Optimal liver metabolism and proliferation require the tight junction protein claudin-3. (28th May 2021) - Baier, F A
Abstract: Objective: The expression of hepatic tight junction proteins and their contribution to homeostasis and regeneration remained largely unexplored. Here, we determine the cell type specific expression of tight junction genes in murine livers. We further explore the regulation and functional importance of the transmembrane protein CLDN3 in normal and regenerating livers. Methods: Murine livers were used for tissue- and single cell RNA-seq. CLDN3 localization was determined by immunofluorescence. CLDN3+/+ or CLDN3-/- livers were analysed by electron microscopy, fluorescence-activated cell sorting and liquid chromatography mass spectrometry. Lipid content was quantified with oil-red. Mice were subjected to 2/3 partial hepatectomy. Proliferation was quantified with Ki67 and pHH3 stainings. Cell cycle gene expression was determined by RT-qPCR. Barrier impairments were assessed with total bile acid measurements. Differential gene expression was analysed by tissue RNAseq with DESeq2. Results: We determined the profile of tight junction gene expression the main liver cell types, showing that tight junction transcripts can be found in hepatocytes and cholangiocytes but also on non-parenchymal cell populations. CLDN3 was among the highly expressed- and regulated genes in native and regenerating livers. CLDN3 had a zonated expression pattern. CLDN3-/- mice had microscopically intact tight junctions, but showed significantly downregulated hepatic energy metabolism and suboptimal cell proliferation in the regeneration model. Conclusion: Our data suggests a functional role of CLDN3 for maintenance of energy homeostasis and optimal regeneration, proving that the function of hepatic tight junction proteins extends beyond basic membrane sealing.