The role of Gr-1(+) cells and tumour necrosis factor-α signalling during Clostridium difficile colitis in mice

Dual RNA-seq identifies genes and pathways modulated during Clostridioides difficile colonization

IMPORTANCE

The initial interactions between the colonic epithelium and the bacterium are likely critical in the establishment of Clostridioides difficile infection, one of the major causes of hospital-acquired diarrhea worldwide. Molecular interactions between C. difficile and human gut cells have not been well defined mainly due to the technical challenges of studying cellular host-pathogen interactions with this anaerobe. Here we have examined transcriptional changes occurring in the pathogen and host cells during the initial 24 hours of infection. Our data indicate several changes in metabolic pathways and virulence-associated factors during the initial bacterium-host cell contact and early stages of infection. We describe canonical pathways enriched based on the expression profiles of a dual RNA sequencing in the host and bacterium, and functions of bacterial factors that are modulated during infection. This study thus provides fresh insight into the early C. difficile infection process.

Olfactomedin-4 + neutrophils exacerbate intestinal epithelial damage and worsen host survival after Clostridioides difficile infection

Neutrophils are key first responders to Clostridioides difficile infection (CDI). Excessive tissue and blood neutrophils are associated with worse histopathology and adverse outcomes, however their functional role during CDI remains poorly defined. Utilizing intestinal epithelial cell (IEC)-neutrophil co-cultures and a pre-clinical animal model of CDI, we show that neutrophils exacerbate C. difficile -induced IEC injury. We utilized cutting-edge single-cell transcriptomics to illuminate neutrophil subtypes and biological pathways that could exacerbate CDI-associated IEC damage. As such, we have established the first transcriptomics atlas of bone marrow (BM), blood, and colonic neutrophils after CDI. We found that CDI altered the developmental trajectory of BM and blood neutrophils towards populations that exhibit gene signatures associated with pro-inflammatory responses and neutrophil-mediated tissue damage. Similarly, the transcriptomic signature of colonic neutrophils was consistent with hyper-inflammatory and highly differentiated cells that had amplified expression of cytokine-mediated signaling and degranulation priming genes. One of the top 10 variable features in colonic neutrophils was the gene for neutrophil glycoprotein, Olfactomedin 4 (OLFM4). CDI enhanced OLFM4 mRNA and protein expression in neutrophils, and OLFM4 + cells aggregated to areas of severe IEC damage. Compared to uninfected controls, both humans and mice with CDI had higher concentrations of circulating OLFM4; and in mice, OLFM4 deficiency resulted in faster recovery and better survival after infection. Collectively, these studies provide novel insights into neutrophil-mediated pathology after CDI and highlight the pathogenic role of OLFM4 + neutrophils in regulating CDI-induced IEC damage.

One Sentence Summary

Utilizing single-cell transcriptomics, IEC-epithelial co-cultures, and pre-clinical models of CDI, we have identified a subset of neutrophils that are marked by OLFM4 expression as pathogenic determinants of IEC barrier damage after CDI.

ADS024, a Bacillus velezensis strain, protects human colonic epithelial cells against C. difficile toxin-mediated apoptosis

Clostridioides difficile infection (CDI) causes intestinal injury. Toxin A and toxin B cause intestinal injury by inducing colonic epithelial cell apoptosis. ADS024 is a Bacillus velezensis strain in development as a single-strain live biotherapeutic product (SS-LBP) to prevent the recurrence of CDI following the completion of standard antibiotic treatment. We evaluated the protective effects of the sterile filtrate and ethyl acetate extract of conditioned media from ADS024 and DSM7 (control strain) against mucosal epithelial injury in toxin-treated human colonic tissues and apoptosis in toxin-treated human colonic epithelial cells. Ethyl acetate extracts were generated from conditioned culture media from DSM7 and ADS024. Toxin A and toxin B exposure caused epithelial injury in fresh human colonic explants. The sterile filtrate of ADS024, but not DSM7, prevented toxin B-mediated epithelial injury in fresh human colonic explants. Both sterile filtrate and ethyl acetate extract of ADS024 prevented toxin-mediated apoptosis in human colonic epithelial cells. The anti-apoptotic effects of ADS024 filtrate and ethyl acetate extract were dependent on the inhibition of caspase 3 cleavage. The sterile filtrate, but not ethyl acetate extract, of ADS024 partially degraded toxin B. ADS024 inhibits toxin B-mediated apoptosis in human colonic epithelial cells and colonic explants.

