Capacity Of Hematopoietic Stem Cells Research Articles

USP4 regulates ribosome biogenesis and protein synthesis for hematopoietic stem cell regeneration and leukemia progression.

Enhanced ribosome biogenesis and protein synthesis are required for cell proliferation. During hematopoietic regeneration, hematopoietic stem cells (HSCs) proliferate rapidly to replenish the hematopoietic system. How HSCs respond and regulate ribosome biogenesis and protein synthesis during regeneration remains unclear. Here, we analyzed the expression of a series of ubiquitin-specific-proteases (USPs) during HSC regeneration. We found USP4 expression is significantly increased in proliferating HSCs. Further functional and mechanistic investigations revealed a crucial regulatory function of USP4 in HSC regeneration and leukemia progression by modulating ribosome biogenesis and protein synthesis. USP4 deubiquitinates and stabilizes PES1 to facilitate ribosome biogenesis and protein synthesis in proliferative HSCs and leukemic cells. Usp4 deletion significantly decreases protein synthesis, proliferation and reconstitution capacity of HSCs. Usp4 inhibition suppresses ribosome biogenesis and proliferation of leukemic cells, and prolongs the survival of AML (Acute myeloid leukemia) mice. These findings provide a new insight into the response mechanism of ribosome biogenesis and protein synthesis in HSCs, and their contribution to leukemia progression.

Effect of Post-transplant Dietary Restriction on Hematopoietic Reconstitution and Maintenance of Reconstitution Capacity of Hematopoietic Stem Cells.

Hematopoietic cell transplantation (HCT) is an important therapy for many hematological malignancies as well as some non-malignant diseases. Post-transplant hematopoiesis is affected by multiple factors, and the mechanisms of delayed post-transplant hematopoiesis remain poorly understood. Patients undergoing HCT often suffer from significantly reduced food intake due to complications induced by preconditioning treatments. Here, we used a dietary restriction (DR) mouse model to study the effect of post-transplant dietary reduction on hematopoiesis and hematopoietic stem cells (HSCs). We found that post-transplant DR significantly inhibited both lymphopoiesis and myelopoiesis in the primary recipient mice. However, when bone marrow cells (BMCs) from the primary recipient mice were serially transplanted into secondary and tertiary recipient mice, the HSCs derived from the primary recipient mice, which were exposed to post-transplant DR, exhibited a much higher reconstitution capacity. Transplantation experiments with purified HSCs showed that post-transplant DR greatly inhibited hematopoietic stem cell (HSC) expansion. Additionally, post-transplant DR reshaped the gut microbiotas of the recipient mice, which inhibited inflammatory responses and thus may have contributed to maintaining HSC function. Our findings may have important implications for clinical work because reduced food intake and problems with digestion and absorption are common in patients undergoing HCT.

Systemic knockout of Tmem175 results in aberrant differentiation but no effect on hematopoietic reconstitution

Lysosomes play crucial roles in regulating cell metabolism, and K+ channels are critical for controlling various aspects of lysosomal function. Additionally, lysosomal activity is essential for maintaining the quiescence of hematopoietic stem cells (HSCs) under both steady-state and stress conditions. Tmem175 is a lysosomal potassium channel protein. To further investigate the role of K+ channels in HSCs, our study employed knockout mice to examine the function of Tmem175. Our research findings demonstrate that the deletion of Tmem175 does not disrupt the functionality of HSCs in both stable and stressed conditions, including irradiation and intraperitoneal 5-FU injections. However, we did observe that the absence of Tmem175 impairs the long-term differentiation capacity of HSCs into myeloid differentiated subpopulation cells（In this paper, it is referred to simply as M cells）in HSC transplantation test, while promoting their differentiation into T cells. This suggests that Tmem175 plays a role in the lineage differentiation of HSCs without being essential for their self-renewal or long-term regenerative capabilities.

Heart failure promotes multimorbidity through innate immune memory.

