title: Molecular constituents of the extracellular matrix in rat liver mounting a hepatic progenitor cell response for tissue repair.
abstract: BACKGROUND
  Tissue repair in the adult mammalian liver occurs in two distinct processes, referred to as the first and second tiers of defense. We undertook to characterize the changes in molecular constituents of the extracellular matrix when hepatic progenitor cells (HPCs) respond in a second tier of defense to liver injury.
  
  
  RESULTS
  We used transcriptional profiling on rat livers responding by a first tier (surgical removal of 70% of the liver mass (PHx protocol)) and a second tier (70% hepatectomy combined with exposure to 2-acetylaminofluorene (AAF/PHx protocol)) of defense to liver injury and compared the transcriptional signatures in untreated rat liver (control) with those from livers of day 1, day 5 and day 9 post hepatectomy in both protocols. Numerous transcripts encoding specific subunits of collagens, laminins, integrins, and various other extracellular matrix structural components were differentially up- or down-modulated (P < 0.01). The levels of a number of transcripts were significantly up-modulated, mainly in the second tier of defense (Agrn, Bgn, Fbn1, Col4a1, Col8a1, Col9a3, Lama5, Lamb1, Lamb2, Itga4, Igtb2, Itgb4, Itgb6, Nid2), and their signal intensities showed a strong or very strong correlation with Krt1-19, a well-established marker of a ductular/HPC reaction. Furthermore, a significant up-modulation and very strong correlation between the transcriptional profiles of Krt1-19 and St14 encoding matriptase, a component of a novel protease system, was found in the second tier of defense. Real-time PCR confirmed the modulation of St14 transcript levels and strong correlation to Krt-19 and also showed a significant up-modulation and strong correlation to Spint1 encoding HAI-1, a cognate inhibitor of matriptase. Immunodetection and three-dimensional reconstructions showed that laminin, Collagen1a1, agrin and nidogen1 surrounded bile ducts, proliferating cholangiocytes, and HPCs in ductular reactions regardless of the nature of defense. Similarly, matriptase and HAI-1 were expressed in cholangiocytes regardless of the tier of defense, but in the second tier of defense, a subpopulation of HPCs in ductular reactions co-expressed HAI-1 and the fetal hepatocyte marker Dlk1.
  
  
  CONCLUSIONS
  Transcriptional profiling and immunodetection, including three-dimensional reconstruction, generated a detailed overview of the extracellular matrix constituents expressed in a second tier of defense to liver injury.
authors.forename: Peter Siig
authors.initials: PS
authors.lastname: Vestentoft
authors.forename: Peter
authors.initials: P
authors.lastname: Jelnes
authors.forename: Jesper B
authors.initials: JB
authors.lastname: Andersen
authors.forename: Thi Anh Thu
authors.initials: TA
authors.lastname: Tran
authors.forename: Tenna
authors.initials: T
authors.lastname: Jørgensen
authors.forename: Morten
authors.initials: M
authors.lastname: Rasmussen
authors.forename: Jette
authors.initials: J
authors.lastname: Bornholdt
authors.forename: Lene Melsæther
authors.initials: LM
authors.lastname: Grøvdal
authors.forename: Charlotte Harken
authors.initials: CH
authors.lastname: Jensen
authors.forename: Lotte Katrine
authors.initials: LK
authors.lastname: Vogel
authors.forename: Snorri S
authors.initials: SS
authors.lastname: Thorgeirsson
authors.affiliation: Department of Cellular and Molecular Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3, DK-2200 Copenhagen, Denmark. hcb@sund.ku.dk.
authors.forename: Hanne Cathrine
authors.initials: HC
authors.lastname: Bisgaard