS-induced CD-like colitis, followed by treatment with saline or 10, 20, or 40 mg/kg acetylcorynoline by gavage. The protective effect of acetylcorynoline against colitis was evaluated by monitoring body weight changes, measurement of DAI and colon length, and histological examination. The colon tissues and cultured colon organoids treated with LPS and acetylcorynoline were examined for expressions of tight junction proteins and apoptosis-related proteins using immunofluorescence assay, Western blotting, and TUNEL staining. The mechanism of acetylcorynoline-induced inhibition of intestinal epithelial cell apoptosis was predicted by network pharmacology and verified by Western blotting.

RESULTS

Acetylcorynoline treatment significantly alleviated weight loss and colon length shortening and reduced DAI score and inflammation score in TNBS mice (P < 0.05). Claudin-1 was significantly upregulated in the colon tissue of acetylcorynolinetreated mice (P < 0.05), where the protein levels of claudin-1, ZO-1, and Bcl-2 were increased and C-caspase3 and Bax were reduced (P < 0.05) and the number of apoptotic intestinal epithelial cells decreased (P < 0.05). In cultured colon organoids, acetylcorynoline significantly increased ZO-1, claudin-1 and Bcl-2 expressions and decreased C-caspase3 and Bax expressions (P < 0.05). KEGG pathway enrichment analysis suggested that the PI3K- AKT signaling pathway was correlated with acetylcorynoline treatment for CD, and the expressions of p-AKT and p-PI3K decreased significantly after the treatment in both the in vivo and in vitro models (P < 0.05). The PI3K-AKT activator (740Y-P) significantly promoted the expressions of p-PI3K, p-AKT, C-caspase3 and Bax and inhibited Bcl-2 in the colon organoids (P < 0.05).

CONCLUSION

Acetylcorynoline protects against TNBS-induced CDlike colitis in mice possibly by suppressing the activation of the PI3K/AKT signaling pathway, thereby inhibiting apoptosis of the intestinal epithelial cells.

A gut-restricted glutamate carboxypeptidase II inhibitor reduces monocytic inflammation and improves preclinical colitis

There is an urgent need to develop therapeutics for inflammatory bowel disease (IBD) because up to 40% of patients with moderate-to-severe IBD are not adequately controlled with existing drugs. Glutamate carboxypeptidase II (GCPII) has emerged as a promising therapeutic target. This enzyme is minimally expressed in normal ileum and colon, but it is markedly up-regulated in biopsies from patients with IBD and preclinical colitis models. Here, we generated a class of GCPII inhibitors designed to be gut-restricted for oral administration, and we interrogated efficacy and mechanism using in vitro and in vivo models. The lead inhibitor, (S)-IBD3540, was potent (half maximal inhibitory concentration = 4 nanomolar), selective, gut-restricted (AUCcolon/plasma > 50 in mice with colitis), and efficacious in acute and chronic rodent colitis models. In dextran sulfate sodium-induced colitis, oral (S)-IBD3540 inhibited >75% of colon GCPII activity, dose-dependently improved gross and histologic disease, and markedly attenuated monocytic inflammation. In spontaneous colitis in interleukin-10 (IL-10) knockout mice, once-daily oral (S)-IBD3540 initiated after disease onset improved disease, normalized colon histology, and attenuated inflammation as evidenced by reduced fecal lipocalin 2 and colon pro-inflammatory cytokines/chemokines, including tumor necrosis factor-α and IL-17. Using primary human colon epithelial air-liquid interface monolayers to interrogate the mechanism, we further found that (S)-IBD3540 protected against submersion-induced oxidative stress injury by decreasing barrier permeability, normalizing tight junction protein expression, and reducing procaspase-3 activation. Together, this work demonstrated that local inhibition of dysregulated gastrointestinal GCPII using the gut-restricted, orally active, small-molecule (S)-IBD3540 is a promising approach for IBD treatment.

Genistein and/or sulfasalazine ameliorate acetic acid-induced ulcerative colitis in rats via modulating INF-γ/JAK1/STAT1/IRF-1, TLR-4/NF-κB/IL-6, and JAK2/STAT3/COX-2 crosstalk

Ulcerative Colitis (UC) is a chronic idiopathic inflammatory bowel disease in which the colon's lining becomes inflamed. Exploring herbal remedies that can recover mucosal damage is becoming popular in UC. The study aims to investigate the probable colo-protective effect of a natural isoflavone, genistein (GEN), and/or a drug, sulfasalazine (SZ), against acetic acid (AA)-induced UC in rats, in addition to exploring the possible underlying mechanisms. UC was induced by the intrarectal installation of 1-2 ml of 5% diluted AA for 24 hours. Ulcerated rats were allocated into the disease group and three treated groups, with SZ (100 mg/kg), GEN (100 mg/kg), and their combination for 14 days, besides the control groups. The anti-colitic efficacy of GEN and/or SZ was evidenced by hindering the AA-induced weight loss, colon edema, and macroscopic scores, besides reduced disease activity index and weight/length ratio. Furthermore, treatments attenuated the colon histopathological injury scores, increased the number of goblet cells, and lessened fibrosis. Both treatments reduced the up-regulation of INF-γ/JAK1/STAT1 and INF-γ /TLR-4/ NF-κB signaling pathways and modulated the IRF-1/iNOS/NO and IL-6/JAK2/STAT3/COX-2 pathways and consequently, reduced the levels of TNF-α and IL-1β. Moreover, both treatments diminished oxidative stress, which appeared by reducing the MPO level and elevating the SOD activity, and hindered apoptosis; by decreasing the immunohistochemical expression of caspase-3. The current findings offer novel insights into the protective effects of GEN and suggest a superior benefit of combining GEN with SZ, over either drug alone, in the UC management.