Patients with heart failure (HF) often experience repeated acute decompensation and develop comorbidities such as chronic kidney disease and frailty syndrome. Although this suggests pathological interaction among comorbidities, the mechanisms linking them are poorly understood. Here, we identified alterations in hematopoietic stem cells (HSCs) as a critical driver of recurrent HF and associated comorbidities. Bone marrow transplantation from HF-experienced mice resulted in spontaneous cardiac dysfunction and fibrosis in recipient mice, as well as increased vulnerability to kidney and skeletal muscle insults. HF enhanced the capacity of HSCs to generate proinflammatory macrophages. In HF mice, global chromatin accessibility analysis and single-cell RNA-seq showed that transforming growth factor-β (TGF-β) signaling was suppressed in HSCs, which corresponded with repressed sympathetic nervous activity in bone marrow. Transplantation of bone marrow from mice in which TGF-β signaling was inhibited similarly exacerbated cardiac dysfunction. Collectively, these results suggest that cardiac stress modulates the epigenome of HSCs, which in turn alters their capacity to generate cardiac macrophage subpopulations. This change in HSCs may be a common driver of repeated HF events and comorbidity by serving as a key carrier of "stress memory."

Ultraviolet Light-Emitting Diode Radiation Kills Leukemia Cells Without Affecting Hematopoiesis of Hematopoietic Stem Cells in Mice.

The eradication of leukemia cells while sparing hematopoietic stem cells in the graft before autologous hematopoietic stem cell transplant is critical to prevention of leukemia relapse. Proliferating cells have been shown to be more prone to apoptosis than differentiated cells in response to ultraviolet radiation; however, whether leukemia cells are more sensitive to ultraviolet LED radiation than hematopoietic stem cells remains unclear. We compared the in vitro responses between murine leukemia L1210 cells and murine hematopoietic stem cells to 280-nm ultraviolet LED radiation. We also investigated the effects of ultraviolet LED radiation on the tumorigenic and metastatic capacity of L1210 cells and hematopoietic stem cell hematopoiesis in a mouse model of hematopoietic stem cell transplant. L1210 cells were more sensitive to ultraviolet LED radiation than hematopoietic stem cells in vitro, as evidenced by significantly reduced colony formation rates and cell proliferation rates, along with remarkably increased apoptosis rates in L1210 cells. Compared with corresponding unirradiated cells, ultraviolet LED-irradiated L1210 cells failed to generate palpable tumors in mice, whereas ultraviolet LED-irradiated bone marrow cells restored hematopoiesis in vivo. Furthermore, transplant with an irradiated mixture of L1210 cells and bone marrow cells showed later onset of leukemia, milder leukemic infiltration, and prolonged survival in mice, compared with unirradiated cell transplant. Our results suggest that ultraviolet LED radiation can suppress the proliferative and tumorigenic abilities of leukemia cells without reducing the hematopoietic reconstitution capacity of hematopoietic stem cells, serving as a promising approach to kill leukemia cells in autograft before autologous hematopoietic stem cell transplant.

NEAR-INFRARED DYE IR-780 ALLEVIATES HEMATOPOIETIC SYSTEM DAMAGE BY PROMOTING HEMATOPOIETIC STEM CELLS INTO QUIESCENCE.

Potential radiation exposure is a general concern, but there still lacks radioprotective countermeasures. Here, we found a small molecular near-infrared dye IR-780, which promoted hematopoietic stem cells (HSCs) into quiescence to resist stress. When mice were treated with IR-780 before stress, increased HSC quiescence and better hematopoietic recovery were observed in mice in stress conditions. However, when given after radiation, IR-780 did not show obvious benefit. Transplantation assay and colony-forming assay were carried out to determine self-renewal ability and repopulation capacity of HSCs. Furthermore, IR-780 pretreatment reduced the generation of reactive oxygen species (ROS) and DNA damage in HSCs after radiation. In homeostasis, the percentage of Lineage - , Sca-1 + , and c-Kit + cells and long-term HSCs (LT-HSCs) were improved, and more HSCs were in G0 state after administration of IR-780. Further investigations showed that IR-780 selectively accumulated in mitochondria membrane potential high LT-HSCs (MMP-high LT-HSCs). Finally, IR-780 promoted human CD34 + HSC reconstruction ability in NOD-Prkdc scid Il2rg null mice after transplantation and improved repopulation capacity in vitro culture. Our research showed that IR-780 selectively entered MMP-high LT-HSCs and promoted them into dormancy, thus reducing hematopoietic injury and improving regeneration capacity. This novel approach might hold promise as a potential countermeasure for radiation injury.

Ferritin-mediated mitochondrial iron homeostasis is essential for the survival of hematopoietic stem cells and leukemic stem cells.

