Liver regeneration by stem/progenitor cells.

UNLABELLED: The liver is renowned for its strong, robust regenerative capacity, employing different modes of regeneration according to type and extent of injury. The process of compensatory hypertrophy of the liver upon partial hepatectomy has been standing as a classical model for studying organ regeneration in mammals and a subject of exhaustive analyses. Meanwhile, in view of the physiological relevance for many of the human liver pathologies induced upon toxic insults or hepatitis, other injury models have recently drawn increasing attention. In those damaged livers where hepatocyte proliferation is compromised, adult liver stem/progenitor cells (LPCs) are activated and differentiate to hepatocytes and cholangiocytes, leading to functional recovery of the organ. Here, we summarize and discuss recent findings on the mechanisms underlying the regeneration process of the liver. Whereas the primary focus of this article is on those related to LPC-mediated regeneration, we also introduce topics on compensatory hypertrophy, where application of new technologies and molecular genetics approaches in mice has gained a paradigm shift. Identification of various markers for LPC populations has expedited their characterization and enabled us to examine their differentiation potential in vivo using genetic lineage-tracing approaches. Comprehensive studies regarding intercellular signaling pathways and their modes of action have succeeded in elucidating novel frameworks for the LPC-niche interaction functioning in the regenerating liver.
CONCLUSION: Advancing our understanding of the cellular and molecular mechanisms for liver regeneration should provide a basis for developing therapeutic strategies to treat patients with liver disease.