RESUMO
BACKGROUND AND AIMS: 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. APPROACH AND RESULTS: 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. 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.
RESUMO
In cases of end-stage liver diseases, the proliferation of existing hepatocytes is compromised, a feature of human chronic liver disease, in which most hepatocytes are dysfunctional. So far, liver transplantation represents the only curative therapeutic solution for advanced liver diseases, and the shortage of donor organs leads to high morbidity and mortality worldwide. The promising treatment is to prompt the biliary epithelial cells (BECs) transdifferentiation. However, the critical factors governing the initiation of BEC-derived liver regeneration are largely unknown. The zebrafish has advantages in large-scale genetic screens to identify the critical factors involved in liver regeneration. Here, we combined N-ethyl-N-nitrosourea screen, positional cloning, transgenic lines, antibody staining, and in situ hybridization methods and identified a liver regeneration defect mutant ( lrd ) using the zebrafish extensive liver injury model. Through positional cloning and genomic sequencing, we mapped the mutation site to rngtt . Loss of rngtt leads to the defects of BEC dedifferentiation, bipotential progenitor cell activation, and cell proliferation in the initiation stage of liver regeneration. The transdifferentiation from BECs to hepatocytes did not occur even at the late stage of liver regeneration. Mechanically, Rngtt transcriptionally regulates the attachment of mRNA cap to mTOR complex 1 (mTORC1) components and dnmt1 to maintain the activation of mTORC1 and DNA methylation in BECs after severe liver injury and prompt BEC to hepatocyte conversion. Furthermore, rptor and dnmt1 mutants displayed the same liver regeneration defects as rngtt mutation. In conclusion, our results suggest Rngtt is a new factor that initiates BEC-derived liver regeneration.
Assuntos
Regeneração Hepática , Peixe-Zebra , Animais , Humanos , DNA (Citosina-5-)-Metiltransferase 1 , Células Epiteliais , Hepatócitos/fisiologia , Fígado , Regeneração Hepática/genética , Alvo Mecanístico do Complexo 1 de Rapamicina , Proteínas de Peixe-Zebra/genéticaRESUMO
When the proliferation of residual hepatocytes is prohibited, biliary epithelial cells (BECs) transdifferentiate into nascent hepatocytes to accomplish liver regeneration. Despite significant interest in transdifferentiation, little is known about the maintenance of nascent hepatocytes in post-injured environments. Here, we perform an N-ethyl-N-nitrosourea (ENU) forward genetic screen and identify a mutant containing a nonsense mutation in the gene nibrin (nbn), which encodes a component of the Mre11-Rad50-Nbn (MRN) complex that activates DNA damage response (DDR). The regenerated hepatocytes cannot be maintained and exhibit apoptosis in the mutant. Mechanistically, the nbn mutation results in the abrogation of ATR-Chk1 signaling and accumulations of DNA damage in nascent hepatocytes, which eventually induces p53-mediated apoptosis. Furthermore, loss of rad50 or mre11a shows similar phenotypes. This study reveals that the activation of DDR by the MRN complex is essential for the survival of BEC-derived hepatocytes, addressing how to maintain nascent hepatocytes in the post-injured environments.
RESUMO
In cases of extensive liver injury, biliary epithelial cells (BECs) dedifferentiate into bipotential progenitor cells (BPPCs), then redifferentiate into hepatocytes and BECs to accomplish liver regeneration. Whether epigenetic regulations, particularly DNA methylation maintenance enzymes, play a role in this biliary-mediated liver regeneration remains unknown. Here we show that in response to extensive hepatocyte damages, expression of dnmt1 is upregulated in BECs to methylate DNA at the p53 locus, which represses p53 transcription, and in turn, derepresses mTORC1 signaling to activate BEC dedifferentiation. After BEC dedifferentiation and BPPC formation, DNA methylation at the p53 locus maintains in BPPCs to continue blocking p53 transcription, which derepresses Bmp signaling to induce BPPC redifferentiation. Thus, this study reveals promotive roles and mechanisms of DNA methylation at the p53 locus in both dedifferentiation and redifferentiation stages of biliary-mediated liver regeneration, implicating DNA methylation and p53 as potential targets to stimulate regeneration after extensive liver injury.