Methylation-Regulated Long Non-Coding RNA Expression in Ulcerative Colitis

Long non-coding RNAs (lncRNAs) have been shown to play a role in the pathogenesis of ulcerative colitis (UC). Although epigenetic processes such as DNA methylation and lncRNA expression are well studied in UC, the importance of the interplay between the two processes has not yet been fully explored. It is, therefore, believed that interactions between environmental factors and epigenetics contribute to disease development. Mucosal biopsies from 11 treatment-naïve UC patients and 13 normal controls were used in this study. From each individual sample, both whole-genome bisulfite sequencing data (WGBS) and lncRNA expression data were analyzed. Correlation analysis between lncRNA expression and upstream differentially methylated regions (DMRs) was used to identify lncRNAs that might be regulated by DMRs. Furthermore, proximal protein-coding genes associated with DMR-regulated lncRNAs were identified by correlating their expression. The study identified UC-associated lncRNAs such as MIR4435-2HG, ZFAS1, IL6-AS1, and Pvt1, which may be regulated by DMRs. Several genes that are involved in inflammatory immune responses were found downstream of DMR-regulated lncRNAs, including SERPINB1, CCL18, and SLC15A4. The interplay between lncRNA expression regulated by DNA methylation in UC might improve our understanding of UC pathogenesis.

Differently surface-labeled polystyrene nanoplastics at an environmentally relevant concentration induced Crohn's ileitis-like features via triggering intestinal epithelial cell necroptosis

Nanoplastics (NPs), regarded as the emerging contaminants, can enter and be mostly accumulated in the digest tract, which pose the potential threat to intestinal health. In this study, mice were orally exposed to polystyrene (PS), PS-COOH and PS-NH₂ NPs with the size of ∼100 nm at a human equivalent dose for 28 consecutive days. All three kinds of PS-NPs triggered Crohn's ileitis-like features, such as ileum structure impairment, increased proinflammatory cytokines and intestinal epithelial cell (IEC) necroptosis, and PS-COOH/PS-NH₂ NPs exhibited higher adverse effects on ileum tissues. Furthermore, we found PS-NPs induced necroptosis rather than apoptosis via activating RIPK3/MLKL pathway in IECs. Mechanistically, we found that PS-NPs accumulated in the mitochondria and subsequently caused mitochondrial stress, which initiated PINK1/Parkin-mediated mitophagy. However, mitophagic flux was blocked due to lysosomal deacidification caused by PS-NPs, and thus led to IEC necroptosis. We further found that mitophagic flux recovery by rapamycin can alleviate NP-induced IEC necroptosis. Our findings revealed the underlying mechanisms concerning NP-triggered Crohn's ileitis-like features and might provide new insights for the further safety assessment of NPs.

Insights into radiation carcinogenesis based on dose-rate effects in tissue stem cells

PURPOSE

Increasing epidemiological and biological evidence suggests that radiation exposure enhances cancer risk in a dose-dependent manner. This can be attributed to the 'dose-rate effect,' where the biological effect of low dose-rate radiation is lower than that of the same dose at a high dose-rate. This effect has been reported in epidemiological studies and experimental biology, although the underlying biological mechanisms are not completely understood. In this review, we aim to propose a suitable model for radiation carcinogenesis based on the dose-rate effect in tissue stem cells.

METHODS

We surveyed and summarized the latest studies on the mechanisms of carcinogenesis. Next, we summarized the radiosensitivity of intestinal stem cells and the role of dose-rate in the modulation of stem-cell dynamics after irradiation.

RESULTS

Consistently, driver mutations can be detected in most cancers from past to present, supporting the hypothesis that cancer progression is initiated by the accumulation of driver mutations. Recent reports demonstrated that driver mutations can be observed even in normal tissues, which suggests that the accumulation of mutations is a necessary condition for cancer progression. In addition, driver mutations in tissue stem cells can cause tumors, whereas they are not sufficient when they occur in non-stem cells. For non-stem cells, tissue remodeling induced by marked inflammation after the loss of tissue cells is important in addition to the accumulation of mutations. Therefore, the mechanism of carcinogenesis differs according to the cell type and magnitude of stress. In addition, our results indicated that non-irradiated stem cells tend to be eliminated from three-dimensional cultures of intestinal stem cells (organoids) composed of irradiated and non-irradiated stem cells, supporting the stem-cell competition.

CONCLUSIONS

We propose a unique scheme in which the dose-rate dependent response of intestinal stem cells incorporates the concept of the threshold of stem-cell competition and context-dependent target shift from stem cells to whole tissue. The concept highlights four key issues that should be considered in radiation carcinogenesis: i.e. accumulation of mutations; tissue reconstitution; stem-cell competition; and environmental factors like epigenetic modifications.

A Living Organoid Biobank of Crohn's Disease Patients Reveals Molecular Subtypes for Personalized Therapeutics

Crohn's disease (CD) is a complex, clinically heterogeneous disease of multifactorial origin; there is no perfect pre-clinical model, little insight into the basis for such heterogeneity, and still no cure. To address these unmet needs, we sought to explore the translational potential of adult stem cell-derived organoids that not only retain their tissue identity, but also their genetic and epigenetic disease-driving traits. We prospectively created a biobank of CD patient-derived organoid cultures (PDOs) using biopsied tissues from colons of 34 consecutive subjects representing all clinical subtypes (Montreal Classification B1-B3 and perianal disease). PDOs were generated also from healthy subjects. Comparative gene expression analyses enabled benchmarking of PDOs as tools for modeling the colonic epithelium in active disease and revealed that despite the clinical heterogeneity there are two major molecular subtypes: immune-deficient infectious-CD [IDICD] and stress and senescence-induced fibrostenotic-CD [S2FCD]. The transcriptome, genome and phenome show a surprising degree of internal consistency within each molecular subtype. The spectrum of morphometric, phenotypic, and functional changes within the "living biobank" reveals distinct differences between the molecular subtypes. These insights enabled drug screens that reversed subtype-specific phenotypes, e.g., impaired microbial clearance in IDICD was reversed using agonists for nuclear receptors, and senescence in S2FCD was rectified using senotherapeutics, but not vice versa . Phenotyped-genotyped CD-PDOs may fill the gap between basic biology and patient trials by enabling pre-clinical Phase '0' human trials for personalized therapeutics.

