Intestinal barrier:Molecular pathways and modifiers

The gastrointestinal tract is frequently challenged by pathogens/antigens contained in food and water and the intestinal epithelium must be capable of rapid regeneration in the event of tissue damage. Disruption of the intestinal barrier leads to a number of immune-mediated diseases, including inflammatory bowel disease, food allergy, and celiac disease. The intestinal mucosa is composed of different types of epithelial cells in specific barrier functions. Epithelial cells control surfaceassociated bacterial populations without disrupting the intestinal microflora that is crucial for host health. They are also capable of modulating mucosal immune system, and are thus essential in maintaining homeostasis in the gut. Thus, the regulation of intestinal epithelial homeostasis is crucial for the maintenance of the structure of the mucosa and the defensive barrier functions. Recent studies have demonstrated that multiple molecular pathways are involved in the regulation of intestinal epithelial cell polarity. These include the Wnt, Notch, Hippo, transforming growth factor-β(TGF-β)/bone morphogenetic protein(BMP) and Hedgehog pathways, most of which were identified in lower organisms where they play important roles during embryogenesis. These pathways are also used in adult organisms to regulate multiple self-renewing organs. Understanding the interactions between these molecular mechanisms and intestinal barrier function will therefore provide important insight into the pathogenesis of intestinal-based immune-mediated diseases.

Modulating effects of acyl-CoA synthetase 5-derived mitochondrial Wnt2B palmitoylation on intestinal Wnt activity

AIM: To investigate the role of acyl-CoA synthetase 5 (ACSL5) activity in Wnt signaling in intestinal surface epithelia.

Intestinal acyl-CoA synthetase 5: Activation of long chain fatty acids and behind

The intestinal mucosa is characterized by a high complexity in terms of structure and functions and allows for a controlled demarcation towards the gut lumen.On the one hand it is responsible for pulping and selective absorption of alimentary substances ensuring the immunological tolerance,on the other hand it prevents the penetration of micro-organisms as well as bacterial outgrowth.The continuous regeneration of surface epithelia along the crypt-villus-axis in the small intestine is crucial to assuring these various functions.The core phenomena of intestinal epithelia regeneration comprise cell proliferation,migration,differentiation,and apoptosis.These partly contrarily oriented processes are molecularly balanced through numerous interacting signaling pathways like Wnt/β-catenin,Notch and Hedgehog,and regulated by various modifying factors.One of these modifiers is acyl-CoA synthetase 5(ACSL5).It plays a key role in de novo lipid synthesis,fatty acid degradation and membrane modifications,and regulates several intestinal processes,primarily through different variants of protein lipidation,e.g.,palmitoylation.ACSL5 was shown to interact with proapoptotic molecules,and besides seems to inhibit proliferation along the crypt-villus-axis.Because of its proapoptotic and antiproliferative characteristics it could be of significant relevance for intestinal homeostasis,cellular disorder and tumor development.

Beta-7 integrin controls enterocyte migration in the small intestine

AIM:To hypothesize that beta-7 integrin affects cellularmigration of both,lymphocytes and enterocytes.METHODS:The nucleoside analog Brd U was ip injected in beta-7-deficient mice(C57BL/6-Itgbtmlcgn/J)of male gender and age-matched male C57BL/J J mice(wild type)4,20,or 40 h before analysis.The total small intestine was isolated,dissected,and used for morphometrical studies.Brd U-positive epithelial cells were numbered in at least 15 hemi-crypts per duodenum,jejunum,and ileum of each animal.The outer most Brd U-positive cell(cellmax)was determined per hemi-crypt,numerically documented,and statistically analysed.RESULTS:Integrins containing the beta-7-chain were exclusively expressed on leukocytes.In the small intestinal mucosa of beta-7 integrin-deficient mice the number of intraepithelial lymphocytes was drastically decreased.Moreover,the Peyer’s patches of beta-7integrin-deficient mice appeared hypoplastic.In beta-7integrin-deficient mice the location of cellmax was found in a higher position than it was the case for the controls.The difference was already detected at 4 h after Brd U application,but significantly increased with time(40 h after Brd U injection)in all small intestinal segments investigated,i.e.,duodenum,jejunum,and ileum.Migration of small intestinal enterocytes was different between the experimental groups measured by cellmax locations.CONCLUSION:The E-cadherin beta-7 integrin pathway probably controls migration of enterocytes within the small intestinal surface lining epithelial layer.