Iron metabolism plays a crucial role in cell viability, but its relationship with adult stem cells and cancer stem cells is not fully understood. The ferritin complex, responsible for intracellular iron storage, is important in this process. We report that conditional deletion of ferritin heavy chain 1 (Fth1) in the hematopoietic system reduced the number and repopulation capacity of hematopoietic stem cells (HSCs). These effects were associated with a decrease in cellular iron level, leading to impaired mitochondrial function and the initiation of apoptosis. Iron supplementation, antioxidant, and apoptosis inhibitors reversed the reduced cell viability of Fth1-deleted hematopoietic stem and progenitor cells (HSPCs). Importantly, leukemic stem cells (LSCs) derived from MLL-AF9-induced acute myeloid leukemia (AML) mice exhibited reduced Fth1 expression, rendering them more susceptible to apoptosis induced by the iron chelation compared to normal HSPCs. Modulating FTH1 expression using mono-methyl fumarate increased LSCs resistance to iron chelator-induced apoptosis. Additionally, iron supplementation, antioxidant, and apoptosis inhibitors protected LSCs from iron chelator-induced cell death. Fth1 deletion also extended the survival of AML mice. These findings unveil a novel mechanism by which ferritin-mediated iron homeostasis regulates the survival of both HSCs and LSCs, suggesting potential therapeutic strategies for blood cancer with iron dysregulation.

Tgfb1 deficiency impairs the self-renewal capacity of murine hematopoietic stem/progenitor cells in vivo

Transforming growth factor β1 (TGFB1) refers to a pleiotropic cytokine exerting contrasting roles in hematopoietic stem cells (HSCs) functions in vitro and in vivo. However, the understanding of hematopoiesis in vivo, when TGFB1 is constantly deactivated, is still unclear, mainly due to significant embryonic lethality and the emergence of a fatal inflammatory condition, which makes doing these investigations challenging. Our study aims to find the specific role of TGFB1 in regulating hematopoiesis in vivo. We engineered mice strains (Vav1 or Mx1 promoter-driven TGFB1 knockout) with conditional knockout of TGFB1 to study its role in hematopoiesis in vivo. In fetal and adult hematopoiesis, TGFB1 KO mice displayed deficiency and decreased self-renewal capacity of HSCs with myeloid-biased differentiation. The results were different from the regulating role of TGFB1 in vitro. Additionally, our results showed that TGFB1 deficiency from fetal hematopoiesis stage caused more severe defect of HSCs than in the adult stage. Mechanistically, our findings identified TGFB1-SOX9-FOS/JUNB/TWIST1 signal axis as an essential regulating pathway in HSCs homeostasis. Our study may provide a scientific basis for clinical HSC transplantation and expansion.

Age-related noncanonical TRMT6-TRMT61A signaling impairs hematopoietic stem cells.

Aged hematopoietic stem cells (HSCs) exhibit compromised reconstitution capacity and differentiation bias toward myeloid lineages. However, the molecular mechanism behind HSC aging remains largely unknown. In this study, we observed that RNA N1-methyladenosine-generating methyltransferase TRMT6-TRMT61A complex is increased in aged murine HSCs due to aging-declined CRL4DCAF1-mediated ubiquitination degradation signaling. Unexpectedly, no difference of tRNA N1-methyladenosine methylome is observed between young and aged hematopoietic stem and progenitor cells, suggesting a noncanonical role of the TRMT6-TRMT61A complex in the HSC aging process. Further investigation revealed that enforced TRMT6-TRMT61A impairs HSCs through 3'-tiRNA-Leu-CAG and subsequent RIPK1-RIPK3-MLKL-mediated necroptosis cascade. Deficiency of necroptosis ameliorates the self-renewal capacity of HSCs and counters the physiologically deleterious effect of enforced TRMT6-TRMT61A on HSCs. Together, our work uncovers a nonclassical role for the TRMT6-TRMT61A complex in HSC aging and highlights a therapeutic target.

