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Data-guided direct reprogramming of human fibroblasts into the hematopoietic lineage

ABSTRACT: Direct reprogramming of human fibroblasts into hematopoietic stem cells (HSCs) shows promise for generating autologous cells for treatment of blood and immune-related diseases. However, low conversion efficiency of existing protocols points to gaps in our understanding and opportunities for identification of optimal transcription factor (TF) combinations, which is a major bottleneck for HSC generation. In this study, we tested a novel algorithmically-predicted TF recipe (GATA2, GFIB1, FOS, REL, and STAT5A) for inducing HSC-like states. Our recipe induced CD34+ surface expression and single-cell transcriptomic signatures similar to those of native HSCs. Transcriptional heterogeneity within reprogrammed cells included differences in expression of HSC and endothelial-associated genes and in alternatively spliced transcripts as measured by single-cell long-read RNA-sequencing. Further, we proposed an approach to quantify the relative position of reprogrammed cells within the spectrum of initial and target cell states. This study lays the foundation for efficient optimization of direct reprogramming protocols.

ORGANISM(S): Homo sapiens

PROVIDER: GSE283658 | GEO | 2024/12/09

REPOSITORIES: GEO

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Project description:Transcriptome analysis of adult hematopoietic stem cells (HSC) and their progeny has informed our understanding of blood differentiation and leukemogenesis, but a similarly transformative analysis of the embryonic origins of hematopoiesis is lacking. To address this issue, we acquired gene expression profiles of developing HSC purified from over 2500 dissected murine embryos and adult mice, and applied a network biology-based analysis to reconstruct the gene regulatory networks of sequential stages of HSC development. We found that embryonic hematopoietic elements clustered into three distinct transcriptional states characteristic of the definitive yolk sac, HSCs emerging from hemogenic endothelium, and definitive HSCs. We functionally validated several candidate transcriptional regulators of HSC ontogeny by morpholino-mediated knock-down in zebrafish embryos, confirming changes in the expression of HSC markers runx1 and c-myb in the aorta-gonads-mesonephros (AGM), the site of definitive HSC specification. Moreover, we found that HSCs derived from differentiating embryonic stem cells in vitro (ESC-HSC) most closely resemble definitive HSC, yet lack a signature indicative of specification by Notch signaling, which likely accounts for their deficient lymphoid development. Our analysis and accompanying web resource will accelerate the characterization of regulators of HSC ontogeny, facilitate efforts to direct hematopoietic differentiation and cell fate conversion, and serve as a model to study the origins of other adult stem cells. Hematopoietic stem cells and their precursors were isolated from mouse embryos and distinct stages and sites during development, purified by fluorescence activated cell sorting, and gene expression profiled on Affymetrix arrays. We also profiled HSCs and their precurors derived by in vitro differentitation of embryonic stem cells [expression data from GSE16925 and GSE14012 was used for mESCs, available at http://hsc.hms.harvard.edu/].

Project description:To guarantee blood supply throughout adult life hematopoietic stem cells (HSCs) need to carefully balance between self-renewing cell divisions and quiescence. Identification of genes controlling HSC self-renewal is of utmost importance given that HSCs are the only stem cells with broad clinical applications. Transcription factor PU.1 is one of the major regulators of myeloid and lymphoid development. Recent reports suggest that PU.1 mediates its functions via gradual expression level changes rather than binary on/off states. So far, this has not been considered in any study of HSCs and thus, PU.1’s role in HSC function has remained largely unclear. Here we demonstrate using hypomorphic mice with an engineered disruption of an autoregulatory feedback loop that decreased PU.1 levels resulted in loss of key HSC functions, all of which could be fully rescued by restoration of proper PU.1 levels via a human PU.1 transgene. Mechanistically, we found excessive HSC cell divisions and altered expression of cell cycle regulators whose promoter regions were bound by PU.1 in normal HSCs. Adequate PU.1 levels were maintained by a mechanism of direct autoregulation restricted to HSCs through a physical interaction of a -14kb enhancer with the proximal promoter. Our findings identify PU.1 as novel regulator controling the switch between cell division and quiescence in order to prevent exhaustion of HSCs. Given that even moderate level changes greatly impact stem cell function, our data suggest important therapeutic implications for leukemic patients with reduced PU.1 levels. Moreover, we provide first proof, that autoregulation of a transcription factor, PU.1, has a crucial function in vivo. We anticipate that our concept of how autoregulation forms an active chromosomal conformation will impact future research on transcription factor networks regulating stem cell fate. HSCs of Pu.1 knock-in (PU.1ki/ki) mice were used for RNA extraction and hybridization on Affymetrix microarrays. We compared these microarray samples with the corresponding wild type.

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Data-guided direct reprogramming of human fibroblasts into the hematopoietic lineage

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