Expression of acidic fibroblast growth factor in regenerating liver and during hepatic differentiation

Abstract

Background: Acidic fibroblast growth factor belongs to a family of growth factors that show a high affinity for heparin sulfate proteoglycans. In vitro, it participates in various cellular functions including proliferation, differentiation, angiogenesis, and cell migration, but in vivo, the physiologic role of this growth factor is still not clearly defined.

Experimental design: The level of expression and also cellular distribution of transcripts for acidic fibroblast growth factor (aFGF) were studied in adult rat liver after partial hepatectomy and during hepatic differentiation in fetal, neonatal, and adult livers by Northern analysis and in situ hybridization techniques.

Results: After partial hepatectomy a significant increase in the transcripts for aFGF was observed at 24 hours, whereas at 4 and 12 hours after the operation, the level of transcripts were similar to those of sham-operated animals. In the postnatal liver a high level of aFGF expression was present when the most evident transition from 2 to 3 cell thick hepatic cords to normal hepatic structure is taking place (Ogawa K, Medine A, Farber E. Br J Cancer 1979;40: 782-90). In contrast during the prenatal period, when the liver is still a hemopoietic organ and only a small number of sinusoids are present, low level of aFGF transcripts could be found. Animals treated with 2-acetylaminofluorene and partial hepatectomy (Evarts RP, Nagy P, Marsden E, Thorgeirsson SS. Carcinogenesis 1987;8:1737-40) displayed a marked increase in hepatic aFGF transcripts at the peak of proliferation of primitive liver epithelial cells (oval cells) and perisinusoidal stellate cells (Ito cells) in addition to hepatocytes. In situ hybridization combined with immunocytochemistry using oval and Ito cell specific antibodies revealed the presence of transcripts both in oval cells and Ito cells. Basophilic areas composed of small hepatocytes had a 3-fold increase in the level of transcripts as compared with the surrounding hepatocytes.

Conclusions: These experiments demonstrate that the expression of aFGF is highest during the late stages of hepatic morphogenesis in newborn animals as well as during hepatic differentiation in adult liver.