Introduction
Barrett’s esophagus (BE), the major precursor of esophageal adenocarcinoma (EAC), is a condition where the normal stratified squamous esophageal epithelium undergoes transdifferentiation into the specialized, intestinal-like epithelium. This reprogramming, also termed ‘paligenosis’, is predominantly caused by gastroesophageal reflux disease (GERD)1. On the other hand, hydrogen sulfide (H2S) next to carbon monixide (CO) is an important endogenous gaseous mediator. H2S is biosynthesized by cystathionine β-synthase (CBS) and cystathionine γ-lyase (CTH). Both, H2S and CO have been shown to maintain gastrointestinal (GI) integrity2,3,4. However, the contribution of gaseous mediators signaling to esophageal transdifferentiation process is overlooked.
Aims & Methods
Thus, in this study we aimed to explore the role of H2S bioavailability in mTOR-dependent paligenosis induced by chronic epithelial injury. Furthermore, we evaluated the relationship between GERD, the barrier function of cultured cells, and the pattern of selected components involved in the formation of the tight junctions (TJs) and responsible for epithelial barrier integrity.
We implemented an animal model of GERD, based on Male Wistar rats with esophagogastroduodenal anastomosis (EGDA) treated i.g. for 8 weeks with vehicle or with H2S- releasing chemicals: GYY4137 (5.0 mg/kg)/NaHS (1.0 mg/kg) or CTH/CBS inhibitors: PAG (15 mg/kg)/AOAA (11 mg/kg). In parallel, we employed optimized in-vitro GERD model based on human-derived esophageal epithelial (EPC2) cells +/- CRISPR-Cas9-induced knockout of H2S-producing enzymes that were treated with acidified bile mixture (BM) or with GYY4137/NaHS (100 µM). We evaluated activation of AKT/mTOR pathway by multiplex microbeads fluorescent assay and an expression of TJ-associated protein (ZO-1) and occludin by capillary immunoblotting. The barrier function of cultured cells was evaluated by measurement of transepithelial electrical resistance (TER).
Results
We observed that either chronic reflux in EGDA-rats and/or treatment of human esophageal cells with BM led to a slight or a significant activation of AKT/mTOR signaling pathway and its down-stream effector - p70S6K. Additionally, we observed that pharmacologically-derived H2S reversed this effect, while inhibition of endogenous H2S biosynthesis (pharmacological or induced by knockout of H2S-producing enzymes) had either no effect or increased GERD-induced phosphorylation of AKT/mTOR pathway components. Moreover, we showed that ZO-1 is highly expressed in BM treated EPC2 cells and this was reflected by the increase in TER measurment. Level of occludin remained unchanged. We did not observe any changes in expression of ZO-1 and occludin after GYY4137 treatment; however, TER measurment decreased in comparison to BM treated cells. Selective knockout of H2S-producing enzymes led to a decrease in ZO-1 protein content in comparison to wild-type cells.
Conclusion
We conclude that interventional enhancing or decreasing of H2S bioavailability in esophageal epithelium respectively delay or accelerate the GERD-induced paligenosis process via regulation of the mTOR pathway. H2S-prodrugs may provide a protective effect on the esophageal epithelium by substituting the phisiological defensive response of the tissue against GERD, which is reflected by an increase in the expression of ZO-1 and tightening of the cellular barrier.
References
1. Souza RF, Spechler SJ. Mechanisms and pathophysiology of Barrett oesophagus. Nat Rev Gastroenterol Hepatol 2022.
2. Fiorucci S, Distrutti E, Cirino G, Wallace JL. The emerging roles of hydrogen sulfide in the gastrointestinal tract and liver. Gastroenterology 2006.
3. Magierowska K, Korbut E, Wójcik-Grzybek D, Bakalarz D, Sliwowski Z, Cieszkowski J, Szetela M, Torregrossa R, Whiteman M, Magierowski M. Mitochondria-targeted hydrogen sulfide donors versus acute oxidative gastric mucosal injury. J Control Release 2022.
4. Magierowska K, Brzozowski T , Magierowski M. Emerging role of carbon monoxide in regulation of cellular pathways and in the maintenance of gastric mucosal integrity. Pharmacol Res 2018.
[Funding: National Science Centre, Poland (UMO-2016/23/D/NZ4/01913, UMO-2019/33/B/NZ4/00616) and Statutory Grant (N41/DBS/000874), Jagiellonian University Medical College].