Upregulation of cIAP2 in regenerating colonocytes in ulcerative colitis

Inhibition of cIAP1/2 reduces RIPK1 phosphorylation in pulmonary endothelial cells and alleviate sepsis-induced lung injury and inflammatory response

Acute respiratory distress syndrome (ARDS)/acute lung injury (ALI) is a severe complication of sepsis characterized by acute respiratory distress, hypoxemia, and diffuse bilateral pulmonary infiltrates. The regulation of RIPK1 is an important part of the inflammatory response, and cIAP1/2 serves as the E3 ubiquitin ligase for RIPK1. In this study, we investigated the effect and mechanism of cIAP1/2 inhibition on sepsis-induced lung injury. Our results showed that cIAP1/2 inhibition can alleviate sepsis-induced lung injury and reduce the inflammatory response, which is accompanied by downregulation of RIPK1 phosphorylation and ubiquitination. Additionally, cIAP1/2 inhibition led to the up-regulation of programmed cell death, including apoptosis, necroptosis, and pyroptosis, and inhibiting these three cell death pathways can further reduce the inflammatory response, which is similar to the recently discovered programmed cell death pathway PANoptosis. Our findings suggest that cIAP1/2 and PANoptosis inhibition may be a new strategy for treating sepsis-induced lung injury and provide important references for further exploring the mechanism of sepsis-induced lung injury and identifying new therapeutic targets.

IAPs and RIPK1 mediate LPS-induced cytokine production in healthy subjects and Crohn's disease

Innate immune activity fuels intestinal inflammation in Crohn's disease (CD), an inflammatory bowel disease. Identification and targeting of new molecular regulators of the innate activity are warranted to control the disease. Inhibitor of apoptosis proteins (IAPs) regulate both cell survival and inflammatory signaling. We investigated the effects of IAP inhibition by second mitochondria-derived activator of caspases (SMAC) mimetics (SMs) on innate responses and cell death to pathogen-associated molecular patterns in peripheral blood mononuclear cells (PBMCs) and monocytes. IAPs inhibited lipopolysaccharide (LPS)-induced expression of proinflammatory interleukin (IL)-1β, IL-6. Likewise, LPS (but not muramyl dipeptide or Escherichia coli) induced TNF-α was inhibited in CD and control PBMCs. The SM effect was partially reversed by inhibition of receptor-interacting serine/threonine-protein kinase 1 (RIPK1). The effect was mainly cell death independent. Thus, IAP inhibition by SMs leads to reduced production of proinflammatory cytokines and may be considered in the efforts to develop new therapeutic strategies to control CD.

CIAP1/2 can regulate the inflammatory response and lung injury induced by apoptosis in septic rats

Acute lung injury (ALI)/acute respiratory distress syndrome (ARDS), induced by sepsis, is predominantly caused by inflammation injury. However, there is no clear consensus on how to regulate the inflammatory response. The TNF pathway is one of the primary inflammatory pathways activated in sepsis. cIAP1/2, an essential E3 ubiquitin ligase in the TNF pathway, plays a pivotal role in positively regulating the activation of nuclear factor κB (NF-κB) and mitogen-activated protein kinase (MAPK) signaling pathways to promote inflammation while inhibiting apoptosis. We found that Birc2 is the only differential expression gene in TNF pathway, and both cIAP1/2 upregulated in lung lysate with worsen lung injury. However, upon inhibiting cIAP1/2 using AZD5582, lung cell apoptosis was reactivated, and a significant improvement in lung injury was observed. Our study shows that cIAP1/2 expression increased in the lung tissue of a CLP rat ALI model. Inhibiting cIAP1/2 with AZD5582, a second mitochondria-derived activator of caspases (SMAC) mimetic, induced increased apoptosis and reduced lung injury. Therefore, inhibiting cIAP1/2 can alleviate sepsis-induced ALI, providing a new target for regulating organ damage induced by sepsis-induced inflammatory responses.

The Role of E3 Ubiquitin Ligases and Deubiquitinases in Inflammatory Bowel Disease: Friend or Foe?

