Crohn's disease: NOD2, autophagy and ER stress converge

Polymorphisms in NOD2, encoding an intracellular pattern recognition receptor, contribute the largest fraction of genetic risk for Crohn's disease among the >40 risk loci identified so far. Autophagy plays a prominent role in the innate immune response towards intracellular bacteria. The discovery of the autophagy genes ATG16L1 and IRGM as risk factors for Crohn's disease turned autophagy into the spotlight in inflammatory bowel disease (IBD). Remarkably, NOD2 has recently been identified as a potent autophagy inducer. A physical interaction of NOD2 and ATG16L1 appears to be required for autophagic clearance of intracellular pathogens. Moreover, Crohn's disease-associated NOD2 and ATG16L1 variants exhibit a defect in the induction of an autophagic response and hence predict autophagy as a key converging mechanism that leads to Crohn's disease. Another pathway that is closely intertwined with autophagy and mutually cross-regulated is the unfolded protein response (UPR), which is induced by endoplasmic reticulum (ER) stress. Genes involved in the UPR (XBP1, ORMDL3) have also been genetically associated with Crohn's disease and ulcerative colitis. Moreover, the intestinal epithelium at the interface between host and microbe appears particularly affected by IBD-associated hypomorphic function of autophagy and the UPR. The functional convergence of main genetic risk factors for IBD on these innate immune pathways has hence important implications for the host's interaction with the microbiota. Moreover, the genetic convergence on these molecular mechanisms may open novel therapeutic options for IBD that deserve further exploration.     

Role of genetics in the diagnosis and prognosis of Crohn's disease

Considering epidemiological, genetic and immunological data, we can conclude that the inflammatory bowel diseases are heterogeneous disorders of multifactorial etiology in which hereditability and environment interact to produce the disease. It is probable that patients have a genetic predisposition for the development of the disease coupled with disturbances in immunoregulation. Several genes have been so far related to the diagnosis of Crohn's disease. Those genes are related to innate pattern recognition receptors, to epithelial barrier homeostasis and maintenance of epithelial barrier integrity, to autophagy and to lymphocyte differentiation. So far, the most strong and replicated associations with Crohn's disease have been done with NOD2, IL23R and ATG16L1 genes. Many genes have so far been implicated in prognosis of Crohn's disease and many attempts have been made to classify genetic profiles in Crohn's disease. CARD15 seems not only a susceptibility gene, but also a disease-modifier gene for Crohn's disease. Enriching our understanding on Crohn's disease genetics is important but when combining genetic data with functional data the outcome could be of major importance to clinicians.     

Autophagy: a primer for the gastroenterologist/hepatologist

Autophagy is a conserved cellular pathway that maintains intracellular homeostasis by degrading proteins and cytosolic contents of eukaryotic cells. Autophagy clears misfolded and long-lived proteins, damaged organelles and invading microorganisms from cells, and provides nutrients and energy in response to exposure to cell stressors such as starvation. Defective autophagy has recently been linked to a diverse range of disease processes of relevance to gastroenterologists and hepatologists including Crohn's disease, pancreatitis, hepatitis and cancer. The present article provides an overview of the autophagy pathway and discusses gastrointestinal disease processes in which alterations in autophagy have been implicated. The clinical significance of autophagy as a potential therapeutic option is also discussed.     

A nonsynonymous SNP in ATG16L1 predisposes to ileal Crohn's disease and is independent of CARD15 and IBD5

