Autophagy levels are elevated in barrett's esophagus and promote cell survival from acid and oxidative stress

Abstract

Autophagy is a highly conserved mechanism that is activated during cellular stress. We hypothesized that autophagy may be induced by acid reflux, which causes injury and inflammation, and therefore contributes to the pathogenesis of Barrett’s esophagus (BE) and esophageal adenocarcinoma (EAC). Currently, the role of autophagy in BE and EAC is poorly studied. We quantitatively define autophagy levels in human BE cell lines, a transgenic mouse model of BE, and human BE and EAC biopsies. Human non-dysplastic BE had the highest basal number of autophagic vesicles (AVs), while AVs were reduced in normal squamous cells and dysplastic BE cells, and nearly absent in EAC. To demonstrate a functional role for autophagy in BE pathogenesis, normal squamous (STR), non-dysplastic BE (CPA), dysplastic BE (CPD), and esophageal adenocarcinoma (OE19) cell lines were exposed to an acid pulse (pH3.5) followed by incubation in the presence or absence of chloroquine, an autophagy inhibitor. Acid exposure increased reactive oxygen species (ROS) levels in STR and CPA cells. Chloroquine alone had a small impact on intracellular ROS or cell survival. However, combination of chloroquine with the acid pulse resulted in a significant increase in ROS levels at 6 hours in STR and CPA cells, and increased cell death in all cell lines. These findings establish increased numbers of AVs in human BE compared to normal squamous or EAC, and suggest that autophagy functions to improve cell survival after acid reflux injury. Autophagy may thus play a critical role in BE pathogenesis and progression.

Role of ion transporters in the bile acid-induced esophageal injury

“…It has been described earlier that dysplastic Barrett's mucosa has more severe and prolonged acidic and biliary reflux exposure (41). Furthermore, it has also been observed that CP-D cells are more resistant to GERD-like stimuli compared with CP-A cells (28). The mechanism for this alteration and its potential physiological role cannot be explained by the present studies and are areas of focus for future work.…”

Autophagy mediates epithelial cytoprotection in eosinophilic oesophagitis

“…41 PPI usage prior to endoscopy in 65 of the 67 human subjects in the current study precludes evaluation of the influence of refluxassociated inflammation upon autophagy; however, we find that autophagy facilitates survival in the context of acid stress in EPC2-hTERT cells and Barrett's oesophagus (BE)-derived cell lines. 42 Moreover, AV content is increased in oesophagi of mice with IL-1β-mediated inflammation prior to the onset of columnar metaplasia as well as in oesophageal biopsies from BE patients. 42 43 Thus, it is plausible that keratinocyte autophagy is activated in response to a diverse spectrum of stress signals, potentially contributing to the pathogenesis of multiple oesophageal disorders.…”

Autophagy and its current relevance to the diagnosis and clinical management of esophageal diseases

“…While Beclin‐1 expression and autophagy could be induced in these BE cell lines by acute exposure to deoxycholic acid, levels of this moiety decreased after chronic exposure. In contrast, other investigators, analyzing morphologic features of autophagic vesicles in biopsy specimens, showed that autophagy levels are increased in BE compared with normal squamous mucosa, though they are generally diminished relative to normal cells in dysplastic BE . Separate studies have demonstrated that the esophageal microbiome is altered in BE and esophageal adenocarcinoma.…”

“…In contrast, other investigators, analyzing morphologic features of autophagic vesicles in biopsy specimens, showed that autophagy levels are increased in BE compared with normal squamous mucosa, though they are generally diminished relative to normal cells in dysplastic BE. 53 Separate studies have demonstrated that the esophageal microbiome is altered in BE and esophageal adenocarcinoma. Interactions of this microbiome with autophagy have yet to be discovered.…”