Transient expression of laminin α1 chain in regenerating murine liver: Restricted localization of laminin chains and nidogen-1

Most interstitia between epithelial and endothelial cells contain basal laminae (BLs), as defined by electron microscopy. However, in liver, the sinusoidal interstitium (called space of Disse) between hepatocytes and sinusoidal endothelial cells (SECs) lacks BLs. Because laminins are major components of BLs throughout the body, whether laminins exist in sinusoids has been a controversial issue. Despite recent advances, the distribution and expression of laminin chains have not been well defined in mammalian liver. Here, using a panel of antibodies, we examined laminins in normal and regenerating mouse livers. Of α chains, α5 was widely observed in all BLs except for sinusoids, while the other α chains were variously expressed in Glisson's sheath and central veins. Laminin γ1 was also distributed to all BLs except for sinusoids. Although the β2 chain was observed in all BLs and sinusoids, the expression of β1 chain was restricted to Glisson's sheath. Detailed analysis of regenerating liver revealed that α1 and γ1 chains appeared in sinusoids and were produced by stellate cells. The staining of α1 and γ1 chains reached its maximum intensity at 6 days after two-thirds partial hepatectomy (PHx). Moreover, in vitro studies showed that α1-containing laminin promoted spreading of sinusoidal endothelial cells (SECs) isolated from normal liver, but not other hepatic cells. In addition, SECs isolated from regenerating liver elongated pseudopodia on α1-containing laminin more so than did cells from normal liver. The transient expression of laminin α1 may promote formation of sinusoids after PHx.