Mechanisms underlying human hemogenic reprogramming

The direct conversion of somatic cells into hematopoietic stem cells (HSCs) by ectopic expression of transcription factors (TFs) is a promising approach for regenerative medicine. Our lab demonstrated recently the conversion of mouse fibroblasts into hemogenic cells with just 3 core TFs (Gata2, Gfi-1b, cFos) (Pereira et al 2013). The transduced cells undergo an endothelial-to-hematopoietic transition (EHT) as they acquire progenitor activity, and the entire process appears to recapitulate developmental hematopoiesis “in a dish”. Here we demonstrate that human adult dermal fibroblasts can be reprogrammed using the same core TFs. The induced cells show multi-lineage engraftment capacity, express HSCs-related cell surface markers and have a transcriptional profile similar to HSCs. The induced cells also undergo EHT “in a dish”. This phenomena allows us to determine the mechanisms mediating this process at the level of DNA and chromatin. We are using ChIP-seq to determine the genomic binding sites of the TF and to define genetic networks. The data show that the TFs interact with each other and we hypothesize that GATA2 acts as a “pioneer factor” that recruit the others and initiates changes in cell fate. These studies will allow insights in the reprogramming process that will both further its potential clinical application and help us to understand human developmental hematopoiesis.