Regulation of human enteric α-defensins by NOD2 in the Paneth cell lineage

Mechanisms and regulation of defensins in host defense

As a family of cationic host defense peptides, defensins are mainly synthesized by Paneth cells, neutrophils, and epithelial cells, contributing to host defense. Their biological functions in innate immunity, as well as their structure and activity relationships, along with their mechanisms of action and therapeutic potential, have been of great interest in recent years. To highlight the key research into the role of defensins in human and animal health, we first describe their research history, structural features, evolution, and antimicrobial mechanisms. Next, we cover the role of defensins in immune homeostasis, chemotaxis, mucosal barrier function, gut microbiota regulation, intestinal development and regulation of cell death. Further, we discuss their clinical relevance and therapeutic potential in various diseases, including infectious disease, inflammatory bowel disease, diabetes and obesity, chronic inflammatory lung disease, periodontitis and cancer. Finally, we summarize the current knowledge regarding the nutrient-dependent regulation of defensins, including fatty acids, amino acids, microelements, plant extracts, and probiotics, while considering the clinical application of such regulation. Together, the review summarizes the various biological functions, mechanism of actions and potential clinical significance of defensins, along with the challenges in developing defensins-based therapy, thus providing crucial insights into their biology and potential clinical utility.

Multifaceted involvements of Paneth cells in various diseases within intestine and systemically

Serving as the guardians of small intestine, Paneth cells (PCs) play an important role in intestinal homeostasis maintenance. Although PCs uniquely exist in intestine under homeostasis, the dysfunction of PCs is involved in various diseases not only in intestine but also in extraintestinal organs, suggesting the systemic importance of PCs. The mechanisms under the participation of PCs in these diseases are multiple as well. The involvements of PCs are mostly characterized by limiting intestinal bacterial translocation in necrotizing enterocolitis, liver disease, acute pancreatitis and graft-vs-host disease. Risk genes in PCs render intestine susceptible to Crohn’s disease. In intestinal infection, different pathogens induce varied responses in PCs, and toll-like receptor ligands on bacterial surface trigger the degranulation of PCs. The increased level of bile acid dramatically impairs PCs in obesity. PCs can inhibit virus entry and promote intestinal regeneration to alleviate COVID-19. On the contrary, abundant IL-17A in PCs aggravates multi-organ injury in ischemia/reperfusion. The pro-angiogenic effect of PCs aggravates the severity of portal hypertension. Therapeutic strategies targeting PCs mainly include PC protection, PC-derived inflammatory cytokine elimination, and substituting AMP treatment. In this review, we discuss the influence and importance of Paneth cells in both intestinal and extraintestinal diseases as reported so far, as well as the potential therapeutic strategies targeting PCs.

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

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

Paneth cells as the cornerstones of intestinal and organismal health: a primer

Paneth cells are versatile secretory cells located in the crypts of Lieberkühn of the small intestine. In normal conditions, they function as the cornerstones of intestinal health by preserving homeostasis. They perform this function by providing niche factors to the intestinal stem cell compartment, regulating the composition of the microbiome through the production and secretion of antimicrobial peptides, performing phagocytosis and efferocytosis, taking up heavy metals, and preserving barrier integrity. Disturbances in one or more of these functions can lead to intestinal as well as systemic inflammatory and infectious diseases. This review discusses the multiple functions of Paneth cells, and the mechanisms and consequences of Paneth cell dysfunction. It also provides an overview of the tools available for studying Paneth cells.

Role of Paneth cells-associated Crohn's disease susceptibility genes in development of Crohn's disease

Crohn's disease (CD) is a chronic inflammatory digestive tract disease, and its pathogenesis involves many factors such as genetics, environment, and flora. In terms of genetic factors, many susceptibility genes and pathogenic pathways of CD are associated with Paneth cells (PCs). Numerous studies have demonstrated that PCs are involved in the pathogenesis of CD by affecting the gut microbiota and inducing intestinal epithelial barrier dysfunction and immune abnormalities. These advances provide new ideas for the prevention of CD and potential therapeutic targets for this disease. This article reviews the role of PCs-associated CD susceptibility genes in the pathogenesis of CD.

An IRF1-dependent Pathway of TNFα-induced Shedding in Intestinal Epithelial Cells

BACKGROUND

Shedding of intestinal epithelial cells [IECs] is a potent cause of barrier loss which plays an important role in the pathogenesis of inflammatory bowel disease [IBD]. TNFα can induce IEC shedding, but little is known about this process.

