Introduction: Eosinophilic esophagitis (EoE) is an inflammatory disorder characterized by esophageal eosinophilia, basal cell hyperplasia (BCH), and epithelial barrier dysfunction promoted by inflammatory cytokines, including interleukin (IL)-13. Mitochondria are critical to cellular energy production and redox homeostasis. While EoE-related BCH involves oxidative stress, the role of mitochondria in EoE pathobiology remains unknown. Additionally, the mechanism of action for proton pump inhibitors (PPIs) in EoE therapy remains elusive.

Methods: Mitochondrial membrane potential and mass were evaluated by flow cytometry for MitoTracker dyes-stained esophageal epithelial cells (CD45+ immune cells were excluded) from pediatric patient biopsies [active EoE (≥15 eosinophils/high-power field; n=5), EoE remission (n=5), normal mucosa (n=5)], a novel L2-IL-33 transgenic mouse model of EoE (EoE33), and esophageal organoids [human and mouse (C57BL/6)] treated with IL-13 ± omeprazole, an PPI. In organoids, mitochondrial functions were evaluated by respirometry, ATP assays, and MitoSOX flow cytometry for mitochondrial superoxide. Mitochondrial structural changes were documented by confocal laser microscopy. Immunoblotting was done to assess redox signaling.

Results: Flow cytometry revealed esophageal epithelial mitochondrial depolarization and a decrease in mitochondrial mass in patients with active EoE compared with EoE remission or normal mucosa. A similar, yet greater, change was observed in esophageal epithelia from EoE33 transgenic mice with IL-13-mediated robust eosinophil infiltrate and BCH. In human and mouse tissue-derived esophageal organoids, IL-13 induced BCH-like epithelial changes and the mitochondrial changes were accompanied by a decrease in the ATP level as well as decreased oxidative and glycolytic respiratory capacities under enhanced metabolic demand. Mitochondrial dysfunction was further corroborated by an elevation of mitochondrial superoxide and activation of the AMP-activated protein kinase (AMPK) stress response pathway with concomitant decrease in mTORC1 activity. In both human and mouse esophageal epithelial cell culture devoid of immune cells, IL-13 induced mitochondrial damage as evidenced by ring-shaped mitochondria and disruption of mitochondrial network. Treatment of organoids with omeprazole was sufficient to reverse mitochondrial dysfunction and restore mTORC1 activity even in the presence of IL-13.

Conclusions: These studies indicate that mitochondrial dysfunction is linked to perturbation of redox homeostasis in EoE-related BCH that is promoted by IL-13 via an epithelial intrinsic mechanism. PPIs may improve EoE symptoms through direct effect on esophageal epithelial cells, providing proof of principle that targeting pathways relevant to esophageal epithelial biology may suppress EoE disease progression.

Masaki Morimoto

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