Toll-like receptor 9-induced type I IFN protects mice from experimental colitis

Functional fractions of Astragalus polysaccharides as a potential prebiotic to alleviate ulcerative colitis

Ulcerative colitis (UC) is a chronic inflammatory disease of the intestine that is significantly influenced by an imbalance in the gut microbiota. Astragalus membranaceus, particularly its polysaccharide components, has shown therapeutic potential for the treatment of UC, although the specific active constituents and their mechanistic pathways remain to be fully elucidated. In this study, we investigated two molecular weight fractions of Astragalus polysaccharides (APS), APS1 (Mw < 10 kDa) and APS2 (10 kDa < Mw < 50 kDa), isolated by ultrafiltration, focusing on their prebiotic effects, effects on UC, and the underlying mechanism. Our results showed that both APS1 and APS2 exhibit prebiotic properties, with APS1 significantly outperforming APS2 in ameliorating UC symptoms. APS1 significantly attenuated weight loss and UC manifestations, reduced colonic pathology, and improved intestinal mucosal barrier integrity. In addition, APS1 significantly reduced the levels of inflammatory cytokines in the serum and colonic tissue, and downregulated colonic chemokines. Furthermore, APS1 ameliorated dextran sulfate sodium salt (DSS)-induced intestinal dysbiosis by promoting the growth of beneficial microbes and inhibiting the proliferation of potential pathogens, leading to a significant increase in short-chain fatty acids. In conclusion, this study highlights the potential of APS1 as a novel prebiotic for the prevention and treatment of UC.

Subchronic inhalation exposure to ultrafine particulate matter alters the intestinal microbiome in various mouse models

Exposure to ultrafine particles (UFPs) has been associated with multiple adverse health effects. Inhaled UFPs could reach the gastrointestinal tract and influence the composition of the gut microbiome. We have previously shown that oral ingestion of UFPs alters the gut microbiome and promotes intestinal inflammation in hyperlipidemic Ldlr-/- mice. Particulate matter (PM)2.5 inhalation studies have also demonstrated microbiome shifts in normolipidemic C57BL/6 mice. However, it is not known whether changes in microbiome precede or follow inflammatory effects in the intestinal mucosa. We hypothesized that inhaled UFPs modulate the gut microbiome prior to the development of intestinal inflammation. We studied the effects of UFP inhalation on the gut microbiome and intestinal mucosa in two hyperlipidemic mouse models (ApoE-/- mice and Ldlr-/- mice) and normolipidemic C57BL/6 mice. Mice were exposed to PM in the ultrafine-size range by inhalation for 6 h a day, 3 times a week for 10 weeks at a concentration of 300-350 μg/m3.16S rRNA gene sequencing was performed to characterize sequential changes in the fecal microbiome during exposures, and changes in the intestinal microbiome at the end. PM exposure led to progressive differentiation of the microbiota over time, associated with increased fecal microbial richness and evenness, altered microbial composition, and differentially abundant microbes by week 10 depending on the mouse model. Cross-sectional analysis of the small intestinal microbiome at week 10 showed significant changes in α-diversity, β-diversity, and abundances of individual microbial taxa in the two hyperlipidemic models. These alterations of the intestinal microbiome were not accompanied, and therefore could not be caused, by increased intestinal inflammation as determined by histological analysis of small and large intestine, cytokine gene expression, and levels of fecal lipocalin. In conclusion, 10-week inhalation exposures to UFPs induced taxonomic changes in the microbiome of various animal models in the absence of intestinal inflammation.

Cmtm4 deficiency exacerbates colitis by inducing gut dysbiosis and S100A8/9 expression

The dysfunction of innate immunity components is one of the major drivers for ulcerative colitis (UC), and increasing reports indicate that the gut microbiome serves as an intermediate between genetic mutations and UC development. Here, we find that the IL-17 receptor subunit, CMTM4, is reduced in UC patients and dextran sulfate sodium (DSS)-induced colitis. The deletion of CMTM4 (Cmtm4-/-) in mice leads to a higher susceptibility to DSS-induced colitis than in wild-type, and the gut microbiome significantly changes in composition. The causal role of the gut microbiome is confirmed with a cohousing experiment. We further identify that S100a8/9 is significantly up-regulated in Cmtm4-/- colitis, with the block of its receptor RAGE that reverses the phenotype associated with the CMTM4 deficiency. CMTM4 deficiency rather suppresses S100a8/9 expression in vitro via the IL17 pathway, further supporting that the elevation of S100a8/9 in vivo is most likely a result of microbial dysbiosis. Taken together, the results suggest that CMTM4 is involved in the maintenance of intestinal homeostasis, suppression of S100a8/9, and prevention of colitis development. Our study further shows CMTM4 as a crucial innate immunity component, confirming its important role in the UC development and providing insights into potential targets for the development of future therapies.

Type I Interferon, Induced by Adenovirus or Adenoviral Vector Infection, Regulates the Cytokine Response to Lipopolysaccharide in a Macrophage Type-Specific Manner

INTRODUCTION

While TLR ligands derived from microbial flora and pathogens are important activators of the innate immune system, a variety of factors such as intracellular bacteria, viruses, and parasites can induce a state of hyperreactivity, causing a dysregulated and potentially life-threatening cytokine over-response upon TLR ligand exposure. Type I interferon (IFN-αβ) is a central mediator in the induction of hypersensitivity and is strongly expressed in splenic conventional dendritic cells (cDC) and marginal zone macrophages (MZM) when mice are infected with adenovirus. This study investigates the ability of adenoviral infection to influence the activation state of the immune system and underlines the importance of considering this state when planning the treatment of patients.

METHODS

Infection with adenovirus-based vectors (Ad) or pretreatment with recombinant IFN-β was used as a model to study hypersensitivity to lipopolysaccharide (LPS) in mice, murine macrophages, and human blood samples. The TNF-α, IL-6, IFN-αβ, and IL-10 responses induced by LPS after pretreatment were measured. Mouse knockout models for MARCO, IFN-αβR, CD14, IRF3, and IRF7 were used to probe the mechanisms of the hypersensitive reaction.

RESULTS

We show that, similar to TNF-α and IL-6 but not IL-10, the induction of IFN-αβ by LPS increases strongly after Ad infection. This is true both in mice and in human blood samples ex vivo, suggesting that the regulatory mechanisms seen in the mouse are also present in humans. In mice, the scavenger receptor MARCO on IFN-αβ-producing cDC and splenic marginal zone macrophages is important for Ad uptake and subsequent cytokine overproduction by LPS. Interestingly, not all IFN-αβ-pretreated macrophage types exposed to LPS exhibit an enhanced TNF-α and IL-6 response. Pretreated alveolar macrophages and alveolar macrophage-like murine cell lines (MPI cells) show enhanced responses, while bone marrow-derived and peritoneal macrophages show a weaker response. This correlates with the respective absence or presence of the anti-inflammatory IL-10 response in these different macrophage types. In contrast, Ad or IFN-β pretreatment enhances the subsequent induction of IFN-αβ in all macrophage types. IRF3 is dispensable for the LPS-induced IFN-αβ overproduction in infected MPI cells and partly dispensable in infected mice, while IRF7 is required. The expression of the LPS co-receptor CD14 is important but not absolutely required for the elicitation of a TNF-α over-response to LPS in Ad-infected mice.

CONCLUSION

Viral infections or application of virus-based vaccines induces type I interferon and can tip the balance of the innate immune system in the direction of hyperreactivity to a subsequent exposure to TLR ligands. The adenoviral model presented here is one example of how multiple factors, both environmental and genetic, affect the physiological responses to pathogens. Being able to measure the current reactivity state of the immune system would have important benefits for infection-specific therapies and for the prevention of vaccination-elicited adverse effects.

Effects of four food hydrocolloids on colitis and their regulatory effect on gut microbiota

Hydrocolloids are important food additives and have potential regulatory effects on gut microbiota. The development of colitis is closely related to changes in gut microbiota. The effect of food hydrocolloids on the structure of the gut microbiota and their impact on colitis has not been well investigated. Therefore, this study investigated the effects of four hydrocolloids (carrageenan, guar gum, xanthan gum, and pectin) on colitis, and explored their regulatory effects on gut microbiota. The results indicated that pectin and guar effectively alleviated body weight loss and disease activity index, reduced inflammatory cytokine levels, and promoted short-chain fatty acids (SCFAs) production. They increased the abundance of Akkermansia muciniphila, Oscillospira, and Lactobacillus, and Akkermansia abundance had a negative correlation with the severity of colitis. In contrast, carrageenan and xanthan gum did not significantly improve colitis, and carrageenan reduced the production of SCFAs. Both carrageenan and xanthan gum increased the abundance of Ruminococcus gnavus, and Ruminococcus abundance was positively correlated with the severity of colitis. These findings suggest that food additives have an impact on host health and provide guidance for the diet of patients with colitis.

The dichotomic role of single cytokines: Fine-tuning immune responses

Cytokines are known for their pleiotropic effects. They can be classified by their function as pro-inflammatory, such as tumor necrosis factor (TNF), interleukin (IL) 1 and IL-12, or anti-inflammatory, like IL-10, IL-35 and transforming growth factor β (TGF-β). Though this type of classification is an important simplification for the understanding of the general cytokine's role, it can be misleading. Here, we discuss recent studies that show a dichotomic role of the so-called pro and anti-inflammatory cytokines, highlighting that their function can be dependent on the microenvironment and their concentrations. Furthermore, we discuss how the back-and-forth interplay between cytokines and immunometabolism can influence the dichotomic role of inflammatory responses as an important target to complement cytokine-based therapies.

