Expression of tricellular tight junction proteins and the paracellular macromolecule barrier are recovered in remission of ulcerative colitis

Background: Ulcerative colitis (UC) has a relapsing and remitting pattern, wherein the underlying mechanisms of the relapse might involve an enhanced uptake of luminal antigens which stimulate the immune response. The tricellular tight junction protein, tricellulin, takes charge of preventing paracellular passage of macromolecules. It is characterized by downregulated expression in active UC and its correct localization is regulated by angulins. We thus analyzed the tricellulin and angulin expression as well as intestinal barrier function and aimed to determine the role of tricellulin in the mechanisms of relapse. Methods: Colon biopsies were collected from controls and UC patients who underwent colonoscopy at the central endoscopy department of Campus Benjamin Franklin, Charite - Universitatsmedizin Berlin. Remission of UC was defined basing on the clinical appearance and a normal Mayo endoscopic subscore. Intestinal barrier function was evaluated by electrophysiological and paracellular flux measurements on biopsies mounted in Ussing chambers. Results: The downregulated tricellulin expression in active UC was recovered in remission UC to control values. Likewise, angulins were in remission UC at the same levels as in controls. Also, the epithelial resistance which was decreased in active UC was restored in remission to the same range as in controls, along with the unaltered paracellular permeabilities for fluorescein and FITC-dextran 4 kDa. Conclusions: In remission of UC, tricellulin expression level as well as intestinal barrier functions were restored to normal, after they were impaired in active UC. This points toward a re-sealing of the impaired tricellular paracellular pathway and abated uptake of antigens to normal rates in remission of UC

GPCRdb:an information system for G protein-coupled receptors

Recent developments in G protein-coupled receptor (GPCR) structural biology and pharmacology have greatly enhanced our knowledge of receptor structure-function relations, and have helped improve the scientific foundation for drug design studies. The GPCR database, GPCRdb, serves a dual role in disseminating and enabling new scientific developments by providing reference data, analysis tools and interactive diagrams. This paper highlights new features in the fifth major GPCRdb release: (i) GPCR crystal structure browsing, superposition and display of ligand interactions; (ii) direct deposition by users of point mutations and their effects on ligand binding; (iii) refined snake and helix box residue diagram looks; and (iii) phylogenetic trees with receptor classification colour schemes. Under the hood, the entire GPCRdb front- and back-ends have been re-coded within one infrastructure, ensuring a smooth browsing experience and development. GPCRdb is available at http://www.gpcrdb.org/ and it's open source code at https://bitbucket.org/gpcr/protwis

Human small intestinal infection by SARS-CoV-2 is characterized by a mucosal infiltration with activated CD8+ T cells

The SARS-CoV-2 pandemic has so far claimed over three and a half million lives worldwide. Though the SARS-CoV-2 mediated disease COVID-19 has first been characterized by an infection of the upper airways and the lung, recent evidence suggests a complex disease including gastrointestinal symptoms. Even if a direct viral tropism of intestinal cells has recently been demonstrated, it remains unclear, whether gastrointestinal symptoms are caused by direct infection of the gastrointestinal tract by SARS-CoV-2 or whether they are a consequence of a systemic immune activation and subsequent modulation of the mucosal immune system. To better understand the cause of intestinal symptoms we analyzed biopsies of the small intestine from SARS-CoV-2 infected individuals. Applying qRT-PCR and immunohistochemistry, we detected SARS-CoV-2 RNA and nucleocapsid protein in duodenal mucosa. In addition, applying imaging mass cytometry and immunohistochemistry, we identified histomorphological changes of the epithelium, which were characterized by an accumulation of activated intraepithelial CD8(+) T cells as well as epithelial apoptosis and subsequent regenerative proliferation in the small intestine of COVID-19 patients. In summary, our findings indicate that intraepithelial CD8(+) T cells are activated upon infection of intestinal epithelial cells with SARS-CoV-2, providing one possible explanation for gastrointestinal symptoms associated with COVID-19

PuraStat in gastrointestinal bleeding: results of a prospective multicentre observational pilot study

