Extension of long cellular processes of hepatic stellate cells cultured on extracellular type I collagen gel by microtubule assembly: observation utilizing time-lapse video-microscopy.

Hepatic stellate cells cultured on or in freshly prepared type I collagen gel as a substratum were induced to elongate long cellular processes. The extension of the cellular processes was monitored by using video-enhanced optical microscopy. The cellular processes seemed to extend along the extracellular type I collagen fibers. Once extended cellular processes after overnight culture on type I collagen gel were retracted by cytoskeleton degradation with colchicine or cytochalasin B. The cellular processes were also retracted by treatment with protein kinase inhibitor, herbimycin A or staurosporin, or with phosphatidylinositol 3-kinase inhibitor, wortmannin. The effects of colchicine, herbimycin A, staurosporin, or wortmannin were drastic, and the cells were finally changed to a round shape within a few hours, as seen also after cold-treatment at 4 degrees C. Cytochalasin B also time-dependently retracted the extended cellular processes. These results indicated that the cultured stellate cells were induced to elongate cellular processes by cell surface binding to type I collagen fibrils, followed by protein or phosphatidylinositol phosphorylation and finally F-actin and microtubule assembly. Extended long cellular processes seem to reflect the in vivo structure of hepatic stellate cells, and molecular mechanism for the extension and maintenance of cellular processes was proposed.