COOPERATION OF ITO CELLS AND HEPATOCYTES IN THE DEPOSITION OF AN EXTRACELLULAR-MATRIX IN-VITRO

Cellular and molecular mechanisms involved in the deposition of extrac ellular matrix components in both normal and fibrotic liver are still poorly understood. We have investigated the influence of cooperation b etween Ito cells and hepatocytes in matrix deposition in vitro. Immuno precipitation of radiolabeled proteins from media of 5-day-old Ito cel l primary cultures showed that these cells secreted high levels of the major basement membrane components, ie, collagen IV, laminin, and ent actin/nidogen. By immunocytochemistry, precursors of basement membrane components were found intracellularly, but only scarce deposits were seen around the cells. When hepatocytes were added to 2-day-old Ito ce ll primary cultures, they established close contacts with Ito cells in less than 24 hours and expressed ZO-1, a tight junction-associated pr otein not detectable in standard hepatocyte culture. Cytochemistry ana lysis revealed an abundant extracellular matrix deposited over hepatoc yte cords and between hepatocytes and Ito cells. Immunocytochemistry s tudies showed that this matrix contained laminin, fibronectin, and col lagens proIII and IV. These data indicate that a high level of matrix protein synthesis by liver cells in vitro is not sufficient to induce extracellular matrix deposition, and that cell-cell interactions are s trongly involved in this process. Hepatocyte/Ito cell co-culture, whic h may reflect the actual situation in vivo, represents a useful tool f or studying liver fibrogenesis.