Inflammatory bowel disease (IBD), which include Crohn’s disease (CD) and ulcerative colitis (UC), exhibits a complex multifactorial pathogenesis involving genetic susceptibility, imbalance of gut microbiota, mucosal immune disorder and environmental factors. Recent studies reported associations between ubiquitination and deubiquitination and the occurrence and development of inflammatory bowel disease. Ubiquitination modification, one of the most important types of post-translational modifications, is a multi-step enzymatic process involved in the regulation of various physiological processes of cells, including cell cycle progression, cell differentiation, apoptosis, and innate and adaptive immune responses. Alterations in ubiquitination and deubiquitination can lead to various diseases, including IBD. Here, we review the role of E3 ubiquitin ligases and deubiquitinases (DUBs) and their mediated ubiquitination and deubiquitination modifications in the pathogenesis of IBD. We highlight the importance of this type of posttranslational modification in the development of inflammation, and provide guidance for the future development of targeted therapeutics in IBD.

SMAC mimetics and RIPK inhibitors as therapeutics for chronic inflammatory diseases

New therapeutic approaches for chronic inflammatory diseases such as inflammatory bowel disease, rheumatoid arthritis, and psoriasis are needed because current treatments are often suboptimal in terms of both efficacy and the risks of serious adverse events. Inhibitor of apoptosis proteins (IAPs) are E3 ubiquitin ligases that inhibit cell death pathways and are themselves inhibited by second mitochondria-derived activator of caspases (SMAC). SMAC mimetics (SMs), small-molecule antagonists of IAPs, are being evaluated as cancer therapies in clinical trials. IAPs are also crucial regulators of inflammatory pathways because they influence both the activation of inflammatory genes and the induction of cell death through the receptor-interacting serine-threonine protein kinases (RIPKs), nuclear factor κB (NF-κB)-inducing kinase, and mitogen-activated protein kinases (MAPKs). Furthermore, there is an increasing interest in specifically targeting the substrates of IAP-mediated ubiquitylation, especially RIPK1, RIPK2, and RIPK3, as druggable nodes in inflammation control. Several studies have revealed an anti-inflammatory potential of RIPK inhibitors that either block inflammatory signaling or block the form of inflammatory cell death known as necroptosis. Expanding research on innate immune signaling through pattern recognition receptors that stimulate proinflammatory NF-κB and MAPK signaling may further contribute to uncovering the complex molecular roles used by IAPs and downstream RIPKs in inflammatory signaling. This may benefit and guide the development of SMs or selective RIPK inhibitors as anti-inflammatory therapeutics for various chronic inflammatory conditions.

Altered expression of Tumor Necrosis Factor Alpha -Induced Protein 3 correlates with disease severity in Ulcerative Colitis

Ulcerative colitis (UC), an inflammatory disorder of the colon arises from dysregulated immune response towards gut microbes. Transcription factor NFκB is a major regulatory component influencing mucosal inflammation. We evaluated expression of Tumor Necrosis Factor Alpha Induced Protein3 (TNFAIP3), the inhibitor of NFκB activation and its associated partners ITCH, RNF11 and Tax1BP1 in inflamed mucosa of UC patients. We found highly significant up-regulated mRNA expression of TNFAIP3 that negatively correlated with disease activity in UC. mRNA levels of ITCH, RNF11 and Tax1BP1 were significantly down-regulated. Significant positive correlation with disease activity was noted for Tax1BP1. All four genes showed significant down-regulation at protein level. mRNA levels of inducers of TNFAIP3 expression, NFκB p65 subunit and MAST3 was determined. There was significant increase in p65 mRNA expression and down-regulated MAST3 expression. This suggested that increase in NFκB expression regulates TNFAIP3 levels. Deficiency of TNFAIP3 expression resulted in significant up-regulation of NFκB p65 sub-unit as well as its downstream genes such as iNOS, an inflammatory marker, inhibitors of apoptosis like cIAP2 and XIAP and mediators of anti-apoptotic signals TRAF1 and TRAF2. Taken together, decreased expression of TNFAIP3 and its partners contribute to inflammation and up-regulation of apoptosis inhibitors that may create microenvironment for colorectal cancer.

Circadian rhythm disruption impairs tissue homeostasis and exacerbates chronic inflammation in the intestine