BACKGROUND & AIMS: A genome-wide association scan of nonsynonymous DNA polymorphisms identified association of a threonine-to-alanine substitution (T300A) in the autophagy-related 16-like gene ATG16L1 with Crohn's disease. We investigated this association in independent U.K. cohorts of Crohn's disease and ulcerative colitis. METHODS: The T300A variant (rs2241880) was genotyped in an independent sample of 727 Crohn's disease and 877 ulcerative colitis cases, and in 579 controls. We then performed an extension analysis combining these data with the U.K. data from the initial study to give a total of 1236 U.K. Crohn's disease cases and 1235 controls to estimate disease risk and test for interaction with the CARD15 and IBD5 risk loci and for association with disease subtypes. RESULTS: The association of T300A was replicated in the independent sample of 727 Crohn's disease cases (P = .001), and was strongly associated in the extended analysis of 1236 Crohn's cases (P = 2.4 x 10(-6)). The 300A/A genotype conferred a 1.65-fold risk of Crohn's disease, with a 2.2-fold risk of ileal disease. Analysis of the interaction of ATG16L1 with CARD15 and IBD5 indicated that all 3 loci contribute independently to disease risk. Homozygosity for the risk allele at all 3 loci conferred a combined risk of 20.4 (95% confidence interval: 8.71, 47.7) for Crohn's disease. The ATG16L1 risk genotype showed a modest but significant association with ulcerative colitis (P = .026). CONCLUSIONS: The association of ATG16L1 with Crohn's disease and possibly with ulcerative colitis supports a role for autophagy in the pathogenesis of inflammatory bowel disease.     

Autophagy, microbial sensing, endoplasmic reticulum stress, and epithelial function in inflammatory bowel disease

Increasing evidence has emerged that supports an important intersection between 3 fundamental cell biologic pathways in the pathogenesis of inflammatory bowel disease. These include the intersection between autophagy, as revealed by the original identification of ATG16L1 and IRGM as major genetic risk factors for Crohn's disease, and intracellular bacterial sensing, as shown by the importance of NOD2 in autophagy induction upon bacterial entry into the cell. A pathway closely linked to autophagy and innate immunity is the unfolded protein response, initiated by endoplasmic reticulum stress due to the accumulation of misfolded proteins, which is genetically related to ulcerative colitis and Crohn's disease (XBP1 and ORMDL3). Hypomorphic ATG16L1, NOD2, and X box binding protein-1 possess the common attribute of profoundly affecting Paneth cells, specialized epithelial cells at the bottom of intestinal crypts involved in antimicrobial function. Together with their functional juxtaposition in the environmentally exposed intestinal epithelial cell, their remarkable functional convergence on Paneth cells and their behavior in response to environmental factors, including microbes, these 3 pathways are of increasing importance to understanding the pathogenesis of inflammatory bowel disease. Moreover, in conjunction with studies that model deficient nuclear factor-κB function, these studies suggest a central role for altered intestinal epithelial cell function as one of the earliest events in the development of inflammatory bowel disease.     

Inflammatory bowel disease： Genetic and epidemiologic considerations

Genome-wide association studies have firmly established that many genomic loci contribute to inflammatory bowel disease, especially in Crohn＇s disease. These studies have newly-established the importance of the interleukin 23 and autophagy pathways in disease pathogenesis. Future challenges include： （1） the establishment of precisely causal alleles, （2） definition of altered functional outcomes of associated and causal alleles and （3） integration of genetic findings with environmental factors.     

Interplay of autophagy and innate immunity in Crohn’s disease: A key immunobiologic feature

Crohn’s disease representing a clinical phenotype of inflammatory bowel disease is a polygenic immune disorder with complex multifactor etiology. Recent genome-wide association studies of susceptibility loci have highlighted on the importance of the autophagy pathway, which previously had not been implicated in disease pathology. Autophagy represents an evolutionarily highly conserved multi-step process of cellular self-digestion due to sequestration of excessive, damaged, or aged proteins and intracellular organelles in double-membranous vesicles of autophagosomes, terminally self-digested in lysosomes. Autophagy is deeply involved in regulation of cell development and differentiation, survival and senescence, and it also fundamentally affects the inflammatory pathways, as well as the innate and adaptive arms of immune responses. Autophagy is mainly activated due to sensors of the innate immunity, i.e., by pattern recognition receptor signaling. The interplay of genes regulating immune functions is strongly influenced by the environment, especially gut resident microbiota. The basic challenge for intestinal immune recognition is the requirement of a simultaneous delicate balance between tolerance and responsiveness towards microbes. On the basis of autophagy-related risk genetic polymorphisms (ATG16L1, IRGM , NOD2 , XBP1 ) impaired sensing and handling of intracellular bacteria by innate immunity, closely interrelated with the autophagic and unfolded protein pathways seem to be the most relevant immunobiologic events. Autophagy is now widely considered as a key regulator mechanism with the capacity to integrate several aspects of Crohn’s disease pathogenesis. In this review, recent advances in the exciting crosstalk of susceptibility coding variants-related autophagy and innate immunity are discussed.     

