Alveolar Type 2 Cell Dysfunction Is Associated with Bile Acid Alterations in Experimental Hepatopulmonary Syndrome.

Hepatopulmonary syndrome (HPS) is a severe complication of cirrhosis characterized by pulmonary microvascular dilation, hypoxemia, and increased mortality. Patients often exhibit unexplained restrictive ventilatory defects that correlate with circulating bile acids, suggesting superimposed alveolar dysfunction. To investigate this, we evaluated alveolar function, cell types, and the potential role of altered bile acids in the experimental HPS. Common bile duct ligation (CBDL) mice were assessed for pulmonary and surfactant function. AT2 cell-specific RiboTag RNA sequencing, single-cell RNA sequencing (scRNA-seq), and mass spectrometry-based bile acid profiling were performed. MLE12 cells were treated with bile acids in vitro, and an FXR agonist was administered in vivo to test effects on AT2 cell. CBDL mice developed HPS with restrictive defects due to reduced AT2 cell-derived surfactant-protein-C (SP-C), increased alveolar surface tension, and elevated plasma and bronchoalveolar bile acid levels. ScRNA-seq demonstrated a decrease in AT2 cells and an increase in AT2-to-AT1 transitional cells. AT2-specific RNA-seq revealed upregulated bile acid and cholesterol metabolism and downregulated proliferative pathways. In vitro, bile acids mimicking FXR antagonists reduced SP-C in MLE12 cells, while in vivo FXR agonist decreased circulating bile acids and restored SP-C-producing AT2 cells in CBDL mice. Our data demonstrates alterations in AT2 cell biology, including reduced surfactant expression, in the setting of elevated bile acids. These finding indicate an association between bile acid levels and AT2 cell alterations in cirrhosis and identify bile acid signaling and AT2 cell integrity as areas for future mechanistic investigation.