Tight junctions in the liver are essential to maintain the blood-biliary-barrier, however the functional contribution of individual tight junction proteins to barrier- and metabolic homeostasis remains largely unexplored. Here, we describe the cell type specific expression of tight junction genes in the murine liver, and explore the regulation and functional importance of the transmembrane protein claudin-3 in liver metabolism, barrier function and cell proliferation.
METHODS
The cell type specific expression of hepatic tight junction genes is described using our mouse liver single cell sequencing dataset. Differential gene expression in Cldn3-/- and Cldn3+/+ livers was assessed in young and aged mice by RNA-seq and hepatic tissue was analysed for lipid content and bile acid composition. A surgical model of partial hepatectomy (PHx) was used to induce liver cell proliferation.
RESULTS
Claudin-3 is a highly expressed tight junction protein found in the liver and is expressed predominantly in hepatocytes and cholangiocytes. The histology of Cldn3-/- livers showed no overt phenotype, and the canalicular tight junctions appeared intact. Nevertheless, by RNAseq we detected a downregulation of metabolic pathways in the livers of Cldn3-/- young and aged mice as well as a decrease in lipid content and a weakened biliary-barrier for primary bile acids, such as TCA, TCDCA and TMCA. Coinciding with defects in the biliary barrier and lower lipid metabolism, there was a diminished hepatocyte proliferative response in Cldn3-/- mice following PHx.
CONCLUSION
Our data shows that in the liver, claudin-3 is necessary to maintain metabolic homeostasis, retention of bile acids, and optimal hepatocyte proliferation during liver regeneration.
