Z Gastroenterol 2013; 51 - P_4_37
DOI: 10.1055/s-0032-1332082

p21 regulates liver progenitor cell activation and hepatocarcinogenesis in inflammation-associated liver disease

S Marhenke 1, LE Buitrago-Molina 1, J Endig 1, J Lamlé 1, T Longerich 2, R Geffers 3, C Dorrell 4, A Lechel 5, SF Katz 5, MP Manns 1, A Vogel 1
  • 1Hannover Medical School, Department of Gastroenterology, Hepatology and Endocrinology, Hannover, Germany
  • 2University Hospital Heidelberg, Institute of Pathology, Heidelberg, Germany
  • 3Helmholtz Centre for Infection Research, Department of Cell Biology, Braunschweig, Germany
  • 4Oregon Health & Science University, Department of Genetics, Portland, United States
  • 5Ulm University, Institute of Molecular Medicine, Ulm, Germany

Introduction: Hepatocellular carcinoma (HCC) is the fifth most common cancer worldwide. Given the poor prognosis in metastatic stage of the disease, new therapies are urgently needed. Previously it has been shown that loss of the cell-cycle regulator p21 dramatically accelerates hepatocarcinogenesis suggesting that p21 acts as tumor suppressor. In order to determine the impact of p21 in inflammation-induced carcinogenesis the Mdr2 mouse model was used. In Mdr2-/- mice, loss of the Abc4 protein leads to regurgitation of bile acids into the liver causing inflammation, fibrosis and tumor development.

Methods: To evaluate the role of p21 in liver carcinogenesis Mdr2-/- mice were crossbred with p21-/- mice to generate Mdr2/p21-/- mice. The degree of liver damage, inflammation, fibrosis, apoptosis, proliferation and tumor formation was analyzed by immunohistochemistry, Western blotting and mircoarray analysis.

Results: As previously shown, Mdr2-/- mice spontaneously developed a severe liver disease characterized by cholestasis, liver fibrosis and multiple liver tumors later in life. Altogether, histological and biochemical examinations revealed that loss of p21 did not affect bile acid induces liver injury in Mdr2 deficient mice. Surprisingly however, loss of p21 significantly impaired liver regeneration in these mice compared to Mdr2-/- controls. In line with these findings, expression profiling identified cell cycle related genes to be most significantly differently regulated between both groups. However, partial hepatectomies and hepatocyte transplantations revealed that loss of p21 per se did not impair proliferation of hepatocytes. FACS and IHC analysis revealed a strong compensatory activation of liver progenitor cells (LPC) in Mdr2-/- mice. Interestingly, LPC activation was significantly impaired in Mdr2/p21-/- mice suggesting that p21 is required for LPC expansion during chronic liver injury. Molecular profiling of p21 deficient LPCs is currently ongoing. Interestingly, hepatocarcinogenesis was significantly delayed in Mdr2/p21-/- mice. Overall, only 40% of Mdr2/p21-/- compared to 80% of Mdr2-/- mice developed liver tumors indicating that p21 significantly contributes to tumor initiation in this model.

Conclusion: We provide experimental evidence that p21 is required for liver regeneration during chronic liver injury. Compensatory liver LPC activation and hepatocyte proliferation was significantly impaired in Mdr2/p21-/- mice. Importantly, our data reveal that loss of p21 does not affect chronic liver injury, but significantly delays tumor development in a mouse model of inflammation-induced hepatocarcinogenesis. So far tumor-initiating cells are not yet identified in human and rodent HCCs, however our data imply that impaired LPC activation after loss of p21 contributes to carcinogenesis in the Mdr2-/- mouse model.