METHODS

To investigate the molecular mechanism regulating IEC shedding, mice lacking interferon regulatory factor1 [IRF1], caspase-3, or gasdermin E [GSDME] and their control wild-type [WT] littermates were intravenously injected with tumour necrosis factor alpha [TNFα] to establish an IEC shedding model. A dual-luciferase reporter assay and a chromatin immunoprecipitation assay were used to determine the role of IRF1 in regulating caspase-3 expression.

RESULTS

TNFα administration induced obvious IEC shedding in WT mice, but IRF1-/- and caspase-3-/-mice were completely protected from TNFα-induced IEC shedding. As a critical transcription factor, IRF1 was found to be required for caspase-3 expression in IECs by binding to IRF1-binding sites in the caspase-3 promoter. In WT mice, plasma membrane integrity was disrupted in shed IECs; these cells were swollen and contained GSDME-N terminal [NT] fragments which are responsible for the induction of pyroptosis. However, in GSDME-/- mice, plasma membrane integrity was not disrupted in shed IECs, which were not swollen and did not contain GSDME-NT, indicating that GSDME converted TNFα-induced IEC shedding into a pyroptotic cell death process. In addition, IRF1 deficiency resulted in decreases in mucosal inflammation and mucosal bacteria levels in TNFα-challenged colons.

CONCLUSIONS

IRF1 deficiency maintains intestinal barrier integrity by restricting TNFα-induced IEC shedding.

Radiosensitivity of colorectal cancer and radiation-induced gut damages are regulated by gasdermin E

Although radiotherapy is an important clinical option available for colorectal cancer (CRC), its use is restricted due to low radiosensitivity of CRC and high toxicity to surrounding normal tissues. The purpose of this study is to investigate the molecular mechanism by which CRC is not sensitive to radiation and radiation causes toxicity to surrounding normal tissues. Here we found that GSDME was silenced in CRC but markedly expressed in their surrounding normal tissues. GSDME determines radiation-induced pyroptosis in CRC cells and normal epithelial cells through the caspase-3-dependent pathway. GSDME expression sensitizes radioresistant CRC cells to radiation. In the homograft model, after radiation treatment, the tumor volume and weight were significantly decreased in GSDME-expressed homograft tumors compared to GSDME-knockout homograft tumors. On the mechanism, radiation induced GSDME-mediated pyroptosis in CRC cells, which recruited and activated NK cells to enhance antitumor immunity. In addition, GSDME-knockout mice were protected from radiation-induced weight loss and tissue damages in the intestine, stomach, liver and pancreas compared to wild-type control littermates. In summary, we show that GSDME determines CRC radiosensitivity and radiation-related toxicity to surrounding normal tissues through caspase-3-dependent pyroptosis. Our finding reveals a previously unrecognized link between radiation and pyroptosis.

Gasdermin-E-mediated pyroptosis participates in the pathogenesis of Crohn's disease by promoting intestinal inflammation

Crohn's disease (CD) is a kind of refractory intestinal inflammatory diseases. Pyroptosis was recently identified as a gasdermin-mediated proinflammatory cell death. However, it is unclear whether gasdermin-mediated pyroptosis participates in the pathogenesis of CD. Here, we show that the pyroptosis-inducing fragment GSDME N-terminal is obviously detected in the inflamed colonic mucosa but not in the uninflamed mucosa of patients with CD, suggesting that GSDME-mediated pyroptosis may be correlated with intestinal mucosal inflammation in CD. To investigate the role of GSDME in colitis development, Gsdme-/- mice and wild-type (WT) littermate controls were treated with 2,4,6-trinitrobenzenesulfonic acid (TNBS) to induce colitis. We found that Gsdme-/- mice exhibit less-severe intestinal inflammation than WT controls do. Furthermore, our results indicate that GSDME-mediated epithelial-cell pyroptosis induces intestinal inflammation through the release of proinflammatory intracellular contents. In summary, we show that GSDME participates in the pathogenesis of CD through GSDME-mediated pyroptosis to release proinflammatory cytokines.

