Abstract
Previous studies have shown that various cell-cell interactions between hepatoblasts and nonparenchymal cells, including sinusoidal endothelial cells and stellate cells, are indispensable for the development of fetal murine hepatic architecture. The present study was undertaken to determine the effects of hepatoblasts on the sinusoidal structural formation using a culture system of fetal mouse livers. Primitive sinusoidal structures extensively developed in fetal livers, and were composed of LYVE-1- and PECAM-1-positive endothelial cells, desmin-positive stellate cells and F4/80-positive macrophages. When fetal liver cells at 12.5 days of gestation were cultured in vitro, hepatoblasts spread on glass slides and gave rise to hepatocytes on day 5. Desmin-positive stellate cells also spread on the glass slides. PECAM-1-positive endothelial cells became slender and developed into anastomosing capillary networks. When fetal liver cells were cultured without hepatoblasts, which were excluded by an immunomagnetic method using anti-E-cadherin antibodies, endothelial cells had impaired growth and capillary formation. These results demonstrated that capillary formation of endothelial cells was induced by the presence of hepatoblasts. VEGF and the conditioned medium containing humoral factors produced by hepatoblasts/hepatocytes did not induce capillary formation of endothelial cells in cultures of nonparenchymal cells, although they significantly increased the number of endothelial cells on the glass slides. The presence of hepatoblasts also significantly stimulated expression of CD32b mRNA, which is a sinusoidal endothelial marker. Hepatoblasts may work as a positive stimulator of sinusoid morphogenesis and maturation in liver development, in which a signal other than VEGF may play a decisive role, together with VEGF.