Hematopoietic Homeostasis Research Articles

Metabolism as master of hematopoietic stem cell fate.

HSCs have a fate choice when they divide; they can self-renew, producing new HSCs, or produce daughter cells that will mature to become committed cells. Technical challenges, however, have long obscured the mechanics of these choices. Advances in flow-sorting have made possible the purification of HSC populations, but available HSC-enriched fractions still include substantial heterogeneity, and single HSCs have proven extremely difficult to track and observe. Advances in single-cell approaches, however, have led to the identification of a highly purified population of hematopoietic stem cells (HSCs) that make a critical contribution to hematopoietic homeostasis through a preference for self-renewing division. Metabolic cues are key regulators of this cell fate choice, and the importance of controlling the population and quality of mitochondria has recently been highlighted to maintain the equilibrium of HSC populations. Leukemic cells also demand tightly regulated metabolism, and shifting the division balance of leukemic cells toward commitment has been considered as a promising therapeutic strategy. A deeper understanding of precisely how specific modes of metabolism control HSC fate is, therefore, of great biological interest, and more importantly will be critical to the development of new therapeutic strategies that target HSC division balance for the treatment of hematological disease.

SRC-3 is involved in maintaining hematopoietic stem cell quiescence by regulation of mitochondrial metabolism in mice

AbstractQuiescence maintenance is an important property of hematopoietic stem cells (HSCs), whereas the regulatory factors and underlying mechanisms involved in HSC quiescence maintenance are not fully uncovered. Here, we show that steroid receptor coactivator 3 (SRC-3) is highly expressed in HSCs, and SRC-3–deficient HSCs are less quiescent and more proliferative, resulting in increased sensitivity to chemotherapy and irradiation. Moreover, the long-term reconstituting ability of HSCs is markedly impaired in the absence of SRC-3, and SRC-3 knockout (SRC-3−/−) mice exhibit a significant disruption of hematopoietic stem and progenitor cell homeostasis. Further investigations show that SRC-3 deficiency leads to enhanced mitochondrial metabolism, accompanied by overproduction of reactive oxygen species (ROS) in HSCs. Notably, the downstream target genes of peroxisome proliferator–activated receptor-coactivators 1α (PGC-1α) involved in the regulation of mitochondrial metabolism are significantly upregulated in SRC-3–deficient HSCs. Meanwhile, a significant decrease in the expression of histone acetyltransferase GCN5 accompanied by downregulation of PGC-1α acetylation is observed in SRC-3–null HSCs. Conversely, overexpression of GCN5 can inhibit SRC-3 deficiency-induced mitochondrial metabolism enhancement and ROS overproduction, thereby evidently rescuing the impairment of HSCs in SRC-3−/− mice. Collectively, our findings demonstrate that SRC-3 plays an important role in HSC quiescence maintenance by regulating mitochondrial metabolism.

Self-repopulating recipient bone marrow resident macrophages promote long-term hematopoietic stem cell engraftment

AbstractDistinct subsets of resident tissue macrophages are important in hematopoietic stem cell niche homeostasis and erythropoiesis. We used a myeloid reporter gene (Csf1r-eGFP) to dissect the persistence of bone marrow and splenic macrophage subsets following lethal irradiation and autologous hematopoietic stem cell transplantation in a mouse model. Multiple recipient bone marrow and splenic macrophage subsets survived after autologous hematopoietic stem cell transplantation with organ-specific persistence kinetics. Short-term persistence (5 weeks) of recipient resident macrophages in spleen paralleled the duration of extramedullary hematopoiesis. In bone marrow, radiation-resistant recipient CD169+ resident macrophages and erythroid-island macrophages self-repopulated long-term after transplantation via autonomous cell division. Posttransplant peak expansion of recipient CD169+ resident macrophage number in bone marrow aligned with the persistent engraftment of phenotypic long-term reconstituting hematopoietic stem cells within bone marrow. Selective depletion of recipient CD169+ macrophages significantly compromised the engraftment of phenotypic long-term reconstituting hematopoietic stem cells and consequently impaired hematopoietic reconstitution. Recipient bone marrow resident macrophages are essential for optimal hematopoietic stem cell transplantation outcomes and could be an important consideration in the development of pretransplant conditioning therapies and/or chemoresistance approaches.