Endogenous circadian clocks regulate 24-h rhythms of physiology and behavior. Circadian rhythm disruption (CRD) is suggested as a risk factor for inflammatory bowel disease. However, the underlying molecular mechanisms remain unknown. Intestinal biopsies from Per1/2 mutant and wild-type (WT) mice were investigated by electron microscopy, immunohistochemistry, and bromodeoxyuridine pulse-chase experiments. TNF-α was injected intraperitoneally, with or without necrostatin-1, into Per1/2 mice or rhythmic and externally desynchronized WT mice to study intestinal epithelial cell death. Experimental chronic colitis was induced by oral administration of dextran sodium sulfate. In vitro, caspase activity was assayed in Per1/2-specific small interfering RNA-transfected cells. Wee1 was overexpressed to study antiapoptosis and the cell cycle. Genetic ablation of circadian clock function or environmental CRD in mice increased susceptibility to severe intestinal inflammation and epithelial dysregulation, accompanied by excessive necroptotic cell death and a reduced number of secretory epithelial cells. Receptor-interacting serine/threonine-protein kinase (RIP)-3-mediated intestinal necroptosis was linked to increased mitotic cell cycle arrest via Per1/2-controlled Wee1, resulting in increased antiapoptosis via cellular inhibitor of apoptosis-2. Together, our data suggest that circadian rhythm stability is pivotal for the maintenance of mucosal barrier function. CRD increases intestinal necroptosis, thus rendering the gut epithelium more susceptible to inflammatory processes.-Pagel, R., Bär, F., Schröder, T., Sünderhauf, A., Künstner, A., Ibrahim, S. M., Autenrieth, S. E., Kalies, K., König, P., Tsang, A. H., Bettenworth, D., Divanovic, S., Lehnert, H., Fellermann, K., Oster, H., Derer, S., Sina, C. Circadian rhythm disruption impairs tissue homeostasis and exacerbates chronic inflammation in the intestine.

Exome Analysis of Rare and Common Variants within the NOD Signaling Pathway

Pediatric inflammatory bowel disease (pIBD) is a chronic heterogeneous disorder. This study looks at the burden of common and rare coding mutations within 41 genes comprising the NOD signaling pathway in pIBD patients. 136 pIBD and 106 control samples underwent whole-exome sequencing. We compared the burden of common, rare and private mutation between these two groups using the SKAT-O test. An independent replication cohort of 33 cases and 111 controls was used to validate significant findings. We observed variation in 40 of 41 genes comprising the NOD signaling pathway. Four genes were significantly associated with disease in the discovery cohort (BIRC2 p = 0.004, NFKB1 p =  0.005, NOD2 p = 0.029 and SUGT1 p = 0.047). Statistical significance was replicated for BIRC2 (p = 0.041) and NOD2 (p = 0.045) in an independent validation cohort. A gene based test on the combined discovery and replication cohort confirmed association for BIRC2 (p = 0.030). We successfully applied burden of mutation testing that jointly assesses common and rare variants, identifying two previously implicated genes (NFKB1 and NOD2) and confirmed a possible role in disease risk in a previously unreported gene (BIRC2). The identification of this novel gene provides a wider role for the inhibitor of apoptosis gene family in IBD pathogenesis.

Emerging Roles for Noncanonical NF-κB Signaling in the Modulation of Inflammatory Bowel Disease Pathobiology

Crohn's disease and ulcerative colitis are common and debilitating manifestations of inflammatory bowel disease (IBD). IBD is characterized by a radical imbalance in the activation of proinflammatory and anti-inflammatory signaling pathways in the gut. These pathways are controlled by NF-κB, which is a master regulator of gene transcription. In IBD patients, NF-κB signaling is often dysregulated resulting in overzealous inflammation. NF-κB activation occurs through 2 distinct pathways, defined as either canonical or noncanonical. Canonical NF-κB pathway activation is well studied in IBD and is associated with the rapid, acute production of diverse proinflammatory mediators, such as COX-2, IL-1β, and IL-6. In contrast to the canonical pathway, the noncanonical or "alternative" NF-κB signaling cascade is tightly regulated and is responsible for the production of highly specific chemokines that tend to be associated with less acute, chronic inflammation. There is a relative paucity of literature regarding all aspects of noncanonical NF-ĸB signaling. However, it is clear that this alternative signaling pathway plays a considerable role in maintaining immune system homeostasis and likely contributes significantly to the chronic inflammation underlying IBD. Noncanonical NF-κB signaling may represent a promising new direction in the search for therapeutic targets and biomarkers associated with IBD. However, significant mechanistic insight is still required to translate the current basic science findings into effective therapeutic strategies.

