Sadatsugu Sakane received his M.D. from Osaka University in Japan in 2009. After six years of clinical experience as a physician, he engaged in basic research on nonalcoholic fatty liver disease and received his Ph.D. from Osaka University in 2021. He joined Dr. Kisseleva's lab in the summer of 2022 and is conducting his basic research on chronic liver disease.
Liver cancer arises from advanced liver fibrosis induced by chronic liver injury. Portal fibroblasts (PFs) are fibroblasts located around the bile ducts, and account for only 0.1% of the liver under normal conditions. We have previously reported that PFs play an important role in the process of liver fibrosis in cholestatic liver injury. However, the significance of PFs in carcinogenesis is unclear. In this study, we investigated the role of portal fibroblasts in hepatocarcinogenesis in cholestatic fibrosis using multidrug resistance protein 2 (Abcb4) knockout mice (Mdr2 KO mice), which develop sclerosing cholangitis and biliary fibrosis due to lack of phosphatidylcholine excretion into bile. Sixteen-month-old Mdr2 KO mice developed numerous tumors morphologically similar to hepatocellular carcinoma. The nontumorous liver showed lobular inflammation and progressive fibrosis. Next, we focused on mesothelin (Msln), mucin16 (Muc16), and thy-1 cell surface antigen (Thy1), which are specific markers of PFs. Since Msln and Muc16 are involved in the activation of TGFβ in PFs, and Thy1 is involved in the suppression of TGFβ in PFs, all 3 genes regulate PF activation. We crossed Mdr2 KO mice with Msln KO mice, Muc16 KO mice, or Thy1 KO mice and observed differences in tumor growth and progression. Mdr2 Msln KO mice and Mdr2 Muc16 KO mice showed significantly reduced tumor number and size compared to Mdr2 KO mice. Mdr2 Thy1 KO mice showed no change. Mdr2 Msln KO mice and Mdr2 Muc16 KO mice showed reduced PFs and fibrosis, as well as reduced bile duct proliferation in the nontumorous liver. KO of Msln or Muc16 showed decreased expression of Cd68 and Ly6G and fewer F4/80 positive cells in the nontumorous liver, suggesting reduced inflammatory cell infiltration. The expression of IL1β and TNF was also reduced. In addition, the expressions of Nox2 and p67phox, which are involved in ROS production, are decreased in the tumors of Mdr2 Msln KO and Mdr2 Muc16 KO compared to Mdr2 KO mice. These results suggest that PFs contributed to the exacerbation of inflammation in the nontumorous liver and were involved in hepatocarcinogenesis.
Conclusion: PFs play an important role not only in fibrosis but also in hepatocarcinogenesis in cholestatic fibrosis.