The esophageal epithelium in systemic sclerosis: cellular and molecular dysregulation revealed by single-cell RNA sequencing

Systemic sclerosis (SSc) is a rare autoimmune disease characterized by vasculopathy and fibrosis of the skin and internal organs. Individuals with SSc often suffer from chronic acid reflux and dysphagia due to loss of esophageal motility. However, the pathogenesis of esophageal dysmotility in SSc is poorly understood. To determine whether distinct changes in esophageal epithelial cells contribute to impaired motility in SSc, we investigated the stratified squamous esophageal epithelium from proximal and distal biopsies using single-cell RNA sequencing (n=306,372 cells) in individuals with SSc compared those with gastroesophageal reflux disease (GERD) as well as healthy controls. The proportion of epithelial cells in the apical, superficial compartment of the esophageal epithelium was significantly reduced in SSc (9.4% vs 21.6% in HCs). Differential gene expression in SSc was primarily limited to the superficial compartment (3,572 genes vs. 232 in all other compartments, based on pseudobulk analysis), with significant upregulation of extracellular matrix and keratinization genes. These cellular and molecular changes in SSc were highly correlated with those seen in GERD, indicating they were secondary to reflux; however, their magnitudes were more pronounced in the proximal esophagus, suggesting that esophageal dysmotility leads to greater proximal acid exposure, which may contribute to aspiration. SSc-specific gene dysregulation implicated immunoregulatory pathways likely pertinent to pathogenic mechanisms. Cell type localization and SSc-specific changes were confirmed by spatial molecular imaging. By offering a comprehensive view of transcriptional dysregulation at single-cell resolution in human esophageal epithelial cells in SSc compared to GERD and healthy tissue, this work clarifies the state of epithelial cells in SSc-induced esophageal dysfunction.