GRAPHIC ABSTRACT

In Brief

This work creates a prospectively biobanked phenotyped-genotyped Crohn's disease patient-derived organoids (CD-PDOs) as platforms for molecular subtyping of disease and for ushering personalized therapeutics.

HIGHLIGHTS

Prospectively biobanked CD-organoids recapitulate the disease epithelium in patientsThe phenome-transcriptome-genome of CD-organoids converge on two molecular subtypesOne subtype shows impaired microbial clearance, another increased cellular senescencePhenotyped-genotyped PDOs are then used for integrative and personalized therapeutics.

From birth to death: The hardworking life of Paneth cell in the small intestine

Paneth cells are a group of unique intestinal epithelial cells, and they play an important role in host-microbiota interactions. At the origin of Paneth cell life, several pathways such as Wnt, Notch, and BMP signaling, affect the differentiation of Paneth cells. After lineage commitment, Paneth cells migrate downward and reside in the base of crypts, and they possess abundant granules in their apical cytoplasm. These granules contain some important substances such as antimicrobial peptides and growth factors. Antimicrobial peptides can regulate the composition of microbiota and defend against mucosal penetration by commensal and pathogenic bacteria to protect the intestinal epithelia. The growth factors derived from Paneth cells contribute to the maintenance of the normal functions of intestinal stem cells. The presence of Paneth cells ensures the sterile environment and clearance of apoptotic cells from crypts to maintain the intestinal homeostasis. At the end of their lives, Paneth cells experience different types of programmed cell death such as apoptosis and necroptosis. During intestinal injury, Paneth cells can acquire stem cell features to restore the intestinal epithelial integrity. In view of the crucial roles of Paneth cells in the intestinal homeostasis, research on Paneth cells has rapidly developed in recent years, and the existing reviews on Paneth cells have mainly focused on their functions of antimicrobial peptide secretion and intestinal stem cell support. This review aims to summarize the approaches to studying Paneth cells and introduce the whole life experience of Paneth cells from birth to death.

Intestinal epithelial barrier integrity investigated by label-free techniques in ulcerative colitis patients

The intestinal epithelial barrier, among other compartments such as the mucosal immune system, contributes to the maintenance of intestinal homeostasis. Therefore, any disturbance within the epithelial layer could lead to intestinal permeability and promote mucosal inflammation. Considering that disintegration of the intestinal epithelial barrier is a key element in the etiology of ulcerative colitis, further assessment of barrier integrity could contribute to a better understanding of the role of epithelial barrier defects in ulcerative colitis (UC), one major form of chronic inflammatory bowel disease. Herein, we employ fast, non-destructive, and label-free non-linear methods, namely coherent anti-Stokes Raman scattering (CARS), second harmonic generation (SHG), two-photon excited fluorescence (TPEF), and two-photon fluorescence lifetime imaging (2P-FLIM), to assess the morpho-chemical contributions leading to the dysfunction of the epithelial barrier. For the first time, the formation of epithelial barrier gaps was directly visualized, without sophisticated data analysis procedures, by the 3D analysis of the colonic mucosa from severely inflamed UC patients. The results were compared with histopathological and immunofluorescence images and validated using transmission electron microscopy (TEM) to indicate structural alterations of the apical junction complex as the underlying cause for the formation of the epithelial barrier gaps. Our findings suggest the potential advantage of non-linear multimodal imaging is to give precise, detailed, and direct visualization of the epithelial barrier in the gastrointestinal tract, which can be combined with a fiber probe for future endomicroscopy measurements during real-time in vivo imaging.

Ferulic acid relieved ulcerative colitis by inhibiting the TXNIP/NLRP3 pathway in rats

Ulcerative colitis (UC) is a disorder of the bowel that is characterized by a chronic inflammatory response. The traditional Chinese herbal medicine ferulic acid (FA) is known for its antioxidant, antiapoptotic, and antiinflammatory properties. However, its role in UC is still unclear. Thus, the current study was conducted to investigate the role of FA in UC. Rats were treated with 2,4,6-triabrobenzene sulfonic acid to induce UC and subjected to FA. Human intestinal microvascular endothelial cells (HIMECs) were treated with tumor necrosis factor-α (TNF-α) and pretreated with FA. Pathological changes in colonic tissues were visualized via hematoxylin-eosin staining. Enzyme linked immunosorbent assay was conducted to detect interleukin (IL)-6, IL-12, and IL-1β levels. Cell morphology was visualized by using a microscope, and viability was detected by using MTT. The percentage of apoptosis was detected via flow cytometry. Western blot analysis was performed to detect the expression of the apoptosis-related proteins thioredoxin-interacting protein (TXNIP) and NOD-like receptor pyrin domain-containing 3 (NLRP3). In vivo FA administration alleviated intestinal injury in UC rats and inhibited inflammatory factor levels (IL-6, IL-12, and IL-1β), apoptosis-related protein expression (caspase-1 and caspase-3) and the TXNIP/NLRP3 signaling pathway. In vitro, TNF-α treatment reduced HIMEC viability, increased cell apoptosis and inflammatory factor levels and activated the TXNIP/NLRP3 signaling pathway. However, FA treatment restored the viability of HIMECs, reduced TNF-α-induced cell apoptosis and inflammation and inhibited the TXNIP/NLRP3 signaling pathway. Furthermore, with increasing FA concentration, the effects were stronger. In summary, FA inhibits the inflammatory injury of endothelial cells in ulcerative colitis or alleviates TNF-α-induced HIMEC injury by inhibiting the TXNIP/NLRP3 signaling pathway.

