Immunohistochemical characterization of hepatic stem cell-related cells in developing human liver

Little is known about the expression characteristics of the various kinds of possible markers in hepatic stem cells (HSCs) and other HSC-related cells in human fetal liver in various developmental stages. It is significant to investigate the immunohistochemical expression for better understanding of the origin, differentiation and migration of HSCs in the developing human liver. H-E staining and immunohistochemical methods were used to observe the expression of hepatic/cholangiocellular differentiation markers (AFP, GST-π, CK7, CK19) and hematopoietic stem cell markers(CD34 and c-kit) in several kinds of HSC-related cells in thirty cases of fetal liver samples (4-35 weeks after pregnancy). AFP expression appears in fetal hepatocytes at four weeks' gestation. It peaks at 16-24 weeks' gestation and decreases gradually afterwards. Finally, weak signals were only found in some ductal plate cells and a few limiting plate cells. GST-π was detected in hepatic cord cells from the sixth week and in the ductal plate cells from the eighth week. Twenty-six weeks later, only some ductal plate cells and a few limiting plate cells show positive signals. CK19 expression peaks during the 6th-11th weeks in hepatic cord cells and decreases gradually afterwards, except for the ductal plates. CK7 expression was limited in the ductal plate cells and bile ducts cells from the 14th week. CD34 and c-kit were detected at the eighth week in some ductal plate cells and a few mononuclear cells in the hepatic cords/mesenchymal tissue of portal areas. After 21 weeks, CD34 and c-kit were found only in ductal plate cells and a few mononuclear cells in the hepatic mesenchymal tissue of portal areas. Fetal hepatocytes at 4-16 weeks' gestation are mainly constituted by HSCs characterized with bi-potential differentiation capacity. At 16 weeks' gestation, most hepatic cord cells begin to differentiate into hepatocytes and abundant HSCs remain in ductal plate (the origin site of Hering canals). It is also indicated that the hematopoietic stem cells may give rise to some HSCs in embryonic liver. These indirectly support the hypothesis about the location and origin of HSCs in "liver valley hypothesis" reported previously.