Role of genetics in the diagnosis and prognosis of Crohn's disease

Considering the epidemiological, genetic and immunological data, we can conclude that the inflammatory bowel diseases are heterogeneous disorders of multifactorial etiology in which hereditability and environment interact to produce the disease. It is probable that patients have a genetic predisposition for the development of the disease coupled with disturbances in immunoregulation. Several genes have so far been related to the diagnosis of Crohn's disease. These genes are related to innate pattern recogni...     

Role of wireless capsule endoscopy in inflammatory bowel disease

Capsule endoscopy (CE) offers state-of-the-art imaging of the small bowel. In Crohn's disease its clinical role is still uncertain. This report analyses the usefulness of CE in patients with suspected Cronh's disease, in patients with established Crohn's disease (when assessing severity, occult gastrointestinal bleeding and/or as a guide to therapy), in patients with inflammatory bowel disease unclassified (IBDU), and in individuals with ulcerative colitis. The first item in this group is the most important although there is no strong evidence to establish the position of CE in the diagnostic workup. In patients with established Crohn's disease, recently developed activity scores are promising tools for an accurate assessment of severity. As a guide to therapy, CE should be focused on patients with unexplained symptoms when other investigations are inconclusive. In postoperative Crohn's Disease, international consensus recommended considering CE only if ileocolonoscopy is contraindicated or unsuccessful. In the case of IBDU, studies have shown a significant proportion of patients reclassified with Crohn's disease. In this setting, CE could have a role determining small bowel involvement. The role of CE in ulcerative colitis is limited. Some authors advocate CE before colectomy for refractory cases in order to exclude Crohn's disease. In summary, CE offers a new horizon in inflammatory bowel disease, and a better knowledge of mucosal abnormalities that could offer a paradigm shift: changing from symptom-based disease activity estimation to direct mucosal healing monitoring. Nevertheless, randomized controlled studies are still needed to provide stronger evidence in this setting.     

The role of bacteria and pattern-recognition receptors in Crohn's disease

Crohn's disease is widely regarded as a multifactorial disease, and evidence from human and animal studies suggests that bacteria have an instrumental role in its pathogenesis. Comparison of the intestinal microbiota of patients with Crohn's disease to that of healthy controls has revealed compositional changes. In most studies these changes are characterized by an increase in the abundance of Bacteroidetes and Proteobacteria and a decrease in that of Firmicutes. In addition, a number of specific mucosa-associated bacteria have been postulated to have a role in Crohn's disease, including Mycobacterium avium subspecies paratuberculosis, adherent and invasive Escherichia coli, Campylobacter and Helicobacter species. The association between mutations in pattern-recognition receptors (Toll-like receptors and Nod-like receptors) and autophagy proteins and Crohn's disease provides further evidence to suggest that defective sensing and killing of bacteria may drive the onset of disease. In this Review, we present recent advances in understanding the role of bacteria and the contribution of pattern-recognition receptors and autophagy in the pathogenesis of Crohn's disease.     

Predicting, treating and preventing postoperative recurrence of Crohn's disease: the state of the field

The majority of patients diagnosed with Crohn's disease eventually require surgical intervention. Unfortunately, postsurgical remission tends to be short lived; a significant number of patients experience clinical relapse and many require additional operations. The pathogenesis of this postoperative recurrence is poorly understood and, currently, there are no reliable tools to predict when and in whom the disease will recur. Furthermore, the postoperative prophylaxis profiles of available Crohn's disease therapeutic agents such as 5-aminosalicylates, immunomodulators, steroids and probiotics have been disappointing. Recently, the combination of antibiotics and azathioprine in selected high-risk patients has demonstrated some potential for benefit. The goal of the present article is to provide a coherent summary of previous and new research to guide clinicians in managing the challenging and complex problem of postoperative Crohn's disease recurrence.     