Hederacoside C ameliorates colitis via restoring impaired intestinal barrier through moderating S100A9/MAPK and neutrophil recruitment inactivation

Hederacoside C (HSC) has attracted much attention as a novel modulator of inflammation, but its anti-inflammatory mechanism remains elusive. In the present study, we investigated how HSC attenuated intestinal inflammation in vivo and in vitro. HSC injection significantly alleviated TNBS-induced colitis by inhibiting pro-inflammatory cytokine production and colonic epithelial cell apoptosis, and partially restored colonic epithelial cell proliferation. The therapeutic effect of HSC injection was comparable to that of oral administration of mesalazine (200 mg·kg^-1·d^-1, i.g.). In LPS-stimulated human intestinal epithelial Caco-2 cells, pretreatment with HSC (0.1, 1, 10 μM) significantly inhibited activation of MAPK/NF-κB and its downstream signaling pathways. Pretreatment with HSC prevented LPS-induced TLR4 dimerization and MyD88 recruitment in vitro. Quantitative proteomic analysis revealed that HSC injection regulated 18 proteins in the colon samples, mainly clustered in neutrophil degranulation. Among them, S100A9 involved in the degranulation of neutrophils was one of the most significantly down-regulated proteins. HSC suppressed the expression of S100A9 and its downstream genes including TLR4, MAPK, and NF-κB axes in colon. In Caco-2 cells, recombinant S100A9 protein activated the MAPK/NF-κB signaling pathway and induced inflammation, which were ameliorated by pretreatment with HSC. Notably, HSC attenuated neutrophil recruitment and degranulation as well as S100A9 release in vitro and in vivo. In addition, HSC promoted the expression of tight junction proteins and repaired the epithelial barrier via inhibiting S100A9. Our results verify that HSC ameliorates colitis via restoring impaired intestinal barrier through moderating S100A9/MAPK and neutrophil recruitment inactivation, suggesting that HSC is a promising therapeutic candidate for colitis.

Toxicity, Genotoxicity, and Carcinogenicity of Isotretinoin

BACKGROUND

Acne is a chronic inflammatory disease mainly observed in adolescence, but it can also be seen during the neonatal, infantile, pre-pubertal, and adult periods. Isotretinoin (13-cis-retinoic acid) is a first-generation retinoid and is the most effective treatment for acne vulgaris.

OBJECTIVE

The present study has been systematically designed to figure out the toxic, genotoxic, and carcinogenic activities of isotretinoin.

METHODS

In this study, a systematic approach was followed by focusing on the possible links between these topics. The search of the databases was carried out author in accordance with the guidelines of the Centre for Reviews and Dissemination (2009) developed by York University National Institute of Health Research. The search was concentrated on the Web of Science, PubMed, Science Direct, Scopus, EBSCO Host, and Google Scholar databases.

RESULTS

Isotretinoin was found as a toxic agent in all studies. All researchers proposed that apoptosis is the only pathway of adverse effects of isotretinoin. However, genotoxicity, teratogenicity, and carcinogenicity information of isotretinoin is very limited and controversial.

CONCLUSION

More detailed studies need to clarify the genotoxic and carcinogenic potential of isotretinoin. Patients should be informed correctly, the risks of treatment should be explained, and awareness should be raised.

A novel oral formulation of the melanocortin-1 receptor agonist PL8177 resolves inflammation in preclinical studies of inflammatory bowel disease and is gut restricted in rats, dogs, and humans

Introduction

PL8177 is a potent and selective agonist of the melanocortin 1 receptor (MC1R). PL8177 has shown efficacy in reversing intestinal inflammation in a cannulated rat ulcerative colitis model. To facilitate oral delivery, a novel, polymer-encapsulated formulation of PL8177 was developed. This formulation was tested in 2 rat ulcerative colitis models and evaluated for distribution, in vivo, in rats, dogs, and humans.

Methods

The rat models of colitis were induced by treatment with 2,4-dinitrobenzenesulfonic acid or dextran sulfate sodium. Single nuclei RNA sequencing of colon tissues was performed to characterize the mechanism of action. The distribution and concentration of PL8177 and the main metabolite within the GI tract after a single oral dose of PL8177 was investigated in rats and dogs. A phase 0 clinical study using a single microdose (70 µg) of [¹⁴C]-labeled PL8177 investigated the release of PL8177 in the colon of healthy men after oral administration.

Results

Rats treated with 50 µg oral PL8177 demonstrated significantly lower macroscopic colon damage scores and improvement in colon weight, stool consistency, and fecal occult blood vs the vehicle without active drug. Histopathology analysis resulted in the maintenance of intact colon structure and barrier, reduced immune cell infiltration, and increased enterocytes with PL8177 treatment. Transcriptome data show that oral PL8177 50 µg treatment causes relative cell populations and key gene expressions levels to move closer to healthy controls. Compared with vehicle, treated colon samples show negative enrichment of immune marker genes and diverse immune-related pathways. In rats and dogs, orally administered PL8177 was detected at higher amounts in the colon vs upper GI tract. [¹⁴C]-PL8177 and the main metabolite were detected in the feces but not in the plasma and urine in humans. This suggests that the parent drug [¹⁴C]-PL8177 was released from the polymer formulation and metabolized within the GI tract, where it would be expected to exert its effect.

Conclusion

Collectively, these findings support further research into the oral formulation of PL8177 as a possible therapeutic for GI inflammatory diseases in humans.

Skatole: A thin red line between its benefits and toxicity

Skatole (3-methylindole) is a heterocyclic compound naturally found in the feces of vertebrates and is produced by certain flowers. Skatole has been used in specific products of the perfume industry or as a flavor additive in ice cream. Additionally, skatole is formed by tryptophan pyrolysis of tobacco and has been demonstrated to be a mutagen. Skatole-induced pulmonotoxicity was reliably described in ruminants and rodents, but no studies have been conducted in humans. Initially, we provide basic knowledge and a historical overview of skatole. Then, skatole bacterial formation in the intestine is described, and the importance of the microbiome during this process is evaluated. Increased skatole concentrations could serve as a marker for intestinal disease development. Therefore, the human molecular targets of skatole that may have significant effects on various processes in the human body are described. Ultimately, we suggest a link between skatole intestinal formation in humans and skatole-induced pulmonotoxicity, which should be explored further in the future.

