Bromodomain and extraterminal (BET) proteins regulate biliary-driven liver regeneration.
OBJECTIVE
During liver regeneration, hepatocytes are derived from pre-existing hepatocytes. However, if hepatocyte proliferation is compromised, biliary epithelial cells (BECs) become the source of new hepatocytes. We recently reported on a zebrafish liver regeneration model in which BECs extensively contribute to hepatocytes. Using this model, we performed a targeted chemical screen to identify important factors that regulate BEC-driven liver regeneration, the mechanisms of which remain largely unknown.


METHODS
Using Tg(fabp10a:CFP-NTR) zebrafish, we examined the effects of 44 selected compounds on BEC-driven liver regeneration. Liver size was assessed by fabp10a:DsRed expression; liver marker expression was analyzed by immunostaining, in situ hybridization and quantitative PCR. Proliferation and apoptosis were also examined. Moreover, we used a mouse liver injury model, choline-deficient, ethionine-supplemented (CDE) diet.


RESULTS
We identified 10 compounds that affected regenerating liver size. Among them, only bromodomain and extraterminal domain (BET) inhibitors, JQ1 and iBET151, blocked both Prox1 and Hnf4a induction in BECs. BET inhibition during hepatocyte ablation blocked BEC dedifferentiation into hepatoblast-like cells (HB-LCs). Intriguingly, after JQ1 washout, liver regeneration resumed, indicating temporal, but not permanent, perturbation of liver regeneration by BET inhibition. BET inhibition after hepatocyte ablation suppressed the proliferation of newly generated hepatocytes and delayed hepatocyte maturation. Importantly, Myca overexpression, in part, rescued the proliferation defect. Furthermore, oval cell numbers in mice fed CDE diet were greatly reduced upon JQ1 administration, supporting the zebrafish findings.


CONCLUSIONS
BET proteins regulate BEC-driven liver regeneration at multiple steps: BEC dedifferentiation, HB-LC proliferation, the proliferation of newly generated hepatocytes, and hepatocyte maturation.
Department of Developmental Biology, McGowan Institute for Regenerative Medicine, University of Pittsburgh, Pittsburgh, PA 15260, USA.
Sungjin
S
Ko
Department of Developmental Biology, McGowan Institute for Regenerative Medicine, University of Pittsburgh, Pittsburgh, PA 15260, USA.
Tae-Young
TY
Choi
Department of Pathology, University of Pittsburgh, Pittsburgh, PA 15260, USA.
Jacquelyn O
JO
Russell
Department of Developmental Biology, McGowan Institute for Regenerative Medicine, University of Pittsburgh, Pittsburgh, PA 15260, USA.
Juhoon
J
So
Department of Pathology, University of Pittsburgh, Pittsburgh, PA 15260, USA.
Satdarshan P S
SPS
Monga
Department of Developmental Biology, McGowan Institute for Regenerative Medicine, University of Pittsburgh, Pittsburgh, PA 15260, USA. Electronic address: donghuns@pitt.edu.
Donghun
D
Shin
D000818:Animals; D001381:Azepines / Q000378:metabolism*; D001659:Biliary Tract / Q000473:pathology; D002460:Cell Line; D049109:Cell Proliferation / Q000502:physiology; D054338:Cell Transdifferentiation / Q000502:physiology; D004847:Epithelial Cells / Q000502:physiology*; D022781:Hepatocytes / Q000502:physiology*; D006576:Heterocyclic Compounds, 4 or More Rings / Q000378:metabolism*; D008099:Liver / Q000378:metabolism / Q000473:pathology; D008115:Liver Regeneration / Q000502:physiology*; D051379:Mice; D009929:Organ Size; D014157:Transcription Factors / Q000037:antagonists & inhibitors; D015533:Transcriptional Activation / Q000502:physiology; D014230:Triazoles / Q000378:metabolism*; D015027:Zebrafish
C561695:(+)-JQ1 compound; D001381:Azepines; C568713:GSK1210151A; D006576:Heterocyclic Compounds, 4 or More Rings; D014157:Transcription Factors; D014230:Triazoles
BET inhibitors; Dedifferentiation; JQ1; Liver progenitor cells; Liver regeneration; Oval cells; Zebrafish