Impaired intestinal epithelial barrier (IEB) function with loss of desmosomal junctional protein desmoglein 2 (DSG2) is a hallmark in the pathogenesis of inflammatory bowel disease (IBD). While previous studies have reported that glial cell line–derived neurotrophic factor (GDNF) promotes IEB function, the mechanisms are poorly understood. We hypothesized that GDNF is involved in the loss of DSG2, resulting in impaired IEB function as seen in IBD. In the inflamed intestine of patients with IBD, there was a decrease in GDNF concentrations accompanied by a loss of DSG2, changes of the intermediate filament system, and increased phosphorylation of p38 MAPK and cytokeratins. DSG2-deficient and RET-deficient Caco2 cells revealed that GDNF specifically recruits DSG2 to the cell borders, resulting in increased DSG2-mediated intercellular adhesion via the RET receptor. Challenge of Caco2 cells and enteroids with proinflammatory cytokines as well as dextran sulfate sodium–induced (DSS-induced) colitis in C57Bl/6 mice led to impaired IEB function with reduced DSG2 mediated by p38 MAPK–dependent phosphorylation of cytokeratins. GDNF blocked all inflammation-induced changes in the IEB. GDNF attenuates inflammation-induced impairment of IEB function caused by the loss of DSG2 through p38 MAPK–dependent phosphorylation of cytokeratin. The reduced GDNF in patients with IBD indicates a disease-relevant contribution to the development of IEB dysfunction.

Enteric glial cells (EGCs) of the enteric nervous system are critically involved in the maintenance of intestinal epithelial barrier function (IEB). The underlying mechanisms remain undefined. Glial cell line-derived neurotrophic factor (GDNF) contributes to IEB maturation and may therefore be the predominant mediator of this process by EGCs. Using GFAP^cre x Ai14^floxed mice to isolate EGCs by Fluorescence-activated cell sorting (FACS), we confirmed that they synthesize GDNF in vivo as well as in primary cultures demonstrating that EGCs are a rich source of GDNF in vivo and in vitro. Co-culture of EGCs with Caco2 cells resulted in IEB maturation which was abrogated when GDNF was either depleted from EGC supernatants, or knocked down in EGCs or when the GDNF receptor RET was blocked. Further, TNFα-induced loss of IEB function in Caco2 cells and in organoids was attenuated by EGC supernatants or by recombinant GDNF. These barrier-protective effects were blunted when using supernatants from GDNF-deficient EGCs or by RET receptor blockade. Together, our data show that EGCs produce GDNF to maintain IEB function in vitro through the RET receptor.

The measurement of transepithelial electrical resistance (TEER) is a common technique to determine the barrier integrity of epithelial cell monolayers. However, it is remarkable that absolute TEER values of similar cell types cultured under comparable conditions show an immense heterogeneity. Based on previous observations, we hypothesized that the heterogeneity of absolute TEER measurements can not only be explained by maturation of junctional proteins but rather by dynamics in the absolute length of cell junctions within monolayers. Therefore, we analyzed TEER in epithelial cell monolayers of Caco2 cells during their differentiation, with special emphasis on both changes in the junctional complex and overall cell morphology within monolayers. We found that in epithelial Caco2 monolayers TEER increased until confluency, then decreased for some time, which was then followed by an additional increase during junctional differentiation. In contrast, permeability of macromolecules measured at different time points as 4 kDA fluorescein isothiocyanate (FITC)-dextran flux across monolayers steadily decreased during this time. Detailed analysis suggested that this observation could be explained by alterations of junctional length along the cell borders within monolayers during differentiation. In conclusion, these observations confirmed that changes in cell numbers and consecutive increase of junctional length have a critical impact on TEER values, especially at stages of early confluency when junctions are immature.

