Wnt7a is a Novel Lymphangiocrine Factor Driving Cholangiocyte Proliferation during Liver Regeneration

The significance of lymphatic vessels (LVs) and lymphatic endothelial cells (LyECs) during liver regeneration remains unexplored. We aimed to characterize contribution of LVs and LyECs in liver regeneration using two-thirds partial hepatectomy (PHx) models. An increased number and diameter of CD31+PDPN+ LVs was observed at day 2 and 5 post-PHx. Proteomic analysis of LyECs and ELISA studies in conditioned media of LyECs revealed that one of the secreted proteins, Wnt7a was uniquely expressed at day 2 post PHx. In vitro studies confirmed that Wnt7a is a potent stimulator of proliferation for both hepatocytes and cholangiocytes. In vivo inhibition of lymphangiogenesis and reduction in Wnt7a led to a decline in the percentage of CK19+ cholangiocytes and bile ducts. Western blot analysis showed that Wnt7a activated the downstream Frizzled 7 receptor and non-canonical planar-cell-polarity pathway to drive the proliferation of cholangiocytes. In vivo, Wnt7a loss-of-function experiments in zebrafish along with inhibitor studies in rat models of PHx further re-iterated clear links between Wnt7a and proliferation of bile ducts. Pro-regenerative effects of Wnt7a were demonstrated in a model of small-for-size syndrome (80% PHx), where administering recombinant Wnt7a enhanced both cholangiocyte and hepatocyte proliferation. Elevated Wnt7a levels were seen in donors of liver transplant patients at day 1 and 2 post-hepatectomy and Wnt7a also facilitated growth of human cholangiocyte organoids in vitro. Our findings uncover the novel role of Wnt7 as one of the key lymphangiocrine signals that facilitates proliferation of cholangiocytes during liver regeneration.