1026 - Insights Into the Metabolic Control of Hematopoietic Stem Cell Fate

Hematopoietic stem cell (HSC) divisions result in either self-renewal or differentiation, with the balance between the two directly impacting hematopoietic homeostasis. Extensive research combining genetic models and metabolic analyses have highlighted the critical contributions of metabolic cues to the controlled equilibrium of HSCs; however, the heterogeneity of available HSC-enriched fractions, together with the technical challenges of observing HSC behavior, has long hindered the analysis of individual HSCs, and prevented the elucidation of this process. To address this gap, we recently implemented single-cell approaches and a new transplantation system to identify a subset of HSCs at the top of the HSC hierarchy. These HSCs produce two daughter cells which both retain self-renewal capacity, and one of the mechanisms of this self-renewing expansion is the induction of mitophagy by fatty acid metabolisms. Our data suggest that deeper insights into the metabolic mode governing these fate decisions will lead to techniques of cell-fate manipulation through metabolic pathways, with important implications for the development of new therapies for hematological disease.

3025 - Ebf1 as a Transcriptional Regulator of Bone Marrow Mesenchymal Stromal Cells

Mesenchymal stem and progenitor cells (MSPC), a crucial component of BM niche orchestrate maintenance, trafficking and stage specific differentiation of hematopoietic stem and progenitor cells (HSPCs). Although, it is generally accepted that MSPCs are essential for hematopoietic homeostasis, little is known about the transcriptional networks governing MSPCs biology. Here, we identified Early B-cell factor 1 (Ebf1) as new transcription regulator of MSPCs activity. MSPCs isolated from Ebf1-/- mice show diminished capacity to form fibroblastic colonies (CFU-F) indicating reduced self-renewal. Cells expanded from these colonies display impaired in vitro differentiation towards osteoblasts, chondrocytes and adipocytes. Adoptive transfers of wild type HSPCs to Ebf1+/- recipient mice showed a decrease in the absolute numbers of HSPCs in primary recipients and reduced donor chimerism within the HSCP compartment in competitive secondary transplant experiments. Additionally, Prx1-Cre-mediated deletion of Ebf1 in MSPCs in vivo leads to reduced numbers of HSPCs and myeloid cells in the bone marrow. Single cell and bulk transcriptome analysis of MSPCs lacking Ebf1 revealed differences in the niche composition and decreased expression of lineage-instructive signals for myeloid cells. Interestingly, we also observed a reduced ability of HSPCs sorted from Prx1CreEbf1 fl/fl mice to form colonies in methylcellulose, suggesting not only impaired maintenance but also hindered function of these cells. HSPCs exposed to Ebf1-deficient niche exhibit reduced chromatin accessibility for AP-1, ETS, Runx and IRF transcription factors that are crucial for myeloid differentiation, which is consistent with decreased myeloid output observed in Prx1CreEbf1 fl/fl mice. These results support the hypothesis that defective niche can cause epigenetic reprograming of HSPCs. In conclusion, our study establishes Ebf1 as a novel regulator of MSPCs playing a crucial role in the maintenance and differentiation of HSPCs.

Epithelial-mesenchymal transition in haematopoietic stem cell development and homeostasis.

Epithelial-mesenchymal transition (EMT) is a morphogenetic process of cells that adopt an epithelial organization in their developmental ontogeny or homeostatic maintenance. Abnormalities in EMT regulation result in many malignant tumours in the human body. Tumours associated with the haematopoietic system, however, are traditionally not considered to involve EMT and haematopoietic stem cells (HSCs) are generally not associated with epithelial characteristics. In this review, we discuss the ontogeny and homeostasis of adult HSCs in the context of EMT intermediate states. We provide evidence that cell polarity regulation is critical for both HSC formation from embryonic dorsal aorta and HSC self-renewal and differentiation in adult bone marrow. HSC polarity is controlled by the same set of surface and transcriptional regulators as those described in canonical EMT processes. With an emphasis on partial EMT, we propose that the concept of EMT can be similarly applied in the study of HSC generation, maintenance and pathogenesis.

ETS transcription factor ETV2/ER71/Etsrp in haematopoietic regeneration.

Recent studies have established that haematopoietic stem cells (HSCs) remain quiescent in homeostatic conditions, and minimally contribute to haematopoietic homeostasis. However, they undergo extensive cell cycle and expansion upon bone marrow transplantation or haematopoietic injury to reestablish the haematopoietic system. Molecular basis for the HSC activation and expansion is not completely understood. Here, we review the recent study elucidating the role of the developmentally critical Ets transcription factor Etv2 in reestablishing haematopoietic system upon injury through promoting HSC regeneration. We recently demonstrated that the ETS transcription factor Etv2, a critical factor for haematopoietic and vascular development, is also required for haematopoietic regeneration. Etv2, which is silent in homeostatic HSCs, was transiently activated in regenerating HSPCs and was required for the HSC expansion and regeneration following bone marrow transplantation or haematopoietic injury. As such, while Etv2 is dispensable for maintaining HSCs in steady states, it is required for emergency haematopoiesis. Etv2 has been identified as a novel regulator of haematopoietic regeneration. Comprehensive understanding of the upstream regulators and downstream effectors of Etv2 in haematopoietic regeneration would be critical for fundamental understanding of haematopoietic stem cell biology, and the findings will be broadly applicable to clinical practice involving haematopoietic regenerative medicine; bone marrow transplantation, gene therapy and in-vitro HSC expansion.