Comparison between Symptomatic and Asymptomatic Mice after Clostridioides difficile Infection Reveals Novel Inflammatory Pathways and Contributing Microbiota

Clostridioides difficile causes the highest number of nosocomial infections. Currently, treatment options for C. difficile infection (CDI) are very limited, resulting in poor treatment outcomes and high recurrence rates. Although the disease caused by CDI is inflammatory in nature, the role of inflammation in the development of CDI symptoms is contradictory and not completely understood. Hence, the use of anti-inflammatory medication is debatable in CDI. In the current study, we evaluated the genetic and microbiome profiles of mice after infection with C. difficile. These mice were categorized based on the severity of CDI and the results were viewed accordingly. Our results indicate that certain genes are upregulated in severe CDI more than in the moderate case. These include oncostatin-M (OSM), matrix metalloprotease 8 (MMP8), triggering receptor expressed on myeloid cells 1 (Trem-1), and dual oxidase 2 (Duox2). We also investigated the microbiome composition of CDI mice before and after infecting with C. difficile. The results show that C. difficile abundance is not indicative of diseases severity. Certain bacterial species (e.g., Citrobacter) were enriched while others (e.g., Turicibacter) were absent in severe CDI. This study identifies novel inflammatory pathways and bacterial species with a potential role in determining the severity of CDI.

Pomegranate peel extract reduced colonic damage and bacterial translocation in a mouse model of infectious colitis induced by Citrobacter rodentium

The pomegranate fruit peel is a rich source of polyphenols including punicalins, punicalagins, and ellagic acids, but is considered an agricultural waste product. Pomegranate derived products have been reported to have a wide variety of health promoting benefits including antibacterial properties in vitro but there is limited evidence of their antibacterial properties in vivo. The purpose of this study was to test the in vivo antibacterial properties of a pomegranate peel extract (PPX) containing punicalin, punicalagin, and ellagic acid. C3H/He mice were orally pre-treated with water or PPX prior to infection with the mouse bacterial pathogen, Citrobacter rodentium (Cr) that mimics many aspects of human enteropathogenic Escherichia coli infections. Fecal excretion of Cr was monitored and mice were euthanized on day 12 post-infection to assess Cr colonization of the colon and spleen, histological changes, and gene expression. PPX-treatment reduced Cr infection induced weight loss and mortality that was observed in water-treated infected mice. However, Cr colonization of the colon and clearance was unaffected by PPX-treatment. Consistent with this, PPX treatment did not alter the potent Th1/Th17 pro-inflammatory response elicited by Cr infection. Significant colonization of the spleen was only seen in water-treated infected mice and was inversely correlated with the dose of PPX administered. PPX treatment decreased the extent of Cr-induced colon damage that correlated with decreased mortality and reduced colonization of the spleen. Thus, a pomegranate peel extract contains bioactive compounds that mitigate the deleterious effects of an in vivo infection with the model enteropathogenic bacteria, Cr.