Paneth cells: Maintaining dynamic microbiome-host homeostasis, protecting against inflammation and cancer

The human intestines are constantly under the influence of numerous pathological factors: enteropathogenic microorganisms, food antigens, physico-chemical stress associated with digestion and bacterial metabolism, therefore it must be provided with a system of protection against adverse impact. Recent studies have shown that Paneth cells play a crucial role in maintaining homeostasis of the small intestines. Paneth cells perform many vital functions aimed at maintaining a homeostatic balance between normal microbiota, infectious pathogens and the human body, regulate the qualitative composition and number of intestinal microorganisms, prevent the introduction of potentially pathogenic species, and protect stem cells from damage. Paneth cells take part in adaptive and protective-inflammatory reactions. Paneth cells maintain dynamic balance between microbial populations, and the macroorganism, preventing the development of intestinal infections and cancer. They play a crucial role in gastrointestinal homeostasis and may be key factors in the etiopathological progression of intestinal diseases.

The roles and functions of Paneth cells in Crohn's disease: A critical review

Paneth cells (PCs) are located at the base of small intestinal crypts and secrete the α‐defensins, human α‐defensin 5 (HD‐5) and human α‐defensin 6 (HD‐6) in response to bacterial, cholinergic and other stimuli. The α‐defensins are broad‐spectrum microbicides that play critical roles in controlling gut microbiota and maintaining intestinal homeostasis. Inflammatory bowel disease, including ulcerative colitis and Crohn's disease (CD), is a complicated autoimmune disorder. The pathogenesis of CD involves genetic factors, environmental factors and microflora. Surprisingly, with regard to genetic factors, many susceptible genes and pathogenic pathways of CD, including nucleotide‐binding oligomerization domain 2 (NOD2), autophagy‐related 16‐like 1 (ATG16L1), immunity‐related guanosine triphosphatase family M (IRGM), wingless‐related integration site (Wnt), leucine‐rich repeat kinase 2 (LRRK2), histone deacetylases (HDACs), caspase‐8 (Casp8) and X‐box‐binding protein‐1 (XBP1), are relevant to PCs. As the underlying mechanisms are being unravelled, PCs are identified as the central element of CD pathogenesis, integrating factors among microbiota, intestinal epithelial barrier dysfunction and the immune system. In the present review, we demonstrate how these genes and pathways regulate CD pathogenesis via their action on PCs and what treatment modalities can be applied to deal with these PC‐mediated pathogenic processes.

HMGB1 released from GSDME-mediated pyroptotic epithelial cells participates in the tumorigenesis of colitis-associated colorectal cancer through the ERK1/2 pathway

Background

Pyroptosis is a form of proinflammatory gasdermin-mediated programmed cell death. Abnormal mucosal inflammation in the intestine is a critical risk factor for colitis-associated colorectal cancer (CAC). However, it is unknown whether pyroptosis participates in the development of CAC.

Methods

To investigate the role of gasdermin E (GSDME)-mediated pyroptosis in the development of CAC, Gsdme^−/− mice and their wild-type (WT) littermate controls were challenged with azoxymethane (AOM) and dextran sodium sulfate (DSS) to induce a CAC model. Neutralizing antibodies against high-mobility group box protein 1 (HMGB1) were used to determine the role of HMGB1 in CAC. To identify the role of ERK1/2 in HMGB1-induced colon cancer cell proliferation, we performed western blotting and CCK8 assays using the ERK1/2-specific inhibitor U0126 in CT26 colon cancer cells.

Results

In the CAC model, Gsdme^−/− mice exhibited reduced weight loss and colon shortening, attenuated rectal prolapse, and reduced tumor numbers and sizes compared to WT littermates. Furthermore, treatment with neutralizing anti-HMGB1 antibodies decreased the numbers and sizes of tumors, ERK1/2 activation and proliferating cell nuclear antigen (PCNA) expression in AOM/DSS-challenged WT mice. In addition, our in vitro experiments demonstrated that HMGB1 induced proliferation and PCNA expression in CT26 colon cancer cells through the ERK1/2 pathway.

Conclusion

GSDME-mediated pyroptosis promotes the development of CAC by releasing HMGB1, which induces tumor cell proliferation and PCNA expression through the ERK1/2 pathway. This finding reveals a previously unrecognized link between pyroptosis and CAC tumorigenesis and offers new insight into CAC pathogenesis.

