Tissue substructure-specific deposition of the β3-containing laminin-332 in the biliary epithelium of human and mouse livers.

Laminin is a family of basement membrane proteins, whose selective and spatiotemporal expression profiles are linked to their various functions in development, maintenance, and functional regulation of different tissues. In the liver, α1-and α5-containing laminin isoforms have been documented to be critically involved in the developmental process of the epithelial tissue of the bile duct. However, possible roles of other laminin isoforms in bile duct formation and function remain elusive. Here, we evaluated public single-cell RNA sequencing databases on human liver cells to reveal expression landscape of laminin genes, and found that genes for laminin-332 subunits were conjointly expressed in the EPCAM⁺ biliary epithelial cell population. Expression of the β3 and γ2 subunit genes was restricted to biliary epithelial cells in the liver and, remarkably, showed apparent heterogeneity among them. We confirmed the heterogeneous nature of the laminin-β3 expression in murine livers, which was firmly related to morphological substructures in the biliary epithelium. Finally, we generated the liver epithelial tissue-specific laminin- β3 knockout mice and found that this laminin subunit was dispensable under physiological conditions. Together, our present findings have identified the β3 subunit and the related laminin-332 isoform as useful markers and potentially important regulatory molecules for future understanding of pathophysiology in the hepatobiliary system.

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