Dietary fiber guar gum-induced shift in gut microbiota metabolism and intestinal immune activity enhances susceptibility to colonic inflammation

With an increasing interest in dietary fibers (DFs) to promote intestinal health and the growth of beneficial gut bacteria, there is a continued rise in the incorporation of refined DFs in processed foods. It is still unclear how refined fibers, such as guar gum, affect the gut microbiota activity and pathogenesis of inflammatory bowel disease (IBD). Our study elucidated the effect and underlying mechanisms of guar gum, a fermentable DF (FDF) commonly present in a wide range of processed foods, on colitis development. We report that guar gum containing diet (GuD) increased the susceptibility to colonic inflammation. Specifically, GuD-fed group exhibited severe colitis upon dextran sulfate sodium (DSS) administration, as evidenced by reduced body weight, diarrhea, rectal bleeding, and shortening of colon length compared to cellulose-fed control mice. Elevated levels of pro-inflammatory markers in both serum [serum amyloid A (SAA), lipocalin 2 (Lcn2)] and colon (Lcn2) and extensive disruption of colonic architecture further affirmed that GuD-fed group exhibited more severe colitis than control group upon DSS intervention. Amelioration of colitis in GuD-fed group pre-treated with antibiotics suggest a vital role of intestinal microbiota in GuD-mediated exacerbation of intestinal inflammation. Gut microbiota composition and metabolite analysis in fecal and cecal contents, respectively, revealed that guar gum primarily enriches Actinobacteriota, specifically Bifidobacterium. Guar gum also altered multiple genera belonging to phyla Bacteroidota and Firmicutes. Such shift in gut microbiota composition favored luminal accumulation of intermediary metabolites succinate and lactate in the GuD-fed mice. Colonic IL-18 and tight junction markers were also decreased in the GuD-fed group. Importantly, GuD-fed mice pre-treated with recombinant IL-18 displayed attenuated colitis. Collectively, unfavorable changes in gut microbiota activity leading to luminal accumulation of lactate and succinate, reduced colonic IL-18, and compromised gut barrier function following guar gum feeding contributed to increased colitis susceptibility.

Commensal bacteria promote type I interferon signaling to maintain immune tolerance in mice

Type I interferons (IFNs) exert a broad range of biological effects important in coordinating immune responses, which have classically been studied in the context of pathogen clearance. Yet, whether immunomodulatory bacteria operate through IFN pathways to support intestinal immune tolerance remains elusive. Here, we reveal that the commensal bacterium, Bacteroides fragilis, utilizes canonical antiviral pathways to modulate intestinal dendritic cells (DCs) and regulatory T cell (Treg) responses. Specifically, IFN signaling is required for commensal-induced tolerance as IFNAR1-deficient DCs display blunted IL-10 and IL-27 production in response to B. fragilis. We further establish that IFN-driven IL-27 in DCs is critical in shaping the ensuing Foxp3+ Treg via IL-27Rα signaling. Consistent with these findings, single-cell RNA sequencing of gut Tregs demonstrated that colonization with B. fragilis promotes a distinct IFN gene signature in Foxp3+ Tregs during intestinal inflammation. Altogether, our findings demonstrate a critical role of commensal-mediated immune tolerance via tonic type I IFN signaling.

Clostridium butyricum and Clostridium tyrobutyricum: angel or devil for necrotizing enterocolitis?

IMPORTANCE

This study sheds light on that treatment with Clostridium tyrobutyricum but not Clostridium butyricum is entitled to protect against necrotizing enterocolitis (NEC) development potentially. The mechanisms behind the opposite effect on NEC may result in different modulation on the level of Akkermansia muciniphila, which is deeply associated with intestinal homoeostasis. Briefly, through improving the abundance of A. muciniphila to alleviate intestinal inflammation and enhance intestinal barrier integrity, C. tyrobutyricum supplement may become a promising therapy for NEC.

Epithelially Restricted Interferon Epsilon Protects Against Colitis

BACKGROUND & AIMS

Type I interferon (T1IFN) signalling is crucial for maintaining intestinal homeostasis. We previously found that the novel T1IFN, IFNε, is highly expressed by epithelial cells of the female reproductive tract, where it protects against pathogens. Its function has not been studied in the intestine. We hypothesize that IFNε is important in maintaining intestinal homeostasis.

METHODS

We characterized IFNε expression in mouse and human intestine by immunostaining and studied its function in the dextran sulfate sodium (DSS) colitis model using both genetic knockouts and neutralizing antibody.

RESULTS

We demonstrate that IFNε is expressed in human and mouse intestinal epithelium, and expression is lost in inflammation. Furthermore, we show that IFNε limits intestinal inflammation in mouse models. Regulatory T cell (Treg) frequencies were paradoxically decreased in DSS-treated IFNε-/- mice, suggesting a role for IFNε in maintaining the intestinal Treg compartment. Colitis was ameliorated by transfer of wild-type Tregs into IFNε-/- mice. This demonstrates that IFNε supports intestinal Treg function.

CONCLUSIONS

Overall, we have shown IFNε expression in intestinal epithelium and its critical role in gut homeostasis. Given its known role in the female reproductive tract, we now show IFNε has a protective role across multiple mucosal surfaces.

Regulation of type I IFN responses by deubiquitinating enzyme A in inflammatory bowel diseases

The development of Inflammatory bowel disease (IBD) is driven by excessive production of pro-inflammatory cytokines including TNF-α, IL-12, and IL-23. This notion is supported by the remarkable clinical success of biologics targeting these cytokines. Recognition of cell wall components derived from intestinal bacteria by Toll-like receptors (TLRs) induces the production of these pro-inflammatory cytokines by macrophages and dendritic cells in human IBD and experimental colitis model. Although sensing of bacterial nucleic acids by endosomal TLRs, specifically TLR3, TLR7, and TLR9 leads to robust production of type I IFNs, it remains debatable whether TLR-mediated type I IFN responses are pathogenic or protective in IBD patients. Additionally, recent studies identified deubiquitinating enzyme A (DUBA) as a novel negative regulator of TLR-mediated type I IFN responses. In light of these observations and their potential applications, in this review, we summarize recent findings on the roles of type I IFN responses and DUBA-mediated negative regulation of these responses in human IBD and experimental colitis model.

Inflammatory Bowel Disease: Emerging Therapies and Future Treatment Strategies

Inflammatory bowel disease (IBD) is a term used to represent a group of chronic, relapsing inflammatory disorders of the gastrointestinal tract. Crohn's disease (CD) and ulcerative colitis (UC) are the two major clinical forms. The global incidence and prevalence of IBD have increased over the last 2-4 decades. Despite the specific etiopathogenesis of IBD still being unknown, it is widely recognized that immunological, genetic, and environmental factors are implicated. A greater understanding of the multiple signaling pathways involved has led to the development of biologic therapies in the last two decades. Although these treatments have dramatically transformed the course of IBD, there is not a definitive cure and available therapies may cause adverse events (AEs), limiting their use, or have an inadequate effect in some patients. In this context, emerging therapies addressing new specific pathogenetic mechanisms have shown promising efficacy and safety data in early clinical trials. The purpose of this review is to highlight the available clinical trial data for these new drugs, such as more preferential JAK inhibitors, anti-IL-23 antibodies, sphingosine-1-phosphate receptor modulators, anti-integrin therapies, and other small molecules that are currently under research. We will emphasize the potential significance of these agents in shaping future treatment options.

IL-17-driven induction of Paneth cell antimicrobial functions protects the host from microbiota dysbiosis and inflammation in the ileum

Interleukin (IL)-17 protects epithelial barriers by inducing the secretion of antimicrobial peptides. However, the effect of IL-17 on Paneth cells (PCs), the major producers of antimicrobial peptides in the small intestine, is unclear. Here, we show that the targeted ablation of the IL-17 receptor (IL-17R) in PCs disrupts their antimicrobial functions and decreases the frequency of ileal PCs. These changes become more pronounced after colonization with IL-17 inducing segmented filamentous bacteria. Mice with PCs that lack IL-17R show an increased inflammatory transcriptional profile in the ileum along with the severity of experimentally induced ileitis. These changes are associated with a decrease in the diversity of gut microbiota that induces a severe ileum pathology upon transfer to genetically susceptible mice, which can be prevented by the systemic administration of IL-17a/f in microbiota recipients. In an exploratory analysis of a small cohort of pediatric patients with Crohn's disease, we have found that a portion of these patients exhibits a low number of lysozyme-expressing ileal PCs and a high ileitis severity score, resembling the phenotype of mice with IL-17R-deficient PCs. Our study identifies IL-17R-dependent signaling in PCs as an important mechanism that maintains ileal homeostasis through the prevention of dysbiosis.

Temporary consumption of western diet trains the immune system to reduce future gut inflammation

Urbanization drives the popularity of western diet (WD), which increased burden in metabolic diseases but also in inflammatory diseases. Here, we show continuous WD disrupted the gut barrier, initiating low-grade inflammation and enhancing the colitis response. Nevertheless, transient WD consumption followed by ad libitum normal diet enhanced mucin production and tight junction protein expression in recovered mice. Furthermore, transient WD consumption surprisingly reduced the subsequent inflammatory response in DSS colitis and Citrobacter rodentium-infection induced colitis. The protective effect of WD training was not sex-dependent, and co-housing experiments suggested microbiota changes were not responsible. We identified important roles for cholesterol biosynthesis pathway and macrophages, pointing to innate myeloid training. Together, these data suggest detrimental effects of WD consumption can be reversed on return to a healthier diet. Furthermore, transient WD consumption leads to beneficial immune training, suggesting an evolutionary mechanism to benefit from feasting when abundant food is available.