Background: A recently developed haemostatic peptide gel for endoscopic application has been introduced to improve the management of gastrointestinal bleeding. The aim of this pilot study was to evaluate the feasibility, safety, efficacy and indication profiles of PuraStat in a clinical setting. Methods: In this prospective observational multicentre pilot study, patients with acute non-variceal gastrointestinal bleeding (upper and lower) were included. Primary and secondary application of PuraStat was evaluated. Haemoglobin, prothrombin time, platelets and transfusion behaviour were documented before and after haemostasis. The efficacy of PuraStat was assessed during the procedure, at 3 days and 1 week after application. Results: 111 patients with acute gastrointestinal bleeding were recruited into the study. 70 percent (78/111) of the patients had upper gastrointestinal bleeding and 30% (33/111) had lower gastrointestinal bleeding. After primary application of PuraStat, initial haemostatic success was achieved in 94% of patients (74/79, 95% CI 88-99%), and in 75% of the patients when used as a secondary haemostatic product, following failure of established techniques (24/32, 95% CI 59-91%). The therapeutic success rates (absence of rebleeding) after 3 and 7 days were 91% and 87% after primary use, and 87% and 81% in all study patients. Overall rebleeding rate at 30 day follow-up was 16% (18/111). In the 5 patients who finally required surgery (4.5%), PuraStat allowed temporary haemostasis and stabilisation. Conclusions: PuraStat expanded the therapeutic toolbox available for an effective treatment of gastrointestinal bleeding sources. It could be safely applied and administered without complications as a primary or secondary therapy. PuraStat may additionally serve as a bridge to surgery in order to achieve temporary haemostasis in case of refractory severe bleeding, possibly playing a role in preventing immediate emergency surgery

The Overlapping Area of Non-Celiac Gluten Sensitivity (NCGS) and Wheat-Sensitive Irritable Bowel Syndrome (IBS): An Update

Gluten-related disorders have recently been reclassified with an emerging scientific literature supporting the concept of non-celiac gluten sensitivity (NCGS). New research has specifically addressed prevalence, immune mechanisms, the recognition of non-immunoglobulin E (non-IgE) wheat allergy and overlap of NCGS with irritable bowel syndrome (IBS)-type symptoms. This review article will provide clinicians with an update that directly impacts on the management of a subgroup of their IBS patients whose symptoms are triggered by wheat ingestion

Towards interpreting recurrent neural networks through probabilistic abstraction

National Research Foundation (NRF) Singapore under its AI Singapore Programm

Influence of epithelial apoptosis on barrier function in physiologocially normal and inflamed intestinal epithelium

