Aspp1 Preserves Hematopoietic Stem Cell Pool Integrity and Prevents Malignant Transformation
ABSTRACT: Quiescent hematopoietic stem cells (HSCs) are prone to mutagenesis, and accumulation of mutations can result in hematological malignancies. The mechanisms through which HSCs prevent such detrimental accumulation, however, are unclear. Here, we show that Aspp1 coordinates with p53 to maintain the genomic integrity of the HSC pool. Aspp1 is preferentially expressed in HSCs and restricts HSC pool size by attenuating self-renewal under steady state conditions. After genotoxic stress, Aspp1 promotes HSC cycling and induces p53-dependent apoptosis in cells with persistent DNA damage foci. Beyond these p53-dependent functions, Aspp1 attenuates HSC self-renewal and accumulation of DNA damage in p53-null HSCs. Consequently, concomitant loss of Aspp1 and p53 leads to the development of hematological malignancies, especially T-cell leukemia and lymphoma. Together, these data highlights coordination between Aspp1 and p53 in regulating HSC self-renewal and DNA damage tolerance, and suggest that HSCs possess specific mechanisms that prevent accumulation of mutations and malignant transformation. 8-week-old WT, Aspp1-/-, Mx1-Cre(+)p53flox/flox and Mx1-Cre(+)Aspp1-/-p53flox/flox mice were intraperitoneally administered with 400 μg pIpC five times every other day to obtain WT, Aspp1-/-, p53-/- and Aspp1-/-p53-/- bone marrow. 4 weeks after pIpC treatment, bone marrow lineage(-) Sca-1(+) cKit(+) cells were isolated. RNA was extracted and pooled from 3 independent mice per genotype. RNA samples were then amplified, labeled, and hybridized to independent arrays.
Project description:LRF, which is encoded by the ZBTB7A gene and formerly known as POKEMON (POK erythroid myeloid ontogenic factor), was originally identified as a PLZF (promyelocytic leukemia zinc finger) homologue interacting with BCL6 (B-cell lymphoma 6). LRF is a transcription factor that is broadly expressed in hematopoietic lineage cells, but its expression is particularly high in erythroblasts and germinal center (GC) B-cells. The goal of this study is to assess the effect of LRF loss on the LT-HSC transcriptome. Nine days after injection of adult mice with polyinosinic polycytidylic acid (pIpc) to activate Cre, total RNAs were isolated from double-sorted LT-HSCs from LRF Flox/+ Mx1-Cre+ and LRF Flox/Flox Mx1-Cre+ mice and processed for microarray analysis. We performed gene expression microarray analysis of FACS-sorted LT-HSCs (LSK IL7Ra-Flt3-CD150+CD48-) to assess the effect of Lrf loss on the LT-HSC transcriptome. Zbtb7a Flox/+ Mx1-Cre+ mice were used as a control to normalize the potential effects of Cre recombinase. LT-HSCs were FACS-sorted from three Lrf knockout (Zbtb7a Flox/Flox Mx1-Cre+) and two control (Zbtb7a Flox/+ Mx1-Cre+) mice, nine days after the first pIpC injection.
Project description:Autophagy deficiency caused by conditional knockout of Atg7 results in severe hepatitis accompanied by abundant accumulation of p62. p62 stablizes Nrf2 by disrupting the association between Keap1 and Nrf2. To understand the pathogenesis of hepatitis under the autophagy deficiency, we examined gene expression profiles of livers from Atg7-null, Nrf2-null and Atg7-Nrf2 double mutant mice. Eight week old Atg7F/F:Mx1-Cre mice and Atg7F/F:Mx1-Cre:Nrf2-/- together with control mice were injected with pIpC. At 4 weeks after pIpC injection, total RNAs were purified from each mouse liver.
