Identification and Characterization of Stem Cells in Mammalian Esophageal Stratified Squamous Epithelia

Somatic stem cells are essential for maintenance of cell proliferation-differentiation homeostasis in organs. Despite the importance, how the esophageal epithelium that executes its self-renewal and maintenance remains elusive. In this study, using 5-bromo-2'-deoxyuridine (BrdU) label-chase in rat and rat esophageal keratinocyte cell line-derived organoids together with genome-wide DNA methylation profiling and single-cell RNA sequencing (scRNA-seq), we identify slow cycling/quiescent stem cell population that contain high levels of hemidesmosome (HD)’s and low levels of Wnt signaling localized spatially and randomly at the basal layer of the esophageal epithelium. Pseudo-time cell trajectory from scRNA-seq indicates that cell fates begin from quiescent basal cells (the stem cells) of the basal layer that produce proliferating and/or differentiating cells in the basal layer, which, in turn, progress into differentiating cells in the suprabasal layer, ultimately transforming into differentiated keratinocytes in the differentiated layer. Perturbations of HD component expressions and/or Wnt signaling reduce stem cell in the basal layer of esophageal keratinocyte organoids, resulting in alterations of organoid formation rate, size, morphogenesis and proliferation-differentiation homeostasis. Furthermore, we show that not only high levels of HDs and low levels of Wnt signaling but also an interplay between HD and Wnt signaling defined stem cells of the basal layer in the esophageal squamous epithelium. Hence, HDs and Wnt signaling are the critical determinants for defining stem cells of the basal layer required for proliferation-differentiation homeostasis and maintenance in the mammalian esophageal squamous epithelium.

Modern concepts on the state of esophagus epithelial barrier at gastroesophageal reflux disease and possibilities of correction with alginates

Gastroesophageal reflux disease (GERD) remains an urgent problem in clinical medicine. The search for ways of effective treatment leads to the need to set new accents in the multifactorial pathogenesis of the disease. According to current trends, special attention is paid to the epithelial barrier of the esophagus. The article presents considerations of the structure of the mucosal epithelial layer, the features of transport routes and intercellular interactions of the esophageal epithelium. Special attention is paid to the phenomenon of the Dilated Intercellular Spaces (DIS) and the syndrome of increased epithelial permeability (SІEP) at GERD. An interpretation of these concepts is given, their role in the implementation of inflammatory processes and the formation of clinical manifestations of the disease, such as heartburn and pain, is revealed. The data on the possible mechanisms of the formation of the DIS and SІEP phenomenon, methods of their diagnosis and aspects that are discussed in the scientific world are presented. The possibilities of cytoprotective therapy using alginate preparations have been shown. Among the alginates, available on the pharmaceutical market of Ukraine, the pharmacological line Gaviscon® (LLC Reckitt Benckiser Ukraine, Great Britain) is presented. The results of experimental studies with the use of the latest technologies, and data from randomized clinical trials confirming the alginates’ clinical efficacy, have been outlined. The phenomenon of DIS of the esophageal epithelium and SІEP for aggression factors is one of the leading links in GERD pathogenesis, in particular, its non‑erosive form, and to some extent determines the features of the clinical manifestations of the disease. Treatment of GERD with the use of alginates is logically justified, successfully used in clinical practice, and continues to be actively studied. The use of Gaviscon® products is expedient due to their unique mechanism of action to increase the resistance of the esophagus.

Identification of Chicken Transglutaminase 1 and In Situ Localization of Transglutaminase Activity in Avian Skin and Esophagus

Transglutaminase 1 (TGM1) is a membrane-anchored enzyme that cross-links proteins during terminal differentiation of epidermal and esophageal keratinocytes in mammals. The current genome assembly of the chicken, which is a major model for avian skin biology, does not include an annotated region corresponding to TGM1. To close this gap of knowledge about the genetic control of avian cornification, we analyzed RNA-sequencing reads from organotypic chicken skin and identified TGM1 mRNA. By RT-PCR, we demonstrated that TGM1 is expressed in the skin and esophagus of chickens. The cysteine-rich sequence motif required for palmitoylation and membrane anchorage is conserved in the chicken TGM1 protein, and differentiated chicken keratinocytes display membrane-associated transglutaminase activity. Expression of TGM1 and prominent transglutaminase activity in the esophageal epithelium was also demonstrated in the zebra finch. Altogether, the results of this study indicate that TGM1 is conserved among birds and suggest that chicken keratinocytes may be a useful model for the study of TGM1 in non-mammalian cornification.

Resistivity Technique for the Evaluation of the Integrity of Buccal and Esophageal Epithelium Mucosa for In Vitro Permeation Studies: Swine Buccal and Esophageal Mucosa Barrier Models

Permeation assays are important for the development of topical formulations applied on buccal mucosa. Swine buccal and esophageal epithelia are usually used as barriers for these assays, while frozen epithelia have been used to optimize the experimental setup. However, there is no consensus on these methods. In transdermal studies, barrier integrity has been evaluated by measuring electrical resistance (ER) across the skin, which has been demonstrated to be a simple, fast, safe, and cost-effective method. Therefore, the aims here were to investigate whether ER might also be an effective method to evaluate buccal and esophageal epithelium mucosa integrity for in vitro permeation studies, and to establish a cut-off ER value for each epithelium mucosa model. We further investigated whether buccal epithelium could be substituted by esophageal epithelium in transbuccal permeation studies, and whether their permeability and integrity were affected by freezing at −20 °C for 3 weeks. Fresh and frozen swine buccal and esophageal epithelia were mounted in Franz diffusion cells and were then submitted to ER measurement. Permeation assays were performed using lidocaine hydrochloride as a hydrophilic drug model. ER was shown to be a reliable method for evaluating esophageal and buccal epithelia. The esophageal epithelium presented higher permeability compared to the buccal epithelium. For both epithelia, freezing and storage led to decreased electrical resistivity and increased permeability. We conclude that ER may be safely used to confirm tissue integrity when it is equal to or above 3 kΩ for fresh esophageal mucosa, but not for buccal epithelium mucosa. However, the use of esophageal epithelium in in vitro transmucosal studies could overestimate the absorption of hydrophilic drugs. In addition, fresh samples are recommended for these experiments, especially when hydrophilic drugs are involved.