Tumour Necrosis Factor Alpha in Intestinal Homeostasis and Gut Related Diseases

The intestinal epithelium constitutes an indispensable single-layered barrier to protect the body from invading pathogens, antigens or toxins. At the same time, beneficial nutrients and water have to be absorbed by the epithelium. To prevent development of intestinal inflammation or tumour formation, intestinal homeostasis has to be tightly controlled and therefore a strict balance between cell death and proliferation has to be maintained. The proinflammatory cytokine tumour necrosis factor alpha (TNFα) was shown to play a striking role for the regulation of this balance in the gut. Depending on the cellular conditions, on the one hand TNFα is able to mediate cell survival by activating NFκB signalling. On the other hand, TNFα might trigger cell death, in particular caspase-dependent apoptosis but also caspase-independent programmed necrosis. By regulating these cell death and survival mechanisms, TNFα exerts a variety of beneficial functions in the intestine. However, TNFα signalling is also supposed to play a critical role for the pathogenesis of inflammatory bowel disease (IBD), infectious diseases, intestinal wound healing and tumour formation. Here we review the literature about the physiological and pathophysiological role of TNFα signalling for the maintenance of intestinal homeostasis and the benefits and difficulties of anti-TNFα treatment during IBD.

Neutralization of macrophage migration inhibitory factor improves host survival after Clostridium difficile infection

Clostridium difficile is an important cause of nosocomial diarrhea in the western world. Toxins (A, B, and binary toxins) generated by C. difficile bacteria damage intestinal epithelial cells. Hallmarks of host response to C. difficile infection (CDI) include upregulation of inflammatory mediators and tissue infiltration by immune cells. Macrophage migration inhibitory factor (MIF) is an inflammatory cytokine that is known to enhance the host immune response to infectious pathogens. Additionally, MIF can adversely impact host survival to numerous infections. The role of MIF in the pathogenesis of CDI remains poorly understood. Here, we show that patients with CDI had significantly higher circulating MIF compared to patients who had diarrhea but tested negative for C. difficile (non-CDI controls). Similarly, in a mouse model, C. difficile challenge significantly increased levels of plasma and tissue MIF. Antibody-mediated depletion of MIF decreased C. difficile-induced inflammatory responses, clinical disease, and mortality. Together, these results uncover a potential role for MIF in exacerbating CDI and suggest that use of anti-MIF antibodies may represent a therapeutic strategy to curb host inflammatory responses and improve disease outcomes in CDI.

The Role of Neonatal Gr-1+ Myeloid Cells in a Murine Model of Rhesus-Rotavirus-Induced Biliary Atresia

Activation of innate immunity together with cholangiocyte damage occurs in biliary atresia (BA). However, detailed information on the inflammatory cells involved is lacking. This study investigates both the pathophysiology of CD11b⁺Gr-1⁺ cells in a mouse model of BA and their presence in BA patients. CD11b⁺Gr-1⁺ cells were targeted by an anti-Ly6G antibody in murine BA induced by inoculation with rhesus rotavirus. Expression of the Ly6G homolog CD177⁺ was examined in biopsies from BA patients. The symptoms of BA were ameliorated, and survival was prolonged in those mice receiving 5 to 10 μg of antibody per mouse every 3 days for four times compared with the mice treated with virus alone. However, the mice later developed chronic BA with persistent low body weight and jaundice. Hepatic inflammatory cells were reduced compared with acute BA. Blockade of extrahepatic bile ducts occurred, whereas intrahepatic ductules were partially preserved, and a progressive increase in liver fibrosis was observed. High levels of CD11b⁺Gr-1⁺ cells were present in these mice. The administration of an anti-Ly6G antibody again in those chronic BA mice reduced jaundice and restored body weight. In BA patients CD177⁺ cells were highly expressed in the liver. Our data suggest that the chronic mouse BA model shares key characteristics with clinical BA and indicates the importance of CD11b⁺Gr-1⁺ cells in the initiation and progression of BA.