Butyric Acid and Leucine Induce α-Defensin Secretion from Small Intestinal Paneth Cells

The intestine not only plays a role in fundamental processes in digestion and nutrient absorption, but it also has a role in eliminating ingested pathogenic bacteria and viruses. Paneth cells, which reside at the base of small intestinal crypts, secrete α-defensins and contribute to enteric innate immunity through potent microbicidal activities. However, the relationship between food factors and the innate immune functions of Paneth cells remains unknown. Here, we examined whether short-chain fatty acids and amino acids induce α-defensin secretion from Paneth cells in the isolated crypts of small intestine. Butyric acid and leucine elicit α-defensin secretion by Paneth cells, which kills Salmonella typhimurium. We further measured Paneth cell secretion in response to butyric acid and leucine using enteroids, a three-dimensional ex vivo culture system of small intestinal epithelial cells. Paneth cells expressed short-chain fatty acid receptors, Gpr41, Gpr43, and Gpr109a mRNAs for butyric acid, and amino acid transporter Slc7a8 mRNA for leucine. Antagonists of Gpr41 and Slc7a8 inhibited granule secretion by Paneth cells, indicating that these receptor and transporter on Paneth cells induce granule secretion. Our findings suggest that Paneth cells may contribute to intestinal homeostasis by secreting α-defensins in response to certain nutrients or metabolites.

Interactions Between the Gut Microbiota and the Host Innate Immune Response Against Pathogens

The mammalian intestine is colonized by over a trillion microbes that comprise the "gut microbiota," a microbial community which has co-evolved with the host to form a mutually beneficial relationship. Accumulating evidence indicates that the gut microbiota participates in immune system maturation and also plays a central role in host defense against pathogens. Here we review some of the mechanisms employed by the gut microbiota to boost the innate immune response against pathogens present on epithelial mucosal surfaces. Antimicrobial peptide secretion, inflammasome activation and induction of host IL-22, IL-17, and IL-10 production are the most commonly observed strategies employed by the gut microbiota for host anti-pathogen defense. Taken together, the body of evidence suggests that the host gut microbiota can elicit innate immunity against pathogens.

Cellular and Molecular Therapeutic Targets in Inflammatory Bowel Disease-Focusing on Intestinal Barrier Function

The human gut relies on several cellular and molecular mechanisms to allow for an intact and dynamical intestinal barrier. Normally, only small amounts of luminal content pass the mucosa, however, if the control is broken it can lead to enhanced passage, which might damage the mucosa, leading to pathological conditions, such as inflammatory bowel disease (IBD). It is well established that genetic, environmental, and immunological factors all contribute in the pathogenesis of IBD, and a disturbed intestinal barrier function has become a hallmark of the disease. Genetical studies support the involvement of intestinal barrier as several susceptibility genes for IBD encode proteins with key functions in gut barrier and homeostasis. IBD patients are associated with loss in bacterial diversity and shifts in the microbiota, with a possible link to local inflammation. Furthermore, alterations of immune cells and several neuro-immune signaling pathways in the lamina propria have been demonstrated. An inappropriate immune activation might lead to mucosal inflammation, with elevated secretion of pro-inflammatory cytokines that can affect the epithelium and promote a leakier barrier. This review will focus on the main cells and molecular mechanisms in IBD and how these can be targeted in order to improve intestinal barrier function and reduce inflammation.

Deoxynivalenol Impairs Porcine Intestinal Host Defense Peptide Expression in Weaned Piglets and IPEC-J2 Cells

Host defense peptides (HDPs) are efficient defense components of the innate immune system, playing critical roles in intestinal homeostasis and protection against pathogens. This study aims to investigate the interference effects of DON on the intestinal porcine HDPs expression in piglets and intestinal porcine epithelial cell line (IPEC-J2) cells, and elucidate the underlying mechanisms through which it functions. In an animal experiment, intestinal HDPs were determined in weaned piglets fed control and 1.28 mg/kg or 2.89 mg/kg DON-contaminated diets. Dietary exposure to DON significantly decreased piglet average daily gain, increased intestinal permeability and depressed the expression of porcine β-defensin1 (pBD1), pBD2, pBD3, epididymis protein 2 splicing variant C (pEP2C), PMAP23, and proline/arginine-rich peptide of 39 amino acids (PR39) in the intestine (p < 0.05). In IPEC-J2 cells, DON decreased cell viability and inhibited the expression of pBD1, pBD3, pEP2C, PG1-5, and PR39 (p < 0.05). NOD2, key regulator that is responsible for HDPs production, was markedly downregulated, whereas caspase-12 was activated in the presence of DON. In conclusion, DON induced caspase-12 activation and inhibited the NOD2-mediated HDPs production, which led to an impaired intestinal barrier integrity of weaned piglets. Our study provides a promising target for future therapeutic strategies to prevent the adverse effects of DON.