Atg4a Promotes Mitochondrial Quality Control and Hemoglobin Production In Vivo

Mitochondrial quality control is essential for maintaining cellular homeostasis and contributes to the regenerative capacity of hematopoietic stem cells and the differentiation of lineage-committed progeny. During red blood cell (RBC) production, mitochondria contribute to the production of hemoglobin and are the site for heme synthesis. Mitochondrial dysfunction is found in patients with mtDNA mutations, sickle cell disease, and myelodysplastic syndromes; therefore, it is critical to delineate the molecular mediators of mitochondrial quality control during erythropoiesis. While it is established that autophagy contributes to mitochondrial clearance during reticulocyte maturation, less is known about the regulation of mitochondrial quality control in erythroid progenitors. Our previous study identified an erythroid-specific role for the autophagy-related protease ATG4A in human erythropoiesis (Stolla MC et al., Blood Advances, 2022). To better understand the contribution of Atg4a-dependent autophagy to erythropoiesis in vivo, we have developed a new genetically modified mouse model . To evaluate the role of Atg4a in vivo, we disrupted the expression of Atg4a by targeting exons 5/6 using CRISPR/Cas9 in C57/BL6 embryos. Analysis of the peripheral blood of adult Atg4a-/- (KO) and Atg4a+/+ (WT) mice revealed a normal hematocrit (47.5% WT vs. 47% KO), but elevated numbers of red blood cells (10.7 M/μL WT vs. 11.2 M/μL KO, p=0.012) and a compensatory 5.8 % decrease in RBC volume (MCV: 44.3 fl WT vs. 41.7 fl KO, p=0.0004). Consistent with a reduction in RBC size, we observed a modest reduction in total hemoglobin (16.8 g/dl WT vs. 16.0 g/dl KO, p=0.054) and a profound decrease in the mean corpuscular hemoglobin concentration (MCHC: 35.39 g/dl WT vs. 34.17 g/dl KO, p=0.038) in Atg4a -/- (KO) mice. To determine if Atg4a-/- mice are iron deficient, we evaluated iron parameters in peripheral blood. While Atg4a-/- mice had slightly lower values of serum iron (152 μg/dl WT vs. 128.7 μg/dl KO, p=0.21) and total-iron binding capacity (511 μg/dl WT vs. 456 μg/dl KO, p=0.04) they had comparable levels of transferrin saturation (29.9% WT vs. 28.1% KO, p=0.65). Furthermore, we found similar amounts of EPO in the serum of Atg4a-/- and Atg4a+/+ mice (314 pg/ml WT vs. 345 pg/ml KO, p=0.78). Thus, loss of Atg4a leads to a reduction in hemoglobin production and RBC size without overt iron deficiency. To determine if alterations in erythroid maturation contributed to the decrease in MCV and MCHC, we used flow cytometry to quantify bone marrow erythroid progenitors (I), basophilic erythroblasts (II), polychromatic and orthochromatic erythroblasts (III), and reticulocytes (IV) using CD44, Ter119, CD71, and lineage markers (CD11b, B220, Gr-1) in Atg4a-/- mice. Similar numbers of erythroid populations (I-IV) were observed in the bone marrow and spleen of Atg4a-/- and Atg4a+/+ mice suggesting that erythroid maturation was not significantly altered in vivo. Since Atg4a is known to facilitate mitochondrial clearance during human erythropoiesis, we next evaluated mitochondrial dynamics in murine erythroid populations I-IV using dyes for active (TMRM) and total mitochondria (Mitotracker Green, MTG). Compared to Atg4a+/+ mice, Atg4a-/- mice had increased MTG fluorescence in erythroid populations I and II and a 25% decrease in TMRM fluorescence. Therefore, loss of Atg4a significantly reduces the ratio of active-to-total mitochondria in erythroid progenitors and basophilic erythroblasts, indicating that elimination of inactive mitochondria promotes mitochondrial function early in erythropoiesis. Since mitochondria are the site for heme synthesis, we sorted erythroid populations from Atg4a-/- and Atg4a+/+ mice and measured total heme content. While in Atg4a +/+ mice heme content increased by 3-fold between erythroid populations III and IV, heme content did not increase between erythroid populations III and IV from Atg4a-/- mice resulting in significantly reduced heme content in reticulocytes. Our study highlights an important protective role for autophagy in erythropoiesis where it mediates the elimination of dysfunctional mitochondria. Loss of mitochondrial quality control restricts heme production reducing the hemoglobin concentration of circulating RBCs. Further investigation will determine if the absence of Atg4a compromises the response to stress erythropoiesis.

