The Development and Compensation of Biliary Cirrhosis in Interleukin-6-Deficient Mice

Abstract

In an effort to understand the role of IL-6/gp130 signaling in chronic liver injury, IL-6 deficient (IL-6 ؊/؊ ) and wild-type control (IL-6 ؉/؉ ) mice were subjected to bile duct ligation (BDL) for 12 weeks. This maneuver causes chronic biomechanical stress and liver injury, fueling sustained biliary epithelial and hepatocyte proliferation. By 12 weeks after BDL, IL-6 ؊/؊ mice develop significantly higher total serum bilirubin levels (23.2 ؎ 2.3 versus 14.9 ؎ 2.1 mg/dl, P < 0.0001; delta bilirubin subfraction 16.7 ؎ 4.0% versus 9.2 ؎ 1.8%; P < 0.002), and the majority (15/18) show "black" gallbladder bile, compared to IL-6 ؉/؉ mice (5/16; P < 0.003). The IL-6 ؊/؊ mice also cannot sustain the compensatory liver mass increase commonly seen with chronic obstructive cholangiopathy, because of less hepatocyte proliferation, despite a rate of hepatocyte apoptosis similar to that of IL-6 ؉/؉ mice. Moreover, IL-6 ؊/؊ mice show a more advanced stage of biliary fibrosis and a higher mortality rate than the IL-6 ؉/؉ controls (51% versus 23%; P < 0.02). These phenotypic changes in the IL-6 ؊/؊ mice are associated with decreased expression and phosphorylation of gp130 and the transcription factor STAT3, compared to IL-6 ؉/؉ mice. Daily treatment with exogenous recombinant IL-6 for 3-6 weeks starting at 6 weeks after BDL significantly lowers the serum total bilirubin in both groups. In the IL-6 ؊/؊ mice, exogenous IL-6 treatment also increases the level of gp130 protein expression and completely reverses the loss of liver mass by increasing the hepatocyte proliferation. In conclusion, IL-6 appears to contribute to biliary tree integrity and maintenance of hepatocyte mass during chronic injury. Interleukin-6 (IL-6)/gp-130 signaling is involved acutely in hepatocyte 1,2 and biliary epithelial cell (BEC) growth control and pathobiology. For example, liver regeneration after partial hepatectomy (PH) is delayed in IL-6 Ϫ/Ϫ mice, 1,2 whereas IL-6/sIL-6R double transgenic mice develop hepatocellular hyperplasia and adenomas. 3 Although data on the in vitro effects of IL-6 on hepatocyte proliferation are conflicting, 4,5 there are at least two mechanisms by which IL-6/gp-130 promotes BEC growth in vitro. IL-6 is able to directly stimulate BEC DNA synthesis 6 and inhibit apoptosis, via an increase of the bcl-2/ bax ratio. 7 When stimulated by other proinflammatory cytokines or phorbol esters, nonneoplastic BEC can also produce and secrete IL-6, which can then act as an autocrine growth factor under conditions of BEC stress. 6,8,9 Serum and liver IL-6 levels are also elevated in patients with chronic inflammatory liver diseases. 10 -13 In this setting, IL-6 has traditionally been considered to exert a profibrogenic and mitoinhibitory influence on the development of cirrhosis. 10,14 -17 However, in other "chronic inflammatory proliferative disorders," such as psoriasis and rheumatoid arthritis, IL-6 has been linked with keratinocyte and synovial cell proliferation, respectively. 18 In addition, recent studies have shown that gp130 sign...

Regulation and Function of Trefoil Factor Family 3 Expression in the Biliary Tree

“…Whole liver, including equal amounts of perihilar tissue, was used for RNA and protein isolation. Some of the analyses on whole mouse liver after BDL were conducted on tissues saved from previous experiments, 7,14 but none of the results have been previously reported.…”

“…and 12 weeks after BDL. 6,7,14 A group of IL-6 Ϫ/Ϫ mice was treated with exogenous rIL-6 or normal saline as a control to determine the effect of IL-6 replacement therapy on IL-6 Ϫ/Ϫ mice. This daily treatment was started at 6 weeks after BDL and continued for 1 or 6 weeks.…”

“…Biliary insults such as bile duct ligation (BDL) also trigger production of other cytokines and growth factors, such as tumor necrosis factor (TNF)-␣, hepatocyte growth factor (HGF), transforming growth factor (TGF)-␤ that are produced primarily by peribiliary stromal and hematolymphoid cells, and not by BECs, but contribute to BEC pathophysiology in vivo. 6,13 A previous study from our lab showed that interleukin-6-deficient (IL-6 Ϫ/Ϫ ) mice develop decompensated biliary cirrhosis at a higher rate than wild-type (IL-6 ϩ/ϩ ) controls 14 after BDL because of impaired biliary tree integrity. 14 However, the molecular mechanisms responsible for impaired biliary tree integrity remain undefined.…”

“…6,13 A previous study from our lab showed that interleukin-6-deficient (IL-6 Ϫ/Ϫ ) mice develop decompensated biliary cirrhosis at a higher rate than wild-type (IL-6 ϩ/ϩ ) controls 14 after BDL because of impaired biliary tree integrity. 14 However, the molecular mechanisms responsible for impaired biliary tree integrity remain undefined.…”

“…14 A microarray analysis identified the trefoil factor family (TFF) 15,16 of peptides as candidate genes expressed in BECs and regulated by IL-6 signaling that could potentially contribute to biliary tree integrity. TFF are mucin-associated proteins that increase the viscosity of mucins and help protect epithelial linings from insults.…”