Magnolia officinalis Bark Extract Prevents Enterocyte Death in a Colitis Mouse Model by Inhibiting ROS-Mediated Necroptosis

Necroptosis is a form of programmed cell death with features of necrosis and apoptosis that occurs in the intestinal epithelium of patients with inflammatory bowel disease (IBD), including ulcerative colitis and Crohn's disease. In addition, necroptosis has also been observed in enterocytes in animal models of dextran sulfate sodium (DSS)-induced colitis. Thus, the discovery of natural products for regulating necroptosis may represent an important therapeutic strategy for improving IBD. We found that Magnolia officinalis bark extract (MBE) prevented weight loss and suppressed the activation of the proinflammatory cytokine IL6 in DSS-induced colitis. Furthermore, MBE restored the length of the damaged colon and decreased the expression of necroptosis markers in mice with DSS-induced colitis. In vitro, necroptosis-induced reactive oxygen species (ROS) production was reduced by MBE, and the expression of COX2, a target protein of ROS, was simultaneously suppressed. Both magnolol and honokiol, the two major bioactive compounds in MBE, inhibited necroptosis in human primary intestinal epithelial cells and colorectal adenocarcinoma cells. Our findings highlight the effectiveness of MBE in modulating enterocyte necroptosis and suggest that MBE may be developed as a natural, disease-targeting drug for the treatment of colitis.

Prevention of ulcerative colitis by Huangqin decoction: reducing the intestinal epithelial cell apoptosis rate through the IFN-γ/JAK/ETS signalling pathway

CONTEXT

Ulcerative colitis (UC) is a chronic idiopathic inflammatory bowel disease that is closely related to inflammation and apoptosis. The traditional Chinese medicine compound preparation Huangqin decoction (HQD) has been widely used in the clinical treatment of UC, but the specific mechanism of its function is still inconclusive.

OBJECTIVE

To explore the pathogenesis of UC based on the IFN-γ/JAK/ETS signalling pathway, and to clarify the biological mechanism of HQD.

MATERIALS AND METHODS

Forty 8-week-old male C57BL/6 mice were randomly divided into four groups: normal control, model, model + salazosulfapyridine group (500 mg/kg, p.o., pd) and model + HQD (9.1 g/kg, p.o., pd). Using Dextran sulphate sodium (DSS) salt (2.5%, p.o.)+high-fat diet + hot and humid environment to build a mouse model of UC. One month later, the changes of colon morphology, serum inflammatory factors, intestinal epithelial cell apoptosis and IFN-γ/JAK/ETS signalling pathway related protein changes in mice were observed.

RESULTS

Compared with the model group, HQD significantly reduced the pathological score of the model mice's colon (2.60 ± 0.25 vs. 4.80 ± 0.37), and reduced the serum IFN-γ (200.30 ± 8.45 vs. 413.80 ± 6.97) and other inflammatory factors, and reduced intestinal epithelial cell apoptosis (24.85 ± 4.87 vs. 214.90 ± 39.21). In terms of mechanism, HQD down-regulated IFN-γ/JAK/ETS signalling pathway related proteins in colon tissue of UC model mice.

CONCLUSIONS

These data indicate that HQD can improve UC by reducing intestinal inflammation and apoptosis, providing experimental evidence for the wide application of HQD in clinical practice of UC.

TRAF3/p38-JNK Signalling Crosstalk with Intracellular-TRAIL/Caspase-10-Induced Apoptosis Accelerates ROS-Driven Cancer Cell-Specific Death by CD40

The capacity to induce tumour-cell specific apoptosis represents the most unique feature of the TNF receptor (TNFR) family member CD40. Recent studies on the signalling events triggered by its membrane-presented ligand CD40L (mCD40L) in normal and malignant epithelial cells have started to unravel an exquisite context and cell type specificity for the functional effects of CD40. Here, we demonstrate that, in comparison to other carcinomas, mCD40L triggered strikingly more rapid apoptosis in colorectal carcinoma (CRC) cells, underpinned by its ability to entrain two concurrently operating signalling axes. CD40 ligation initially activates TNFR-associated factor 3 (TRAF3) and subsequently NADPH oxidase (NOX)/Apoptosis signal-regulating kinase 1 (ASK1)-signalling and induction of reactive oxygen species (ROS) to mediate p38/JNK- and ROS-dependent cell death. At that point, p38/JNK signalling directly activates the mitochondrial pathway, and triggers rapid induction of intracellular TNF-related apoptosis-inducing ligand (TRAIL) that signals from internal compartments to initiate extrinsic caspase-10-asscociated apoptosis, leading to truncated Bid (tBid)-activated mitochondrial signalling. p38 and JNK are essential both for direct mitochondrial apoptosis induction and the TRAIL/caspase-10/tBid pathway, but their involvement follows functional hierarchy and temporally controlled interplay, as p38 function is required for JNK phosphorylation. By engaging both intrinsic and extrinsic pathways to activate apoptosis via two signals simultaneously, CD40 can accelerate CRC cell death. Our findings further unravel the multi-faceted properties of the CD40/mCD40L dyad, highlighted by the novel TNFR crosstalk that accelerates tumour cell-specific death, and may have implications for the use of CD40 as a therapeutic target.

Stand by me: Fibroblasts regulation of the intestinal epithelium during development and homeostasis

The epithelium of the small intestine is composed of a single layer of cells that line two functionally distinct compartments, the villi that project into the lumen of the gut and the crypts that descend into the underlying connective tissue. Stem cells are located in crypts, where they divide and give rise to transit-amplifying cells that differentiate into secretory and absorptive epithelial cells. Most differentiated cells travel upwards from the crypt towards the villus tip, where they shed into the lumen. While some of these cell behaviors are an intrinsic property of the epithelium, it is becoming evident that tight coordination between the epithelium and the underlying fibroblasts plays a critical role in tissue morphogenesis, stem-cell niche maintenance and regionalized gene expression along the crypt-villus axis. Here, we will review the current literature describing the interaction between epithelium and fibroblasts during crypt-villus axis development and intestinal epithelium renewal during homeostasis.

