Project description:HOXB4 mediates expansion of adult and embryo-derived hematopoietic stem cells (HSCs) when expressed ectopically. To define the underlying molecular mechanisms, we performed gene expression profiling in combination with subsequent functional analysis using enriched adult HSCs expressing inducible HOXB4. A substantial number of the identified HOXB4 target genes are involved in signaling pathways important for controlling self-renewal, maintenance and differentiation of stem cells. Functional assays performed on selected pathways confirmed the biological coherence of the array results. HOXB4 activity protected adult HSCs from the detrimental effects mediated by the proinflammatory cytokine TNF-alpha. Furthermore, we demonstrate that HOXB4 activity and FGF-signaling are intertwined. HOXB4-mediated expansion of adult HSCs was enhanced by specific and complete inhibition of FGF-receptors. Based on our results we propose that HOXB4 governs pivotal cell-intrinsic pathways involved in the regulation of cell cycle, differentiation and apoptosis. Our results strongly suggest that HOXB4 modulates the response of HSCs to multiple extrinsic signals in a concerted manner, thereby shifting the balance towards stem cell self-renewal. Experiment Overall Design: To understand the mechanisms of HOXB4 activity, we wished to identify target genes of HOXB4 in adult hematopoietic stem and progenitor cells (HSC/HPCs). We thus transduced murine HSC/HPCs with a retroviral vector that co-expresses EGFP and a tamoxifen-inducible form of HOXB4 (HOXB4-ER). Upon addition of 4-hydroxytamoxifen (TMX), the HOXB4-ER fusion protein translocates from the cytoplasm to the nucleus, consequently being capable of modulating gene expression. Transduced cell populations were expanded for 14 days in the presence of TMX. Thereafter, HOXB4-ER+LSK (GFP+ , lineage negative, Sca1+, ckit+) cells were flow cytometrically isolated and cultivated either with or without TMX for 1 or 4 hours. Inactivation of HOXB4 activity by TMX withdrawal was intended to mimic the naturally occurring down-regulation of HOXB4 in differentiating stem cells. RNA was prepared after the aforementioned times and the transcriptional profiles of HOXB4-ER+LSK +/- TMX analyzed using the Affymetrix⢠platform. As a control, profiling was also performed with LSK cells expressing unmodified constitutively active HOXB4 (HOXB4const) ± TMX, to exclude changes in gene expression due to unknown effects of tamoxifen itself. RNAs from adult LSK cells were processed for use on Affymetrix GeneChips Mouse Genome 430 2.0. All quality parameters for the arrays were confirmed to be in the recommended range.
Project description:Enforced expression of the homeobox transcription factor HOXB4 has been shown to enhance hematopoietic stem cell (HSC) self-renewal and expansion ex vivo and in vivo. In order to investigate the largely unknown downstream targets of HOXB4 in hematopoietic progenitor cells, HOXB4 was constitutively overexpressed in the primitive hematopoietic progenitor cell line, EML. Gene expression differences were compared between KLS (c-Kit+, Lin-, Sca-1+)-EML cells that overexpressed HOXB4 (KLS-EML-HOXB4) to control KLS-EML cells that were transduced with vector alone. ChIP-chip was used to identify promoter regions bound by HOXB4.
Project description:Enforced expression of the homeobox transcription factor HOXB4 has been shown to enhance hematopoietic stem cell (HSC) self-renewal and expansion ex vivo and in vivo. In order to investigate the largely unknown downstream targets of HOXB4 in hematopoietic progenitor cells, HOXB4 was constitutively overexpressed in the primitive hematopoietic progenitor cell line, EML. Gene expression differences were compared between KLS (c-Kit+, Lin-, Sca-1+)-EML cells that overexpressed HOXB4 (KLS-EML-HOXB4) to control KLS-EML cells that were transduced with vector alone. ChIP-chip was used to identify promoter regions bound by HOXB4. We overexpressed HOXB4 in EML cells. We isolated 3 separate single cell clones as assessed by Southern Blot Analysis (3 clones for EML-HOXB4 and 3 clones for control EML-GFP cells). RNA was isolated from the KLS (c-Kit+, Lin-, Sca-1+) fraction of each single cell clone population and processed for hybridization to array chips using established lab protocols. Chip-Chip analysis of the three HOXB4 overexpressing clones was performed to identify HOXB4 bound promoters.
Project description:Latexin is a hematopoietic stem cells (HSCs) and progenitor cells (HPCs) regulatory gene. Its deletion leads to the expansion of HSC and HPC population. The underlying mechanims are largely unknown. We therefore perfored microarrary analysis in HPCs with (Lxn-/-) and without (wild-type, WT) latexin deletion, and determined genes that were altered by latexin deletion. This led us to identify the molecular mechanims by which latexin regulates HSC function.
Project description:Hematopoietic stem and progenitor cells are a rare, self-renewing bone marrow resident population capable of giving rise to all circulating hematopoietic cells. They can be used therapuetically for reconstituting defective or ablated hematopoietic systems following chemotherapy, and for inducing tolerance toward allografts of the same haplotype as the HSC donor. There are several sources for HSCs, such as the adult bone marrow, or umblical cord blood, which is more replete with such HSCs. However, HSCs obtained from such sources may be immunogenic, especially if isolated from adult bone marrow. To overcome this issue, our lab has establsihed human induced pluripotent stem cell-derived HPCs with the hope of creating a nonimmunogenic, readily available and unlimited source of HSCs to use for therapy. The goal of this study was to compare the gene expression profiles of naturally found HSCs (UCB-CD34+ HSCs) and HPCs differentiated from 4 different human iPS cell lines (iPS-HPCs), so as to determine the variation between the four iPS-HPCs and whether there were any differences between these HPCs and naturally found HSCs. We utilized 4 iPS cells for this study (detailed descriptions are provided below). iPS cells were differentiated into hematopoietic progenitor cells by coculture on OP9 stromal cells, followed by enrichment of CD34+ cells through immunomagnetic bead separation. The UCB-CD34+ cells were isolated from frozen cord samples through immunomagnetic bead separation. Total RNA was isolated and human gene Affymetrix ST 1.0 arrays performed at the University of Iowa DNA core facility. Data was analyzed, normalized and plotted on BRB Array Tools.