Is Crohn's Disease an Immunodeficiency?

The current hypothesis for the etiology of Crohn's disease proposes an excessive immune response, largely T-cell driven, possibly against endogenous bacteria. Standard therapy is therefore directed towards suppression of this immune response. An alternative theory of pathogenesis accounts for epidemiologic and pathophysiologic observations that have been hitherto underemphasized, namely, (1) genetic disorders with deficiencies in neutrophil function can give rise to a clinical and pathologic syndrome indistinguishable from Crohn's; (2) abnormal neutrophil function is well described in Crohn's disease; (3) a group of bacteria implicated in other chronic inflammatory disorders causes impairment of neutrophil function; and (4) 20th century environmental risk factors for Crohn's disease may directly suppress neutrophil function and may have led to a shift in the dominant gut flora with similar effects. We propose that some cases of Crohn's disease result from the interaction of environmental and genetic influences leading to impaired mucosal neutrophil function, resulting in failure to effectively clear intramucosal microbes effectively. While encompassing existing data, this hypothesis proposes a proximate defect in the mucosal immune response. If this paradigm were correct, new therapeutic approaches might involve strategies to alter intestinal flora and stimulate neutrophil function.     

Epidemiology, genes and inflammatory bowel diseases in childhood

There is evidence that inflammatory bowel disease is immunologically mediated and that genetic factors play an important aetiological role. The identification of disease susceptibility genes has led to significant progress in our understanding of the pathogenesis of Crohn's disease. Genes linked to Crohn's disease play critical roles in the normal function of the innate immune system, and genes linked to epithelial integrity may play a role in the pathogenesis of inflammatory bowel disease as well. However, the dynamic epidemiology of both Crohn's disease and ulcerative colitis suggests that extrinsic environmental factors acting at the population level may be involved in their pathogenesis. These environmental factors may be responsible for the rising incidence of inflammatory bowel disease.     

Crohn＇s disease： Innate immunodeficiency？

In the past, Crohn's disease (CD) has been understood primarily as an immunologic disorder characterized by an abnormal T-cell response. Recent in vitro and in vivo data suggests that CD may instead be precipitated by innate immune dysfunction resulting from a combination of genetic and environmental factors. Some reports have demonstrated a defective immune response in a variety of other cellular components, including neutrophils, monocytes and dendritic cells. Recent studies of granulocyte-macrophage colony-stimulating factor (GM-CSF) in CD, aiming to stimulate the innate immune system with the conception that an innate immune defect underlies the development of the disease, have been demonstrated a clinical benefit and reinforce this evolving understanding of the disease.     

Incidence of juvenile-onset Crohn's disease in Scotland: association with northern latitude and affluence

BACKGROUND & AIMS: The incidence of Crohn's disease in Scottish children has increased steadily over 30 years. Many studies have investigated genetic influence or possible links with childhood events. We aimed to study sociodemographic and/or geographic distribution of juvenile=onset Crohn's disease in Scotland. METHODS: Using a previously established and validated database covering the entire Scottish population, 580 Scottish children (<16 years of age at symptom onset) with inflammatory bowel disease incident between 1981 and 1995 were identified. Postcodes of incident cases were classed for geographic location and material deprivation. Incidence rates (/100,000/year) were sex standardized to the 1991 census population. The effects of sex, geographic location, time, and deprivation category were estimated from a multifactorial Poisson regression model. RESULTS: The incidence of juvenile-onset Crohn's disease was 2.3 (95% CI: 2.0-2.5) for the time period 1981 to 1995 and was significantly higher in northern (3.1, 95% CI: 2.6-3.8) than in southern Scotland (2.1, 95% CI: 1.9-2.4, P < 0.001). The incidence of juvenile-onset ulcerative colitis did not show north/south variation ( P = 0.677). The relative risks of developing CD were significantly lower in postcode areas with deprivation categories 2-7 as compared with deprivation score 1 (most affluent, P = 0.033). This pattern was not seen for UC. CONCLUSIONS: There was an increased incidence of juvenile-onset Crohn's disease in northern compared with southern Scotland. Children from more affluent areas had a higher relative risk of developing Crohn's disease. Juvenile onset ulcerative colitis did not show north/south variation in incidence or association with affluence.     