NOD2 Expression in Intestinal Epithelial Cells Protects Toward the Development of Inflammation and Associated Carcinogenesis

Nucleotide-binding oligomerization domain 2 (NOD2) is an intracellular pattern recognition receptor that senses bacterial peptidoglycan-conserved motifs in cytosol and stimulates host immune response including epithelial and immune cells. The association of NOD2 mutations with a number of inflammatory pathologies including Crohn's disease (CD), graft-versus-host diseases, or Blau syndrome, highlights its pivotal role in inflammatory response and the associated-carcinogenesis development. Since its identification in 2001 and its association with CD, the role of NOD2 in epithelial cells and immune cells has been investigated extensively but the precise mechanism by which NOD2 mutations lead to CD and the associated carcinogenesis development is largely unknown. In this review, we present and discuss recent developments about the role of NOD2 inside epithelial cells on the control of the inflammatory process and its linked carcinogenesis development.

Microbial Host Interactions and Impaired Wound Healing in Mice and Humans: Defining a Role for BD14 and NOD2

Chronic wounds cause significant patient morbidity and mortality. A key factor in their etiology is microbial infection, yet skin host-microbiota interactions during wound repair remain poorly understood. Microbiome profiles of noninfected human chronic wounds are associated with subsequent healing outcome. Furthermore, poor clinical healing outcome was associated with increased local expression of the pattern recognition receptor NOD2. To investigate NOD2 function in the context of cutaneous healing, we treated mice with the NOD2 ligand muramyl dipeptide and analyzed wound repair parameters and expression of antimicrobial peptides. Muramyl dipeptide treatment of littermate controls significantly delayed wound repair associated with reduced re-epithelialization, heightened inflammation, and up-regulation of murine β-defensins 1, 3, and particularly 14. We postulated that although murine β-defensin 14 might affect local skin microbial communities, it may further affect other healing parameters. Indeed, exogenously administered murine β-defensin 14 directly delayed mouse primary keratinocyte scratch wound closure in vitro. To further explore the role of murine β-defensin 14 in wound repair, we used Defb14^-/- mice and showed they had a global delay in healing in vivo, associated with alterations in wound microbiota. Taken together, these studies suggest a key role for NOD2-mediated regulation of local skin microbiota, which in turn affects chronic wound etiology.

NOD2 up-regulates TLR2-mediated IL-23p19 expression via NF-κB subunit c-Rel in Paneth cell-like cells

IL-23p19 plays important roles in intestinal antimicrobial immunity, while its over-expression can lead to intestinal inflammation. However, the bacterial compounds and the type of pattern recognition receptor involved in the inducible expression of IL-23p19 in Paneth cells remain unclear. Here we show that the mRNA expression of IL-23p19 was increased in Paneth cell (PC)-like cells stimulated by Toll-like receptor 2 (TLR2) ligands, peptidoglycan (PGN) and Pam3CSK4, and was further increased in the presence of nucleotide-binding oligomerization domain 2 (NOD2)-ligand muramyl dipeptide (MDP). However, its mRNA expression was decreased in NOD2-knockdown PC-like cells. Additionally, the c-Rel activation was increased in Pam3CSK4- or PGN-stimulated PC-like cells, but the PGN-induced c-Rel activation was decreased in NOD2-knockdown PC-like cells and had no significant difference compared with Pam3CSK4-induced c-Rel activation. Our results suggest that NOD2 up-regulates TLR2-mediated IL-23p19 expression via increasing c-Rel activation in PC-like cells. This finding might provide us with a novel therapeutic target for inflammatory bowel disease to inhibit IL-23p19 over-expression via the NOD2-c-Rel pathway.

