Liver stem cells are thought to preside in bile ducts and the canals of Hering. They extend into the liver parenchyma at a time when normal liver cell proliferation is suppressed and liver regeneration is stimulated. In the present study 69 liver biopsies and surgically excised liver tumors were studied for the presence of liver stem cells. It was found that human cirrhotic livers and hepatocellular carcinomas (HCC) frequently exhibited isolated single scattered hepatocyte stem cells within the liver parenchyma rather than in the portal tract, bile duct or the canal of Hering. These cells expressed liver stem cell markers. HCCs also contained isolated tumor cell which expressed the same stem cell markers. The markers used were GST-P, OV-6, CK-19, Oct-3/4 and FAT10. They were identified by immunofluorescent antibody staining. HGF, EGF, CK19, AIR, H19, Nanog, Oct-3/4 and FAT10 were identified by RNA-FISH. H19 is a non-coding RNA, which is expressed in most HCCs.
Results: Immunohistochemistry and RNA-FISH performed on human livers identified isolated stem cells in liver parenchyma as follows: Stem cells identified by immunohistochemical markers (OV-6 and GST-P) and RNA-FISH markers (HGF, EGF, CK19 and H19) were found scattered in the liver parenchyma of cirrhotic livers and within hepatocellular carcinomas (HCCs). Precirrhotic ASH or NASH all stained negative for these stem cells. In HCCs, 13 out of 15 had stem cells located within the tumor (78%). In cirrhotic livers, 12 out of 28 (37%) had liver parenchymal stem cells present. In one case of stage 3 precirrhosis, stem cells were also found. Double staining for the markers showed colocalization of the markers in stem cells. Stem cells were found in 33% of HBV, 47% of HCV, 25% of alcoholic steatohepatitis (ASH) and 17% of non-alcoholic steatohepatitis (NASH). The frequency of stem cells found in the different disease categories correlates with the frequency of HCC occurring in these different diseases.
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