Regulation of antiapoptotic and cytoprotective pathways in colonic epithelial cells in ulcerative colitis

Ulcerative colitis is an inflammatory bowel disease involving the colon resulting in bloody diarrhea and increased risk of colorectal cancer in certain patient subgroups. Increased apoptosis in the epithelial cell layer causes increased permeability, especially during flares; this leads to translocation of luminal pathogens resulting in a continued inflammatory drive. The present work investigates how epithelial apoptosis is regulated in ulcerative colitis. The main results are that Fas mediated apoptosis is inhibited during flares of ulcerative colitis, probably by an upregulation of cellular inhibitor of apoptosis protein 2 (cIAP2) and cellular FLICE-like inhibitory protein. cIAP2 is upregulated in regenerative epithelial cells both in ulcerative colitis and in experimental intestinal wounds. Inhibition of cIAP2 decreases wound healing in vitro possibly through inhibition of migration. Altogether, it is shown that epithelial cells in ulcerative colitis responds to the hostile microenvironment by activation of cytoprotective pathways that tend to counteract the cytotoxic effects of inflammation. However, the present studies also show that epithelial cells produce increased amounts of reactive oxygen species during stimulation with tumor necrosis factor-α and interferon-γ resulting in DNA instability. The combined effect of increased DNA-instability and decreased apoptosis responses could lead to neoplasia.

A critical role for cellular inhibitor of protein 2 (cIAP2) in colitis-associated colorectal cancer and intestinal homeostasis mediated by the inflammasome and survival pathways

Cellular inhibitors of apoptosis proteins (cIAPs) are critical arbiters of cell death and key mediators of inflammation and innate immunity. cIAP2 is frequently overexpressed in colorectal cancer and in regenerating crypts of ulcerative colitis patients. However, its corresponding functions in intestinal homeostasis and underlying mechanisms in disease pathogenesis are poorly understood. We found that mice deficient in cIAP2 exhibited reduced colitis-associated colorectal cancer tumor burden but, surprisingly, enhanced susceptibility to acute and chronic colitis. The exacerbated colitis phenotype of cIAP2-deficient mice was mediated by increased cell death and impaired activation of the regenerative inflammasome-interleukin-18 (IL-18) pathway required for tissue repair following injury. Accordingly, administration of recombinant IL-18 or pharmacological inhibition of caspases or the kinase RIPK1 protected cIAP2-deficient mice from colitis and restored intestinal epithelial barrier architecture. Thus, cIAP2 orchestrates intestinal homeostasis by exerting a dual function in suppressing cell death and promoting intestinal epithelial cell proliferation and crypt regeneration.

Cell death at the intestinal epithelial front line

The intestinal epithelium represents the largest epithelial surface in our body. This single-cell-layer epithelium mediates important functions in the absorption of nutrients and in the maintenance of barrier function, preventing luminal microorganisms from invading the body. Due to its constant regeneration the intestinal epithelium is a tissue not only with very high proliferation rates but also with very prominent physiological and pathophysiological cell death induction. The normal physiological differentiation and maturation of intestinal epithelial cells leads to their shedding and apoptotic cell death within a few days, without disturbing the epithelial barrier integrity. In contrast excessive intestinal epithelial cell death induced by irradiation, drugs and inflammation severely impairs the vital functions of this tissue. In this review we discuss cell death processes in the intestinal epithelium in health and disease, with special emphasis on cell death triggered by the tumour necrosis factor receptor family.

Cellular inhibitor of apoptosis protein 2 controls human colonic epithelial restitution, migration, and Rac1 activation

Identification of pathways involved in wound healing is important for understanding the pathogenesis of various intestinal diseases. Cellular inhibitor of apoptosis protein 2 (cIAP2) regulates proliferation and migration in nonepithelial cells and is expressed in human colonocytes. The aim of the study was to investigate the role of cIAP2 for wound healing in the normal human colon. Wound tissue was generated by taking rectosigmoidal biopsies across an experimental ulcer in healthy subjects after 5, 24, and 48 h. In experimental ulcers, the expression of cIAP2 in regenerating intestinal epithelial cells (IECs) was increased at the wound edge after 24 h (P < 0.05), returned to normal after reepithelialization, and correlated with the inflammatory reaction in the experimental wounds (P < 0.001). cIAP2 was induced in vitro in regenerating Caco2 IECs after wound infliction (P < 0.01). Knockdown of cIAP2 caused a substantial impairment of the IEC regeneration through inhibition of migration (P < 0.005). cIAP2 overexpression lead to formation of migrating IECs and upregulation of expression of RhoA and Rac1 as well as GTP-activation of Rac1. Transforming growth factor-β1 enhanced the expression of cIAP2 but was not upregulated in wounds in vivo and in vitro. NF-κB and MAPK pathways did not affect cIAP2 expression. cIAP2 is in conclusion a regulator of human intestinal wound healing through enhanced migration along with activation of Rac1, and the findings suggest that cIAP2 could be a future therapeutic target to improve intestinal wound healing.

