Telomerase activity and regulation in human liver stem cells

Abstract

Introduction The liver has been found to comprise maturational lineages of cells and is known for its regenerative capacity. Yet it has not been determined whether telomerase activity, assumed to indicate regenerative capacity, is evident in adult human liver. We analyzed telomerase activity in liver cell subpopulations that express epithelial cell adhesion molecule, EpCAM, a marker of hepatic progenitor cells. Also, telomerase levels have been compared in freshly isolated cells versus those under maximal ex vivo expansion conditions. Methods Human adult and fetal liver cell suspensions were separated by magnetic activated cell sorting. Additionally, fetal liver cells were cultured under selective conditions for stem cells, with and without growth factors or various MAP kinase inhibitors. Telomerase activity was analyzed using a modified Telomeric Repeat Amplification Protocol. Results Telomerase activity was observed in hepatic stem cells at high levels. Immuncytochemistry on stem cells in culture confirmed existence of the active subunit of telomerase. Treatment of stem cells with HGF and EGF increased telomerase activity; by contrast, p44/42 but not p38 MAP kinase inhibitors reduced telomerase activity in stem cells. Conclusions Telomerase activity is evident in hepatic stem cells and regulated by the p44/42 MAP kinase pathway. Sponsored by Vesta Therapeutics, NIH, and Department of Energy Grant.