Extracellular matrix

The hepatic extracellular matrix (ECM) is a complex network of macromolecules that not only provides cells with an extracellular scaffold but also plays an important role in the regulation of cellular activities. In normal liver, the ECM comprises less than 3% of the relative area on a tissue section and approximately 0.5% of the wet weight. In addition to Glisson's capsule, ECM is found mainly in the portal tracts and the central veins. Small amounts of ECM, the perisinusoidal matrix, are also found in the subendothelial space of Disse. The sinusoids are lined by fenestrated endothelial cells which lack an electron-dense basement membrane, which facilitates the bidirectional flow of plasma between the sinusoidal lumen and the hepatocytes. The strategic position of the perisinusoidal matrix at the interface between blood and the epithelial components of the liver explains why quantitative or qualitative changes in the ECM may significantly influence hepatic function. Greater understanding of the structure and function of ECM in liver is vital not only to defining new therapeutic targets, but also to replicating functions of liver ex vivo using tissue engineering approaches in the hope of developing liver assist devices.