The association between acute graft-versus-host disease and antimicrobial peptide expression in the gastrointestinal tract after allogeneic stem cell transplantation

Intestinal microbiota disruption is associated with acute gastrointestinal (GI) Graft-versus-Host Disease (GvHD) and poor outcome after allogeneic stem cell transplantation (ASCT). Here, in a retrospective analysis of 200 patients undergoing ASCT at the Regensburg University Medical Center, we assessed the relative expression of Paneth cell antimicrobial peptides (AMPs), Human Defensins (HD) 5 and 6 and regenerating islet-derived 3α (Reg3α), in 292 human intestinal biopsies as well as Reg3α serum levels in relation to acute GI GvHD. In the absence of GI GvHD, the relative expression of Paneth cell AMPs was significantly higher in the small intestine (duodenum to ileum) than in the stomach and large intestine (cecum to rectum) for Reg3α (p≤0.001), HD5 (p≤0.002) and HD6 (p≤0.02). Acute stage 2-4 GI GvHD was associated with reduced expression of AMPs in the small intestine (p≤0.01) in comparison to stage 0-1 disease, accompanied by a decrease in Paneth cell count in case of severe acute GI GvHD (p<0.001). The opposite held true for the large intestine as we found stage 2-4 GI GvHD correlated with significantly higher expression of HD5, HD6, and Reg3α compared to mild or no acute GI GvHD (p≤0.002). Severe GI GvHD in both the lower and the upper GI tract also correlated with higher serum concentrations of Reg3α (p = 0.002). As indirect markers of intestinal microbiome diversity low levels of urinary 3-indoxyl sulfate levels were associated with severe stages of acute GI GvHD compared to mild stage or no acute GI GvHD (p = 0.05). In conclusion, acute GI GvHD correlates with intestinal expression of HD5, HD6 and Reg3α as well as Reg3α serum levels and is associated with intestinal dysbiosis.

Absence of the NOD2 protein renders epithelia more susceptible to barrier dysfunction due to mitochondrial dysfunction

Irregular mitochondria structure and reduced ATP in some patients with IBD suggest that metabolic stress contributes to disease. Loss-of-function mutation in the nucleotide-binding oligomerization domain (NOD)-2 gene is a major susceptibility trait for IBD. Hence, we assessed if loss of NOD2 further impairs the epithelial barrier function instigated by disruption of mitochondrial ATP synthesis via the hydrogen ionophore dinitrophenol (DNP). NOD2 protein (virtually undetectable in epithelia under basal conditions) was increased in T84 (human colon cell line) cells treated with noninvasive Escherichia coli + DNP (16 h). Increased intracellular bacteria in wild-type (WT) and NOD2 knockdown (KD) cells and colonoids from NOD2^-/- mice were mediated by reactive oxygen species (ROS) and the MAPK ERK1/2 pathways as determined by cotreatment with the antioxidant mitoTEMPO and the ERK inhibitor U0126: ROS was upstream of ERK1/2 activation. Despite increased E. coli in DNP-treated NOD2 KD compared with WT cells, there were no differences in the internalization of fluorescent inert beads or dead E. coli particles. This suggests that lack of killing in the NOD2 KD cells was responsible for the increased numbers of viable intracellular bacteria; a conclusion supported by evidence of reduced autophagy in NOD2 KD T84 epithelia. Thus, in a two-hit hypothesis, decreased barrier function due to dysfunctional mitochondrial is amplified by lack of NOD2 in transporting enterocytes: subsequently, greater numbers of bacteria entering the mucosa would be a significant inflammatory threat especially since individuals with NOD2 mutations have compromised macrophage and Paneth cell responses to bacteria.NEW & NOTEWORTHY Increased internalization of bacteria by epithelia with dysfunctional mitochondria (reduced ATP) is potentiated if the cells lack nucleotide-binding oligomerization domain 2 (NOD2), mutations in which are inflammatory bowel disease-susceptibility traits. Uptake of bacteria was dependent on reactive oxygen species and MAP-kinase activity, and the increased viable intracellular bacteria in NOD2^-/- cells likely reflect a reduced ability to recognize and kill bacteria. Thus a significant barrier defect occurs with NOD2 deficiency in conjunction with metabolic stress that could contribute to inflammation.