Molecular classification of colorectal carcinomas:The genotype-to-phenotype relation

Colorectal carcinomas(CRCs)are frequently found in industrialized countries and lead to a high incidence of malignancy-related mortality.Defined by histomorphological features,CRCs and their pre-invasive lesions are quite heterogeneous.The underlying molecular mechanisms include genomic instability,genomic mutation of tumor suppressor genes or oncogenes,epigenetic changes,and the microRNA network.The molecular mechanisms are guided by repeated clonal selections.The genotype-to-phenotype relation is assumed to be the great challenge of cancer research and the development of effective targeted therapies.At present a strong genotype-to-phenotype relation is characterized only for a minority of CRCs.Consequently,the molecular characterization of CRCs is essential to interpret histological patterns and to identify prognostic groups as well as patients for targeted therapy.

Intestinal genetic inactivation of caspase-8 diminishes migration of enterocytes

AIM: To verify the hypothesis that caspase-8(Casp8), which regulates cellular apoptosis and necroptosis, is critically involved in enterocyte migration.METHODS: Casp8-silenced Caco2 cells were used in migration assays. In addition, enterocyte-specific Casp8 heterozygous(Casp8+/?int) or homozygous knockout mice(Casp8?int) were generated by crossing genetically modified mice carrying lox P recombination sites in intron 2 and 4 of the murine Casp8 gene with transgenic animals expressing a cre-transgene under control of the villin promoter in a pure C57/BL6 genetic background. The nucleoside analog Brd U was injected i.p. in male Casp8+/?int and Casp8?int animals 4 h, 20 h, or 40 h before performing morphometric studies. Locations of anti-Brd U-immunostained cells(cellmax) in at least 50 hemi-crypts of 6 histoanatomically distinct intestinal mucosal regions were numbered and extracted for statistical procedures. For the mice cohort(n = 28), the walking distance of enterocytes was evaluated from cellmax within crypt(n = 57), plateau(n = 19), and villus(n = 172) positions, resulting in a total of 6838 observations. Data analysis was performed by fitting a three-level mixed effects modelto the data.RESULTS: In cell culture experiments with Caco2 cells, Casp8 knockdown efficiency mediated by RNA interference on Casp8 transcripts was 80% controlled as determined by Western blotting. In the scratch assay, migration of Casp8-deleted Caco2 cells was significantly diminished when compared with controls(Casp8?scramble and Caco2). In Brd U-labeled Casp8?int mice, cellmax locations were found along the hemi-crypts in a lower position than it was for Casp8+/?int or control(cre-negative) animals. Statistical data analysis with a three-level mixed effects model revealed that in the six different intestinal locations(distinct segments of the small and large intestine), cell movement between the three mice groups differed widely. Especially in duodenal hemi-crypts, enterocyte movement was different between the groups. At 20 h, duodenal cellmax location was significantly lower in Casp8?int(25.67 ± 2.49) than in Casp8+/?int(35.67 ± 4.78; P < 0.05) or control littermates(44.33 ± 0.94; P < 0.01).CONCLUSION: C a s p 8- d e p e n d e n t m i g ra t i o n o f enterocytes is likely involved in intestinal physiology and inflammation-related pathophysiology.

Modifier-concept of colorectal carcinogenesis: Lipidomics as a technical tool in pathway analysis

In the modifier concept of intestinal carcinogenesis, lipids have been established as important variables and one focus is given to long-chain fatty acids. Increased consumption of long-chain fatty acids is in discussion to modify the development of colorectal carcinoma in humans. Saturated long-chain fatty acids, in particular, are assumed to promote carcinogenesis, whereas poly-unsaturated forms are likely to act in the opposite way. At present, the molecular mechanisms behind these effects are not well understood. Recently, it has been demonstrated by lipidomics and associated molecular techniques, that activation and metabolic channeling of long-chain fatty acids are important mechanisms to modify colorectal carcinogenesis. In this Editorial, an overview about the present concept of long-chain fatty acids and its derivatives in colorectal carcinogenesis as well as technical algorithms in lipid analysis is given.

Fatty acid binding receptors in intestinal physiology and pathophysiology

Free fatty acids are essential dietary components and recognized as important molecules in the maintenance of cellular homeostasis.In the last decade,the molecular pathways for free fatty acid sensing in the gastrointestinal tract have been further elucidated by molecular identification and functional characterization of fatty acid binding receptors.These sensing molecules belong to the family of G proteincoupled receptors.In the intestine,four important receptors have been described so far.They differ in molecular structure,ligand specificity,expression pattern,and functional properties.In this review,an overview of intestinal fatty acid binding receptors and their role in intestinal physiology and pathophysiology is given.