MIA mice exhibit enteric nerve defects and are more susceptible to dextran sulfate sodium-induced colitis

Maternal immune activation (MIA) during pregnancy impairs the development of the central nervous system as well as the peripheral nervous system. Emerging evidence indicates that individuals with MIA suffer more from gastrointestinal disorders. The present study aims to test the hypothesis that MIA-induced susceptibility to inflammatory bowel disease is due to defects in the innervation of mucosal sensory nerves. Acute dextran sulfate sodium (DSS) colitis was induced in MIA and control adult mice. Body weight loss, disease activity index and colonic histological changes were measured during colitis. The study found that MIA mice were hypersusceptible to DSS-induced colitis and that macrophage infiltration and cytokine production were elevated in the colon of MIA mice. In vitro experiments also demonstrated that colonic macrophages from MIA mice presented hyperinflammatory responses to LPS stimulation. Sensory nerve-secreted calcitonin gene-related peptide (CGRP) is an important neuropeptide in modulating enteric inflammation. Intriguingly, we found that CGRP-positive nerves were sparsely distributed in the colon of MIA mice regardless of DSS treatment. And the protein level of CGRP was significantly reduced in colon of MIA mice. However, there was no decrease in the number of CGRP-positive cell bodies in either the DRG or vagal ganglion, suggesting that innervation defects of CGRP mucosal sensory nerves exist in the colon of MIA mice. Critically, administration of recombinant CGRP to MIA mice during DSS colitis significantly reversed their hyperinflammatory pathology. Additionally, the hyperinflammatory phenotype of colonic macrophages of MIA mice could also be reversed by CGRP treatment in vitro. Collectively, these findings suggested that the sensor nerve innervation defect-induced CGRP deficiency in MIA mice participates in their increased susceptibility to colitis. Thus, sensor nerve-secreted CGRP may be a new therapeutic target for autism combined with inflammatory bowel disease.

Cell-penetrating TLR inhibitor peptide alleviates ulcerative colitis by the functional modulation of macrophages

Toll-like receptors (TLRs) have a crucial role not only in triggering innate responses against microbes but in orchestrating an appropriate adaptive immunity. However, deregulated activation of TLR signaling leads to chronic inflammatory conditions such as inflammatory bowel disease (IBD). In this study, we evaluated the immunomodulatory potential of a TLR inhibitor in the form of a cell-penetrating peptide using an ulcerative colitis animal model. A peptide derived from the TIR domain of the TLR adaptor molecule TIRAP that was conjugated with a cell-penetrating sequence (cpTLR-i) suppressed the induction of pro-inflammatory cytokines such as TNF-α and IL-1β in macrophages. In DSS-induced colitis mice, cpTLR-i treatment ameliorated colitis symptoms, colonic tissue damage, and mucosal inflammation. Intriguingly, cpTLR-i attenuated the induction of TNF-α-expressing proinflammatory macrophages while promoting that of regulatory macrophages expressing arginase-1 and reduced type 17 helper T cell (Th17) responses in the inflamed colonic lamina propria. An in vitro study validated that cpTLR-i enhanced the differentiation of monocyte-driven macrophages into mature macrophages with a regulatory phenotype in a microbial TLR ligand-independent manner. Furthermore, the cocultivation of CD4 T cells with macrophages revealed that cpTLR-i suppressed the activation of Th17 cells through the functional modulation of macrophages. Taken together, our data show the immunomodulatory potential of the TLR inhibitor peptide and suggest cpTLR-i as a novel therapeutic candidate for the treatment of IBD.

Diet prevents the expansion of segmented filamentous bacteria and ileo-colonic inflammation in a model of Crohn's disease

BACKGROUND

Crohn's disease (CD) is associated with changes in the microbiota, and murine models of CD-like ileo-colonic inflammation depend on the presence of microbial triggers. Increased abundance of unknown Clostridiales and the microscopic detection of filamentous structures close to the epithelium of Tnf ΔARE mice, a mouse model of CD-like ileitis pointed towards segmented filamentous bacteria (SFB), a commensal mucosal adherent bacterium involved in ileal inflammation.

RESULTS

We show that the abundance of SFB strongly correlates with the severity of CD-like ileal inflammation in two mouse models of ileal inflammation, including Tnf ΔARE and SAMP/Yit mice. SFB mono-colonization of germ-free Tnf ΔARE mice confirmed the causal link and resulted in severe ileo-colonic inflammation, characterized by elevated tissue levels of Tnf and Il-17A, neutrophil infiltration and loss of Paneth and goblet cell function. Co-colonization of SFB in human-microbiota associated Tnf ΔARE mice confirmed that SFB presence is indispensable for disease development. Screening of 468 ileal and colonic mucosal biopsies from adult and pediatric IBD patients, using previously published and newly designed human SFB-specific primer sets, showed no presence of SFB in human tissue samples, suggesting a species-specific functionality of the pathobiont. Simulating the human relevant therapeutic effect of exclusive enteral nutrition (EEN), EEN-like purified diet antagonized SFB colonization and prevented disease development in Tnf ΔARE mice, providing functional evidence for the protective mechanism of diet in modulating microbiota-dependent inflammation in IBD.

CONCLUSIONS

We identified a novel pathogenic role of SFB in driving severe CD-like ileo-colonic inflammation characterized by loss of Paneth and goblet cell functions in Tnf ΔARE mice. A purified diet antagonized SFB colonization and prevented disease development in Tnf ΔARE mice in contrast to a fiber-containing chow diet, clearly demonstrating the important role of diet in modulating a novel IBD-relevant pathobiont and supporting a direct link between diet and microbial communities in mediating protective functions. Video Abstract.

Analysis of PTPN22 -1123 G>C, +788 G>A and +1858 C>T Polymorphisms in Patients with Primary Sjögren's Syndrome

BACKGROUND

Primary Sjögren's syndrome (pSS) is an autoimmune exocrinopathy characterized by lymphocytic infiltration, glandular dysfunction and systemic manifestations. Lyp protein is a negative regulator of the T cell receptor encoded by the tyrosine phosphatase nonreceptor-type 22 (PTPN22) gene. Multiple single-nucleotide polymorphisms (SNPs) in the PTPN22 gene have been associated with susceptibility to autoimmune diseases. This study aimed to investigate the association of PTPN22 SNPs rs2488457 (-1123 G>C), rs33996649 (+788 G>A), rs2476601 (+1858 C>T) with pSS susceptibility in Mexican mestizo subjects.

METHODS

One hundred fifty pSS patients and 180 healthy controls (HCs) were included. Genotypes of PTPN22 SNPs were identified by PCR-RFLP. PTPN22 expression was evaluated through RT-PCR analysis. Serum anti-SSA/Ro and anti-SSB/La levels were measured using an ELISA kit.

RESULTS

Allele and genotype frequencies for all SNPs studied were similar in both groups (p > 0.05). pSS patients showed 17-fold higher expression of PTNP22 than HCs, and mRNA levels correlated with SSDAI score (r² = 0.499, p = 0.008) and levels of anti-SSA/Ro and anti-SSB/La autoantibodies (r² = 0.200, p = 0.03 and r² = 0.175, p = 0.04, respectively). Positive anti-SSA/Ro pSS patients expressed higher PTPN22 mRNA levels (p = 0.008), with high focus scores by histopathology (p = 0.02). Moreover, PTPN22 expression had high diagnostic accuracy in pSS patients, with an AUC = 0.985.

CONCLUSIONS

Our findings demonstrate that the PTPN22 SNPs rs2488457 (-1123 G>C), rs33996649 (+788 G>A) and rs2476601 (+1858 C>T) are not associated with the disease susceptibility in the western Mexican population. Additionally, PTPN22 expression may be helpful as a diagnostic biomarker in pSS.

The protein kinase R modifies gut physiology to limit colitis

Here we investigate the function of the innate immune molecule protein kinase R (PKR) in intestinal inflammation. To model a colitogenic role of PKR, we determine the physiological response to dextran sulfate sodium (DSS) of wild-type and two transgenic mice strains mutated to express either a kinase-dead PKR or to ablate expression of the kinase. These experiments recognize kinase-dependent and -independent protection from DSS-induced weight loss and inflammation, against a kinase-dependent increase in the susceptibility to DSS-induced injury. We propose these effects arise through PKR-dependent alteration of gut physiology, evidenced as altered goblet cell function and changes to the gut microbiota at homeostasis that suppresses inflammasome activity by controlling autophagy. These findings establish that PKR functions as both a protein kinase and a signaling molecule in instituting immune homeostasis in the gut.

Capsaicin shapes gut microbiota and pre-metastatic niche to facilitate cancer metastasis to liver

Dietary factors are fundamental in tumorigenesis throughout our lifetime. A spicy diet has been ambiguous on the development of cancers, especially in the study of colon cancer metastasis. Here, we utilized a mouse metastasis model to test the potential role of capsaicin in influencing metastasis. Long-term continuous administration of capsaicin diet (300 mg/kg) to mice promotes the formation of liver pre-metastatic niche to facilitate the metastasis of colon cancer cells. Bacteria translocation to liver is clearly observed. Capsaicin increases intestinal barrier permeability and disrupts gut vascular barrier by altering the composition of gut microbiota. Capsaicin not only changes the abundance of mucin-related bacteria like Akkermanisa and Muribaculaceae, but also bacteria involved in bile acids metabolism. Dysregulated bile acids profile is related to the recruitment of natural killer T (NKT) cells in pre-metastatic niche, primary bile acid α-Muricholic acid can enhance the recruitment of NKT cells, while secondary bile acids Glycoursodeoxycholic acid and Taurohyodeoxycholic acid impair the recruitment of NKT cells. These findings reveal long term consumption of capsaicin increases the risk of cancer metastasis through modulating the gut microbiota. Capsaicin (300 mg/kg) disrupts gut barrier and promotes the translocation of bacteria to liver, while altered bile acids metabolism affects the recruitment of NKT cells in liver, forming a pre-metastatic niche and promoting cancer metastasis.