Inhibitors of apoptosis (IAPs) regulate intestinal immunity and inflammatory bowel disease (IBD) inflammation

The inhibitor of apoptosis (IAP) family members, notably cIAP1, cIAP2, and XIAP, are critical and universal regulators of tumor necrosis factor (TNF) mediated survival, inflammatory, and death signaling pathways. Furthermore, IAPs mediate the signaling of nucleotide-binding oligomerization domain (NOD)1/NOD2 and other intracellular NOD-like receptors in response to bacterial pathogens. These pathways are important to the pathogenesis and treatment of inflammatory bowel disease (IBD). Inactivating mutations in the X-chromosome-linked IAP (XIAP) gene causes an immunodeficiency syndrome, X-linked lymphoproliferative disease type 2 (XLP2), in which 20% of patients develop severe intestinal inflammation. In addition, 4% of males with early-onset IBD also have inactivating mutations in XIAP. Therefore, the IAPs play a greater role in gut homeostasis, immunity and IBD development than previously suspected, and may have therapeutic potential.

Gene signature distinguishes patients with chronic ulcerative colitis harboring remote neoplastic lesions

BACKGROUND

Individuals with ulcerative colitis (UC) are at increased risk for colorectal cancer. The standard method of surveillance for neoplasia in UC by colonoscopy is invasive and can miss flat lesions. We sought to identify a gene expression signature in nondysplastic mucosa without active inflammation that could serve as a marker for remote neoplastic lesions.

METHODS

Gene expression was analyzed by complementary DNA microarray in 5 normal controls, 4 UC patients without dysplasia, and 11 UC patients harboring remote neoplasia. Common gene ontology pathways of significantly differentially expressed genes were identified. Expression of genes which were progressively and significantly upregulated from controls to UC without neoplasia, to UC with remote neoplasia were evaluated by real-time polymerase chain reaction. Several gene products were also examined by immunohistochemistry.

RESULTS

Four hundred and sixty-eight genes were significantly upregulated, and 541 genes were significantly downregulated in UC patients with neoplasia compared with UC patients without neoplasia. Nine genes (ACSL1, BIRC3, CLC, CREM, ELTD1, FGG, S100A9, THBD, and TPD52L1) were progressively and significantly upregulated from controls to nondysplastic UC to UC with neoplasia. Immunostaining of proteins revealed increased expression of S100A9 and REG1α in UC-associated cancer and in nondysplastic tissue from UC patients harboring remote neoplasia compared with UC patients without neoplasia and controls.

CONCLUSIONS

Gene expression changes occurring as a field effect in the distal colon of patients with chronic UC identify patients harboring remote neoplastic lesions. These markers may lead to a more accurate and less invasive method of detection of neoplasia in patients with inflammatory bowel disease.

Mucosal healing in ulcerative colitis: pathophysiology and pharmacology

Ulcerative colitis (UC) is a colonic inflammatory condition with a substantial impact on the quality of life of affected persons. The disease carries a cumulative risk of need of colectomy of 20-30% and an estimated cumulative risk of colorectal cancer of 18% after 30 years of disease duration. With the introduction of the tumor necrosis factor-alpha inhibitors for the treatment of UC, it has become increasingly evident that the disease course is influenced by whether or not the patient achieves mucosal healing. Thus, patients with mucosal healing have fewer flare-ups, a decreased risk of colectomy, and a lower probability of developing colorectal cancer. Understanding the mechanisms of mucosal wound formation and wound healing in UC, and how they are affected therapeutically is therefore of importance for obtaining efficient treatment strategies holding the potential of changing the disease course of UC. This review is focused on the pathophysiological mechanism of mucosal wound formation in UC as well as the known mechanisms of intestinal wound healing. Regarding the latter topic, pathways of both wound healing intrinsic to epithelial cells and the wound-healing mechanisms involving interaction between epithelial cells and other cells of the mucosa are discussed. The biochemistry of wound healing in UC provides the basis for the subsequent description of how these pathways are affected by the current medications, and what can be learnt on how to design future treatment regimens for UC based on targeting mucosal healing.