Die Mukosa des Gastrointestinaltraktes spielt als Barriere zwischen dem mukosalen und serosalen Kompartiment eine zentrale Rolle für die Koordination von Transportprozessen und sichert eine ausreichende Abwehr von schädlichen Substanzen und Mikroorganismen. Von besonderer Bedeutung ist diese Barriere – neben der Erhaltung einer Homöostase beim gesunden Menschen – vor allem bei Auftreten einer Barrierestörung, beispielsweise bei Infektionen oder chronischen Entzündungen des oberen oder unteren Gastrointestinaltraktes. Darüber hinaus gehört das Mukosa-assoziierte Immunsystem des Gastrointestinaltraktes zu einem komplexen Netzwerk interagierender Immunzellen und bildet mit diesen das größte immunologische Organ innerhalb des menschlichen Organismus aus. Proteine der Tight Junctions gehören zu den am dichtesten unterhalb der Oberfläche der Mukosa gelegenen Zell-Zell- Kontaktstrukturen. Eine Fehlregulation dieses aus einer Vielzahl von Proteinen bestehenden Komplexes hat dramatische Konsequenzen für den gerichteten Transport von Wasser und anderen Soluten in das Körperinnere oder von dort in das Darmlumen. Apoptose ist ein physiologischer Vorgang, der insbesondere in dem sich rasch teilenden Darmepithel notwendig ist, um die Homöostase aufrecht zu erhalten. Eine Fehlregulation der physiologischen Apoptose führt ebenfalls zu dramatischen Veränderungen der Integrität des mukosalen Zellverbandes. Im Rahmen der in dieser Habilitationsschrift vorgestellten Untersuchungen wurde ein Beitrag zum besseren Verständnis der Funktion der Tight Junction-Proteine bei der epithelialen Apoptose geleistet. Erstmals wurde gezeigt, welchen Einfluss Apoptose auf die Leitfähigkeitsveränderungen im Darm hat und wieviel Apoptose ein epithelialer Zellverband toleriert, um seine zentrale Eigenschaften eines mitteldichten Epithels noch zu behalten oder bereits Eigenschaften von durchlässigen („lecken“) Epithelien anzunehmen. Erstmals wurden Zielproteine der epithelialen Apoptose unter den Tight Junction- Proteinen identifziert, die spezifisch von Caspasen und Metalloproteinasen gespalten werden. Im Gegensatz zur weitläufigen Meinung, dass während der Apoptose grundsätzlich alle Proteine proteolytisch fragmentiert werden, fand sich mit Claudin-1 ein Protein des Tight Junction-Komplexes, das äußerst widerstandsfähig gegenüber Apoptosesignalen ist. In den letzten Jahren haben andere Arbeitsgruppen zeigen können, dass die Dysregulation der Tight Junctions und die erhöhte epitheliale Apoptose nicht die einzigen Faktoren der Leitfähigkeits-änderungen sind, sondern weitere Enzyme wie MLCK II oder Mechanismen wie Endozytose von Proteinen der Tight Junctions zur Entstehung einer Barrierefunktionsstörung beitragen. Die in der Zellkultur gewonnenen Erkenntnisse konnten im Weiteren auch für die Untersuchung an humanen Gewebeproben von Patienten mit chronisch entzündlichen Darmerkrankungen sowie bei kollagener Kolitis genutzt werden. Bei der kollagenen Kolitis fanden sich mehrere Diarrhö-mechanismen sowie eine Herabregulation von Proteinen der Tight Junctions, jedoch keine erhöhte Apoptoserate. Bei akutem Morbus Crohn spielt eine hochregulierte epitheliale Apoptoserate in der Mukosa eine bedeutende Rolle und führt zu einer Störung der intestinalen Barriere. Diese Barrierestörung bildet sich innerhalb von 2 Wochen nach Therapie mit TNF-alpha Blockern zurück und geht einher mit einem deutlichen Rückgang der Apoptoserate. Im Gegensatz zum Morbus Crohn spielt bei der Th2-vermittelten Immunantwort der Colitis ulcerosa das Interleukin-13 als Schlüsselzytokin eine entscheidende Rolle. Auch IL-13 induziert im Zellkulturmodell epitheliale Apoptosen und erklärt zusammen mit der Hochregulation von Claudin-2 als Porenbilder sowie einer verzögerten epithelialen Restitution die typischen epithelphysiologischen Veränderungen bei akuter Colitis. Medikamentöse anti- TNF-alpha Strategien werden bereits seit mehreren Jahren zur Therapie von refraktären Verläufen bei chronisch entzündlichen Darmerkrankungen verfolgt. Die Ergebnisse kommender Studien müssen nun zeigen, ob auch eine anti- IL-13-Therapie, wie sie kürzlich bei Patienten mit Asthma bronchiale und chronisch-obstruktiver Lungenerkrankung in klinischen Studien vorgestellt wurde, eine weitere Therapieoption bei Patienten mit refraktären Verläufen bei Colitis ulcerosa darstellt.Proteins of the Tight Junctions are part of the cell-cell contact structures below the surface of the mucosa. Imbalance of this complex has a dramatic effect on several physiological processes. A dysregulation of apoptosis has similar effects. We showed for the first time the effects of apoptosis on changes of permeability and defined targed structures and proteins during apoptotic signalling in different cell culture systems. Furthermore we investigated in human tissue samples from patients with inflammatory bowel disease and collagenous colitis the role and function of apoptosis. With the results we contribute to a better understanding of potential pathomechanisms in normal mucosa and inflamed gastrointestinal tissue