A dynamic notch injury response activates epicardium and contributes to fibrosis repair.
BACKGROUND
Transgenic Notch reporter mice express enhanced green fluorescent protein in cells with C-promoter binding factor-1 response element transcriptional activity (CBF1-RE(x)₄-EGFP), providing a unique and powerful tool for identifying and isolating "Notch-activated" progenitors.


OBJECTIVE
We asked whether, as in other tissues of this mouse, EGFP localized and functionally tagged adult cardiac tissue progenitors, and, if so, whether this cell-based signal could serve as a quantitative and qualitative biosensor of the injury repair response of the heart.


RESULTS
In addition to scattered endothelial and interstitial cells, Notch-activated (EGFP(+)) cells unexpectedly richly populated the adult epicardium. We used fluorescence-activated cell sorting to isolate EGFP(+) cells and excluded hematopoietic (CD45(+)) and endothelial (CD31(+)) subsets. We analyzed EGFP(+)/CD45⁻/CD31⁻ cells, a small (<2%) but distinct subpopulation, by gene expression profiling and functional analyses. We called this mixed cell pool, which had dual multipotent stromal cell and epicardial lineage signatures, Notch-activated epicardial-derived cells (NECs). Myocardial infarction and thoracic aortic banding amplified the NEC pool, increasing fibroblast differentiation. Validating the functional vitality of clonal NEC lines, serum growth factors triggered epithelial-mesenchymal transition and the immobilized Notch ligand Delta-like 1-activated downstream target genes. Moreover, cardiomyocyte coculture and engraftment in NOD-SCID (nonobese diabetic-severe combined immunodeficiency) mouse myocardium increased cardiac gene expression in NECs.


CONCLUSIONS
A dynamic Notch injury response activates adult epicardium, producing a multipotent cell population that contributes to fibrosis repair.
Department of Internal Medicine/Cardiology, UT Southwestern Medical Center, Dallas, 75390-8573, USA.
Jamie L
JL
Russell
Sean C
SC
Goetsch
Nicholas R
NR
Gaiano
Joseph A
JA
Hill
Eric N
EN
Olson
Jay W
JW
Schneider
D000818:Animals; D002135:Calcium-Binding Proteins; D005355:Fibrosis; D020869:Gene Expression Profiling; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D017493:Leukocyte Common Antigens; D051379:Mice; D008822:Mice, Transgenic; D039902:Multipotent Stem Cells / Q000378:metabolism* / Q000473:pathology; D009203:Myocardial Infarction / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D010496:Pericardium / Q000378:metabolism* / Q000473:pathology; D019408:Platelet Endothelial Cell Adhesion Molecule-1; D051880:Receptors, Notch / Q000235:genetics / Q000378:metabolism*
D002135:Calcium-Binding Proteins; C512925:Dlk1 protein, mouse; D036341:Intercellular Signaling Peptides and Proteins; D019408:Platelet Endothelial Cell Adhesion Molecule-1; D051880:Receptors, Notch; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins; D017493:Leukocyte Common Antigens; C516770:Ptprc protein, mouse