Microbiome and colorectal cancer: Unraveling host-microbiota interactions in colitis-associated colorectal cancer development

Dysbiosis of gut microbiota occurs in many human chronic immune-mediated diseases, such as inflammatory bowel disease (IBD) and colitis-associated colorectal cancer (CAC). Reciprocally, uncontrolled immune responses, that may or may not be induced by dysbiosis, are central to the development of IBD and CAC. There has been a surge of interest in investigating the relationship between microbiota, inflammation and CAC. In this review, we discuss recent findings related to gut microbiota and chronic immune-mediated diseases, such as IBD and CAC. Moreover, the molecular mechanisms underlying the roles of chronic inflammation in CAC are examined. Finally, we discuss the development of novel microbiota-based therapeutics for IBD and colorectal cancer.

Paneth cells, antimicrobial peptides, and intestinal mucosal immunity

Paneth cells (PCs) and their antimicrobial peptides (AMPs) are closely related to the ecological unbalance of gut microbiota, intestinal inflammation, and systemic infections. The dysfunction of intestinal mucosal barrier and innate immunity is always accompanied with changes in the levels of AMPs, for example, alpha-defensins and other inflammatory mediators produced by PCs. Studies show that PCs can alter their functional status and release effector molecules under some conditions such as cholinergic agonists, microorganisms and their antigens, enteral nutrition, and genetic susceptibility. Therefore, these conditions can induce inflammatory bowel disease, bacterial translocation, overgrowth of gut microbe, and damage to immune tolerance. The research on PCs can provide new targets and strategies for clinical treatment of the relevant diseases. In this paper, we discuss the relationship of PCs and their AMPs with intestinal mucosal barrier and innate immunity.

Human alpha defensin 5 is a candidate biomarker to delineate inflammatory bowel disease

Inability to distinguish Crohn's colitis from ulcerative colitis leads to the diagnosis of indeterminate colitis. This greatly effects medical and surgical care of the patient because treatments for the two diseases vary. Approximately 30 percent of inflammatory bowel disease patients cannot be accurately diagnosed, increasing their risk of inappropriate treatment. We sought to determine whether transcriptomic patterns could be used to develop diagnostic biomarker(s) to delineate inflammatory bowel disease more accurately. Four patients groups were assessed via whole-transcriptome microarray, qPCR, Western blot, and immunohistochemistry for differential expression of Human α-Defensin-5. In addition, immunohistochemistry for Paneth cells and Lysozyme, a Paneth cell marker, was also performed. Aberrant expression of Human α-Defensin-5 levels using transcript, Western blot, and immunohistochemistry staining levels was significantly upregulated in Crohn's colitis, p< 0.0001. Among patients with indeterminate colitis, Human α-Defensin-5 is a reliable differentiator with a positive predictive value of 96 percent. We also observed abundant ectopic crypt Paneth cells in all colectomy tissue samples of Crohn's colitis patients. In a retrospective study, we show that Human α-Defensin-5 could be used in indeterminate colitis patients to determine if they have either ulcerative colitis (low levels of Human α-Defensin-5) or Crohn's colitis (high levels of Human α-Defensin-5). Twenty of 67 patients (30 percent) who underwent restorative proctocolectomy for definitive ulcerative colitis were clinically changed to de novo Crohn's disease. These patients were profiled by Human α-Defensin-5 immunohistochemistry. All patients tested strongly positive. In addition, we observed by both hematoxylin and eosin and Lysozyme staining, a large number of ectopic Paneth cells in the colonic crypt of Crohn's colitis patient samples. Our experiments are the first to show that Human α-Defensin-5 is a potential candidate biomarker to molecularly differentiate Crohn's colitis from ulcerative colitis, to our knowledge. These data give us both a potential diagnostic marker in Human α-Defensin-5 and insight to develop future mechanistic studies to better understand crypt biology in Crohn's colitis.

The effect of NOD2 on the microbiota in Crohn's disease

Recent advancements toward the treatment of Crohn's disease (CD) indicate great promise for long-term remission. CD patients suffer from a complex host of dysregulated interactions between their innate immune system and microbiome. The most predominant link to the onset of CD is a genetic mutation in the innate immune receptor nucleotide-binding oligomerization domain-containing 2 (NOD2). NOD2 responds to the presence of bacteria and stimulates the immune response. Mutations to NOD2 promote low diversity and dysbiosis in the microbiome, leading to impaired mucosal barrier function. Current treatments suppress the immune response rather than enhancing the function of this critical protein. New progress toward stabilizing NOD2 signaling through its interactions with chaperone proteins holds potential in the development of novel CD therapeutics.