Effect of Clostridium butyricum on High-Fat Diet-Induced Intestinal Inflammation and Production of Short-Chain Fatty Acids

BACKGROUND/AIMS

A high-fat diet (HFD) can cause intestinal inflammation and alter the gut microbiota; probiotics, however, are known to have anti-inflammatory effects. This study aimed to investigate the response of rat colon to HFD and the effect of Clostridium butyricum on HFD-induced intestinal inflammation and production of short-chain fatty acids (SCFAs) according to sex.

METHODS

Male and female 6-week-old Fischer-344 rats were fed a chow diet or HFD for 8 weeks, and Biovita or three different concentrations of C. butyricum were orally gavaged. The levels of tight junction proteins (TJPs), inflammatory markers in the ascending colonic mucosa, and bile acids (BAs) and SCFAs in stool were measured.

RESULTS

HFD significantly increased the histological inflammation scores and fat proportions. Fecal BA levels were higher in the HFD group than in the control group, with a more prominent increase in deoxycholic acid/cholic acid after probiotics administration in females; however, no statistically significant differences were observed. TJPs showed an opposite response to HFD depending on sex, and tended to increase and decrease after HFD in males and females, respectively. The HFD-reduced TJPs were recovered by probiotics, with some statistical significance in females. HFD-decreased butyric acid in stools appeared to be recovered by probiotics in males, but not in females. The expression of inflammatory markers (TNF-α) was increased by HFD in males and decreased with medium-concentration probiotic supplementation. The opposite was observed in females. MPO was increased by HFD in both sexes and decreased by probiotic supplementation.

CONCLUSIONS

The probiotic C. butyricum improved indicators of HFD-induced colonic inflammation such as levels of inflammatory markers and increased the production of SCFAs and the expression of TJPs. These effects tended to be more pronounced in male rats, showing sex difference.

Changes in Gut Microbiome upon Orchiectomy and Testosterone Administration in AOM/DSS-Induced Colon Cancer Mouse Model

PURPOSE

Sex hormones are known to affect the gut microbiota. Previously, we reported that endogenous and exogenous testosterone are associated with colorectal cancer (CRC) development and submucosal invasion. In the present study, we investigated whether the gut microbiota is affected by orchiectomy (ORX) and testosterone propionate (TP) administration using an azoxymethane/dextran sulfate sodium (AOM/DSS)-induced CRC mouse model.

MATERIALS AND METHODS

Gut microbiota was evaluated by means of 16S rRNA gene sequencing of stool DNA extracted from feces that were obtained at 13 weeks after AOM injection (from 22-week-old animals) and stored in a gas-generating pouch.

RESULTS

The increase in microbial diversity (Chao1 and Phylogenetic Diversity index) and Firmicutes/Bacteroidetes (F/B) ratio upon AOM/DSS treatment in ORX mice was significantly decreased by TP supplementation. The ratio of commensal bacteria to opportunistic pathogens was lower in the TP-administered females and ORX mice than in the AOM/DSS group. Opportunistic pathogens (Mucispirillum schaedleri or Akkermansia muciniphila) were identified only in the TP group. In addition, microbial diversity and F/B ratio were higher in male controls than in female and ORX controls. Flintibacter butyricus, Ruminococcus bromii, and Romboutsia timonensis showed similar changes in the male control group as those in the female and ORX controls.

CONCLUSION

In conclusion, testosterone determines the dysbiosis of gut microbiota, which suggests that it plays a role in the sex-related differences in colorectal carcinogenesis.

The HIF-prolyl hydroxylases have distinct and nonredundant roles in colitis-associated cancer

Colitis-associated colorectal cancer (CAC) is a severe complication of inflammatory bowel disease (IBD). HIF-prolyl hydroxylases (PHD1, PHD2, and PHD3) control cellular adaptation to hypoxia and are considered promising therapeutic targets in IBD. However, their relevance in the pathogenesis of CAC remains elusive. We induced CAC in Phd1-/-, Phd2+/-, Phd3-/-, and WT mice with azoxymethane (AOM) and dextran sodium sulfate (DSS). Phd1-/- mice were protected against chronic colitis and displayed diminished CAC growth compared with WT mice. In Phd3-/- mice, colitis activity and CAC growth remained unaltered. In Phd2+/- mice, colitis activity was unaffected, but CAC growth was aggravated. Mechanistically, Phd2 deficiency (i) increased the number of tumor-associated macrophages in AOM/DSS-induced tumors, (ii) promoted the expression of EGFR ligand epiregulin in macrophages, and (iii) augmented the signal transducer and activator of transcription 3 and extracellular signal-regulated kinase 1/2 signaling, which at least in part contributed to aggravated tumor cell proliferation in colitis-associated tumors. Consistently, Phd2 deficiency in hematopoietic (Vav:Cre-Phd2fl/fl) but not in intestinal epithelial cells (Villin:Cre-Phd2fl/fl) increased CAC growth. In conclusion, the 3 different PHD isoenzymes have distinct and nonredundant effects, promoting (PHD1), diminishing (PHD2), or neutral (PHD3), on CAC growth.

Premorbid Steatohepatitis Increases the Seriousness of Dextran Sulfate Sodium-induced Ulcerative Colitis in Mice

BACKGROUND AND AIMS

The concurrence of nonalcoholic steatohepatitis (NASH) and ulcerative colitis (UC) is increasingly seen in clinical practice, but the underlying mechanisms remain unclear. This study aimed to develop a mouse model of the phenomenon by combining high-fat high-cholesterol diet (HFHCD)-induced NASH and dextran sulfate sodium (DSS)-induced UC, that would support mechanistic studies.

METHODS

Male C57BL/6 mice were randomly assigned to two groups receiving either a chow diet or HFHCD for 12 weeks of NASH modeling. The mice were the divided into four subgroups for UC modeling: (1) A control group given a chow diet with normal drinking water; (2) A colitis group given chow diet with 2% DSS in drinking water; (3) A steatohepatitis group given HFHCD with normal drinking water; and (4) A steatohepatitis + colitis group given HFHCD with 2% DSS in drinking water.

RESULTS

NASH plus UC had high mortality (58.3%). Neither NASH nor UC alone were fatal. Although DSS-induced colitis did not exacerbate histological liver injury in HFHCD-fed mice, premorbid NASH significantly increased UC-related gut injury compared with UC alone. It was characterized by a significantly shorter colon, more colonic congestion, and a higher histopathological score (p<0.05). Inflammatory (tumor necrosis factor-alpha, interleukin 1 beta, C-C motif chemokine ligand 2, and nuclear factor kappa B) and apoptotic (Bcl2, Bad, Bim, and Bax) signaling pathways were significantly altered in distal colon tissues collected from mice with steatohepatitis + colitis compared with the other experimental groups.

CONCLUSIONS

Premorbid steatohepatitis significantly aggravated DSS-induced colitis and brought about a lethal phenotype. Potential links between NASH and UC pathogeneses can be investigated using this model.

The intestinal clock drives the microbiome to maintain gastrointestinal homeostasis

Diurnal (i.e., 24-hour) oscillations of the gut microbiome have been described in various species including mice and humans. However, the driving force behind these rhythms remains less clear. In this study, we differentiate between endogenous and exogenous time cues driving microbial rhythms. Our results demonstrate that fecal microbial oscillations are maintained in mice kept in the absence of light, supporting a role of the host's circadian system rather than representing a diurnal response to environmental changes. Intestinal epithelial cell-specific ablation of the core clock gene Bmal1 disrupts rhythmicity of microbiota. Targeted metabolomics functionally link intestinal clock-controlled bacteria to microbial-derived products, in particular branched-chain fatty acids and secondary bile acids. Microbiota transfer from intestinal clock-deficient mice into germ-free mice altered intestinal gene expression, enhanced lymphoid organ weights and suppressed immune cell recruitment. These results highlight the importance of functional intestinal clocks for microbiota composition and function, which is required to balance the host's gastrointestinal homeostasis.

Dextran Sulphate Sodium Acute Colitis Rat Model: A Suitable Tool for Advancing Our Understanding of Immune and Microbial Mechanisms in the Pathogenesis of Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is a group of disorders causing inflammation in the digestive tract. Recent data suggest that dysbiosis may play a pivotal role in the IBD pathogenesis. As microbiome-based therapeutics that modulate the gut ecology have been proposed as a novel strategy for preventing IBD, the aim of presenting study was to evaluate the dextran sulphate sodium (DSS) rat model mainly in terms of microbial shifts to confirm its suitability for dysbiosis study in IBD. Acute colitis was induced using 5% DSS solution for seven days and rats were euthanized five days after DSS removal. The faecal/caecal microbiota was analyzed by next generation sequencing. Disease activity index (DAI) score was evaluated daily. Blood and colon tissue immunophenotyping was assessed by flow cytometry and histological, haematological, and biochemical parameters were also evaluated. The colitis induction was reflected in a significantly higher DAI score and changes in all parameters measured. This study demonstrated significant shifts in the colitis-related microbial species after colitis induction. The characteristic inflammation-associated microbiota could be detected even after a five day-recovery period. Moreover, the DSS-model might contribute to an understanding of the effect of different treatments on extraintestinal organ impairments. The observation that certain bacterial species in the gut microbiota are associated with colitis raises the question of whether these organisms are contributors to, or a consequence of the disease. Despite some limitations, we confirmed the suitability of DSS-induced colitis model to monitor microbial changes during acute colitis, in order to test attractive new microbiome-based therapies.

Experimental Intestinal Stenosis Alters Crohn's Disease-Like Intestinal Inflammation in Ileitis-Prone Mice

BACKGROUND

Clinical observations indicate that mechanical factors contribute to the expression or recurrence of Crohn's disease. We investigated whether the creation of an intestinal stenosis could alter the severity of the expected Crohn-like ileitis, in a Crohn's disease animal model, the TNF^Δare/+ mouse.

