title: Mechanisms controlling the acquisition of a cardiac phenotype by liver stem cells.
abstract: The mechanisms underlying stem cell acquisition of a cardiac phenotype are unresolved. We studied early events during the acquisition of a cardiac phenotype by a cloned adult liver stem cell line (WB F344) in a cardiac microenvironment. WB F344 cells express a priori the transcription factors GATA4 and SRF, connexin 43 in the cell membrane, and myoinositol 1,4,5-triphosphate receptor in the perinuclear region. Functional cell-cell communication developed between WB F344 cells and adjacent cocultured cardiomyocytes in 24 h. De novo cytoplasmic [Ca(2+)](c) and nuclear [Ca(2+)](nu) oscillations appeared in WB F344 cells, synchronous with [Ca(2+)](i) transients in adjacent cardiomyocytes. The [Ca(2+)] oscillations in the WB F344 cells, but not those in the cardiomyocytes, were eliminated by a gap junction uncoupler and reappeared with its removal. By 24 h, WB F344 cells began expressing the cardiac transcription factors Nkx2.5, Tbx5, and cofactor myocardin; cardiac proteins 24 h later; and a sarcomeric pattern 4-6 days later. Myoinositol 1,4,5-triphosphate receptor inhibition suppressed WB F344 cell [Ca(2+)](nu) oscillations but not [Ca(2+)](c) oscillations, and L-type calcium channel inhibition eliminated [Ca(2+)] oscillations in cardiomyocytes and WB F344 cells. The use of these inhibitors was associated with a decrease in Nkx2.5, Tbx5, and myocardin expression in the WB F344 cells. Our findings suggest that signals from cardiomyocytes diffuse through shared channels, inducing [Ca(2+)] oscillations in the WB F344 cells. We hypothesize that the WB F344 cell [Ca(2+)](nu) oscillations activate the expression of a cardiac specifying gene program, ushering in a cardiac phenotype.
authors.affiliation: Department of Internal Medicine, Brody School of Medicine, East Carolina University, Greenville, NC 27834, USA.
authors.forename: Barbara J
authors.initials: BJ
authors.lastname: Muller-Borer
authors.forename: Wayne E
authors.initials: WE
authors.lastname: Cascio
authors.forename: Gwyn L
authors.initials: GL
authors.lastname: Esch
authors.forename: Hyung-Suk
authors.initials: HS
authors.lastname: Kim
authors.forename: William B
authors.initials: WB
authors.lastname: Coleman
authors.forename: Joe W
authors.initials: JW
authors.lastname: Grisham
authors.forename: Page A W
authors.initials: PA
authors.lastname: Anderson
authors.forename: Nadia N
authors.initials: NN
authors.lastname: Malouf
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002454:Cell Differentiation; D002467:Cell Nucleus / Q000378:metabolism; D018031:Connexin 43 / Q000096:biosynthesis; D003593:Cytoplasm / Q000378:metabolism; D017629:Gap Junctions; D008099:Liver / Q000166:cytology*; D009206:Myocardium / Q000378:metabolism*; D009687:Nuclear Proteins / Q000096:biosynthesis; D010641:Phenotype; D051381:Rats; D011916:Rats, Inbred F344; D017207:Rats, Sprague-Dawley; D013234:Stem Cells / Q000166:cytology*; D015534:Trans-Activators / Q000096:biosynthesis; D000099251:Myocardin
chemical_list: D002118:Calcium; D018031:Connexin 43; D009687:Nuclear Proteins; D015534:Trans-Activators; D000099251:Myocardin