The ATF4-RPS19BP1 Axis Modulates Ribosome Biogenesis to Promote Erythropoiesis

The function of hematopoietic stem cells (HSCs) and the process of hematopoiesis are intricately governed by a complex interplay of intrinsic programs and extrinsic signals from the microenvironment (Crane et al., Nat Rev Immunol, 2017). Previous work reported by our group and others has demonstrated that ATF4, a basic region-leucine zipper transcription factor, plays pivotal roles in fetal liver hematopoiesis, HSC maintenance, bone formation and tumorigenesis (Zhao et al., Blood, 2015; Sun et al., Sci Adv, 2021; Yang et al., Cell, 2004). However, the precise function of ATF4 in the bone marrow niche and how ATF4 regulates adult hematopoiesis remain largely unknown. Here, we employ four cell-type-specific mouse Cre lines to conditionally knock out Atf4 in Cdh5 + endothelial cells (ECs), Prx1 + bone marrow stromal cells (BMSCs), Osx + osteo-progenitor cells, and Mx1 + hematopoietic cells, and uncover the role of Atf4 in niche cells and hematopoiesis. We found that Atf4 deletion in BMSCs reduced BMSC numbers and impaired their CFU-F activity as well as differentiation toward osteoblasts, but spares hematopoiesis and HSC function in adult mice. Furthermore, Atf4 depletion in the ECs or osteo-progenitors of adult mice has a very mild effect on the BM hematopoiesis and HSC maintenance. Intriguingly, Atf4 depletion in the hematopoietic system resulted in severe anemia. More than 70% of the Mx1cre; Atf4 fl/fl (Δ/Δ) mice gradually died from anemia. Atf4 deficiency markedly reduced the frequency of erythroid progenitor cells (EPCs) (including MEP, PreCFU-E, and CFU-E cells) and impaired their CFU-E and BFU-E colony-forming ability. Atf4 depletion severely impaired the repopulation ability of BM cells and the self-renewal capacity of HSCs. Single cell RNA-seq (scRNA-seq) analysis of BM Lin -cKit + cells confirmed the defects of erythropoiesis after Atf4 depletion. The absence of ATF4 compelled early erythroid progenitors to enter the S phase, which led to replication stress and in turn activated both the DNA damage response and apoptosis. Subsequently, we conducted an integrative analysis of the genes that were identified as downregulated in MEPs by RNA-seq, ATAC-seq, and H3K4me3 Cut&Tag and genes that were identified as downregulated in erythroid progenitors (i.e., PreMegE, Ery1, and Ery2) by scRNA-seq, which predicted Rps19bp1 as the top target gene of Atf4. Luciferase reporter and quantitative chromatin immunoprecipitation (qChIP) assays confirmed that ATF4 was a transcriptional activator of Rps19bp1. Downregulation of Rps19bp1 caused by Atf4 deletion led to decreased assembles of 40S proteins, such as RPS3, RPS6 and RPS19. O-propargyl-puromycin (OP-Puro) incorporation and SUnSET assay further confirmed the global protein synthesis defect in Atf4-deficient MEP cells. The protein synthesis defects and impaired erythropoiesis were rescued upon RPS19BP1 overexpression in Atf4 knockdown MEL cell line or BM cKit + cells from Atf4-deficient mice. Ribosome profiling of CMP cells from Δ/Δ and fl/fl mice further demonstrated that the expression of proteins involved in ribosome biogenesis was significantly lower in Atf4-depleted than in wildtype CMP cells. The expression of gene sets linked to PreCFU-E signature was also lower in Atf4-depleted than in wildtype CMPs, suggesting that the reduction in ribosome biogenesis significantly affected the translation efficiency of erythroid-related pathway components, thereby impeding erythroid lineage commitment. Finally, we demonstrate that under conditions of 5-fluorouracil-induced stress, Atf4 depletion impedes the recovery of hematopoietic lineages, which requires efficient ribosome biogenesis. Taken together, we demonstrated that, unlike in the fetal liver, ATF4 governs adult HSC function and erythropoiesis in a cell-intrinsic manner. We revealed a novel role for ATF4 in erythropoiesis, which links it to RPS19BP1, ribosome biogenesis and protein translation. Our findings have highlighted the crucial importance of protein synthesis regulation during erythroid lineage commitment. This discovery will likely have extended implications for understanding and treating ribosomopathy-associated erythroid failure.