Increased risk of breast cancer in first-degree relatives of Crohn''s disease patients: An IG-IBD study

BACKGROUND: Increased rates of colorectal cancer have been reported in patients with ulcerative colitis as well as with Crohn's colitis. This risk could be the result of shared genetic susceptibility and could be co-inherited rather than being just secondary to a long-standing, extensive mucosal inflammation. AIM: To assess the prevalence of all malignancies in first-degree relatives of Crohn's disease patients in order to establish whether any association exists. PATIENTS AND METHODS: A total of 632 outpatients with a diagnosis of Crohn's disease and 632 control subjects were recruited. Information concerning the presence of malignancies was collected in 3,292 first-degree relatives of Crohn's disease patients and in 3,303 first-degree relatives of controls. RESULTS: Two hundred and fourteen (6.5%) subjects were found to be affected by malignancy in the first-degree relatives of Crohn's disease patients and 180 (5.5%) in the first-degree relatives of controls. Forty-seven (7.4%) of Crohn's disease patients had a first-degree relative with IBD, but none of them had cancer. The frequency of extra-intestinal malignancies was higher in first-degree relatives of Crohn's disease patients than in those of controls (p=0.011). Frequency of breast cancer in female relatives of Crohn's disease patients, mainly in mothers, was two-fold higher than that in controls (0.91% versus 0.42%; odds ratio=2.16; 95% confidence interval=1.14-4.08; p=0.015). The presence of breast cancer showed no association with any specific phenotype of disease in Crohn's patients. CONCLUSIONS: These results did not corroborate the hypothesis about a common genetic susceptibility between Crohn's disease and colorectal cancer. An unexpected finding was the more frequent occurrence of extra-digestive malignancies. The prevalence of breast cancer in first-degree relatives of Crohn's disease patients, in particular the mothers, was more than double than in those of controls. This association, if confirmed, would suggest that there may exist common genetic and/or environmental factors for Crohn's disease and breast cancer.     

The role of bacteria in the pathogenesis of inflammatory bowel disease

Crohn's disease (CD) and ulcerative colitis (UC) have features that suggest bacterial involvement, and all genetic models of inflammatory bowel disease (IBD) require the presence of commensal bacteria. CD is associated with innate immune response genes such as NOD2/CARD15 and the autophagy genes ATG16L1 and IRGM. However, IBD responds to immunosuppression, suggesting that any bacteria involved are not acting as conventional pathogens. Molecular techniques are rapidly advancing our knowledge of the gut microbiota. In CD there is reduced diversity, and notably a reduction in the probiotic Faecalibacterium prausnitzii, the presence of which in the terminal ileum is associated with a reduced risk of recurrence following surgery. There is also a consistent increase in mucosa-associated Escherichia coli with an "adherent and invasive" phenotype, which allows them to replicate inside macrophages and induce granulomas. Speculation that CD could be caused by the Mycobacterium avium subspecies paratuberculosis (MAP) continues. The response to antitumor necrosis factor treatments suggests that, if relevant at all, MAP is not acting as a conventional pathogen. However, there is increased colonization by MAP in CD, and there is evidence that it could have an indirect effect mediated by the suppression of macrophage function. UC relapse is frequently associated with infection by pathogens, but there is less evidence for involvement of a specific bacterial species. Poor barrier integrity followed by an inflammatory reaction to bacterial components, with chronicity maintained by an autoimmune process, seems a plausible pathogenic model. Bacterial theories of pathogenesis are now becoming testable by targeted therapeutic interventions.     

