Genetic labeling does not detect epithelial-to-mesenchymal transition of cholangiocytes in liver fibrosis in mice.
OBJECTIVE
Chronic injury changes the fate of certain cellular populations, inducing epithelial cells to generate fibroblasts by epithelial-to-mesenchymal transition (EMT) and mesenchymal cells to generate epithelial cells by mesenchymal-to-epithelial transition (MET). Although contribution of EMT/MET to embryogenesis, renal fibrosis, and lung fibrosis is well documented, role of EMT/MET in liver fibrosis is unclear. We determined whether cytokeratin-19 positive (K19(+)) cholangiocytes give rise to myofibroblasts (EMT) and/or whether glial fibrillary acidic protein positive (GFAP(+)) hepatic stellate cells (HSCs) can express epithelial markers (MET) in response to experimental liver injury.


METHODS
EMT was studied with Cre-loxP system to map cell fate of K19(+) cholangiocytes in K19(YFP) or fibroblast-specific protein-1 (FSP-1)(YFP) mice, generated by crossing tamoxifen-inducible K19(CreERT) mice or FSP-1(Cre) mice with Rosa26(f/f-YFP) mice. MET of GFAP(+) HSCs was studied in GFAP(GFP) mice. Mice were subjected to bile duct ligation or CCl(4)-liver injury, and livers were analyzed for expression of mesodermal and epithelial markers.


RESULTS
On Cre-loxP recombination, >40% of genetically labeled K19(+) cholangiocytes expressed yellow fluorescent protein (YFP). All mice developed liver fibrosis. However, specific immunostaining of K19(YFP) cholangiocytes showed no expression of EMT markers alpha-smooth muscle actin, desmin, or FSP-1. Moreover, cells genetically labeled by FSP-1(YFP) expression did not coexpress cholangiocyte markers K19 or E-cadherin. Genetically labeled GFAP(GFP) HSCs did not express epithelial or liver progenitor markers in response to liver injury.


CONCLUSIONS
EMT of cholangiocytes identified by genetic labeling does not contribute to hepatic fibrosis in mice. Likewise, GFAP(Cre)-labeled HSCs showed no coexpression of epithelial markers, providing no evidence for MET in HSCs in response to fibrogenic liver injury.
Scholten
David
D
Department of Medicine, University of California, San Diego, La Jolla, California, USA.
Osterreicher
Christoph H
CH
Scholten
Anjali
A
Iwaisako
Keiko
K
Gu
Guoqiang
G
Brenner
David A
DA
Kisseleva
Tatiana
T
D000818:Animals; D001652:Bile Ducts / Q000601:surgery; D015415:Biomarkers / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000235:genetics; D002251:Carbon Tetrachloride; D019070:Cell Lineage; D054338:Cell Transdifferentiation / Q000235:genetics; D056486:Chemical and Drug Induced Liver Injury / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D024043:Collagen Type II / Q000235:genetics; D003433:Crosses, Genetic; D004195:Disease Models, Animal; D004847:Epithelial Cells / Q000378:metabolism / Q000473:pathology*; D005347:Fibroblasts / Q000378:metabolism / Q000473:pathology*; D017930:Genes, Reporter; D005904:Glial Fibrillary Acidic Protein / Q000235:genetics; D055166:Hepatic Stellate Cells / Q000473:pathology; D007150:Immunohistochemistry; D053539:Keratin-19 / Q000235:genetics; D008026:Ligation; D008099:Liver / Q000378:metabolism / Q000473:pathology*; D008103:Liver Cirrhosis / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D008115:Liver Regeneration / Q000235:genetics; D008164:Luminescent Proteins / Q000096:biosynthesis / Q000235:genetics; D051379:Mice; D008822:Mice, Transgenic; D011401:Promoter Regions, Genetic; D011506:Proteins / Q000235:genetics; D022661:RNA, Untranslated; D000071999:S100 Calcium-Binding Protein A4; D009418:S100 Proteins
D015415:Biomarkers; D002135:Calcium-Binding Proteins; D024043:Collagen Type II; D005904:Glial Fibrillary Acidic Protein; C110853:Gt(ROSA)26Sor non-coding RNA, mouse; D053539:Keratin-19; D008164:Luminescent Proteins; D011506:Proteins; D022661:RNA, Untranslated; D000071999:S100 Calcium-Binding Protein A4; D009418:S100 Proteins; C470944:S100a4 protein, mouse; D002251:Carbon Tetrachloride