VLA-4 Agonist Enhances the Capacity of HSC Engraftment and Immune Reconstitution

Poor donor cell implantation and delayed hematopoietic reconstitution are important factors affecting the prognosis of patients after allogeneic hematopoietic stem cell transplantation (Allo-HSCT). However, our understanding of the critical endogenous signals that reconstitute hematopoiesis in transplant patients remains limited，which is essential for achieving targeted interventions and preventing donor-recipient chimeric states after transplantation. Here, we revealed the reconstitution dynamics of human allogeneic hematopoietic stem and progenitor cells (HSPCs) and immune cell subpopulations in the post-transplantation mixed donor chimerism (MDC) to fully donor chimerism (FDC) state at single-cell resolution. The hematopoietic stem cell (HSC) implantation process involves extensive interactions with immune cells mainly through surface Kcnq5, Itga4 (encoding a subunit of VLA-4), Tfrc, CD44 receptor, and ligands for Rps19, B2m, etc. Further identification of VLA-4(integrin α4β1) as a potential regulatory target for HSC implantation by single-cell sequencing of a stable allogeneic bone marrow transplantation (Allo-BMT) MDC-FDC mouse model. Grafts Itgα4 and Itgβ1 deletion impair donor implantation and further diminish the efficacy of donor lymphocyte infusion (DLI) following Allo-BMT, rather than directly affecting DLI. Critically, we identified a VLA-4 agonist that promotes donor implantation in the mixed chimeric mouse model of Allo-BMT in a time-dependent manner, with the most pronounced promotion of early T cell implantation in particular. Moreover, it was found to enhance the self-renewal capacity of HSC and lymphoid reconstitution in competitive transplantation and human umbilical cord blood transplantation xenograft experiments. Fortunately, VLA-4 agonist does not exacerbate the acute graft-versus-host disease(aGVHD) process while maintaining the graft-versus-leukemia (GVL) effect. VLA-4 agonist not only upregulates of both Itgα4 and Itgβ1 expression, but also promotes the ERK/2 phosphorylation pathway, which affects HSC biological functions, and this process can be inhibited by ERK kinase inhibitors. These results provide insights into the regenerative process of transplanted HSPCs in human patients，and demonstrate a previously unknown positive regulation of HSC engraftment and immune reconstitution by VLA-4, and allow for a new and simple translational strategy to enhance HSC transplantation.

Nicotinamide riboside intervention alleviates hematopoietic system injury of ionizing radiation-induced premature aging mice.

Radiotherapy destroys cancer cells and inevitably harms normal human tissues, causing delayed effects of acute radiation exposure (DEARE) and accelerating the aging process in most survivors. However, effective methods for preventing premature aging induced by ionizing radiation are lacking. In this study, the premature aging mice of DEARE model was established after 6 Gy total body irradiation (TBI). Then the therapeutic effects and mechanism of nicotinamide riboside on the premature aging mice were evaluated. The results showed that 6 Gy TBI induced premature aging of the hematopoietic system in mice. Nicotinamide riboside treatment reversed aging spleen phenotypes by inhibiting cellular senescence and ameliorated serum metabolism profiles. Further results demonstrated that nicotinamide riboside supplementation alleviated the myeloid bias of hematopoietic stem cells and temporarily restored the regenerative capacity of hematopoietic stem cells probably by mitigating the reactive oxygen species activated GCN2/eIF2α/ATF4 signaling pathway. The results of this study firstly indicate that nicotinamide riboside shows potential as a DEARE therapeutic agent for radiation-exposed populations and patients who received radiotherapy.

Alkbh5 plays indispensable roles in maintaining self-renewal of hematopoietic stem cells.

Alkbh5 is one of the primary demethylases responsible for reversing N6-methyladenosine (m6A) modifications on mRNAs, and it plays a crucial role in many physiological and pathological processes. Previous studies have shown that Alkbh5 is required for maintaining the function of leukemia stem cells but is dispensable for normal hematopoiesis. In this study, we found that Alkbh5 deletion led to a moderate increase in the number of multiple progenitor cell populations while compromising the long-term self-renewal capacity of hematopoietic stem cells (HSCs). Here, we used RNA-seq and m6A-seq strategies to explore the underlying molecular mechanism. At the molecular level, Alkbh5 may regulate hematopoiesis by reducing m6A modification of Cebpa and maintaining gene expression levels. Overall, our study unveiled an essential role for Alkbh5 in regulating HSC homeostasis and provides a reference for future research in this area.

Foxm1 haploinsufficiency drives clonal hematopoiesis and promotes a stress-related transition to hematologic malignancy in mice.

