Stem Cells Secrete Factors That Induce Proliferation In Differentiated Cardiomyocytes

Media conditioned by undifferentiated human embryonic stem cells enhanced karyokinesis, cytokinesis and cell proliferation in cultures of differentiated, beating primary rat cardiomyocytes without altering their final contractile phenotype. Transcriptome analysis of proliferating cardiomyocytes revealed comprehensive activation of the ROCK 1 and 2 G-protein coupled receptor (GPCR) pathway associated with cytokinesis, and the RAS/RAF/MEK/ERK receptor tyrosine kinase pathways (RTK) and JAK/STAT-cytokine pathway involved in cell cycle progression. Correlative multi-analyte profiling (85 proteins) of conditioned media identified 33 proteins at significantly elevated levels compared to unconditioned media including ligands specific to the GPCR signal transduction pathways (serum amyloid A, monocyte chemoattractant protein-1, macrophage inhibitory protein, IL-8, macrophage inflammatory protein 1-alpha, eotaxin), RTK activation (IGFbp-1, IGFbp-2, HGF) and JAK-STAT stimulation pathways (IL-6, IFNa) activated in the treated cardiomyocytes. These data indicated that ES cells secreted a unique admixture of factors associated with induction of mitotic replication, cytokinesis and proliferation in cardiomyocytes. Rat neonatal cardiomyocytes were harvested from day 1 ventricles (n=24). Cardiomyocytes were purified via serial Percoll gradients and plated at 2.5x10^5 cells per 100 mm sq dish. Cardiomyocytes were given 24 hours in cardiac media before extracting 6 dishes as time zero controls. Of the remaining 12 dishes, 6 were diluted 50% with unconditioned hesc media and 6 were diluted 50% with stem cell conditioned hesc media. The FBS and HS percentages were held constant at 5% and 10% respectively. Three conditioned and three unconditioned samples were extracted at 24 hours and the same was repeated at 48 hours.