Leptin receptor q223r polymorphism influences neutrophil mobilization after Clostridium difficile infection

Clostridium difficile is the leading cause of nosocomial infections in the United States. Clinical disease outcomes after C. difficile infection (CDI) are dependent on intensity of host inflammatory responses. Specifically, peak peripheral white blood cell (WBC) count >20 × 10⁹ l^-1 is an indicator of adverse outcomes in CDI patients, and is associated with higher 30-day mortality. We show that homozygosity for a common single nucleotide polymorphism (Q to R mutation in leptin receptor that is present in up to 50% of people), significantly increases the risk of having peak peripheral WBC count >20 × 10⁹ l^-1 (odds ratio=5.41; P=0.0023) in CDI patients. In a murine model of CDI, we demonstrate that mice homozygous for the same single nucleotide polymorphism (RR mice) have more blood and tissue leukocytes (specifically neutrophils), exaggerated tissue inflammation, and higher mortality as compared with control mice, despite similar pathogen burden. Further, we show that neutrophilia in RR mice is mediated by gut microbiota-directed expression of CXC chemokine receptor 2 (CXCR2), which promotes the release of neutrophils from bone marrow reservoir. Overall these studies provide novel mechanistic insights into the role of human genetic polymorphisms and gut microbiota in regulating the fundamental biological process of CDI-induced neutrophilia.

Role of the leukocyte response in normal and immunocompromised host after Clostridium difficile infection

Clostridium difficile is the leading cause of healthcare-associated infections in the United States. Clinically, C. difficile-associated disease can present as asymptomatic colonization, self-limited diarrheal illness or severe colitis (that may result in death). This variability in disease course and outcomes suggests that host factors play an important role as key determinants of disease severity. Currently, there are several scoring indices to estimate severity of C. difficile-associated disease. Leukocytosis and renal failure are considered to be the most important predictors of C. difficile disease severity in hosts with a normal immune system. The degree of leukocytosis which is considered significant for severe disease and how it is scored vary amongst scoring indices. None of the scores have been prospectively validated, and while total WBC count is useful to estimate the magnitude of the host response in most patient populations, in immune-compromised patients like those receiving chemotherapy, solid organ transplant patients or hematopoietic stem cell transplants the WBC response can be variable or even absent making this marker of severity difficult to interpret. Other cellular subsets like neutrophils, eosinophils and lymphocytes provide important information about the host immune status and play an important role in the immune response against C. difficile infection. However, under the current scoring systems the role of these cellular subsets have been underestimated and only total white blood cell counts are taken into account. In this review we highlight the role of host leukocyte response to C. difficile challenge in the normal and immunocompromised host, and propose possible ways that would allow for a better representation of the different immune cell subsets (neutrophils, lymphocytes and eosinophils) in the current scoring indices.

Role of interferon-γ and inflammatory monocytes in driving colonic inflammation during acute Clostridium difficile infection in mice

The inflammatory response to the colonic pathogen Clostridium difficile is characterized by the induction of inflammatory cytokines including Interleukin-23 (IL-23) and interferon-γ (IFN-γ) and the recruitment of myeloid cells including Ly6C^High monocytes. IL-23 knockout mice showed reduced expression of the monocyte chemokines Ccl4 and Ccl7, but not Ccl2, as well as reduced Ly6C^High Ly6G^Mid monocyte recruitment to the colon in response to C. difficile colitis. Clostridium difficile-infected CCR2^-/- (CCR2 KO) mice showed a significant defect in Ly6C^High Ly6G^Mid monocyte recruitment to the colon in response to C. difficile. Although there was no decrease in expression of the inflammatory cytokines Il1b, Il6 or Tnf or reduction in the severity of colonic histopathology associated with ablation of monocyte recruitment, Slpi and Inos expression was significantly reduced in the colons of these animals. Additionally, neutralization of IFN-γ through the administration of anti-IFN-γ monoclonal antibody resulted in a significant reduction in the expression of the IFN-γ-inducible chemokines Cxcl9 and Cxcl10, but not a reduction in the neutrophil chemokines Cxcl1, Cxcl2 and Ccl3 or the monocyte chemokine Ccl2. Consistently, monocyte and neutrophil recruitment were unchanged following anti-IFN-γ treatment. Additionally, Inos and Slpi expression were unchanged following anti-IFN-γ treatment, suggesting that Inos and Slpi regulation is independent of IFN-γ during C. difficile colitis. Taken together, these data strongly suggest that IL-23 and CCR2 signalling are required for monocyte recruitment during C. difficile colitis. Additionally, these studies also suggest that monocytes, but not IFN-γ, are necessary for full expression of Inos and Slpi in the colon.

