Abstract 858: Transcriptional Variability in Stem cell Populations Isolated from Adult Mouse Myocardium
Introduction: Although the mammalian heart has low regenerative potential, a number of groups have reported isolation of cardiac stem cells from adult myocardium. Different surface marker patterns have been used to identify these cell populations. It is not known whether these differences reflect the presence of multiple stem cell types, or distinct stages of development of a single pluripotent progenitor.
Methods: We isolated a c-kit/sca-1 positive clonogenic cell population from pooled left ventricular myocardium of 4 mouse hearts. Cells within this initial isolate were morphologically heterogeneous. To correlate these morphological variations with differences in gene expression and function, we isolated individual subclones by serial dilution. We obtained 65 clones, of which 42 have been passaged at least 30 times. We analyzed 6 representative clones exhibiting stable differences in membrane morphologies and nuclear/ cytosolic ratios for expression of 84 stem cell-related genes. Clones were grouped by similarity in gene expression, using an unsupervised Euclidean-distance clustering algorithm.
Results: There was a strong correlation between morphology and expression profile. One subgroup had a high membrane/cytosol ratio and high transcript levels of FGF1 and Notch1. Upon differentiation, members of this subgroup were immunoreactive for GATA-4 and/or desmin at high frequency (>40% of cells). A second group had a more spindle-shaped morphology and expressed high levels of Foxa2 and the chemokine CXCl12. A preponderance of these cells stained positive for smooth muscle actin or von Willebrand Factor after differentiation. Other genes (37 of 84) were highly expressed in all 6 clones, including cell proliferation regulators c-myc, Ccnd1 and p300. Flk-1/KDR, recently identified as a marker for a multipotent cardiac progenitor cell in the early embryo, was differentially expressed by all clones.
Conclusion: At least 2 subtypes of multipotent, clonogenic cells can be defined in the ventricular myocardium based on morphology and transcription profile. These subtypes may differ in their potential to form cardiomyocytes vs vascular tissue, with potential effects on function and clinical outcome after transplantation.