I’ve looked at gut from both sides now: Gastrointestinal tract involvement in the pathogenesis of SARS-CoV-2 and HIV/SIV infections

The lumen of the gastrointestinal (GI) tract contains an incredibly diverse and extensive collection of microorganisms that can directly stimulate the immune system. There are significant data to demonstrate that the spatial localization of the microbiome can impact viral disease pathogenesis. Here we discuss recent studies that have investigated causes and consequences of GI tract pathologies in HIV, SIV, and SARS-CoV-2 infections with HIV and SIV initiating GI pathology from the basal side and SARS-CoV-2 from the luminal side. Both these infections result in alterations of the intestinal barrier, leading to microbial translocation, persistent inflammation, and T-cell immune activation. GI tract damage is one of the major contributors to multisystem inflammatory syndrome in SARS-CoV-2-infected individuals and to the incomplete immune restoration in HIV-infected subjects, even in those with robust viral control with antiretroviral therapy. While the causes of GI tract pathologies differ between these virus families, therapeutic interventions to reduce microbial translocation-induced inflammation and improve the integrity of the GI tract may improve the prognoses of infected individuals.

Disposal of intestinal apoptotic epithelial cells and their fate via divergent routes

Gut epithelial cells are characterized by rapid, constant cell renewal. The disposal of aging epithelial cells around the villus tips of the small intestine occurs so regularly that it has been regarded as a consequence of well-controlled cell death, designated as apoptosis. However, the notion of live cell extrusion in the intestine has been intensively built among researchers, and the disposal processes of effete epithelial cells display species and regional differences. Chemical mediators and mechanical forces rising from surrounding cells contribute to the regulated cell replacement. Cytotoxic intraepithelial lymphocytes and lamina propria macrophages play a leading role in the selection of disposal cells and their extrusion to maintain fully the epithelial homeostasis in tandem with the dynamic reconstruction of junctional devices. Lymphocyte-mediated cell killing is predominant in the mouse and rat, while the disposal of epithelial cells in the guinea pig, monkey, and human is characterized by active phagocytosis by subepithelially gathering macrophages. The fenestrated basement membrane formed by immune cells supports their involvement and explains species differences in the disposal of epithelial cells. Via these fenestrations, macrophages and dendritic cells can engulf apoptotic epithelial cells and debris and convey substantial information to regional lymph nodes. In this review, we attempt to focus on morphological aspects concerning the apoptosis and disposal process of effete epithelial cells; in vitro or ex vivo analyses using cultured monolayer has become predominant in recent studies concerning the exfoliation of apoptotic enterocytes. Furthermore, we give attention to their species differences, which is controversial but crucial to our understanding.

Impact of Epithelial Cell Shedding on Intestinal Homeostasis

The gut barrier acts as a first line of defense in the body, and plays a vital role in nutrition and immunoregulation. A layer of epithelial cells bound together via intercellular junction proteins maintains intestinal barrier integrity. Based on a tight equilibrium between cell extrusion and cell restitution, the renewal of the epithelium (epithelial turnover) permits the preservation of cell numbers. As the last step within the epithelial turnover, cell shedding occurs due to the pressure of cell division and migration from the base of the crypt. During this process, redistribution of tight junction proteins enables the sealing of the epithelial gap left by the extruded cell, and thereby maintains barrier function. Disturbance in cell shedding can create transient gaps (leaky gut) or cell accumulation in the epithelial layer. In fact, numerous studies have described the association between dysregulated cell shedding and infection, inflammation, and cancer; thus epithelial cell extrusion is considered a key defense mechanism. In the gastrointestinal tract, altered cell shedding has been observed in mouse models of intestinal inflammation and appears as a potential cause of barrier loss in human inflammatory bowel disease (IBD). Despite the relevance of this process, there are many unanswered questions regarding cell shedding. The investigation of those mechanisms controlling cell extrusion in the gut will definitely contribute to our understanding of intestinal homeostasis. In this review, we summarized the current knowledge about intestinal cell shedding under both physiological and pathological circumstances.

Targeted Therapy for Inflammatory Diseases with Mesenchymal Stem Cells and Their Derived Exosomes: From Basic to Clinics

Inflammation is a beneficial and physiological process, but there are a number of inflammatory diseases which have detrimental effects on the body. In addition, the drugs used to treat inflammation have toxic side effects when used over a long period of time. Mesenchymal stem cells (MSCs) are pluripotent stem cells that can be isolated from a variety of tissues and can be differentiate into diverse cell types under appropriate conditions. They also exhibit noteworthy anti-inflammatory properties, providing new options for the treatment of inflammatory diseases. The therapeutic potential of MSCs is currently being investigated for various inflammatory diseases, such as kidney injury, lung injury, osteoarthritis (OA), rheumatoid arthritis (RA), and inflammatory bowel disease (IBD). MSCs can perform multiple functions, including immunomodulation, homing, and differentiation, to enable damaged tissues to form a balanced inflammatory and regenerative microenvironment under severe inflammatory conditions. In addition, accumulated evidence indicates that exosomes from extracellular vesicles of MSCs (MSC-Exos) play an extraordinary role, mainly by transferring their components to recipient cells. In this review, we summarize the mechanism and clinical trials of MSCs and MSC-Exos in various inflammatory diseases in detail, with a view to contributing to the treatment of MSCs and MSC-Exos in inflammatory diseases.

Excessive Apoptosis in Ulcerative Colitis: Crosstalk Between Apoptosis, ROS, ER Stress, and Intestinal Homeostasis

Ulcerative colitis (UC), an etiologically complicated and relapsing gastrointestinal disease, is characterized by the damage of mucosal epithelium and destruction of the intestinal homeostasis, which has caused a huge social and economic burden on the health system all over the world. Its pathogenesis is multifactorial, including environmental factors, genetic susceptibility, epithelial barrier defect, symbiotic flora imbalance, and dysregulated immune response. Thus far, although immune cells have become the focus of most research, it is increasingly clear that intestinal epithelial cells play an important role in the pathogenesis and progression of UC. Notably, apoptosis is a vital catabolic process in cells, which is crucial to maintain the stability of intestinal environment and regulate intestinal ecology. In this review, the mechanism of apoptosis induced by reactive oxygen species and endoplasmic reticulum stress, as well as excessive apoptosis in intestinal epithelial dysfunction and gut microbiology imbalance are systematically and comprehensively summarized. Further understanding the role of apoptosis in the pathogenesis of UC may provide a novel strategy for its therapy in clinical practices and the development of new drugs.