Clonal hematopoiesis plays a critical role in the initiation and development of hematologic malignancies. In patients with del(5q) myelodysplastic syndrome (MDS), the transcription factor FOXM1 is frequently downregulated in CD34+ cells. In this study, we demonstrated that Foxm1 haploinsufficiency disturbed normal hematopoiesis and conferred a competitive repopulation advantage for a short period. However, it impaired the long-term self-renewal capacity of hematopoietic stem cells, recapitulating the phenotypes of abnormal hematopoietic stem cells observed in patients with MDS. Moreover, heterozygous inactivation of Foxm1 led to an increase in DNA damage in hematopoietic stem/progenitor cells (HSPCs). Foxm1 haploinsufficiency induced hematopoietic dysplasia in a mouse model with LPS-induced chronic inflammation and accelerated AML-ETO9a-mediated leukemogenesis. We have also identified Parp1, an important enzyme that responds to various types of DNA damage, as a target of Foxm1. Foxm1 haploinsufficiency decreased the ability of HSPCs to efficiently repair DNA damage by downregulating Parp1 expression. Our findings suggest that the downregulation of the Foxm1-Parp1 molecular axis may promote clonal hematopoiesis and reduce genome stability, contributing to del(5q) MDS pathogenesis.

ASXL1 disruption preserves CD8 T cell exhaustion-progenitor epigenetic programming during chronic stimulation

Abstract Differentiation of CD8 T cells into a terminally exhausted state is a major hurdle limiting efficacy of both immune checkpoint blockade and adoptive cellular immunotherapy approaches. Prior studies describing disruption of the epigenetic regulators DNMT3A and TET2 in CD8 T cells have revealed a critical role of DNA methylation in repressing the proliferative capacity and effector potential of CD8 T cells during exhaustion. Disruption of these genes has also been noted to preserve the proliferative capacity of hematopoietic stem cells (HSCs), resulting in clonal hematopoiesis (CH) and establishing the broader concept that these epigenetic regulators control cellular developmental potential. In addition to DNMT3A and TET2, the histone modifier ASXL1 is a critical regulator controlling CH. Here we report that disruption of ASXL1 in CD8 T cells preserved a stem-like phenotype denoted by increased TCF1 expression, IFN-γ production during chronic infection. At the chronic stage of infection, ASXL1 KO CD8 T cells retained a heightened ability to undergo a proliferative burst during PD-L1 blockade. Genome-wide epigenetic profiling demonstrated that disruption of ASXL1 resulted in inhibition of DNA methylation accompanied by changes in chromatin accessibility. These data document crosstalk between histone modifications and DNA methylation in regulating the transition of stem-like progenitor T cells into terminally exhausted T cells. Collectively, these data demonstrate that ASXL1 is a novel epigenetic regulator controlling development of exhausted CD8 T cells and represents a novel immunotherapeutic target for improving responses to T cell-based cancer immunotherapy.

Dose-dependent effect of GFI1 expression in the reconstitution and the differentiation capacity of HSCs.

GFI1 is a transcriptional repressor and plays a pivotal role in regulating the differentiation of hematopoietic stem cells (HSCs) towards myeloid and lymphoid cells. Serial transplantation of Gfi1 deficient HSCs repopulated whole hematopoietic system but in a competitive setting involving wild-type HSCs, they lose this ability. The underlying mechanisms to this end are poorly understood. To better understand this, we used different mouse strains that express either loss of both Gfi1 alleles (Gfi1-KO), with reduced expression of GFI1 (GFI1-KD) or wild-type Gfi1/GFI1 (Gfi1-/GFI1-WT; corresponding to the mouse and human alleles). We observed that loss of Gfi1 or reduced expression of GFI1 led to a two to four fold lower number of HSCs (defined as Lin-Sca1+c-Kit+CD150+CD48-) compared to GFI1-WT mice. To study the functional influence of different levels of GFI1 expression on HSCs function, HSCs from Gfi1-WT (expressing CD45.1 + surface antigens) and HSCs from GFI1-KD or -KO (expressing CD45.2 + surface antigens) mice were sorted and co-transplanted into lethally irradiated host mice. Every 4weeks, CD45.1+ and CD45.2 + on different lineage mature cells were analyzed by flow cytometry. At least 16weeks later, mice were sacrificed, and the percentage of HSCs and progenitors including GMPs, CMPs and MEPs in the total bone marrow cells was calculated as well as their CD45.1 and CD45.2 expression. In the case of co-transplantation of GFI1-KD with Gfi1-WT HSCs, the majority of HSCs (81% ± 6%) as well as the majority of mature cells (88% ± 10%) originated from CD45.2 + GFI1-KD HSCs. In the case of co-transplantation of Gfi1-KO HSCs with Gfi1-WT HSCs, the majority of HSCs originated from CD45.2+ and therefore from Gfi1-KO (61% ± 20%); however, only a small fraction of progenitors and mature cells originated from Gfi1-KO HSCs (<1%). We therefore in summary propose that GFI1 has a dose-dependent role in the self-renewal and differentiation of HSCs.

