Background and Aims: After extensive hepatocyte loss or impaired hepatocyte proliferation, liver regeneration occurs via transdifferentiation of biliary epithelial cells (BECs), which involves dedifferentiation of BECs into bipotential progenitor cells (BP-PCs) and subsequent redifferentiation of BP-PCs into nascent hepatocytes and BECs. Despite several studies on the redifferentiation process of BP-PCs into nascent hepatocytes, the contributions of nonparenchymal cells in this process remain poorly understood. Approach and Results: Using the zebrafish severe liver injury model, we observed specific expression of midkine a (Mdka) in the activated hepatic stellate cells (HSCs) through single-cell analyses and fluorescence in situ hybridization (FISH). Genetic mutation, pharmacological inhibition, whole-mount in situ hybridizations (WISH), 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. Conclusions: 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.

中文翻译：

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斑马鱼胆汁介导的肝再生过程中，激活的肝星状细胞产生的Mdka驱动双能祖细胞再分化


背景和目的：在肝细胞大量丢失或肝细胞增殖受损后，通过胆管上皮细胞（BEC）的转分化发生肝再生，其中涉及BEC去分化为双能祖细胞（BP-PC），以及随后BP-PC再分化为新生肝细胞和 BEC。尽管对 BP-PC 向新生肝细胞的再分化过程进行了多项研究，但非实质细胞在此过程中的贡献仍知之甚少。方法和结果：利用斑马鱼严重肝损伤模型，通过单细胞分析和荧光原位杂交（FISH）观察活化的肝星状细胞（HSC）中中期因子a（Mdka）的特异性表达。基因突变、药理学抑制、整体原位杂交 (WISH) 和抗体染色证明 mdka 在肝再生过程中 BP-PC 的再分化中发挥重要作用。值得注意的是，我们鉴定了核蛋白（Ncl），Mdka 的潜在受体，在 BP-PC 中特异性表达，其突变体重现了 BP-PC 再分化受损的 mdka 突变体表型。从机制上讲，Mdka-Ncl 轴在肝再生过程中驱动 BP-PC 中的 Erk1 激活。此外，激活的 Erk1 的过度表达部分挽救了 mdka 突变体中有缺陷的肝再生。结论：在胆道介导的肝再生过程中，活化的 HSC 产生 Mdka，通过激活 Erk1 来驱动 BP-PC 的再分化过程，这意味着非实质细胞在此再生过程中的贡献之前未被认识到。