Divergent Impact of Enzyme Replacement Therapy on Human Cardiomyocytes and Enterocytes Affected by Fabry Disease: Correlation with Mannose-6-phosphate Receptor Expression

Background: The impact of enzyme replacement therapy (ERT) on cardiomyocytes and intestinal cells, affected by Fabry disease (FD), is still unclear. Methods: Six patients with FD, including five family members with GLA mutation c.666delC and one with GLA mutation c.658C > T, manifesting cardiomyopathy and intestinal symptoms (abdominal pain, diarrhea and malabsorption) were included in the study. Clinical outcome, cardiac magnetic resonance (CMR), endomyocardial and gastro-intestinal biopsies were evaluated before and after 2 years of treatment with agalsidase-α (0.2 mg/kg every other week). Immunohistochemistry and Western blot assessments of mannose-6-phosphate receptors (IGF-II-R) on intestinal and myocardial frozen tissue were obtained at diagnosis and after 2 years of ERT. Results: After ERT left ventricular maximal wall thickness, ranging from pre (<10.5 mm) to mild (<15 mm) and moderate hypertrophy (16 mm), was not associated with significant changes at CMR. Degree of dyspnea, mean cardiomyocyte diameter and % vacuolated areas of cardiomyocytes, representing intracellular GL3, remained unmodified. In contrast, intestinal symptoms improved with disappearance of diarrhea, recovery of anemia and weight gain, correlating with near complete clearance of the enterocytes from GL3 inclusions. IGF-II-R expression was remarkably higher even at histochemistry in intestinal tissue compared with myocardium (p < 0.001) either at baseline and after ERT, thus justifying intestinal recovery. Conclusions: Human cells affected by FD may respond differently to ERT: while cardiomyocytes retain their GL3 content after 2 years of treatment, gastro-intestinal cells show GL3 removal with recovery of function. This divergent response may be related to differences in cellular turnover, as well as tissue IGF-II-R expression.

The Intestinal Effect of Atorvastatin: Akkermansia muciniphila and Barrier Function

Studies have shown that the cholesterol-lowering medicine statins alter the gut microbiome, induce chronic metabolic inflammation, and disrupt glycemic homeostasis. In this study, we aimed to investigate whether effects of atorvastatin (Ator) on gut microbiome and metabolic inflammation could be causally correlated. Mice at 8-week age were fed with high-fat diet (HFD) or HFD with Ator (HFD+Ator) for 16 weeks. 16S rRNA sequencing of stool and RNA sequencing of colon tissue were employed to analyze the intestinal alterations that could be induced by Ator. A human colon carcinoma cell line (Caco₂) was used for in vitro experiments on barrier function. Compared to HFD, HFD+Ator induced more weight gain, impaired glucose tolerance, and led to gut microbiota dysbiosis, such as suppressing Akkermansia muciniphila in mice. The expressions of tight junction (TJ) proteins were attenuated in the colon, and the serum LPS-binding-protein (LBP) level was elevated in HFD+Ator mice, so as to transcriptionally activate the intestinal nuclear factor-k-gene binding (NF-κB) signaling pathway. Consistently, Ator impaired the barrier function of Caco₂, and treatment of supernatant of A. Muciniphila culture could decrease the intestinal permeability and recover the attenuated expression of TJ proteins induced by Ator. In conclusion, long-term use of Ator with HFD may alter gut microbiota, induce intestinal barrier dysfunction, and hence promote chronic inflammation that contributes to disrupted glycemic homeostasis.

Executioner caspases 3 and 7 are dispensable for intestinal epithelium turnover and homeostasis at steady state

Historically, programmed cell death by apoptosis is considered crucial for proper intestinal organogenesis and gut homeostasis. To challenge this concept, we generated caspase-3 and -7 double knockout mice specifically in intestinal epithelial cells (IECs). However, absence of apoptosis in IECs elicits neither morphological and inflammatory changes nor intestinal dysbiosis during gut homeostasis at steady state. This demonstrates the robustness of intestinal homeostasis at steady state for the absence of caspase-3/7 and shows that in contrast to caspase-8, which keeps necroptosis and associated inflammation in check, caspase-3/7–dependent apoptosis of IECs in homeostatic conditions is dispensable for normal intestinal development, immune cell composition, and microbiome control.

Apoptosis is widely believed to be crucial for epithelial cell death and shedding in the intestine, thereby shaping the overall architecture of the gastrointestinal tract, but also regulating tolerance induction, pinpointing a role of apoptosis intestinal epithelial cell (IEC) turnover and maintenance of barrier function, and in maintaining immune homeostasis. To experimentally address this concept, we generated IEC-specific knockout mice that lack both executioner caspase-3 and caspase-7 (Casp3/7^ΔIEC), which are the converging point of the extrinsic and intrinsic apoptotic pathway. Surprisingly, the overall architecture, cellular landscape, and proliferation rate remained unchanged in these mice. However, nonapoptotic cell extrusion was increased in Casp3/7^ΔIEC mice, compensating apoptosis deficiency, maintaining the same physiological level of IEC shedding. Microbiome richness and composition stayed unaffected, bearing no sign of dysbiosis. Transcriptome and single-cell RNA sequencing analyses of IECs and immune cells revealed no differences in signaling pathways of differentiation and inflammation. These findings demonstrate that during homeostasis, apoptosis per se is dispensable for IEC turnover at the top of intestinal villi intestinal tissue dynamics, microbiome, and immune cell composition.