Neutrophil-mediated inflammation in the pathogenesis of Clostridium difficile infections

Clostridium difficile is the most important cause of nosocomial infectious diarrhea in the western world. C. difficile infections are a major healthcare burden with approximately 500,000 new cases every year and an estimated annual cost of nearly $1 billion in the U.S. Furthermore, the infections are no longer restricted to health care facilities, and recent studies indicate spread of C. difficile infection to the community as well. The clinical spectrum of C. difficile infection ranges from asymptomatic colonization to severe diarrhea, fulminant colitis and death. This spectrum results from a complex interplay between bacterial virulence factors, the colonic microbiome and the host inflammatory response. The overall vigor of host inflammatory response is believed to be an important determinant of C. difficile disease severity, and a more robust immune response is associated with worse outcomes. Neutrophils are the primary cells that respond to C. difficile invasion and neutrophilic inflammation is the hallmark of C. difficile-associated disease. In this review, we will focus on the role of neutrophils (infiltration to infected tissue, pathogen clearance and resolution of inflammation) in the immuno-pathogenesis of C. difficile-associated disease (CDAD).

Interleukin-23 (IL-23), independent of IL-17 and IL-22, drives neutrophil recruitment and innate inflammation during Clostridium difficile colitis in mice

Our objective was to determine the role of the inflammatory cytokine interleukin-23 (IL-23) in promoting neutrophil recruitment, inflammatory cytokine expression and intestinal histopathology in response to Clostridium difficile infection. Wild-type (WT) and p19(-/-) (IL-23KO) mice were pre-treated with cefoperazone in their drinking water for 5 days, and after a 2-day recovery period were challenged with spores from C. difficile strain VPI 10463. Interleukin-23 deficiency was associated with significant defects in both the recruitment of CD11b(High) Ly6G(H) (igh) neutrophils to the colon and the expression of neutrophil chemoattractants and stabilization factors including Cxcl1, Cxcl2, Ccl3 and Csf3 within the colonic mucosa as compared with WT animals. Furthermore, the expression of inflammatory cytokines including Il33, Tnf and Il6 was significantly reduced in IL-23-deficient animals. There was also a trend towards less severe colonic histopathology in the absence of IL-23. The induction of Il17a and Il22 was also significantly abrogated in IL-23KO mice. Inflammatory cytokine expression and neutrophilic inflammation were not reduced in IL-17a-deficient mice or in mice treated with anti-IL-22 depleting monoclonal antibody. However, induction of RegIIIg was significantly reduced in animals treated with anti-IL-22 antibody. Taken together, these data indicate that IL-23, but not IL-17a or IL-22, promotes neutrophil recruitment and inflammatory cytokine and chemokine expression in the colon in response to C. difficile infection.

Systems Modeling of Interactions between Mucosal Immunity and the Gut Microbiome during Clostridium difficile Infection