Project description:Human pluripotent stem cells (hPSC) generate hematopoietic progenitor cells (HPC), but fail to engraft xenograft models, which is a hallmark feature of adult/somatic hematopoietic stem cells (HSC) from human donors. Progress to derive hPSC-derived HSCs has relied on cell autonomous approaches that force expression of transcription factors (TF), however the role of bone marrow (BM) niche remains poorly understood. Here, we quantified a failure of hPSC-HPCs to survive even in the first 24 h upon transplantation into the BM. Across several hPSC-HPC differentiation methodologies, we identified the lack of CXCR4 expression and network function. Ectopic CXCR4 conferred CXCL12-dependent signaling of hPSC-HPCs in biochemical assays and increased migration/chemotaxis and progenitor capacity, as well as survival and proliferation following transplantation in vivo. In addition, hPSC-HPCs forced to express CXCR4 demonstrated a transcriptional shift toward somatic HPCs, but this approach failed to produce long-term HSC engraftment. Our results reveal that independent of differentiation methods, networks involving CXCR4 should be targeted to generate HSCs with in vivo function from hPSCs.
Project description:Hematopoietic stem and progenitor cells are a rare, self-renewing bone marrow resident population capable of giving rise to all circulating hematopoietic cells. They can be used therapuetically for reconstituting defective or ablated hematopoietic systems following chemotherapy, and for inducing tolerance toward allografts of the same haplotype as the HSC donor. There are several sources for HSCs, such as the adult bone marrow, or umblical cord blood, which is more replete with such HSCs. However, HSCs obtained from such sources may be immunogenic, especially if isolated from adult bone marrow. To overcome this issue, our lab has establsihed human induced pluripotent stem cell-derived HPCs with the hope of creating a nonimmunogenic, readily available and unlimited source of HSCs to use for therapy. The goal of this study was to compare the gene expression profiles of naturally found HSCs (UCB-CD34+ HSCs) and HPCs differentiated from 4 different human iPS cell lines (iPS-HPCs), so as to determine the variation between the four iPS-HPCs and whether there were any differences between these HPCs and naturally found HSCs.
Project description:We used ChIP-Seq to map Ldb1, Scl and Gata2 binding sites in mouse hematopoietic progenitor cells (HPCs). Together with functional studies using conventional and conditional Ldb1 deficient mouse models and bioinformatics analysis, we systematically determined a transcriptional program controlled by Ldb1 complexes in HSC maintenance. To evaluate the role of Ldb1 in hematopoietic stem cell maintenance.
Project description:Overexpression of HOXB4 in hematopoietic stem cells (HSCs) leads to increased self-renewal without causing hematopoietic malignancies in transplanted mice. The molecular basis of HOXB4-mediated benign HSC expansion in vivo is not well understood. To gain further insight into the molecular events underlying HOXB4-mediated HSC expansion, we analyzed gene expression changes at multiple time points in Lin-Sca1+c-kit+ (LSK) cells from mice transplanted with bone marrow (BM) cells transduced with a MSCV-HOXB4-ires-YFP vector. A distinct HOXB4 transcriptional program was reproducibly induced and stabilized by 12 weeks after transplant. Dynamic expression changes were observed in genes critical for HSC self-renewal as well as genes involved in myeloid and B cell differentiation. Prdm16, a transcription factor associated with human acute myeloid leukemia (AML), was markedly repressed by HOXB4 but upregulated by HOXA9 and HOXA10, suggesting that Prdm16 downregulation was involved in preventing leukemia in HOXB4 transplanted mice. Functional evidence to support this mechanism was obtained by enforcing co-expression of sPrdm16 and HOXB4, which led to enhanced self-renewal, myeloid expansion, and leukemia. Altogether, these studies define the transcriptional pathways involved in HOXB4 HSC expansion in vivo and identify repression of Prdm16 transcription as a mechanism by which expanding HSCs avoid leukemic transformation.
Project description:Activation of mostly quiescent hematopoietic stem cells (HSC) is a prerequisite for life-long blood production1, 2. This process requires major molecular adaptations to meet the regulatory and metabolic requirements for cell division3-8. The mechanisms governing cellular reprograming upon stem cell activation and their subsequent return to quiescence are still not fully characterized. Here, we describe a role for chaperone-mediated autophagy (CMA)9, a selective form of lysosomal protein degradation, in sustaining adult HSC function. CMA is required for stem cell protein quality control and upregulation of fatty acid metabolism upon HSC activation. We identify that CMA activity decreases with age in HSC and show that genetic or pharmacological activation of CMA can restore functionality of old HSC. Together, our findings provide mechanistic insights into a new role for CMA in sustaining quality control, appropriate energetics and overall long-term hematopoietic stem cell function. Our work supports that CMA may be a promising therapeutic target to enhance hematopoietic stem cell function in conditions such as aging or stem cell transplantation.