Modulation of Gut Barrier Functions in Ulcerative Colitis by Hyaluronic Acid System

The active stages of intestinal inflammation and the pathogenesis of ulcerative colitis are associated with superficial mucosal damage and intermittent wounding that leads to epithelial barrier defects and increased permeability. The standard therapeutic interventions for colitis have focused mainly on maintaining the remission levels of the disease. Nonetheless, such treatment strategies (using anti-inflammatory, immunomodulatory agents) do not address colitis' root cause, especially the mucosal damage and dysregulated intestinal barrier functions. Restoration of barrier functionality by mucosal healing or physical barrier protecting strategies shall be considered as an initial event in the disease suppression and progression. Herein, a biphasic hyaluronan (HA) enema suspension, naïve-HA systems that protect the dysregulated gut epithelium by decreasing the inflammation, permeability, and helping in maintaining the epithelial barrier integrity in the dextran sodium sulfate-induced colitis mice model is reported. Furthermore, HA-based system modulates intestinal epithelial junctional proteins and regulatory signaling pathways, resulting in attenuation of inflammation and mucosal protection. The results suggest that HA-based system can be delivered as an enema to act as a barrier protecting system for managing distal colonic inflammatory diseases, including colitis.

Hyperoxia Provokes Time- and Dose-Dependent Gut Injury and Endotoxemia and Alters Gut Microbiome and Transcriptome in Mice

Background: Oxygen therapy usually exposes patients to hyperoxia, which induces injuries in the lung, the heart, and the brain. The gut and its microbiome play key roles in critical illnesses, but the impact of hyperoxia on the gut and its microbiome remains not very clear. We clarified the time- and dose-dependent effects of hyperoxia on the gut and investigated oxygen-induced gut dysbiosis and explored the underlying mechanism of gut injury by transcriptome analysis. Methods: The C57BL/6 mice were randomly divided into the control group and nine different oxygen groups exposed to hyperoxia with an inspired O₂ fraction (FiO₂) of 40, 60, and 80% for 24, 72, and 168 h (7 days), respectively. Intestinal histopathological and biochemical analyses were performed to explore the oxygen-induced gut injury and inflammatory response. Another experiment was performed to explore the impact of hyperoxia on the gut microbiome by exposing the mice to hyperoxia (FiO₂ 80%) for 7 days, with the 16S rRNA sequencing method. We prolonged the exposure (up to 14 days) of the mice to hyperoxia (FiO₂ 80%), and gut transcriptome analysis and western blotting were carried out to obtain differentially expressed genes (DEGs) and signaling pathways related to innate immunity and cell death. Results: Inhaled oxygen induced time- and dose-dependent gut histopathological impairment characterized by mucosal atrophy (e.g., villus shortening: 80% of FiO₂ for 24 h: P = 0.008) and enterocyte death (e.g., apoptosis: 40% of FiO₂ for 7 days: P = 0.01). Administered time- and dose-dependent oxygen led to intestinal barrier dysfunction (e.g., endotoxemia: 80% of FiO₂ for 72 h: P = 0.002) and potentiated gut inflammation by increasing proinflammatory cytokines [e.g., tumor necrosis factor alpha (TNF-α): 40% of FiO₂ for 24 h: P = 0.003)] and reducing anti-inflammatory cytokines [Interleukin 10 (IL-10): 80% of FiO₂ for 72 h: P < 0.0001]. Hyperoxia induced gut dysbiosis with an expansion of oxygen-tolerant bacteria (e.g., Enterobacteriaceae). Gut transcriptome analysis identified 1,747 DEGs and 171 signaling pathways and immunoblotting verified TLR-4, NOD-like receptor, and apoptosis signaling pathways were activated in oxygen-induced gut injury. Conclusions: Acute hyperoxia rapidly provokes gut injury in a time- and dose-dependent manner and induces gut dysbiosis, and an innate immune response is involved in an oxygen-induced gut injury.

Drivers of transcriptional variance in human intestinal epithelial organoids

Human intestinal epithelial organoids (enteroids and colonoids) are tissue cultures used for understanding the physiology of the human intestinal epithelium. Here, we explored the effect on the transcriptome of common variations in culture methods, including extracellular matrix substrate, format, tissue segment, differentiation status, and patient heterogeneity. RNA-sequencing datasets from 276 experiments performed on 37 human enteroid and colonoid lines from 29 patients were aggregated from several groups in the Texas Medical Center. DESeq2 and gene set enrichment analysis (GSEA) were used to identify differentially expressed genes and enriched pathways. PERMANOVA, Pearson's correlation, and dendrogram analysis of the data originally indicated three tiers of influence of culture methods on transcriptomic variation: substrate (collagen vs. Matrigel) and format (3-D, transwell, and monolayer) had the largest effect; segment of origin (duodenum, jejunum, ileum, colon) and differentiation status had a moderate effect; and patient heterogeneity and specific experimental manipulations (e.g., pathogen infection) had the smallest effect. GSEA identified hundreds of pathways that varied between culture methods, such as IL1 cytokine signaling enriched in transwell versus monolayer cultures and E2F target genes enriched in collagen versus Matrigel cultures. The transcriptional influence of the format was furthermore validated in a synchronized experiment performed with various format-substrate combinations. Surprisingly, large differences in organoid transcriptome were driven by variations in culture methods such as format, whereas experimental manipulations such as infection had modest effects. These results show that common variations in culture conditions can have large effects on intestinal organoids and should be accounted for when designing experiments and comparing results between laboratories. Our data constitute the largest RNA-seq dataset interrogating human intestinal epithelial organoids.

Microbiota-Immune Interactions in Ulcerative Colitis and Colitis Associated Cancer and Emerging Microbiota-Based Therapies

Ulcerative colitis (UC) is a chronic autoimmune disorder affecting the colonic mucosa. UC is a subtype of inflammatory bowel disease along with Crohn's disease and presents with varying extraintestinal manifestations. No single etiology for UC has been found, but a combination of genetic and environmental factors is suspected. Research has focused on the role of intestinal dysbiosis in the pathogenesis of UC, including the effects of dysbiosis on the integrity of the colonic mucosal barrier, priming and regulation of the host immune system, chronic inflammation, and progression to tumorigenesis. Characterization of key microbial taxa and their implications in the pathogenesis of UC and colitis-associated cancer (CAC) may present opportunities for modulating intestinal inflammation through microbial-targeted therapies. In this review, we discuss the microbiota-immune crosstalk in UC and CAC, as well as the evolution of microbiota-based therapies.