Clostridium difficile infections are associated with the use of broad-spectrum antibiotics and result in an exuberant inflammatory response, leading to nosocomial diarrhea, colitis and even death. To better understand the dynamics of mucosal immunity during C. difficile infection from initiation through expansion to resolution, we built a computational model of the mucosal immune response to the bacterium. The model was calibrated using data from a mouse model of C. difficile infection. The model demonstrates a crucial role of T helper 17 (Th17) effector responses in the colonic lamina propria and luminal commensal bacteria populations in the clearance of C. difficile and colonic pathology, whereas regulatory T (Treg) cells responses are associated with the recovery phase. In addition, the production of anti-microbial peptides by inflamed epithelial cells and activated neutrophils in response to C. difficile infection inhibit the re-growth of beneficial commensal bacterial species. Computational simulations suggest that the removal of neutrophil and epithelial cell derived anti-microbial inhibitions, separately and together, on commensal bacterial regrowth promote recovery and minimize colonic inflammatory pathology. Simulation results predict a decrease in colonic inflammatory markers, such as neutrophilic influx and Th17 cells in the colonic lamina propria, and length of infection with accelerated commensal bacteria re-growth through altered anti-microbial inhibition. Computational modeling provides novel insights on the therapeutic value of repopulating the colonic microbiome and inducing regulatory mucosal immune responses during C. difficile infection. Thus, modeling mucosal immunity-gut microbiota interactions has the potential to guide the development of targeted fecal transplantation therapies in the context of precision medicine interventions.

Innate Immune Defenses Mediated by Two ILC Subsets Are Critical for Protection against Acute Clostridium difficile Infection

Infection with the opportunistic enteric pathogen Clostridium difficile is an increasingly common clinical complication that follows antibiotic treatment-induced gut microbiota perturbation. Innate lymphoid cells (ILCs) are early responders to enteric pathogens; however, their role during C. difficile infection is undefined. To identify immune pathways that mediate recovery from C. difficile infection, we challenged C57BL/6, Rag1(-/-) (which lack T and B cells), and Rag2(-/-)Il2rg(-/-) (Ragγc(-/-)) mice (which additionally lack ILCs) with C. difficile. In contrast to Rag1(-/-) mice, ILC-deficient Ragγc(-/-) mice rapidly succumbed to infection. Rag1(-/-) but not Ragγc(-/-) mice upregulate expression of ILC1- or ILC3-associated proteins following C. difficile infection. Protection against infection was restored by transferring ILCs into Ragγc(-/-) mice. While ILC3s made a minor contribution to resistance, loss of IFN-γ or T-bet-expressing ILC1s in Rag1(-/-) mice increased susceptibility to C. difficile. These data demonstrate a critical role for ILC1s in defense against C. difficile.

The Src kinase Fyn is protective in acute chemical-induced colitis and promotes recovery from disease

Despite progress in understanding enteric inflammation, current therapies, although effective in many patients with inflammatory bowel disease (IBD), have significant side-effects, and, in many patients, it is refractory to treatment. The Src kinase Fyn mediated IFN-γ-induced increased permeability in model epithelia, and so we hypothesized that inhibition of Fyn kinase would be anti-colitic. Mice [B6.129SF2/J wild-type (WT), Fyn KO, or chimeras] received 2.5% dextran sodium sulfate (DSS) or normal water for 10 d and were necropsied immediately or 3 d later. Gut permeability was assessed by FITC-dextran flux, colitis by macroscopic and histologic parameters, and immune cell status by cytokine production and CD4(+) T cell Foxp3 expression. Fyn KO mice consistently displayed significantly worse DSS-induced disease than WT, correlating with decreased IL-10 and increased IL-17 in splenocytes and the gut; Fyn KO mice failed to thrive after removal of the DSS water. Analysis of chimeric mice indicated that the increased sensitivity to DSS was due to the lack of Fyn kinase in hematopoietic, but not stromal, cells, in accordance with Fyn(+) T cell increases in WT mice exposed to DSS and Fyn KO mice having a reduced number of CD4(+)Foxp3(+) cells in baseline or colitic conditions and a reduced capacity to induce Foxp3 expression in vitro. Other experiments suggest that the colonic microbiota in Fyn KO mice is not preferentially colitogenic. Contrary to our expectation, the absence of Fyn kinase resulted in greater DSS-induced disease, and analysis of chimeric mice indicated that leukocyte Fyn kinase is beneficial in limiting colitis.