Abstract 1816: Epigenetic Control and Gene Expression of Pluripotency Markers in Multipotent Circulating Human Mesoangioblasts
Stem cell therapy is an attractive option to treat patients with heart failure. Recently, we identified multipotent human mesoangioblasts (cMAB) in peripheral blood. cMAB are characterised by a sustained proliferative capacity, and exhibit high telomerase activity. Clonally expanded cMAB expressed the endothelial marker KDR, mesenchymal markers, but were negative for the hematopoietic markers CD34 and CD45 and differentiated into cardiomyocytes, smooth muscle cells, and endothelial cells in vitro and in vivo. Importantly, among the four factors (Oct4, Klf4, c-myc and Sox2), which are sufficient to induce pluripotency in fibroblasts, cMAB expressed Oct4, KLF4, and c-Myc on mRNA level. Oct4 expression was further confirmed by immunohistochemistry. Sox2 and another important stem cell marker, nanog, were not expressed. To investigate whether epigenetic mechanisms account for the differential expression of Oct4 and Klf4 compared to Sox2, we analyzed the chromatin state maps of key histone activating and repressive marks and DNA methylation. Analysis of the DNA methylation of the Oct4 promoter using bisulfite sequencing with 2 different primers revealed a lower incidence of methylated CpG islands in cMAB compared to peripheral blood derived mononuclear cells (primer 1: 44% versus 81%, primer 2: 56% versus 100%, respectively). Thus, DNA hypomethylation correlated with Oct4 expression. At the level of histones, gene expression is controlled by active and repressive modifications. Chromatine immunoprecipitation experiments demonstrated that active marks, acetylated-histone H3 and trimethylation of histone H3 lysine 4 were increased, whereas repressive marks trimethyl-H3 lysine 9 and trimethyl-H3 lysine 27 (H3K27me3) were reduced at the promoter regions of Oct4 and Klf4. In contrast, H3K27me3 was high at Sox2 and nanog promoter regions suggesting that this repressive histone modification contributes to gene silencing of these genes. These data indicate that the epigenetic “signature” corresponds to the expression of pluripotency and stem cell genes. Modification of the epigenetic histone code, e.g. by histone demethylases, may provide an attractive tool to reprogram adult progenitor cells to generate patient-specific stem cells.