METHODS

Thirty-six, 6-weeks-old TNF^Δare/+ mice, were divided into 3 intervention groups: triple suture, single suture and sham. In the terminal ileum, in the first group, a triple suture stenosis was created, whereas, in the second, a loose suture was placed. Same triple-suture stenosis was performed on twelve wild type mice. All animals were sacrificed at 6 weeks post-operatively and the ileum parts were evaluated histopathologically. A summative total ileitis score was applied in each sample using a bespoke semiquantitative histological scoring system for the Crohn-like changes.

RESULTS

The triple suture stenosis induced significant muscular hypertrophy proximal to interventional site which was more prominent in TNF^Δare/+ than wild type mice. In triple suture group, the total ileitis score was significantly increased proximal to the intervention as compared to the single suture (P: 0.004) and the sham groups (P: 0.013). The total ileitis score distally, was unaffected, regardless of the experimental intervention. Intestinal stenosis did not induce intestinal inflammation in wild type mice.

CONCLUSION

The creation of a stenosis in the terminal ileum of TNF^Δare/+ mice alters Crohn-like inflammation. We assume that mechanical forces, such as intraluminal pressure, may contribute as important co-factors to the pathophysiology of Crohn's disease in genetically predisposed subjects.

Cyclic GMP-AMP synthase contributes to epithelial homeostasis in intestinal inflammation via Beclin-1-mediated autophagy

Inflammatory bowel disease (IBD) represents a set of idiopathic and chronic inflammatory diseases of the gastrointestinal tract. Central to the pathogenesis of IBD is a dysregulation of normal intestinal epithelial homeostasis. cGAS is a DNA-sensing receptor demonstrated to promote autophagy, a mechanism that removes dysfunctional cellular components. Beclin-1 is a crucial protein involved in the initiation of autophagy. We hypothesized that cGAS plays a key role in intestinal homeostasis by upregulating Beclin-1-mediated autophagy. We evaluated intestinal cGAS levels in humans with IBD and in murine colonic tissue after performing a 2% dextran sulfate sodium (DSS) colitis model. Autophagy and cell death mechanisms were studied in cGAS KO and WT mice via qPCR, WB analysis, H&E, IF, and TUNEL staining. Autophagy was measured in stimulated intestinal epithelial cells (IECs) via WB analysis. Our data demonstrates cGAS to be upregulated during human and murine colitis. Furthermore, cGAS deficiency leads to worsened colitis and decreased levels of autophagy proteins including Beclin-1 and LC3-II. Co-IP demonstrates a direct binding between cGAS and Beclin-1 in IECs. Transfection of cGAS in stimulated HCT-116 cells leads to increased autophagy. IECs isolated from cGAS KO have diminished autophagic flux. cGAS KO mice subjected to DSS have increased cell death and cleaved caspase-3. Lastly, treatment of cGAS KO mice with rapamycin decreased the severity of colitis. Our data suggest that cGAS maintains intestinal epithelial homeostasis during human IBD and murine colitis by upregulating Beclin-1-mediated autophagy and preventing IEC death. Rescue of autophagy can attenuate the severity of colitis associated with cGAS deficiency.

Antibody-Pattern Recognition Receptor Agonist Conjugates: A Promising Therapeutic Strategy for Cancer

Antibody-drug conjugates (ADCs) are composed of monoclonal antibodies linked to cytotoxic payload drugs, each of which can be diversely designed in accordance with pharmacological and clinical requirements. The use of ADCs is effective for the treatment of different diseases, including cancers, and is gaining widespread attention. To date, 12 ADCs have been approved by the U.S. Food and Drug Administration for treating cancer and improving the quality of life of patients. To expand the application of ADCs and improve their treatment efficiency, various formats have recently been manufactured, including pattern recognition receptor (PRR) agonist-based ADCs. The antibody has a unique structure that enables the specific delivery of PRR agonists to the tumor area, and this improves the therapeutic efficacy while minimizing systemic toxicity. This review briefly discusses the current landscape and future perspectives of antibody-PRR agonist conjugates for cancer therapy.

Multi-omics analyses of the ulcerative colitis gut microbiome link Bacteroides vulgatus proteases with disease severity

Ulcerative colitis (UC) is driven by disruptions in host-microbiota homoeostasis, but current treatments exclusively target host inflammatory pathways. To understand how host-microbiota interactions become disrupted in UC, we collected and analysed six faecal- or serum-based omic datasets (metaproteomic, metabolomic, metagenomic, metapeptidomic and amplicon sequencing profiles of faecal samples and proteomic profiles of serum samples) from 40 UC patients at a single inflammatory bowel disease centre, as well as various clinical, endoscopic and histologic measures of disease activity. A validation cohort of 210 samples (73 UC, 117 Crohn's disease, 20 healthy controls) was collected and analysed separately and independently. Data integration across both cohorts showed that a subset of the clinically active UC patients had an overabundance of proteases that originated from the bacterium Bacteroides vulgatus. To test whether B. vulgatus proteases contribute to UC disease activity, we first profiled B. vulgatus proteases found in patients and bacterial cultures. Use of a broad-spectrum protease inhibitor improved B. vulgatus-induced barrier dysfunction in vitro, and prevented colitis in B. vulgatus monocolonized, IL10-deficient mice. Furthermore, transplantation of faeces from UC patients with a high abundance of B. vulgatus proteases into germfree mice induced colitis dependent on protease activity. These results, stemming from a multi-omics approach, improve understanding of functional microbiota alterations that drive UC and provide a resource for identifying other pathways that could be inhibited as a strategy to treat this disease.

YAP Activates STAT3 Signalling to Promote Colonic Epithelial Cell Proliferation in DSS-Induced Colitis and Colitis Associated Cancer

BACKGROUND AND AIMS

Yes-associated protein (YAP) is a key transcriptional coactivator of cell proliferation and differentiation. In this study, we sought to identify the roles of YAP in colonic epithelial regeneration and tumourigenesis.

METHODS

Murine DSS-induced colitis and YAP overexpression models were constructed via lentiviral intraperitoneal injection. Stable YAP-overexpressing cells, protein immunoprecipitation, and ChIP were used to deeply explore the molecular mechanism.

RESULTS

We found that the expression of YAP was dramatically diminished in the colonic crypts during the acute colitis phase, while YAP was strikingly enhanced to initiate tissue repair after DSS withdrawal. Overexpressing YAP in mice drastically accelerated epithelial regeneration, presenting with more intact structural integrity and reduced inflammatory cell infiltration in the mucosa. Further mechanistic studies showed that the expression of YAP in the nucleus was significantly increased by 2 h post-DSS removal, accompanied by upregulated protein levels of activated STAT3. Overexpression of YAP (YAP^WT) elevated the expression of activated STAT3 and its transcriptional targets and strengthened the proliferation and "wound healing" ability of colonic cells. However, these effects were reversed when STAT3 was silenced in YAP^WT cells. Moreover, YAP could directly interact with STAT3 in the nucleus, and c-Myc and CyclinD1 were the transcriptional targets. Finally, during colitis-associated cancer (CAC), YAP^WT promoted the progression of CAC, while the phosphomimetic YAP downregulated the expression of STAT3 and inhibited the development and progression of CAC.

CONCLUSION

YAP activates STAT3 signalling to facilitate mucosal regeneration after DSS-induced colitis. However, excessive YAP activation in the colonic epithelium promotes CAC development.

Regulation and Function of Interferon-Lambda (IFNλ) and Its Receptor in Asthma

Asthma is a chronic respiratory disease affecting people of all ages, especially children, worldwide. Origins of asthma are suggested to be placed in early life with heterogeneous clinical presentation, severity and pathophysiology. Exacerbations of asthma disease can be triggered by many factors, including viral respiratory tract infections. Rhinovirus (RV) induced respiratory infections are the predominant cause of the common cold and also play a crucial role in asthma development and exacerbations. Rhinovirus mainly replicates in epithelial cells lining the upper and lower respiratory tract. Type III interferons, also known as interferon-lambda (IFNλ), are potent immune mediators of resolution of infectious diseases but they are known to be involved in autoimmune diseases as well. The protective role of type III IFNs in antiviral, antibacterial, antifungal and antiprotozoal functions is of major importance for our innate immune system. The IFNλ receptor (IFNλR) is expressed in selected types of cells like epithelial cells, thus orchestrating a specific immune response at the site of viruses and bacteria entry into the body. In asthma, IFNλ restricts the development of TH2 cells, which are induced in the airways of asthmatic patients. Several studies described type III IFNs as the predominant type of interferon increased after infection caused by respiratory viruses. It efficiently reduces viral replication, viral spread into the lungs and viral transmission from infected to naive individuals. Several reports showed that bronchial epithelial cells from asthmatic subjects have a deficient response of type III interferon after RV infection ex vivo. Toll like Receptors (TLRs) recognize pathogen-associated molecular patterns (PAMPs) expressed on infectious agents, and induce the development of antiviral and antibacterial immunity. We recently discovered that activation of TLR7/8 resulted in enhanced IFNλ receptor mRNA expression in PBMCs of healthy and asthmatic children, opening new therapeutic frontiers for rhinovirus-induced asthma. This article reviews the recent advances of the literature on the regulated expression of type III Interferons and their receptor in association with rhinovirus infection in asthmatic subjects.

