Mdka produced by the activated HSCs drives bipotential progenitor cell redifferentiation during zebrafish...

After extensive hepatocyte loss or impaired hepatocyte proliferation, liver regeneration occurs through trans-differentiation of biliary epithelial cells (BECs), which involves dedifferentiation of biliary epithelial cells into bipotential progenitor cells (BP-PCs) and subsequent redifferentiation of BP-PCs into nascent hepatocytes and biliary epithelial cells. Despite several studies on the redifferentiation process of BP-PCs into nascent hepatocytes, the contributions of nonparenchymal cells in this process remain poorly understood.

Using the zebrafish severe liver injury model, we observed specific expression of midkine a (Mdka) in the activated HSCs through single-cell analyses and fluorescence in situ hybridization. Genetic mutation, pharmacological inhibition, whole-mount in situ hybridizations, and antibody staining demonstrated an essential role of mdka in the redifferentiation of BP-PCs during liver regeneration. Notably, we identified Nucleolin (Ncl), the potential receptor for Mdka, specifically expressed in BP-PCs, and its mutant recapitulated the mdka mutant phenotypes with impaired BP-PC redifferentiation. Mechanistically, the Mdka-Ncl axis drove Erk1 activation in BP-PCs during liver regeneration. Furthermore, overexpression of activated Erk1 partially rescued the defective liver regeneration in the mdka mutant.

The activated HSCs produce Mdka to drive the redifferentiation process of BP-PCs through activating Erk1 during the biliary-mediated liver regeneration, implying previously unappreciated contributions of nonparenchymal cells to this regeneration process.