Standardization of esophageal adenocarcinoma in vitro model and its applicability for model drug testing

FLO-1 cell line represents an important tool in esophageal adenocarcinoma (EAC) research as a verified and authentic cell line to study the disease pathophysiology and antitumor drug screenings. Since in vitro characteristics of cells depend on the microenvironment and culturing conditions, we performed a thorough characterization of the FLO-1 cell line under different culturing conditions with the aim of (1) examining the effect of serum-free growth medium and air–liquid interface (A–L) culturing, which better reflect physiological conditions in vivo and (2) investigating the differentiation potential of FLO-1 cells to mimic the properties of the in vivo esophageal epithelium. Our study shows that the composition of the media influenced the morphological, ultrastructural and molecular characteristics of FLO-1 cells, such as the expression of junctional proteins. Importantly, FLO-1 cells formed spheres at the A–L interface, recapitulating key elements of tumors in the esophageal tube, i.e., direct contact with the gas phase and three-dimensional architecture. On the other hand, FLO-1 models exhibited high permeability to model drugs and zero permeability markers, and low transepithelial resistance, and therefore poorly mimicked normal esophageal epithelium. In conclusion, the identified effect of culture conditions on the characteristics of FLO-1 cells should be considered for standardization, data reproducibility and validity of the in vitro EAC model. Moreover, the sphere-forming ability of FLO-1 cells at the A–L interface should be considered in EAC tumor biology and anticancer drug studies as a reliable and straightforward model with the potential to increase the predictive efficiency of the current in vitro approaches.

A53 STUDYING THE ROLE OF ASCL2 IN THE ESOPHAGEAL EPITHELIUM USING ORGANOIDS

Background The esophagus is lined with a stratified squamous epithelium that assure protection against the austere environment found in the esophageal lumen. The maintenance of this epithelium is ensured by a rare population of cells: stem cells. Those cells have increased capacity of self-renewal and multipotency, which is the capacity to give rise to every cell types of a tissue. The marker Krt15 was used to identify the first stem cell population in the esophagus. Krt15+ cells display an extended lifespan and they are radioresistant, multipotent and capable of self-renewal. Moreover, it was observed by RNA sequencing that the expression of the transcription factor ASCL2 is strongly increased in Krt15+ cells compared to Krt15- cells. Interestingly, ASCL2 is necessary to maintain the stemness of Lgr5+ intestinal stem cells. It is also a target of the Wnt/β-catenin pathway. The overall goal of this project is to determine the role of ACSL2 in the maintenance of esophageal stem cells and to identify its binding partners since ASCL2 needs to dimerize to efficiently bind DNA. Aims Confirm that esophageal organoids are adapted to study ASCL2 in the esophagus. Methods Esophageal organoids were established from esophageal epithelial cells from wildtype mice. Following this, organoids were treated with an inhibitor of the Notch pathway (DAPT) to induce hyperplasia or infected with lentiviruses to invalidate Ascl2 (CRISPR/Cas9 approach). Results To validate that Ascl2 plays an important role in esophageal cell proliferation, Notch pathway was inhibited through DAPT treatment in esophageal organoids to induce hyperplasia, which was confirmed by increased number of proliferative cells (Ki-67+). ASCL2 protein expression was also increased in DAPT-treated organoids supporting its role in proliferation and confirming that organoid is a good model to study ASCL2 role in esophageal epithelial cells. In this optic, organoids lines invalidated for Ascl2 (CRISPR/Cas9 approach) were established. Our preliminary results suggest that Ascl2 loss affects cell proliferation and organoid size under normal conditions. Conclusions The expression of ASCL2 correlates with hyperplasia which supports its role in esophageal epithelium homeostasis. Funding Agencies Canada research chair et NSERC

Promising potential of articaine-loaded poly(epsilon-caprolactone) nanocapules for intraoral topical anesthesia

To determine whether the permeation capacity and analgesic efficacy of articaine (ATC) could be increased and cytotoxicity decreased by encapsulation in poly(ɛ-caprolactone) nanocapsules (ATCnano), aiming at local or topical anesthesia in dentistry. Cellular viability was evaluated (using the MTT test and fluorescence microscopy) after 1 h and 24 h exposure of HaCaT cells to ATC, ATCnano, ATC with epinephrine (ATCepi), and ATC in nanocapsules with epinephrine (ATCnanoepi). The profiles of permeation of 2% ATC and 2% ATCnano across swine esophageal epithelium were determined using Franz-type vertical diffusion cells. Analgesic efficacy was evaluated with a von Frey anesthesiometer in a postoperative pain model in rats, comparing the 2% ATC, 2% ATCnano, 2% ATCepi, and 2% ATCnanoepi formulations to 4% ATCepi (a commercially available formulation). We show that use of the nanocapsules decreased the toxicity of articaine (P<0.0001) and increased its flux (P = 0.0007). The 2% ATCepi and 4% ATCepi formulations provided higher analgesia success and duration (P<0.05), compared to 2% ATC, 2% ATCnano, and 2% ATCnanoepi. Articaine-loaded poly(ɛ-caprolactone) nanocapsules constitute a promising formulation for intraoral topical anesthesia (prior to local anesthetic injection), although it is not effective when injected in inflamed tissues for pain control, such as irreversible pulpitis.