The H3K4 methyltransferase Setd1b is essential for hematopoietic stem and progenitor cell homeostasis in mice.

Hematopoietic stem cells require MLL1, which is one of six Set1/Trithorax-type histone 3 lysine 4 (H3K4) methyltransferases in mammals and clinically the most important leukemia gene. Here, we add to emerging evidence that all six H3K4 methyltransferases play essential roles in the hematopoietic system by showing that conditional mutagenesis of Setd1b in adult mice provoked aberrant homeostasis of hematopoietic stem and progenitor cells (HSPCs). Using both ubiquitous and hematopoietic-specific deletion strategies, the loss of Setd1b resulted in peripheral thrombo- and lymphocytopenia, multilineage dysplasia, myeloid-biased extramedullary hematopoiesis in the spleen, and lethality. By transplantation experiments and expression profiling, we determined that Setd1b is autonomously required in the hematopoietic lineages where it regulates key lineage specification components, including Cebpa, Gata1, and Klf1. Altogether, these data imply that the Set1/Trithorax-type epigenetic machinery sustains different aspects of hematopoiesis and constitutes a second framework additional to the transcription factor hierarchy of hematopoietic homeostasis.

Hematopoietic stem cell fate through metabolic control

Hematopoietic stem cells maintain a quiescent state in the bone marrow to preserve their self-renewal capacity, but also undergo cell divisions as required. Organelles such as the mitochondria sustain cumulative damage during these cell divisions and this damage may eventually compromise the cells' self-renewal capacity. Hematopoietic stem cell divisions result in either self-renewal or differentiation, with the balance between the two affecting hematopoietic homeostasis directly; however, the heterogeneity of available hematopoietic stem cell-enriched fractions, together with the technical challenges of observing hematopoietic stem cell behavior, has long hindered the analysis of individual hematopoietic stem cells and prevented the elucidation of this process. Recent advances in genetic models, metabolomics analyses, and single-cell approaches have revealed the contributions made to hematopoietic stem cell self-renewal by metabolic cues, mitochondrial biogenesis, and autophagy/mitophagy, which have highlighted mitochondrial quality control as a key factor in the equilibrium of hematopoietic stem cells. A deeper understanding of precisely how specific modes of metabolism control hematopoietic stem cells fate at the single-cell level is therefore not only of great biological interest, but will also have clear clinical implications for the development of therapies for hematological diseases.

Regulation of Hematopoietic Cell Development and Function Through Phosphoinositides.

One of the most paramount receptor-induced signal transduction mechanisms in hematopoietic cells is production of the lipid second messenger phosphatidylinositol(3,4,5)trisphosphate (PIP3) by class I phosphoinositide 3 kinases (PI3K). Defective PIP3 signaling impairs almost every aspect of hematopoiesis, including T cell development and function. Limiting PIP3 signaling is particularly important, because excessive PIP3 function in lymphocytes can transform them and cause blood cancers. Here, we review the key functions of PIP3 and related phosphoinositides in hematopoietic cells, with a special focus on those mechanisms dampening PIP3 production, turnover, or function. Recent studies have shown that beyond “canonical” turnover by the PIP3 phosphatases and tumor suppressors phosphatase and tensin homolog (PTEN) and SH2 domain-containing inositol-5-phosphatase-1 (SHIP-1/2), PIP3 function in hematopoietic cells can also be dampened through antagonism with the soluble PIP3 analogs inositol(1,3,4,5)tetrakisphosphate (IP4) and inositol-heptakisphosphate (IP7). Other evidence suggests that IP4 can promote PIP3 function in thymocytes. Moreover, IP4 or the kinases producing it limit store-operated Ca2+ entry through Orai channels in B cells, T cells, and neutrophils to control cell survival and function. We discuss current models for how soluble inositol phosphates can have such diverse functions and can govern as distinct processes as hematopoietic stem cell homeostasis, neutrophil macrophage and NK cell function, and development and function of B cells and T cells. Finally, we will review the pathological consequences of dysregulated IP4 activity in immune cells and highlight contributions of impaired inositol phosphate functions in disorders such as Kawasaki disease, common variable immunodeficiency, or blood cancer.