Loss of intestinal epithelial barrier function is a hallmark in digestive tract inflammation. The detailed mechanisms remain unclear due to the lack of suitable cell-based models in barrier research. Here we performed a detailed functional characterization of human intestinal organoid cultures under different conditions with the aim to suggest an optimized ex-vivo model to further analyse inflammation-induced intestinal epithelial barrier dysfunction. Differentiated Caco2 cells as a traditional model for intestinal epithelial barrier research displayed mature barrier functions which were reduced after challenge with cytomix (TNFα, IFN-γ, IL-1ß) to mimic inflammatory conditions. Human intestinal organoids grown in culture medium were highly proliferative, displayed high levels of LGR5 with overall low rates of intercellular adhesion and immature barrier function resembling conditions usually found in intestinal crypts. WNT-depletion resulted in the differentiation of intestinal organoids with reduced LGR5 levels and upregulation of markers representing the presence of all cell types present along the crypt-villus axis. This was paralleled by barrier maturation with junctional proteins regularly distributed at the cell borders. Application of cytomix in immature human intestinal organoid cultures resulted in reduced barrier function that was accompanied with cell fragmentation, cell death and overall loss of junctional proteins, demonstrating a high susceptibility of the organoid culture to inflammatory stimuli. In differentiated organoid cultures, cytomix induced a hierarchical sequence of changes beginning with loss of cell adhesion, redistribution of junctional proteins from the cell border, protein degradation which was accompanied by loss of epithelial barrier function. Cell viability was observed to decrease with time but was preserved when initial barrier changes were evident. In summary, differentiated intestinal organoid cultures represent an optimized human ex-vivo model which allows a comprehensive reflection to the situation observed in patients with intestinal inflammation. Our data suggest a hierarchical sequence of inflammation-induced intestinal barrier dysfunction starting with loss of intercellular adhesion, followed by redistribution and loss of junctional proteins resulting in reduced barrier function with consecutive epithelial death.

Background: Chronic postsurgical pain (CPSP) is a potential long-term problem following open incisional hernia repair which may affect the quality of life of patients despite successful anatomical repair of the hernia. The aim of this manuscript was to identify the incidence and outcome of patients following open incisional hernia repair in respect of risk factors to develop CPSP. Methods: A single-center retrospective analysis of patients who underwent open incisional hernia repair between 2015 and 2021 was performed. Pre-existing conditions (e.g., diabetes mellitus and malignancy), hernia complexity, postoperative complications, and postoperative pain medication were analyzed using the local database. Quality of life and CPSP were assessed using the EuraHS Quality of Life (QoL) questionnaire. Results: A total of 182 cases were retrospectively included in a detailed analysis based on the complete EuraHS (QoL) questionnaire. During the average follow-up period of 46 months, this long-term follow-up revealed a 54.4% incidence of CPSP and including a rate of 14.8% for severe CPSP (sCPSP) after open incisional hernia surgery. The complexity of the hernia and the demographic variables were not different between the group with and without CPSP. Patients with CPSP reported significantly reduced QoL. The analgesics score which includes the need of pain medication in the initial days after surgery was significantly higher in patients with CPSP than in those without (no CPSP: 2.86 vs. CPSP: 3.35; p = 0.047). Conclusion: The presence of CPSP after open incisional hernia repair represents a frequent and underestimated long-term problem which has been not been recognized to this extent before. CPSP impairs QoL in these patients. Patients at risk to develop CPSP can be identified in the perioperative setting by the need of high doses of pain medication using the analgesics score. Possibly timely adjustment of pain medication, even in the domestic setting, could alleviate the chronicity or severity of CPSP.

Background: Chronic postoperative inguinal pain (CPIP) is a common complication after inguinal hernia surgery and occurs in up to 10–14% of cases. CPIP has a significant impact on daily life, work ability and thus compromises quality of life. The aim of this retrospective study was an in‐depth analysis of patients undergoing inguinal hernia repair to further refine the prediction of the onset of CPIP reliably.Methods: A single center retrospective analysis of patients with who underwent open or minimally invasive inguinal hernia repair from 2016 to 2021 was carried out. Complication rates, detailed analysis of postoperative pain medication and quality of life using the EuraHS Quality of Life questionnaire were assessed.Results: Out of 596 consecutive procedures, 344 patients were included in detailed analyses. While patient cohorts were different in terms of age and co‐morbidities, and the prevalence of CPIP was 12.2% without differences between the surgical procedures (Lichtenstein: 12.8%; TEP 10.9%; TAPP 13.5%). Postoperative pain was evaluated using a newly developed analgesic score. Patients who developed CPIP later had a significant higher consumption of analgesics at discharge (p = 0.016). As additional risk factors for CPIP younger patient age and postoperative complications were identified.Conclusion: The prospective use of the analgesic score established here could be helpful to identify patients that are at risk to develop CPIP. These patients could benefit from a structured follow‐up to allow early therapeutic intervention to prevent chronification and restore the quality of life.