Dynamics of Chromatin Accessibility During Hematopoietic Stem Cell Differentiation Into Progressively Lineage-Committed Progeny.

Epigenetic mechanisms regulate the multilineage differentiation capacity of hematopoietic stem cells (HSCs) into a variety of blood and immune cells. Mapping the chromatin dynamics of functionally defined cell populations will shed mechanistic insight into 2 major, unanswered questions in stem cell biology: how does epigenetic identity contribute to a cell type's lineage potential, and how do cascades of chromatin remodeling dictate ensuing fate decisions? Our recent work revealed evidence of multilineage gene priming in HSCs, where open cis-regulatory elements (CREs) exclusively shared between HSCs and unipotent lineage cells were enriched for DNA binding motifs of known lineage-specific transcription factors. Oligopotent progenitor populations operating between the HSCs and unipotent cells play essential roles in effecting hematopoietic homeostasis. To test the hypothesis that selective HSC-primed lineage-specific CREs remain accessible throughout differentiation, we used ATAC-seq to map the temporal dynamics of chromatin remodeling during progenitor differentiation. We observed epigenetic-driven clustering of oligopotent and unipotent progenitors into distinct erythromyeloid and lymphoid branches, with multipotent HSCs and MPPs associating with the erythromyeloid lineage. We mapped the dynamics of lineage-primed CREs throughout hematopoiesis and identified both unique and shared CREs as potential lineage reinforcement mechanisms at fate branch points. Additionally, quantification of genome-wide peak count and size revealed overall greater chromatin accessibility in HSCs, allowing us to identify HSC-unique peaks as putative regulators of self-renewal and multilineage potential. Finally, CRISPRi-mediated targeting of ATACseq-identified putative CREs in HSCs allowed us to demonstrate the functional role of selective CREs in lineage-specific gene expression. These findings provide insight into the regulation of stem cell multipotency and lineage commitment throughout hematopoiesis and serve as a resource to test functional drivers of hematopoietic lineage fate.

Temporal dynamics of TNF-mediated changes in hematopoietic stem cell function and recovery

While tumor necrosis factor (TNF) is a critical mediator of appropriate immune response and tissue repair, its misregulation is linked to cancer, autoimmunity, bone marrow failure, and aging. Understanding the context-dependent roles of TNF is essential for elucidating normal and pathogenic conditions and to guide clinical therapy advancements. Prior studies suggested that TNF restricts the self-renewal capacity of hematopoietic stem cells (HSCs), but its long-term effect on HSCs remains unclear. Here, we demonstrate that invivo TNF administration results in a transient exit of HSCs from quiescence, which coincides with a compromised repopulation capacity. These functional changes are; however, fully reversible even following prolonged/chronic transient exposure to TNF. Notably, antagonizing TNF signaling in transplantation recipients enhances donor HSC reconstitution. Our findings provide molecular and functional insight into HSC regulation, with implications for both acute and chronic inflammatory conditions.

EVA1A regulates hematopoietic stem cell regeneration via ER-mitochondria mediated apoptosis

Excessive protein synthesis upon enhanced cell proliferation frequently results in an increase of unfolded or misfolded proteins. During hematopoietic regeneration, to replenish the hematopoietic system, hematopoietic stem cells (HSCs) are activated and undergo a rapid proliferation. But how the activated HSCs respond to the proliferation pressure is still ambiguous; The proper control of the functional reservoir in the activated HSCs remains poorly understood. Here, we show a significant upregulation of EVA1A protein associated with the increase of ER stress during hematopoietic regeneration. Deletion of Eva1a significantly enhances the regeneration capacity of HSCs by inhibiting the ER stress-induced apoptosis. Mechanistically, the expression of EVA1A protein was upregulated by CHOP, and thereby promoted the ER-mitochondria interlinking via MCL1, which resulted in mitochondria-mediated apoptosis. These findings reveal a pathway for ER stress responses of HSCs by the EVA1A mediated apoptosis, which play an important role in HSCs regeneration.