The value of histological changes and immunohistochemical markers Ki67 and p53 in the assessment of ulcerative colitis related dysplasia

The risk of carcinoma increases in patients with a 10-year or longer duration of ulcerative colitis (UC). To search for a more objective parameter to assess epithelial dysplasia. The study comprised 25 cases of longstanding UC: 7 cases with regenerative atypia, 7 with low grade dysplasia, 7 with high grade dysplasia, and 4 cases indefinite for dysplasia. The colonic biopsies obtained during endoscopy were stained with H&E to identify the aforementioned categories. Seventy-five sections from biopsy specimens were stained immunohistochemically to detect differences in the frequency and pattern of nuclei positive for the proliferation marker Ki67 and p53. In high grade dysplasia, the distribution of Ki67 positive cells was diffuse throughout the full length of the crypt, whereas low grade dysplasia and epithelium indefinite for dysplasia, as well as regenerative epithelium, showed an expanded basal zone. None of the regenerative atypia cases showed strong intensity p53 staining compared to dysplasia cases. None of the high grade dysplasia cases showed restricted p53 staining to the lower two thirds of the crypt. All the cases of HGD showed extension of Ki67 and p53 staining above the basal two thirds of the crypt. Ki67 and p53 immunostained cell assessment combined with routine histological evaluation of colorectal mucosa can improve the diagnostic accuracy, as well as the assessment of malignant transformation risk.

Epithelial apoptosis: cause or consequence of ulcerative colitis?

OBJECTIVE

Epithelial apoptosis rates are increased in ulcerative colitis (UC). The increased apoptosis rate could expose mucosal cells to luminal pathogens and thereby be regarded as a primary pathogenic factor in UC. On the other hand, the local inflammatory reaction could cause epithelial apoptosis secondary to the release of cytotoxic mediators. If apoptosis is a primary defect, apoptosis rates could influence the degree of spreading of inflammation and the clinical course of UC. If apoptosis is a side effect of local inflammation, apoptosis rates would be expected only to correlate with the degree of local inflammation. The aim of the study was to investigate the relationship between epithelial apoptosis and clinical characteristics of UC.

MATERIAL AND METHODS

Twenty patients with UC (12 with active disease) and 20 control subjects were included. Freshly isolated colonic epithelial cells were cultured. Apoptosis was determined by flow cytometry. Cells were stimulated with Fas ligand. The disease was characterized by endoscopic findings, microscopic inflammation grade, surrogate markers of disease activity (hemoglobin level, white blood cell count, C-reactive protein, or albumin), and the clinical course 6 months after biopsy.

RESULTS

Epithelial apoptosis correlated with local inflammation, both macroscopic (p< 0.02) and microscopic (p< 0.008). Disease extent, disease course, or surrogate markers of disease activity did not correlate with apoptosis rate. However, increased microscopic inflammation inversely correlated with apoptosis response to the Fas ligand (p< 0.06).

CONCLUSIONS

The epithelial apoptosis rate is influenced primarily by the local inflammatory response. Colonocytes upregulate cytoprotective mediators that decrease apoptosis susceptibility during active UC.

Attenuated apoptosis response to Fas-ligand in active ulcerative colitis

BACKGROUND

From mainly carcinoma cell line studies, apoptosis has been thought to play a major role in the pathogenesis of ulcerative colitis (UC). Apoptosis has been suggested to be due to a Fas ligand / Fas receptor interaction, but has never been studied in cells from patients with active UC. The aim was to investigate both the spontaneous and the cell death receptor ligand-induced apoptosis in UC.

METHODS

Twenty patients with UC and 16 control subjects who underwent routine colonoscopy either for the control or surveillance of their disease or where the diagnosis of irritable bowel syndrome was subsequently reached were included. Cultures of isolated colonic crypts were obtained from biopsies and cultured for 4 to 16 hours with Fas ligand or Fas ligand and costimulation with interferon-gamma (IFN-gamma). Control experiments were performed on HT29 cells. Apoptosis was assessed by independent methods.

RESULTS

Isolated colonocytes from healthy subjects or patients with remission in UC had a dose-dependent response to Fas ligand. This response was abolished in patients with active UC (P < 0.002), and costimulation with IFN-gamma did not alter this response. Patients with active UC had an increased apoptosis rate of 9.5% compared with controls (P < 0.05).

CONCLUSIONS

The current study indicates that colonocytes do not respond to cytokine exposure and inflammation by an increased vulnerability, as previously thought. Colonocytes seem to activate cytoprotective programs in response to inflammation. Apart from supporting the regeneration process during inflammation, this response could additionally cause an increased susceptibility to neoplastic transformation.