The Panda-Derived Lactobacillus plantarum G201683 Alleviates the Inflammatory Response in DSS-Induced Panda Microbiota-Associated Mice

Intestinal diseases are one of the main causes of captive giant panda death. Their special dietary habits and gastrointestinal tract structure often lead to intestinal epithelium damage and secondary intestinal infection. The captive giant panda is predisposed to suffer from microbiota dysbiosis due to long-term artificial feeding and antibiotic misuse. However, there are few reported probiotics to treat giant panda enteritis and the associated dysbiosis. This study aims to elucidate the mechanism by which Lactobacillus plantarum G201683 (L. plantarum G83), a promising panda-derived probiotic, exerts a protective effect on intestinal inflammation in the dextran sulfate sodium- (DSS) induced panda microbiota-associated (DPMA) mouse model. The DPMA mouse was generated by antibiotic treatment and 5% DSS drinking water administration to assess the effect of L. plantarum G83 on intestinal inflammation and microbiota in vivo. Our results demonstrated the successful generation of a DPMA mouse model with Enterobacteriaceae enrichment, consistent with the giant panda intestinal microbiota. L. plantarum G83 decreased clinical and histological severity of intestinal inflammation, enhanced intestinal tight junction protein expression (ZO-1, Occludin) and alleviated inflammatory cytokine production (TNF-) in the colon of DPMA mice. The administration of L. plantarum G83 altered the microbiota composition by decreasing pathogen associated taxa such as E. coli and increasing abundance of beneficial bacteria including Bifidobacterium spp. These changes in microbiota composition were associated with an increased concentration of short chain fatty acids (SCFA), reduced NF-κB signaling, and an altered balance of T helper cell subsets. Our findings support L. plantarum G83 as a promising probiotic to treat intestinal inflammation in the giant panda.

Functional screen of inflammatory bowel disease genes reveals key epithelial functions

BACKGROUND

Genetic studies have been tremendously successful in identifying genomic regions associated with a wide variety of phenotypes, although the success of these studies in identifying causal genes, their variants, and their functional impacts has been more limited.

METHODS

We identified 145 genes from IBD-associated genomic loci having endogenous expression within the intestinal epithelial cell compartment. We evaluated the impact of lentiviral transfer of the open reading frame (ORF) of these IBD genes into the HT-29 intestinal epithelial cell line via transcriptomic analyses. By comparing the genes in which expression was modulated by each ORF, as well as the functions enriched within these gene lists, we identified ORFs with shared impacts and their putative disease-relevant biological functions.

RESULTS

Analysis of the transcriptomic data for cell lines expressing the ORFs for known causal genes such as HNF4a, IFIH1, and SMAD3 identified functions consistent with what is already known for these genes. These analyses also identified two major clusters of genes: Cluster 1 contained the known IBD causal genes IFIH1, SBNO2, NFKB1, and NOD2, as well as genes from other IBD loci (ZFP36L1, IRF1, GIGYF1, OTUD3, AIRE and PITX1), whereas Cluster 2 contained the known causal gene KSR1 and implicated DUSP16 from another IBD locus. Our analyses highlight how multiple IBD gene candidates can impact on epithelial structure and function, including the protection of the mucosa from intestinal microbiota, and demonstrate that DUSP16 acts a regulator of MAPK activity and contributes to mucosal defense, in part via its regulation of the polymeric immunoglobulin receptor, involved in the protection of the intestinal mucosa from enteric microbiota.

CONCLUSIONS

This functional screen, based on expressing IBD genes within an appropriate cellular context, in this instance intestinal epithelial cells, resulted in changes to the cell's transcriptome that are relevant to their endogenous biological function(s). This not only helped in identifying likely causal genes within genetic loci but also provided insight into their biological functions. Furthermore, this work has highlighted the central role of intestinal epithelial cells in IBD pathophysiology, providing a scientific rationale for a drug development strategy that targets epithelial functions in addition to the current therapies targeting immune functions.

Thalidomide Attenuates Colitis and Is Associated with the Suppression of M1 Macrophage Polarization by Targeting the Transcription Factor IRF5

BACKGROUND

Ulcerative colitis (UC) is a chronic inflammatory bowel disease. The TNF-α inhibitor thalidomide is reported to be effective for inducing remission in pediatric Crohn's disease (CD) and adults with refractory CD. The mechanisms underlying the immunomodulatory and anti-inflammatory properties of thalidomide are unclear.

METHODS

Histological assessments were firstly performed in thalidomide treated UC patients. Then the effect of thalidomide in vivo was detected in DSS-induced murine colitis. The mechanism involving IRF5, and M1 macrophage polarization was investigated by using plasmid transfection, western blotting, and real-time PCR. Finally, AOM/DSS model was used to detect the role of thalidomide in colitis associated cancer.

RESULTS

We first found that treatment with thalidomide could ameliorate colon inflammation for 8 weeks and promote mucosal healing in human UC. Moreover, treatment with thalidomide protected mice from dextran sodium sulfate (DSS)-induced acute colitis, with treated mice presenting with a higher body weight, lower histological score, and lower DAI. Concomitantly, in comparison with control mice, mice treated with thalidomide showed accelerated recovery following colitis after 10 days of thalidomide treatment. Mechanistically, we observed that thalidomide could increase epithelial cell self-renewal capacity and modulate M1/M2 polarization by decreasing M1 markers CD86 and CCR7 and increasing M2 protein signatures CD206 and Arg-1. Thalidomide controls M1 macrophage polarization by targeting the transcription factor IRF5. Finally, by using the classical AOM/DSS model, we found that thalidomide-treated mice presented with a lower incidence and growth of colitis-associated carcinoma (CAC) than negative control mice.

CONCLUSIONS

In summary, thalidomide suppresses M1 polarization in the inflammatory microenvironment, which not only attenuates colonic inflammation to facilitate mucosal healing after DSS-induced injury but also represses the progression of CAC.

Recombinant CRAMP-producing Lactococcus lactis attenuates dextran sulfate sodium-induced colitis by colonic colonization and inhibiting p38/NF-κB signaling

Background

Inflammatory bowel diseases (IBDs) are generally characterized by persistent abdominal pain and diarrhea caused by chronic inflammation in the intestine. Cathelicidins are antimicrobial peptides with pleiotropic roles in anti-infection, wound healing, and immune modulation. However, the sensitivity to the acidic environment and short half-life of cathelicidins limit their application in IBD treatment. Recombinant cathelicidin-related antimicrobial peptide (CRAMP)-producing Lactococcus lactis may represent a potential approach for IBD therapy.

Objective

The aim of this study was to develop recombinant CRAMP-producing L. lactis NZ9000 and explore the role and mechanism of recombinant L. lactis NZ9000 expressing CRAMP in colitis.

Design

We constructed two strains of CRAMP-producing L. lactis NZ9000 with different plasmids pMG36e (L.L-pMU45CR) or pNZ8148 (L.L-pNU45CR), which use a Usp45 secretion signal to drive the secretion of CRAMP. Bacterial suspensions were orally supplemented to mice with a syringe for 4 days after dextran sodium sulfate (DSS) treatment. Body weight change, disease active score, colon length, and colonic histology were determined. The expression of tight junction (ZO-1, ZO-2, and Occludin) and cytokines (IL-6, IL-1β, TNF-α, and IL-10) in colon was performed by qPCR. The expression of p-ERK, p-p38, and p-p65 was determined by Western blot analysis.

Results

Both CRAMP-producing L. lactis NZ9000 strains protected against colitis, as shown by reduced weight loss and disease activity score, improved colon shortening, and histopathological injury. In addition, CRAMP-producing L. lactis NZ9000 restored gut barrier by upregulating ZO-1, ZO-2, and occludin. Moreover, CRAMP-producing L. lactis NZ9000 regulated the colonic cytokines profile with reduced IL-6, IL-1β, and TNF-α production, and increased IL-10 production. By further analysis, we found that CRAMP-producing L. lactis NZ9000 reduced the expression of p-p38 and p-p65.

Conclusions

Together, our data suggested that CRAMP-secreting L. lactis NZ9000 attenuated dextran sulfate sodium-induced colitis by colonic colonization and inhibiting p38/NF-κB signaling. Orally administered recombinant CRAMP-secreting L. lactis NZ9000 represents a potential strategy for colitis therapy.

Protein arginine methyltransferase 2 (PRMT2) promotes dextran sulfate sodium-induced colitis by inhibiting the SOCS3 promoter via histone H3R8 asymmetric dimethylation

BACKGROUND AND PURPOSE

There is emerging evidence for a critical role for epigenetic modifiers in the development of inflammatory bowel disease (IBD). Protein arginine methyltransferase 2 (PRMT2) is responsible for the methylation of arginine residues on histones and targets transcription factors involved in many cellular processes, including gene transcription, mRNA splicing, cell proliferation, and cell differentiation. In this study, the role and underlying mechanisms of PRMT2 in colitis were studied.

EXPERIMENTAL APPROACH

A mouse dextran sulfate sodium (DSS)-induced experimental colitis model was used to study PRMT2 in colitis. Lentivirus-induced PRMT2 silencing or overexpression in vivo was applied to address the role of PRMT2 in colitis. Detailed western blot and expression analysis were done to understand epigenetic changes induced by PRMT2 in colitis.

KEY RESULTS

PRMT2 is highly expressed in inflammatory bowel disease patients, in inflamed murine colon and in TNF-α stimulated murine gut epithelial cells. PRMT2 overexpression aggravates, while knockdown alleviates DSS-induced colitis, suggesting that PRMT2 is a pivotal mediator of colitis in mice. Mechanistically, PRMT2 mediates colitis by increasing repressive histone mark H3R8 asymmetric methylation (H3R8me2a) at the promoter region of the suppressor of cytokine signalling 3 promoter (SOCS3). Resultant inhibition of SOCS3 expression and inhibition of SOCS3-mediated degradation of TNF receptor associated factor 5 (TRAF5) via ubiquitination led to elevated TRAF5 expression and TRAF5-mediated downstream NF-κB/MAPK activation.

