Class VI intermediate filament protein nestin is induced during activationof rat hepatic stellate cells

Hepatic stellate cells are considered to be liver-specific pericytes that p lay a key role in liver fibrosis. Because these cells express desmin and sm ooth muscle alpha-actin, they were assumed to be of myogenic origin. This h ypothesis became doubtful when it was reported that stellate cells also exp ress glial fibrillary acidic protein and neural cell adhesion molecule. In the present study, we show that activated stellate cells express nestin, a class VI intermediate filament protein originally identified as a marker fo r neural stem cells. Expression of nestin was first studied during spontane ous activation of stellate cells in culture. Immunohistochemistry showed th at nestin-positive stellate cells already appeared at day 3, and nearly all the cells became positive for nestin at day 6 and 15. The immunoreaction w as present in filaments except in dividing cells. The presence of messenger RNA transcript for nestin was shown by reverse transcription polymerase ch ain reaction and sequencing of amplified complementary DNA. We then compare d the presence of nestin with that of other intermediate filament proteins and smooth muscle alpha-actin, Immunoblotting showed that the relative conc entrations of nestin, desmin, and vimentin increased between day 2 and 6 in primary culture. After the initial increase vimentin leveled off, while ne stin and desmin showed a tendency to decrease. This pattern was quite diffe rent from that of glial fibrillary acidic protein, which kept declining, an d smooth muscle alpha-actin, which increased continuously up to day 13 in c ulture. We then studied the presence of nestin in normal and CCl4-injured r at liver. In normal liver, minimal immunoreaction for nestin was observed w ithin the liver parenchyma. During induction of fibrosis by carbon tetrachl oride, nestin-positive stellate cells appeared at 6 weeks, which was late i n comparison with the induction of desmin and smooth muscle alpha-actin. We conclude that nestin is induced in stellate cells during transition from t he quiescent to the activated phenotype; culture activation is a stronger s timulus than in vivo activation by injection of CCl4. Taken together with r eports on expression of glial fibrillary acidic protein and neural cell adh esion molecule by stellate cells, new experimental studies on the embryonic origin of these cells are required.