Genome binding/occupancy profiling by high throughput sequencing
Background & Aims: Tissue metaplasia is uncommon in adults because established cis-element programs resist rewiring. In Barrett’s esophagus, the distal esophageal mucosa acquires predominantly intestinal character, with notable gastric features, and is predisposed to develop invasive cancers. We sought to understand the chromatin underpinnings of Barrett’s metaplasia and why it commonly displays simultaneous gastric and intestinal properties.
Methods: We profiled cis-regulatory elements with active histone modifications in primary human biopsy materials using chromatin immunoprecipitation followed by DNA sequencing (ChIP-seq). Mutations in Barrett’s esophagus were examined in relation to tissue-specific enhancer landscapes using a random-forest machine learning algorithm. We also profiled open chromatin at single-cell resolution in primary Barrett’s biopsy specimens using the assay for transposase-accessible chromatin (ATAC-seq). We used one- and two-color immunohistochemistry to examine protein expression of tissue-restricted genes.
Results: Barrett’s esophagus bears epigenome fingerprints of human stomach and intestinal columnar, but not esophageal squamous, epithelia. Mutational patterns were best explained as arising on the epigenome background of active gastric cis-elements, supporting the view that adjoining stomach epithelium is a likely tissue source. Individual cells in Barrett’s metaplasia co-express gastric and intestinal genes, reflecting concomitant chromatin access at enhancers ordinarily restricted to one or the other epithelium. Protein expression of stomach-specific mucins, CLDN18, and a novel gastric marker, ANXA10, revealed extensive tissue and sub-clonal heterogeneity of dual stomach-intestinal cell states.
Conclusions: These findings reveal mixed and dynamic tissue-restricted chromatin states and phenotypic heterogeneity in Barrett’s esophagus. Pervasive intra-gland variation argues against stem-cell governance of this phenotype.
ChIP-Seq on FFPE human tissue obtained on routine clinical endoscopy
Single Cell ATAC-seq on human Barretts metaplasia biopsy, stomach body biopsy and dudenal biopsy.