Whelan, Kelly A.

Background Eosinophilic oesophagitis (EoE) is a food allergen-induced inflammatory disorder characterised by interleukin (IL)-13-mediated oesophageal inflammation and epithelial basal cell hyperplasia (BCH). The role of mitochondria in EoE pathogenesis remains elusive. Design Prompted by single cell transcriptomics data, we interrogated the role of mitochondria in EoE pathobiology using patient biopsies, EoE-mouse models and oesophageal epithelial cells grown in monolayer and three-dimensional (3D) organoid cultures treated with EoE-relevant cytokines. 3D organoids and EoE-bearing mice were treated with omeprazole—a proton-pump inhibitor used as first-line EoE therapy. We performed CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) interference in mouse organoids to identify the key mitochondrial regulatory genes whose depletion may lead to BCH. We analysed mitochondrial membrane potential, mass and superoxide production by flow cytometry, cellular oxygen consumption by respirometry, mitochondrial structures and perturbation of cellular energy homeostasis by immunoblotting. Results Mitochondrial dysfunction appeared to be a hallmark of EoE-related BCH where mitochondrial structural damage was associated with impaired oxidative respiratory capacity, elevation of mitochondrial superoxide and decreased adenosine triphosphate (ATP) production, as corroborated by activation of the adenosine monophosphate (AMP) -activated protein kinase and suppression of mammalian target-of-rapamycin signalling. Depletion of PGC1A, the master regulator of mitochondria biogenesis, recapitulated EoE-related BCH, suggesting that mitochondrial dysfunction drives BCH. Further, omeprazole alleviated mitochondrial damage and dysfunction in EoE-related BCH modelled in mice and patient-derived organoids. Conclusion Mitochondrial dysfunction is tightly linked to perturbation of redox homeostasis in EoE-related BCH, which is promoted by IL-13 and reversible with omeprazole treatment.

Introduction Visceral obesity is associated with GERD and, traditionally, it has been assumed that visceral fat predisposes to GERD primarily by increasing intra‐abdominal pressure. However, transmission electron microscopy (TEM) of esophageal biopsies from obese individuals without GERD exhibit dilated intercellular spaces (DIS) and, in earlier studies, we found that substances secreted by mature adipocytes in visceral fat from obese patients impair esophageal epithelial barrier function, induce DIS and reduce transepithelial resistance (TER). There is a fat pad at the gastroesophageal junction (GEJ) that is in intimate contact with the distal esophagus. We now explore whether whole GEJ fat tissue of obese individuals secretes substances that impair esophageal barrier function. Methods We obtained GEJ fat from 3 obese (BMI 46, 60, 74) and 3 non‐obese (BMI 24, 26, 27) patients having foregut surgery. Human esophageal squamous cells were seeded into transwells and grown to confluence for 3 days. On day 4, cells were raised to an air‐liquid interface (ALI) to allow for differentiation, stratification, and esophageal barrier formation. ALI cultures were exposed to conditioned media (CM) from GEJ fat or to control medium beginning at day 4. TER was measured on days 4, 6, and 8 using the EVOM2 Epithelial Volt/Ohm Meter. On day 8, ALI cultures were stained with H&E and Ki‐67 and imaged; barrier permeability was assessed by a biotinylation reagent applied to the ALI surface. TEM of ALIs and of esophageal biopsies from 2 non‐obese and 2 obese patients without GERD were assessed. Results CM from all 3 obese patients significantly reduced TER on days 6 and 8; CM from 2 non‐obese patients did not reduce TER whereas CM from 1 non‐obese patient induced a slight reduction in TER at day 8 (Table 1). Marked DIS were found only in ALI cultures grown with CM from obese patients. In ALIs grown with CM from non‐obese patients, the biotinylation reagent stopped at the superficial layers of esophageal cells. In contrast, the biotinylation reagent diffused through all cell layers in ALIs grown with obese patient CM. Increases in basaloid cells and in Ki‐67 were found in ALIs grown with obese patient CM. TEMs of ALIs grown with non‐obese patient CM demonstrated well‐oriented cell‐cell junctions similar to TEMs of non‐obese patient esophageal biopsies. In contrast, ALIs grown with obese patient CM demonstrated cell‐cell junctional structures that were disorganized, aggregated, and floating within the DIS, similar in appearance to TEMs of the obese patients’ esophageal biopsies. Conclusion Substances produced by GEJ fat of obese patients impair esophageal epithelial barrier integrity, cause basal cell hyperplasia and DIS, and disrupt intercellular connections. These findings in ALI cultures recapitulate abnormalities seen by TEM in esophageal biopsies of obese patients.