Project description:The transcriptional coactivator Cbp is critical for hematopoietic stem cell (HSC) development. However, its role in adult HSC and the mechanistic detail of Cbp control of HSC function remains unknown. Using conditional deletion of Cbp in the adult HSC compartment, we demonstrate an altered balance between differentiation and self-renewal with gradual loss of phenotypic HSC, differentiation defects in lower compartments and the development of myeloid malignancies. In addition, we demonstrate that Cbp -/- HSCs reconstitute hematopoiesis with lower efficiency than their wild type counterparts and readily exhaust over time when placed under the replicative stress of serial transplantation. Furthermore, we demonstrate abnormal cell cycle (re)entry and apoptosis in HSC which, with preferential differentiation, also contribute to stem cell exhaustion. Finally we demonstrate global transcriptional abnormalities predicted to alter cell cycle control, balanced differentiation and HSC function upon Cbp deletion and link Cbp to a critical HSC transcriptional regulatory network through genome-wide analysis of Cbp binding. Genome-wide gene expression analysis of LSK population after Cbp deletion. The LSK population of bone marrow is enriched for hematopoietic stem cells. Total RNA was extracted from flow-sorted LSK population of bone marrow, 4 weeks after pIpC induced deletion of Cbp. 2 replicates for Cbp wt control, 2 replicates for Cbp Mx.
Project description:Myeloproliferative neoplasms (MPNs) are diseases caused by mutations in the haematopoietic stem cell (HSC) compartment. Most MPN patients have a common acquired mutation of Janus kinase 2 (JAK2) gene in HSCs that renders this kinase constitutively active, leading to uncontrolled cell expansion. The bone marrow (BM) microenvironment might contribute to the clinical outcomes of this common event. We previously showed that BM nestin+ mesenchymal stem cells (MSCs) innervated by sympathetic nerve fibres regulate normal HSCs. Here we demonstrate that abrogation of this regulatory circuit is essential for MPN pathogenesis. Sympathetic nerve fibres, supporting Schwann cells and nestin+ MSCs are consistently reduced in the BM of MPN patients and mice expressing the human JAK2V617F mutation in HSCs. Unexpectedly, MSC reduction is not due to differentiation but is caused by BM neural damage and Schwann cell death triggered by interleukin-1b produced by mutant HSCs. In turn, in vivo depletion of nestin+ cells or their production of CXCL12 expanded mutant HSCs and accelerated MPN progression. In contrast, administration of neuroprotective or sympathomimetic drugs prevented mutant HSC expansion. Treatment with b3-adrenergic agonists that restored the sympathetic regulation of nestin+ MSCs prevented the loss of these cells and blocked MPN progression by indirectly reducing leukaemic stem cells. Our results demonstrate that mutant HSC-driven niche damage critically contributes to disease manifestation in MPN and identify niche-forming MSCs and their neural regulation as promising therapeutic targets. CD45- CD31- Ter119- GFP+ cells were sorted from the BM of Nes-gfp;Mx1-cre;JAK2-V617F mice and control littermates 6 weeks after pIpC treatment and were subjected to RNA sequencing. Each sample was pooled from 3 animals of the same genotype.
Project description:The B-myb (MYBL2) gene is a member of the MYB family of transcription factors and is involved in cell cycle regulation, DNA replication and maintenance of genomic integrity. However, its function during adult development and hematopoiesis is unknown. We show here that conditional inactivation of B-myb in vivo results in depletion of the HSC pool, leading to profound reductions in mature lymphoid, erythroid and myeloid cells. This defect is autonomous to the bone marrow and is first evident in the HSCs, which accumulate in the S and G2/M phases. B-myb inactivation also causes defects in the myeloid progenitor compartment and results in an accumulation of GMPs. Microarray studies indicate that B-myb null LKS+ cells differentially express genes that direct myeloid lineage development and commitment, suggesting that B-myb is a key player in controlling cell fate. Collectively, these studies demonstrate that B-myb is essential for HSC and progenitor maintenance and survival during hematopoiesis. Total RNA was isolated from FACS purified LKS+ cells isolated from pIpC-treated control and B-myb floxed-MxCre mice. Each sample is derived from a pool of 3-5 mice. 2 samples were analyzed for each genotype.
Project description:Autophagy is critical for protecting HSCs from metabolic stress. Here, we used a genetic approach to inactivate autophagy in adult HSCs by deleting the Atg12 gene. We show that loss of autophagy causes accumulation of mitochondria and an oxidative phosphorylation (OXPHOS)-activated metabolic state, which drives accelerated myeloid differentiation likely through epigenetic deregulations rather than transcriptional changes, and impairs HSC self-renewal activity and regenerative potential. To determine how loss of autophagy affects DNA methylation, we conducted enhanced reduce representation bisulfite sequencing (ERRBS) of purified control and Atg12 conditional knockout HSCs. Overall design: Atg12flox/flox:Mx1-Cre conditional knockout mice and control Atg12flox/flox mice were injected with poly(I:C) at 4 week of age, and HSCs (Lin-/c-Kit+/Sca-1+/Flk2-/CD150+/CD48-) were isolated from the bone marrow of individual mice 2-3 months later. DNA was extracted from 4 mice per group, and ERRBS was conducted as described in the methods.
