Hepatic and pancreatic stellate cells in focus

Stellate cells are vitamin A-storing cells of liver and pancreas and have been described in all vertebrates ranging from lampreys (primitive fish) to humans, demonstrating their major importance. This cell type is thought to contribute to fibrosis, a condition characterized by an excess deposition of extracellular matrix proteins. Recently, the expression of stem/progenitor cell markers, such as CD133 (prominin-1) and Oct4, was discovered in hepatic stellate cells (HSCs) of rats. Moreover, HSCs possess signaling pathways important for maintenance of stemness and cell differentiation, such as hedgehog, beta-catenin-dependent Wnt, and Notch signaling, and are resistant to CD95-mediated apoptosis. In analogy to a stem cell niche, some characteristics of quiescent HSC are maintained by aid of a special microenvironment located in the space of Dissé. Finally, stellate cells display a differentiation potential as investigated in vitro and in vivo. Collectively all these properties are congruently found in stem/progenitor cells and support the concept that stellate cells are undifferentiated cells, which might play an important role in liver regeneration. The present review highlights findings related to this novel aspect of stellate cell biology.