Hepatic progenitor cell activation in liver repair.

The liver possesses an extraordinary ability to regenerate after injury. Hepatocyte-driven liver regeneration is the default pathway in response to mild-to-moderate acute liver damage. When replication of mature hepatocytes is blocked, facultative hepatic progenitor cells (HPCs), also referred to as oval cells (OCs) in rodents, are activated. HPC/OCs have the ability to proliferate clonogenically and differentiate into several lineages including hepatocytes and bile ductal epithelia. This is a conserved liver injury response that has been studied in many species ranging from mammals (rat, mouse, and human) to fish. In addition, improper HPC/OC activation is closely associated with fibrotic responses, characterized by myofibroblast activation and extracellular matrix production, in many chronic liver diseases. Matrix remodeling and metalloprotease activities play an important role in the regulation of HPC/OC proliferation and fibrosis progression. Thus, understanding molecular mechanisms underlying HPC/OC activation has therapeutic implications for rational design of anti-fibrotic therapies.