ORIGINAL PAPER Epigenetic regulation of CD34 and HIF1A expression during the differentiation of human mast cells

Abstract Mast cells differentiate from circulating pluripo-tent hematopoietic progenitors. During this differentiation, the progenitor cells are exposed to changes in oxygen avail-ability. HIF1A is the major sensor of oxygen concentration in mammalian cells. We investigated the expression of HIF1A during the in vitro differentiation of peripheral blood-derived progenitors into human mast cells. In a series of experiments, we determined the changes in CD34 expres-sion, selected mast cell markers, and HIF1A in human mast cell cultures. While the expression of CD34 dramatically decreased, the expression of mast cell-specific genes, in-cluding FCER1A, MS4A2, TPSB2, and CMA1, steadily in-creased. HIF1A expression similarly increased during mast cell differentiation, reaching its maximum level at five weeks of culture. The analysis of the promoter methylation status showed decreasing levels of methylation at the HIF1A promoter, increasing levels of methylation at the CD34 promoter, and no significant changes in other genes. In silico analysis of the promoter regions of these genes re-vealed large CpG islands in close proximity to the HIF1A and CD34 transcription initiation sites, but not in other investigated genes. In conclusion, in vitro mast cell differ-entiation was associated with decreased CD34 expression and increased HIF1A expression. These changes were paralleled with changes in the methylation status of the respective promoters, suggesting that DNA methylation-dependent epigenetic regulation mediates the gene expres-sion changes involved in maintaining the phenotype of hematopoietic stem cells and mature mast cells. Therefore, the baseline expression of HIF1A is epigenetically regulated in a cell type- and differentiation stage-specific fashion