Pathological Changes In Cholestasis-Induced Hepatic Fibrosis And Expression Of FoxL1 In Mouse Liver And Its Significance

Hepatic fibrosis is a wound-healing process responsive to a variety of factors,which involves the abnormal accumulation of collagen, degeneration and necrosis of hepatocytes, and damages to liver architecture and function. It has been proved by clinical research and experimental work on animals that hepatic fibrosis is the key process in the conversion of chronic liver disease into liver cirrhosis. Therefore,Study on the pathological changes of hepatic fibrosis has important significance for further researches on the formation mechanism of hepatic fibrosis.Today,there are several mouse models of liver fibrosis available—induced by administration of hepatotoxins,by bile duct ligation(BDL) or by immunological mechanisms.A well-established experimental animal model of liver fibrosis is bile duct ligation in rodents,ligation of the common hepatic duct leads to cholestasis.Cholestasis results in the accumulation of hydrophobic bile acids, which may be responsible for hepatocellular apoptosis and necrosis in the liver. As a consequence of this initial injury, hepatic inflammation develops, cell activation, the release of cytokines and chemokines,and,subsequently,neutrophil recruitment to the liver, hepatocellular apoptosis and necrosis are associated with inflammatory events including neutrophil extravasation.Here we established and evaluated cholestatic hepatic fibrosis model induced by bile duct ligation in mouse,which was used as a vivo model to test the pathological changes during experimental liver fibrosis.Neutrophil recruitment to sites of liver injury is mediated via secretion of chemotactic factors including the chemokines KC-1 and MIP-2 and membrane expression of cell adhesion molecules including ICAM-1;Cell proliferation is assessed by immunohistochemistry measurement of the expression of proliferation-associated antigens such as PCNA, Ki-67 and CK-19. Hepatocyte apoptosis and liver necrosis in liver sections are quantitated by TUNNEL-positive cells and Hematoxylin&eosin staining.The results show that :the concomitant increase of chemokines and cytokines, and inflammatory cell infiltration may contribute to significant oxidative liver injury in BDL mice after biliary intervention.,hepatocyte proliferation,apoptosis and necrosis in the liver were significantly increased in BDL mice compared with sham mice. Hepatic fibrosis results from the interaction and regulation of many factors and steps,but the exact mechanism is not very clear and needs more investigations. Fox(forkhead/winged helix transcription factor) proteins are transcriptional factors, designated as the unified symbol for all chordate winged helix/forkhead transcription factors by Forkhead/Winged Helix nomenclature committee, and issued in the year of 2000.This family contains a highly conserved Forkhead region,and plays important roles in DNA binding ,transcriptional activation and transcriptional inhibition.It has been shown that HSC activation is the key link in the development of hepatic fibrogenesis,and transforming growth factor-β1/Smads signaling pathway is the main pathway in the evolution of hepatic fibrosis.FoxC1 regulates target genes such as Smad2,BMP-7 and TGF-β1, it suggests that FoxC1 participated in the signal transduction of TGF-β1.FoxL1 is a transcription factor which is mainly expressed in gastrointestinal mesenchyma,the homology of its Forkhead region was 83% at nucleotide level compared with that of FoxC1. It suggests that:FoxL1 may play an important role in the hepatic fibrosis by participating in TGF-β1/Smads signaling pathway.The dynamic expression of FoxL1 in fibrotic mouse liver tissue were determined by reverse transcription-polymerase chain reaction,real time PCR, immunohistochemistry and Western blotting.The results show that :with the development of hepatic fibrosis,The expression of FoxL1 increased significantly in the BDL groups compared to the Sham-operated control group,and the expression of FoxL1 was the highest 7 day after BDL.These data suggest that FoxL1 may play an important role in HSC proliferation and early hepatic fibrogenesis.