Project description:Bone marrow hematopoietic stem cells (HSCs) are crucial to maintain lifelong production of all blood cells. Although HSCs divide infrequently, it is thought that the entire HSC pool turns over every few weeks, suggesting that HSCs regularly enter and exit cell cycle. Here, we combine flow cytometry with label-retaining assays (BrdU and histone H2B-GFP) to identify a population of dormant mouse HSCs (d-HSCs) within the lin(-)Sca1+cKit+CD150+CD48(-)CD34(-) population. Computational modeling suggests that d-HSCs divide about every 145 days, or five times per lifetime. d-HSCs harbor the vast majority of multilineage long-term self-renewal activity. While they form a silent reservoir of the most potent HSCs during homeostasis, they are efficiently activated to self-renew in response to bone marrow injury or G-CSF stimulation. After re-establishment of homeostasis, activated HSCs return to dormancy, suggesting that HSCs are not stochastically entering the cell cycle but reversibly switch from dormancy to self-renewal under conditions of hematopoietic stress
Project description:Long-term hematopoietic stem cells are rare, highly quiescent stem cells of the hematopoietic system with life-long self-renewal potential and the ability to transplant and reconstitute the entire hematopoietic system of conditioned recipients. Most of our understanding of these rare cells has relied on cell surface identification, epigenetic and transcriptomic analyses. Our knowledge of protein synthesis, folding, modification and degradation – broadly termed protein homeostasis or “proteostasis” – in these cells is still in its infancy. Here we report the requirement of the small phospho-binding adaptor proteins, the cyclin dependent kinase subunits (Cks1 and Cks2), for maintaining ordered hematopoiesis and long-term hematopoietic stem cell reconstitution. Cks1 and Cks2 are critical regulators of a myriad of key intracellular signalling pathways that govern hematopoietic stem cell biology and together they balance protein homeostasis and restrain reactive oxygen species to ensure healthy hematopoietic stem cell function.
Project description:Our study disclosed previously unrecognized heterogeneity in fetal liver (FL) hematopoietic stem cells (HSC), highlighting biosynthetic dormancy as a key to symmetric self-renewal of engraftable HSC and supports recent studies demonstrating distinct developmental origins for multipotent progenitors and HSC in definitive hematopoiesis.
Project description:MTD project_description Inflammation and decreased stem cell function characterize organism aging, yet the relationship between these factors remains incompletely understood. This study shows that aged hematopoietic stem and progenitor cells exhibit increased ground-stage NF-κB activity, which enhances their responsiveness to undergo differentiation and loss of self-renewal in response to inflammation. The study identifies Rad21/cohesin as a critical mediator of NF-κB signals, by increasing chromatin accessibility of inter-/intra-genic and enhancer regions. Rad21/NF-κB are required for normal differentiation, but limit self-renewal of hematopoietic stem cells (HSCs) during aging and inflammation in an NF-κB dependent manner. HSCs from aged mice fail to downregulate Rad21/cohesin and inflammation/differentiation inducing signals in the resolution phase after acute inflammation. and The inhibition of cohesin/NF-κB is sufficient to revert the hypersensitivity of aged HSPCs to inflammation-induced differentiation. During aging, myeloid-biased HSCs with disrupted and naturally occurring reduced expression of Rad21/cohesin are increasingly selected over lymphoid-biased HSCs. Together, Rad21/cohesin mediated NF-κB signaling limits HSPC function during aging and selects for cohesin deficient HSCs with myeloid skewed differentiation.
Project description:Increasing evidence links metabolic activity and cell growth to decline in hematopoietic stem cell (HSC) function during aging. The Lin28b/Hmga2 pathway controls tissue development and in the hematopoietic system the postnatal downregulation of this pathway causes a decrease in self renewal of adult HSCs compared to fetal HSCs. Igf2bp2 is an RNA binding protein and a mediator of the Lin28b/Hmga2 pathway, which regulates metabolism and growth signaling by influencing RNA stability and translation of its target genes. It is currently unknown whether Lin28/Hmga2/Igf2bp2 signaling impacts on aging-associated impairments in HSC function and hematopoiesis. Here, we analyzed homozygous Igf2bp2 germline knockout mice and wildtype control animals to address this question. The study shows that Igf2bp2 deletion rescues aging phenotypes of the hematopoietic system, such as the expansion of HSC numbers in bone marrow and the biased increase of myeloid cells in peripheral blood. This rescue of hematopoietic aging coincides with reduced mitochondrial metabolism and glycolysis in Igf2bp2-/- HSCs compared to Igf2bp2+/+ HSCs. Conversely, Igf2bp2 overexpression activates protein synthesis pathways in HSCs and leads to a rapid loss of self renewal by enhancing myeloid skewed differentiation in an mTOR/PI3K-dependent manner. Together, these results show that Igf2bp2 regulates energy metabolism and growth signaling in HSCs and that the activity of this pathways influences self renewal, differentiation, and aging of HSCs.
