Bile acid flux is necessary for normal liver regeneration.
OBJECTIVE
Many signals governing liver regeneration (LR) following 2/3 partial hepatectomy (PH) are recognized, but the primary signal(s) remains unknown. The aim of the study was to confirm that the remnant liver after PH lacks capacity to secrete the BA pool returning via the enterohepatic ciruculation (EHC), which may in turn stimulate LR.


METHODS
After standard PH, BA flux was documented and BA signaling (Fgf15) and synthesis (Cyp7a) determined by qPCR. Rat biliary fistula (BF) and Asbt knockout mouse models interrupted the EHC prior to PH, and standard assays for LR employed along with complete RNA sequencing. CCl4 intoxication after BF tested the hypothesis in an alternate injury model.


RESULTS
BA rise in systemic blood immediately following PH, confirming that the remnant liver cannot handle the BA returning via portal circulation. When the BA pool is drained prior to PH in the rat BF model, LR is markedly attenuated, a phenomenon reversed with duodenal BA replacement. Hepatocyte proliferation is similarly attenuated after PH in the Asbt knockout mouse as well as after CCl44 intoxication in rats with BF. Complete RNA sequencing in the rat PH model shows that early c-jun and AP-1 gene expression pathways are down regulated in the absence of BA, coincident with attenuated LR.


CONCLUSIONS
Absent BA return to the liver after PH or CCl4 injury markedly attenuates LR, though hepatocyte proliferation still occurs, inferring that BA flux and signaling are not the sole signals governing LR. Transcriptional networks involving c-jun and AP-1 are involved in the BA-specific effects on hepatocyte proliferation.
Dept. of Medicine, Division of GI & Hepatology, Oregon Health & Science Center, Portland, Oregon, United States of America; Oregon Stem Cell Center, Oregon Health & Science Center, Portland, Oregon, United States of America.
Willscott E
WE
Naugler
D000818:Animals; D001647:Bile Acids and Salts / Q000378:metabolism*; D006498:Hepatectomy; D008099:Liver / Q000378:metabolism / Q000601:surgery; D008115:Liver Regeneration / Q000502:physiology*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D051381:Rats; D018808:Transcription Factor AP-1 / Q000378:metabolism
D001647:Bile Acids and Salts; D018808:Transcription Factor AP-1