Video capsule endoscopy in inflammatory bowel disease

Video capsule endoscopy(VCE) has evolved to become an important tool for the non-invasive examination of the small bowel, which hitherto had been relatively inaccessible to direct visualisation. VCE has beenshown to play a role in monitoring the activity of small bowel Crohn's disease and can be used to assess the response to anti-inflammatory treatment in Crohn's disease. For those patients with Crohn's disease who have undergone an intestinal resection, VCE has been assessed as a tool to detect post-operative recurrence. VCE may also aid in the reclassification of patients with a diagnosis of Inflammatory Bowel Disease Unclassified to Crohn's disease. The evolution of colon capsule endoscopy(CCE) has expanded the application of this technology further. The use of CCE to assess the activity of ulcerative colitis has been described. This advance in capsule technology has also fuelled interest in its potential role as a minimally invasive tool to assess the whole of GI tract opening the possibility of its use for the panenteric assessment of Crohn's disease. VCE is a safe procedure. However, the risk of a retained capsule is higher in patients with suspected or confirmed Crohn's disease compared with patients having VCE examination for other indications. A retained video capsule is rare after successful passage of a patency capsule which may be utilised to pre-screen patients undergoing VCE. This paper describes the use of VCE in the assessment of inflammatory bowel disease.     

克罗恩病与肠结核临床及病理特征的对比研究

目的 探讨克罗恩病(CD)与肠结核(ITB)临床与病理特征,为两者鉴别诊断提供依据.方法 对1996-2007年四川大学华西医院临床、病理资料完整的33例CD和34例ITB的临床及病理资料进行同顾性分析.结果 CD出现症状到确诊的时间明显长于ITB(P<0.05),CD多因肠梗阻或诊断不明而手术,CD的便血、肠梗阻、肠外表现明显多于ITB(P值均<0.05),而盗汗、合并肺结核、低白蛋白血症和ESR升高、血清结核抗体阳性则更常见于ITB(P值均<0.05),CD患者仅累及空、回肠的情况明显多于ITB(P<0.05);CD患者内镜下纵形溃疡及鹅卵石样外观明显多于ITB(P值均<0.05),而ITB组环形溃疡更多见(P<0.05);ITB组的肉芽肿检出率(70.6%)明显高于CD组(29.4%)(P<0.05),且肉芽肿的位置有助于两者的鉴别;CD的手术标本的固有层底部/黏膜下层淋巴细胞聚集现象明显多于内镜活检标本(P<0.05).结论 尽管CD与ITB临床表现极其相似,但各自仍有一定的特征性,诊断需结合临床及病理资料进行综合分析.肉芽肿出现的几率、位置及炎症细胞分布范围与深度可作为两者病理鉴别要点.     

Metastatic crohn's disease

PURPOSE: Metastatic Crohn's disease is a rare complication of Crohn's disease that has been infrequently reported in the literature. We report a case where submammary, inguinal, and perineal disease was observed in a patient many years after a proctocolectomy. The proliferative and polypoid morphology of the cutaneous lesions has not been previously described. In addition, this case describes severe cutaneous metastatic Crohn's disease in the absence of active gastrointestinal disease, which to our knowledge has not been reported in the literature. RESULTS: A 55-year-old female with a 25-year history of Crohn's disease was investigated and treated over a 12-month period for metastatic Crohn's disease involving the submammary, inguinal, and perineal areas. These proliferative lesions with erythema and ulceration were histologically consistent with metastatic Crohn's disease. Gram and Ziehl Nielsen stains revealed no pathogenic organisms. The use of topical solutions, antibiotics, immunosuppression, and surgery failed to produce any significant benefit. A review of 42 cases of metastatic Crohn's disease in the literature is reported. CONCLUSION: Cutaneous metastatic Crohn's disease has an extremely variable macroscopic appearance and may be a source of considerable morbidity. It can be present without other significant symptomatology, although it more commonly parallels gastrointestinal disease activity. There are no trials to guide current treatment, which is mainly based on anecdotal reporting.