CONCLUSION AND IMPLICATIONS

Our study demonstrates that PRMT2 acts as a transcriptional co-activator for proinflammatory genes during colitis. Hence, targeting PRMT2 may provide a novel therapeutic approach for colitis.

Epithelial wound healing in inflammatory bowel diseases: the next therapeutic frontier

Patients with one of the many chronic inflammatory disorders broadly classified as inflammatory bowel disease (IBD) now have a diverse set of immunomodulatory therapies at their disposal. Despite these recent medical advances, complete sustained remission of disease remains elusive for most patients. The full healing of the damaged intestinal mucosa is the primary goal of all therapies. Achieving this requires not just a reduction of the aberrant immunological response, but also wound healing of the epithelium. No currently approved therapy directly targets the epithelium. Epithelial repair is compromised in IBD and normally facilitates re-establishment of the homeostatic barrier between the host and the microbiome. In this review, we summarize the evidence that epithelial wound healing represents an important yet underdeveloped therapeutic modality for IBD. We highlight 3 general approaches that are promising for developing a new class of epithelium-targeted therapies: epithelial stem cells, cytokines, and microbiome engineering. We also provide a frank discussion of some of the challenges that must be overcome for epithelial repair to be therapeutically leveraged. A concerted approach by the field to develop new therapies targeting epithelial wound healing will offer patients a game-changing, complementary class of medications and could dramatically improve outcomes.

Fermented and Germinated Processing Improved the Protective Effects of Foxtail Millet Whole Grain Against Dextran Sulfate Sodium-Induced Acute Ulcerative Colitis and Gut Microbiota Dysbiosis in C57BL/6 Mice

This study investigated the effects of foxtail millet whole grain flours obtained through different processing methods on alleviating symptoms and gut microbiota dysbiosis in a dextran sulfate sodium (DSS)-induced murine colitis model. Sixty C57BL/6 mice were divided into six groups (n = 10 in each group), including one control group (CTRL) without DSS treatment and five DSS-treated groups receiving one of the following diets: AIN-93M standard diet (93MD), whole grain foxtail millet flour (FM), fermented (F-FM), germinated (G-FM), and fermented-germinated foxtail millet flour (FG-FM). A comparison of the disease activity index (DAI) demonstrated that foxtail millet whole grain-based diets could alleviate the symptoms of enteritis to varying degrees. In addition, 16S rRNA gene sequencing revealed that FG-FM almost completely alleviated DSS-induced dysbiosis. Mice on the FG-FM diet also had the lowest plasma IL-6 levels and claudin2 expression levels in the colon, indicating reduced systemic inflammation and improved gut barrier function. This study suggested that foxtail millet whole grain is an attractive choice for the intervention of IBD and gut microbiota dysbiosis, and its prebiotic properties are highly affected by the processing methods.

Interfering With Inflammation: Heterogeneous Effects of Interferons in Graft-Versus-Host Disease of the Gastrointestinal Tract and Inflammatory Bowel Disease

The intestine can be the target of several immunologically mediated diseases, including graft-versus-host disease (GVHD) and inflammatory bowel disease (IBD). GVHD is a life-threatening complication that occurs after allogeneic hematopoietic stem cell transplantation. Involvement of the gastrointestinal tract is associated with a particularly high mortality. GVHD development starts with the recognition of allo-antigens in the recipient by the donor immune system, which elicits immune-mediated damage of otherwise healthy tissues. IBD describes a group of immunologically mediated chronic inflammatory diseases of the intestine. Several aspects, including genetic predisposition and immune dysregulation, are responsible for the development of IBD, with Crohn’s disease and ulcerative colitis being the two most common variants. GVHD and IBD share multiple key features of their onset and development, including intestinal tissue damage and loss of intestinal barrier function. A further common feature in the pathophysiology of both diseases is the involvement of cytokines such as type I and II interferons (IFNs), amongst others. IFNs are a family of protein mediators produced as a part of the inflammatory response, typically to pathogens or malignant cells. Diverse, and partially paradoxical, effects have been described for IFNs in GVHD and IBD. This review summarizes current knowledge on the role of type I, II and III IFNs, including basic concepts and controversies about their functions in the context of GVHD and IBD. In addition, therapeutic options, research developments and remaining open questions are addressed.

Testosterone strongly enhances azoxymethane/dextran sulfate sodium-induced colorectal cancer development in C57BL/6 mice

Colorectal cancer (CRC) is known to occur more frequently in males than in females, with sex hormones reportedly influencing the development. The purpose of the study was to investigate whether orchiectomy in C57BL/6 male mice reduces colorectal tumorigenesis and whether testosterone administration increases tumorigenesis after orchiectomy in an azoxymethane (AOM)/dextran sulfate sodium (DSS) mouse model. Clinical symptoms, including colitis and tumor incidence, were evaluated in the absence or presence of testosterone in AOM/DSS-treated male, as well as orchiectomized (ORX) male and female mice. The levels of serum testosterone and colonic myeloperoxidase, interleukin (IL)-1β, and IL-6 were measured by ELISA. Target mRNA expression was assessed by quantitative real-time PCR. Orchiectomy significantly diminished the AOM/DSS-induced colitis indices, including disease activity index, colon shortening, and histological severity at week 2, and decreased tumor numbers and incidence rates in the distal part of the colon increased following AOM/DSS administration at week 13; this reduction was reversed by testosterone supplementation. Furthermore, it was confirmed that the ELISA level (MPO and IL-1β) and the mRNA expression of the inflammatory mediators (COX-2 and iNOS) were maintained at high levels in the tumors of the testosterone-treated group compared with AOM/DSS groups. Interestingly, both endogenous and exogenous testosterone administrations were associated with tumor development (> 2 mm in size) and submucosal invasive cancer. Based on multivariate logistic regression analysis, testosterone was identified as a reasonable hazard factor for the progression of submucosal invasive cancer of the distal colon. In conclusion, endogenous and exogenous testosterone presented a stimulating effect on AOM/DSS-induced colitis and carcinogenicity.

Critical role of interferons in gastrointestinal injury repair

The etiology of ulcerative colitis is poorly understood and is likely to involve perturbation of the complex interactions between the mucosal immune system and the commensal bacteria of the gut, with cytokines acting as important cross-regulators. Here we use IFN receptor-deficient mice in a dextran sulfate sodium (DSS) model of acute intestinal injury to study the contributions of type I and III interferons (IFN) to the initiation, progression and resolution of acute colitis. We find that mice lacking both types of IFN receptors exhibit enhanced barrier destruction, extensive loss of goblet cells and diminished proliferation of epithelial cells in the colon following DSS-induced damage. Impaired mucosal healing in double IFN receptor-deficient mice is driven by decreased amphiregulin expression, which IFN signaling can up-regulate in either the epithelial or hematopoietic compartment. Together, these data underscore the pleiotropic functions of IFNs and demonstrate that these critical antiviral cytokines also support epithelial regeneration following acute colonic injury.

Targeted intestinal deletion of Rho guanine nucleotide exchange factor 7, βPIX, impairs enterocyte proliferation, villus maturation, and mucosal defenses in mice

Rho guanine nucleotide exchange factors (RhoGEFs) regulate Rho GTPase activity and cytoskeletal and cell adhesion dynamics. βPix, a CDC42/RAC family RhoGEF encoded by ARHGEF7, is reported to modulate human colon cancer cell proliferation and postwounding restitution of rat intestinal epithelial monolayers. We hypothesized that βPix plays a role in maintaining intestinal epithelial homeostasis. To test this hypothesis, we examined βPix distribution in the human and murine intestine and created mice with intestinal epithelial-selective βPix deletion [βPixflox/flox/Tg(villin-Cre); Arhgef7 CKO mice]. Using Arhgef7 conditional knockout (CKO) and control mice, we investigated the consequences of βPix deficiency in vivo on intestinal epithelial and enteroid development, dextran sodium sulfate-induced mucosal injury, and gut permeability. In normal human and murine intestines, we observed diffuse cytoplasmic and moderate nuclear βPix immunostaining in enterocytes. Arhgef7 CKO mice were viable and fertile, with normal gross intestinal architecture but reduced small intestinal villus height, villus-to-crypt ratio, and goblet cells; small intestinal crypt cells had reduced Ki67 staining, compatible with impaired cell proliferation. Enteroids derived from control mouse small intestine were viable for more than 20 passages, but those from Arhgef7 CKO mice did not survive beyond 24 h despite addition of Wnt proteins or conditioned media from normal enteroids. Adding a Rho kinase (ROCK) inhibitor partially rescued CKO enteroid development. Compared with littermate control mice, dextran sodium sulfate-treated βPix-deficient mice lost more weight and had greater impairment of intestinal barrier function, and more severe colonic mucosal injury. These findings reveal βPix expression is important for enterocyte development, intestinal homeostasis, and resistance to toxic injury.NEW & NOTEWORTHY To explore the role of βPix, a guanine nucleotide exchange factor encoded by ARHGEF7, in intestinal development and physiology, we created mice with intestinal epithelial cell Arhgef7/βPix deficiency. We found βPix essential for normal small intestinal epithelial cell proliferation, villus development, and mucosal resistance to injury. Moreover, Rho kinase signaling mediated developmental arrest observed in enteroids derived from βPix-deficient small intestinal crypts. Our studies provide insights into the role Arhgef7/βPix plays in intestinal epithelial homeostasis.