Project description:The transcription factor Runx1 is essential for the establishment of definitive hematopoiesis during embryonic development. In adult blood homeostasis, Runx1 plays a pivotal role in the maturation of lymphocytes and megakaryocytes. Furthermore, Runx1 is required for the regulation of hematopoietic stem and progenitor cell (HSPC) pools. However, how Runx1 orchestrates self-renewal and lineage choices in combination with other factors is not well understood. Here we describe a genome-scale RNAi screen to detect genes that cooperate with Runx1 in regulating HSPCs. We identify the polycomb group protein Pcgf1 as an epigenetic regulator involved in hematopoietic cell differentiation. We show that simultaneous depletion of Runx1 and Pcgf1 allows sustained self-renewal while blocking differentiation of HSPCs in vitro. We find an upregulation of HoxA cluster genes upon Pcgf1 knockdown that possibly accounts for the increase in self-renewal. Further, our data suggest that cells lacking both Runx1 and Pcgf1 are blocked at an early progenitor stage, indicating that a concerted action of the transcription factor Runx1 together with the epigenetic repressor Pcgf1 is necessary for terminal differentiation. Thus, our work discovers a genetic link between transcriptional and epigenetic regulation that is required for hematopoietic differentiation. Hematopoietic stem and precursor cells freshly isolated from mice were transduced with an shRNA targeting Pcgf1 or a control shRNA. Cells were selected with puromycin for 36 h before total mRNA was isolated.
Project description:Hematopoietic stem cells (HSCs) represent a rare population of cells residing in the Bone Marrow (BM) at the top of hematopoietic hierarchy. A critical balance is maintained between self-renewal and lineage differentiation of HSCs to maintain hematopoietic homeostasis. With aging, this balance is altered with an increase of self-renewal long term HSCs and a myeloid biased differentiation, which favors the appearance of myeloid leukemias and anemias. This experiment aims to understand molecular mechanisms that cause this aged-related disequilibrium in the mouse. To this end, we generated single cell RNA-seq data from pools of young and old hematopoietic stem and progenitor cells (HSPCs), isolated from mouse BMs.
Project description:The balance of self-renewal and differentiation is crucial to ensure the homeostasis of the hematopoietic system, and is a key hallmark of hematopoietic stem cells (HSCs); however, the underlying molecular pathways are not completely understood, including the role of micro-RNAs. To assess micro-RNA contributions, we performed micro-RNA profiling of HSCs and their immediate downstream progeny multi-potent progenitors (MPPs) from wild type control and Pbx1-conditional knockout mice, whose HSCs display a profound self-renewal defect.
Project description:Hematopoietic stem cell metabolic requirements change with their cell cycle activity. However, the underlying role of mitochondria remain ill-defined. The goal of our study is to investigate how hematopoietic stem cells use mitochondria during cell division to control their fate and self-renewal activity. We found that after mitochondrial activation with replication, HSC irreversibly remodel the mitochondrial network and this network is not repaired after HSC re-entry into quiescence. HSC keep and accumulate dysfunctional mitochondria through asymmetric segregation during active division. Single cell RNA seq and bioinformatic analysis are used to characterize hematopoietic stem cell functions before and after replicative stress to uncover novel key drivers that limit hematopoietic stem cell self-renewal after replicative stress.
Project description:How hematopoietic stem cells (HSCs) maintain metabolic homeostasis to support tissue repair and regeneration throughout the lifespan is elusive. Here we show that CD38, a NAD+ metabolic enzyme, promotes HSC proliferation by inducing mitochondrial Ca2+ influx and mitochondrial metabolism at young age. Conversely, aberrant CD38 upregulation during aging is a driver of HSC deterioration due to compromised mitochondrial stress management. Pharmacological inactivation of CD38 reverses HSC aging and the pathophysiological changes of the aging hematopoietic system. Blocking mitochondrial Ca2+ influx inhibits HSC proliferation at young age yet prevents HSC aging. Our study highlights a NAD+ metabolic checkpoint that balances mitochondrial activation to support HSC proliferation and mitochondrial stress to enhance HSC self-renewal throughout the lifespan, and links aberrant Ca2+ signaling to HSC aging.