Connective tissue growth factor and integrin αvβ6: A new pair of regulators critical for ductular reaction and biliary fibrosis in mice

Abstract

Connective tissue growth factor (CTGF) is a matricellular protein that mediates cell-matrix interaction through various subtypes of integrin receptors. This study investigated the role of CTGF and integrin αvβ6 in hepatic progenitor/oval cell activation, which often occurs in the form of ductular reactions (DRs) when hepatocyte proliferation is inhibited during severe liver injury. CTGF and integrin αvβ6 proteins were highly expressed in DRs of human cirrhotic livers and cholangiocarcinoma. Confocal microscopy analysis of livers from Ctgf promoter driven GFP reporter mice suggested that oval cells and cholangiocytes were the main sources of CTGF and integrin αvβ6 during liver injury induced by 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC). Deletion of exon 4 of the Ctgf gene using tamoxifen inducible Cre-loxP system down-regulated integrin αvβ6 in DDC damaged livers of knockout mice. Ctgf deficiency or inhibition of integrin αvβ6 by administrating the neutralizing antibody 6.3G9 (10 mg/kg body weight) caused low levels of EpCAM and CK19 mRNAs. Also, there were smaller oval cell areas, fewer proliferating ductular epithelial cells, and lower cholestasis serum markers within two weeks after DDC treatment. Associated fibrosis was attenuated as indicated by reduced expression of fibrosis-related genes, smaller areas of α smooth muscle actin staining and low collagen production based on hydroxyproline content and the Sirius red staining. Finally, integrin αvβ6 could bind to CTGF mediating oval cell adhesion to CTGF and fibronection substrata and promoting transforming growth factor (TGF)-β1 activation in vitro. Conclusions: CTGF and integrin αvβ6 regulate oval cell activation and fibrosis, probably through interacting with their common matrix and signal partners, fibronectin and TGF-β1. CTGF and integrin αvβ6 are potential therapeutic targets to control DRs and fibrosis in related liver disease.

Stellate Cells and Hepatic Fibrosis

“…Many of these signals may be mediated by membrane adhesion receptors, the most important of which include integrins and ADAM (a disintegrin and metalloproteinase domain) molecules. Integrins expressed by HSCs modulate the function of several key profibrotic pathways and molecules such as connective tissue growth factor (CTGF) [23], Hedgehog [24], TGFβ [2], and are central to the procarcinogenic milieu of fibrotic liver [14]. ADAM molecules are expressed by HSCs and endothelial cells, and mediate profibrotic signals such as those from epidermal growth factor receptor (EGFR), among others [25][26][27].…”

Hepatic progenitor cell activation in liver repair

“…67,68 We have found that CTGF is highly expressed in murine and rat HPC/OCs. 69,70 It binds to integrins on the surface of many cell types and is able to promote cell attachment and migration on provisional matrix. 71 Deletion of this molecule affects HPC/OC activation and biliary fibrosis during DD- induced liver injury in mice.…”

miR-133b Regulation of Connective Tissue Growth Factor

“…Recently, we have shown that CTGF plays an important role in regulating DR in this model. 9 To further understand the role of miR-133b in CTGF regulation and DR/OC response, we fed mice with the DDC diet for 1 day to initiate progenitor activation and infected the damaged livers with recombinant adenovirus overexpressing miR-133b through tail vein injection. GFP that was inserted after ribosomal entry sites was coexpressed with miR-133b precursor.…”

“…1 We have found that connective tissue growth factor (CTGF), a secreted matricellular protein, is highly up-regulated in HPCs/OCs and cholangiocytes after liver damage. 9 CTGF protein, through its four conserved modules that interact with ECM proteins, growth factors, and receptors (ie, integrin avb6), plays pleiotropic roles on different cell types and tissues. 10,11 Both the OC activation and the fibrotic response in the liver are suppressed after down-regulation of CTGF in animal models.…”

“…10,11 Both the OC activation and the fibrotic response in the liver are suppressed after down-regulation of CTGF in animal models. 9,12 Despite these important findings, signaling pathways and molecular mechanisms that control OC activation in liver regeneration remain largely unknown.…”