Nuclear Factor Erythroid 2-related Factor 2 Knockout Suppresses the Development of Aggressive Colorectal Cancer Formation Induced by Azoxymethane/Dextran Sulfate Sodium-Treatment in Female Mice

Colon tumors develop more frequently in male than in female. Nuclear factor erythroid 2-related factor 2 (Nrf2) plays differential roles in the stage of tumorigenesis. The purpose of this study was to investigate the role of Nrf2 on colitis-associated tumorigenesis using Nrf2 knockout (KO) female mice. Azoxymethane (AOM) and dextran sulfate sodium (DSS)-treated wild-type (WT) and Nrf2 KO female mice were sacrificed at week 2 and 16 after AOM injection. Severity of colitis, tumor incidence, and levels of inflammatory mediators were evaluated in AOM/DSS-treated WT and Nrf2 KO mice. Furthermore, qRT-PCR, Western blot abnalysis, and ELISA were performed in colon tissues. At week 2, AOM/DSS-induced colon tissue damages were significantly greater in Nrf2 KO than in WT mice. At week 16, tumor numbers (> 2 mm size) were significantly lower in both the proximal and distal colon in Nrf2 KO compared to WT. The overall incidences of adenoma/cancer of the proximal colon and submucosal invasive cancer of the distal colon were reduced by Nrf2 KO. The mRNA and protein expression levels of NF-κB-related mediators (i.e., iNOS and COX-2) and Nrf2-related antioxidants (i.e., heme oxygenase-1 and glutamate-cysteine ligase catalytic subunit) were significantly lower in the Nrf2 KO than in WT mice. Interestingly, the protein level of 15-hydroxyprostaglandin dehydrogenase (15-PGDH) was higher in AOM/DSS-treated Nrf2 KO than in WT mice. Our results support the oncogenic effect of Nrf2 in the later stage of carcinogenesis and upregulation of tumor suppressor 15-PGDH might contribute to the repression of colitis-associated tumorigenesis in Nrf2 KO female mice.

The dark side of the gut: Virome-host interactions in intestinal homeostasis and disease

The diverse enteric viral communities that infect microbes and the animal host collectively constitute the gut virome. Although recent advances in sequencing and analysis of metaviromes have revealed the complexity of the virome and facilitated discovery of new viruses, our understanding of the enteric virome is still incomplete. Recent studies have uncovered how virome–host interactions can contribute to beneficial or detrimental outcomes for the host. Understanding the complex interactions between enteric viruses and the intestinal immune system is a prerequisite for elucidating their role in intestinal diseases. In this review, we provide an overview of the enteric virome composition and summarize recent findings about how enteric viruses are sensed by and, in turn, modulate host immune responses during homeostasis and disease.

Physiological activity of E. coli engineered to produce butyric acid

Faecalibacterium prausnitzii (F. prausnitzii) is one of the most abundant bacteria in the human intestine, with its anti‐inflammatory effects establishing it as a major effector in human intestinal health. However, its extreme sensitivity to oxygen makes its cultivation and physiological study difficult. F. prausnitzii produces butyric acid, which is beneficial to human gut health. Butyric acid is a short‐chain fatty acid (SCFA) produced by the fermentation of carbohydrates, such as dietary fibre in the large bowel. The genes encoding butyryl‐CoA dehydrogenase (BCD) and butyryl‐CoA:acetate CoA transferase (BUT) in F. prausnitzii were cloned and expressed in E. coli to determine the effect of butyric acid production on intestinal health using DSS‐induced colitis model mice. The results from the E. coli Nissle 1917 strain, expressing BCD, BUT, or both, showed that BCD was essential, while BUT was dispensable for producing butyric acid. The effects of different carbon sources, such as glucose, N‐acetylglucosamine (NAG), N‐acetylgalactosamine (NAGA), and inulin, were compared with results showing that the optimal carbon sources for butyric acid production were NAG, a major component of mucin in the human intestine, and glucose. Furthermore, the anti‐inflammatory effects of butyric acid production were tested by administering these strains to DSS‐induced colitis model mice. The oral administration of the E. coli Nissle 1917 strain, carrying the expression vector for BCD and BUT (EcN‐BCD‐BUT), was found to prevent DSS‐induced damage. Introduction of the BCD expression vector into E. coli Nissle 1917 led to increased butyric acid production, which improved the strain’s health‐beneficial effects.

The role of cGAS/STING in intestinal immunity

The gastrointestinal tract is a highly complex microenvironment under constant interaction with potentially harmful pathogens. Inflammatory bowel disease (IBD) is an archetypical inflammatory disease, in which the intestinal epithelium, defective autophagy, endoplasmic reticulum stress and dysbiosis play a key role. Although no risk-mediating gene variants of STING (TMEM173) have been identified so far, several seminal findings have elucidated a novel understanding of STING in the context of acute and chronic inflammation. STING, an endoplasmic reticulum resident adaptor protein binding cyclic dinucleotides, is a main inducer of type I interferons and canonically involved in antiviral and antibacterial immunity. Recent research has shed light on additional features of STING signaling involved in regulating the microbiota, facilitating autophagy, cell death or ER stress. Importantly, an increasing amount of studies suggests a considerable overlap of IBD pathophysiology and features of STING signaling. Since compelling evidence shows dysregulated type I IFNs in IBD, it is prompting to speculate on the hypothetical role of cGAS/STING/type I IFN signaling in IBD. Here, we summarize recent findings about the origin and function of STING signaling in the gastrointestinal tract and evolve the hypothesis that disturbed STING signaling might be profoundly interconnected with the pathophysiology of IBD.

Loss of Nckx3 Exacerbates Experimental DSS-Induced Colitis in Mice through p53/NF-κB Pathway

Inflammatory bowel diseases (IBDs) comprises a range of chronic inflammatory conditions of the intestinal tract. The incidence and prevalence of IBDs are increasing worldwide, but the precise etiology of these diseases is not completely understood. Calcium signaling plays a regulatory role in cellular proliferation. Nckx3, a potassium-dependent Na⁺/Ca²⁺ exchanger, is not only expressed in the brain but also in the aortic, uterine, and intestinal tissues, which contain abundant smooth muscle cells. This study investigated the role of Nckx3 in intestinal inflammation. Microarray analyses revealed the upregulation of the innate immune response-associated genes in the duodenum of Nckx3 knockout (KO) mice. The Nckx3 KO mice also showed an increase in IBD- and tumorigenesis-related genes. Using dextran sodium sulfate (DSS)-induced experimental colitis mice models, the Nckx3 KO mice showed severe colitis. Furthermore, the pathways involving p53 and NF-κB signaling were significantly upregulated by the absence of Nckx3. Overall, Nckx3 plays a critical role in the innate immune and immune response and may be central to the pathogenesis of IBD.

The role of PTPN22 in the pathogenesis of autoimmune diseases: A comprehensive review

The incidence of autoimmune diseases is increasing worldwide, thus stimulating studies on their etiopathogenesis, derived from a complex interaction between genetic and environmental factors. Genetic association studies have shown the PTPN22 gene as a shared genetic risk factor with implications in multiple autoimmune disorders. By encoding a protein tyrosine phosphatase expressed by the majority of cells belonging to the innate and adaptive immune systems, the PTPN22 gene may have a fundamental role in the development of immune dysfunction. PTPN22 polymorphisms are associated with rheumatoid arthritis, type 1 diabetes, systemic lupus erythematosus, and many other autoimmune conditions. In this review, we discuss the progress in our understanding of how PTPN22 impacts autoimmunity in both humans and animal models. In addition, we highlight the pathogenic significance of the PTPN22 gene, with particular emphasis on its role in T and B cells, and its function in innate immune cells, such as monocytes, dendritic and natural killer cells. We focus particularly on the complexity of PTPN22 interplay with biological processes of the immune system. Findings highlight the importance of studying the function of disease-associated PTPN22 variants in different cell types and open new avenues of investigation with the potential to drive further insights into mechanisms of PTPN22. These new insights will reveal important clues to the molecular mechanisms of prevalent autoimmune diseases and propose new potential therapeutic targets.

Regnase-1 Deficiency Restrains Klebsiella pneumoniae Infection by Regulation of a Type I Interferon Response

Excessive inflammation can cause tissue damage and autoimmunity, sometimes accompanied by severe morbidity or mortality. Numerous negative feedback mechanisms exist to prevent unchecked inflammation, but this restraint may come at the cost of suboptimal infection control. Regnase-1 (MCPIP1), a feedback regulator of IL-17 and LPS signaling, binds and degrades target mRNAs. Consequently, Reg1 deficiency exacerbates autoimmunity in multiple models. However, the role of Reg1 in bacterial immunity remains poorly defined. Here, we show that mice deficient in Reg1 are resistant to Klebsiella pneumoniae (KP). Reg1 deficiency did not accelerate bacterial eradication. Rather, Reg1-deficient alveolar macrophages had elevated Ifnb1 and enrichment of type I IFN genes. Blockade of IFNR during KP infection reversed disease improvement. Reg1 did not impact Ifnb1 stability directly, but Irf7 expression was affected. Thus, Reg1 suppresses type I IFN signaling restricting resistance to KP, suggesting that Reg1 could potentially be a target in severe bacterial infections. IMPORTANCE Klebsiella pneumoniae (KP) can cause life-threatening bacterial pneumonia and is the third most common cause of ventilator-associated pneumonia in the United States. Host inflammatory responses to infection are necessary to control disease, yet at the same time can cause collateral damage or immunopathology. During immune responses, many events are established within the infected tissue to limit unchecked inflammation. However, this restraint of immunity can impair infection control, and it is not fully understood how this balance is maintained during different infection settings. In this study we explored the possibility that a host-derived negative regulator of RNA, Regnase-1, limits immunity to KP by dampening inflammation. Indeed, mice with reduced Regnase-1 levels showed improved survival to KP infection, linked to regulation of type I interferons. Therefore, although restraint of Reg1 is beneficial to prevent immunopathology, temporary blockade of Reg1 could potentially be exploited to improve host defense during infectious settings such as KP.