Project description:Autophagy is critical for protecting HSCs from metabolic stress. Here, we used a genetic approach to inactivate autophagy in adult HSCs by deleting the Atg12 gene. We show that loss of autophagy causes accumulation of mitochondria and an oxidative phosphorylation (OXPHOS)-activated metabolic state, which drives accelerated myeloid differentiation likely through epigenetic deregulations rather than transcriptional changes, and impairs HSC self-renewal activity and regenerative potential. To determine how loss of autophagy affects gene expression, we conducted microarray analysis of purified control and Atg12 conditional knockout HSCs. Overall design: Atg12flox/flox:Mx1-Cre conditional knockout mice and control Atg12flox/flox mice were injected with poly(I:C) at 4 week of age, and HSCs (Lin-/c-Kit+/Sca-1+/Flk2-/CD150+/CD48-) were isolated from the bone marrow of individual mice 2-3 months later. RNA was extracted, and microarray analysis was conducted with Affymetrix Gene ST 1.0 microarrays as described in the methods.
Project description:Quiescent hepatic stem cells (HSCs) can be activated when hepatocyte proliferation is compromised. Chemical injury rodent models have been widely used to study the locazation, biomarkers, and signaling pathways in HSCs, but these models usually exhibit severe promiscuous toxicity and fail to distinguish damaged and non-damaged cells. Our goal is to establish new animal models to overcome these limitations, thereby providing new insights into HSC biology and application. We generated mutant mice with constitutive or inducible deletion of Damaged DNA Binding protein 1 (DDB1), an E3 ubiquitin ligase, in hepatocytes. We show that deletion of DDB1 abolishes self-renewal capacity of mouse hepatocytes in vivo, leading to compensatory activation and proliferation of DDB1-expressing OCs. Importantly, the DDB1 mutant mice exhibit very minor liver damage, compared to a chemical injury model. Microarray analysis reveals several previously unrecognized markers, enriched in oval cells. This genetic model in which irreversible inhibition of hepatocyte duplication results in HSC-driven liver regeneration. The DDB1 mutant mice can be broadly applied to studies of HSC differentiation, HSC niche and HSCs as origin of liver cancer. Total RNA obtained from isolated EpCAM+ cells from DDB1 mutant mice compared to wild type hepatocytes
Project description:Autophagy deficiency caused by conditional knockout of Atg7 results in severe hepatitis accompanied by abundant accumulation of p62. p62 stablizes Nrf2 by disrupting the association between Keap1 and Nrf2. To understand the pathogenesis of hepatitis under the autophagy deficiency, we examined gene expression profiles of livers from Atg7-null, Nrf2-null and Atg7-Nrf2 double mutant mice. Overall design: Eight week old Atg7F/F:Mx1-Cre mice and Atg7F/F:Mx1-Cre:Nrf2-/- together with control mice were injected with pIpC. At 4 weeks after pIpC injection, total RNAs were purified from each mouse liver.
Project description:Meis1 encodes a TALE family homeodomain protein that was first identified as a common retroviral integration site in mouse BHX2 myeloid leukemia. It functions as a DNA binding co-factor of Hox proteins through interacting with Pbx, a member of another TALE family protein. Moreover, Meis1 homozygous knockout mice are embryonic lethal, showing significant defects in vasculogenesis, eye development and hematopoiesis. Severe defects were also observed in adult hematopoiesis by conditional inactivation of Meis1 in vivo. Meis1 is critical to maintain the balance between enter and exit from cell cycles of hematopoietic stem cells (HSCs), indicating that Meis1 regulates self-renewal and quiescence of HSCs. Total RNA was isolated from KSL cells obtained from poly(I:C)-treated Mx1-Cre Meis1fl/fl and sham-treated Meis1fl/fl mice.