795 AXIN2+ PERIBILIARY GLAND CELLS IN PERIAMPULLARY REGION SERVE AS BILIARY EPITHELIAL STEM CELLS AND GIVE RISE TO AMPULLARY CARCINOMA

Background and aims Peribiliary glands (PBGs), clusters of epithelial cells residing in the submucosal compartment of extrahepatic bile ducts, have been suggested as biliary epithelial stem/progenitor cell niche; however, evidence to support this claim is limited due to a lack of PBG-specific markers. We therefore sought to identify PBG-specific markers to investigate the potential role of PBGs as stem/progenitor cell niches, as well as an origin of cancer. Methods We examined the expression pattern of the Wnt target gene Axin2 in extrahepatic bile ducts. We then applied lineage tracing to investigate whether Axin2-expressing cells from PBGs contribute to biliary regeneration and carcinogenesis using Axin2-CreERT mice. Results Wnt signaling activation, marked by Axin2, was limited to PBGs located in the periampullary region. Axin2+ cells in periampullary PBGs expressed stem cell markers as well as cell proliferation markers. Lineage tracing revealed that Axin2-expressing periampullary PBG cells are capable of self-renewal and supplying new biliary epithelial cells (BECs) to the luminal surface. Additionally, the expression pattern of Axin2 and CK19 was mutually exclusive in periampullary region, and fate tracing of CK19+ luminal surface BECs revealed gradual replacement by CK19- cells, further supporting the continuous replenishment of new BECs from PBGs to the luminal surface. We also found that R-spondin3 (Rspo3), an enhancer of Wnt signaling, was strongly expressed in the smooth muscle cells adjacent to the lower part of periampullary PBGs. These smooth muscle cells corresponded to human sphincter of Oddi, and similar expression pattern of Axin2 and Rspo3 was observed in human periampullary region. Notably, smooth muscle cell-specific deletion of Rspo3 in mice markedly decreased Axin2 expression in periampullary PBGs and induced significant atrophy of ampulla of Vater. Furthermore, introduction of PTEN deletion into Axin2+ PBG cells (Axin2;PTENΔ/Δ mice), but not CK19+ luminal surface BECs (CK19;PTENΔ/Δ mice), induced ampullary carcinoma. Ampullary carcinoma organoids generated from Axin2;PTENΔ/Δ mice were dependent on Rspo3 for their growth, suggesting that extrinsic stimulation of Wnt signaling is important for the growth of ampullary tumors. In fact, administration of Wnt inhibitor dramatically suppressed ampullary carcinoma development in Axin2;PTENΔ/Δ mice. Conclusion A specific cell population receiving Wnt-activating signal in periampullary PBGs functions as biliary epithelial stem/progenitor cells and also cellular origin of ampullary carcinoma. These new findings can facilitate the development of new therapeutic strategies to induce biliary regeneration, as well as to treat ampullary carcinoma. Download : Download high-res image (147KB) Download : Download full-size image Graphical Abstract