Spred1 Safeguards Hematopoietic Homeostasis against Diet-Induced Systemic Stress

Stem cell self-renewal is critical for tissue homeostasis, and its dysregulation can lead to organ failure or tumorigenesis. While obesity can induce varied abnormalities in bone marrow components, it is unclear how diet might affect hematopoietic stem cell (HSC) self-renewal. Here, we show that Spred1, a negative regulator of RAS-MAPK signaling, safeguards HSC homeostasis in animals fed a high-fat diet (HFD). Under steady-state conditions, Spred1 negatively regulates HSC self-renewal and fitness, in part through Rho kinase activity. Spred1 deficiency mitigates HSC failure induced by infection mimetics and prolongs HSC lifespan, but it does not initiate leukemogenesisdue to compensatory upregulation of Spred2.In contrast, HFD induces ERK hyperactivation and aberrant self-renewal in Spred1-deficient HSCs, resulting in functional HSC failure, severe anemia, and myeloproliferative neoplasm-like disease. HFD-induced hematopoietic abnormalities are mediated partly through alterations to the gut microbiota. Together, these findings reveal thatdiet-induced stress disrupts fine-tuningof Spred1-mediated signals to govern HSC homeostasis.

Neural Regulation of Bone and Bone Marrow.

Bones provide both skeletal scaffolding and space for hematopoiesis in its marrow. Previous work has shown that these functions were tightly regulated by the nervous system. The central and peripheral nervous systems tightly regulate compact bone remodeling, its metabolism, and hematopoietic homeostasis in the bone marrow (BM). Accumulating evidence indicates that the nervous system, which fine-tunes inflammatory responses and alterations in neural functions, may regulate autoimmune diseases. Neural signals also influence the progression of hematological malignancies such as acute and chronic myeloid leukemias. Here, we review the interplay of the nervous system with bone, BM, and immunity, and discuss future challenges to target hematological diseases through modulation of activity of the nervous system.

Regulation of hematopoietic stem cell homeostasis by Spred1

Various types of stresses account for the dysregulation of the self-renewal activity of stem cells, resulting in the functional failure of tissues or tumorigenesis promotion. Although diets also affect our health, the effect of harmful dietary stresses on the tissue or stem cell homeostasis remains unclear. Recent research has revealed that Spred1, which negatively regulates RAS-MAPK signaling, protects hematopoietic stem cell (HSC) homeostasis against high-fat diet (HFD) -induced systemic stress. In steady-state conditions, Spred1 negatively regulates HSC self-renewal in a manner supported by the Rho kinase (ROCK) activity. In addition, Spred1 deficiency in mice mitigates HSC dysfunction induced by aging or lipopolysaccharide treatment, enhances the HSC self-renewal capacity, and prolongs HSC lifespan, but does not induce leukemia because of the compensatory upregulation of Spred2-the other Spred family member. Conversely, HFD triggers ERK hyperactivation and aberrant self-renewal in Spred1-deficient HSCs, resulting in HSC dysfunction, severe anemia, and the development of lethal myeloproliferative neoplasm-like disease. The depletion of the gut microbiota by antibiotics restored myeloproliferation, anemia, and HSC reconstitution ability in HFD-fed Spred1-deficient mice, suggesting that HFD-induced hematopoietic abnormalities were partially because of alterations in the gut microbiota composition. Thus, HFD-induced systemic stress affects the regulation of HSC self-renewal, and Spred1 safeguards HSC homeostasis against the diet-induced systemic stress.

TRAF6 Mediates Basal Activation of NF-κB Necessary for Hematopoietic Stem Cell Homeostasis

SUMMARYBasal nuclear factor κB (NF-κB) activation is required for hematopoietic stem cell (HSC) homeostasis in the absence of inflammation; however, the upstream mediators of basal NF-κB signaling are less well understood. Here, we describe TRAF6 as an essential regulator of HSC homeostasis through basal activation of NF-κB. Hematopoietic-specific deletion of Traf6 resulted in impaired HSC self-renewal and fitness. Gene expression, RNA splicing, and molecular analyses of Traf6-deficient hematopoietic stem/progenitor cells (HSPCs) revealed changes in adaptive immune signaling, innate immune signaling, and NF-κB signaling, indicating that signaling via TRAF6 in the absence of cytokine stimulation and/or infection is required for HSC function. In addition, we established that loss of IκB kinase beta (IKKβ)- mediated NF-κB activation is responsible for the major hematopoietic defects observed in Traf6-deficient HSPC as deletion of IKKβ similarly resulted in impaired HSC self-renewal and fitness. Taken together, TRAF6 is required for HSC homeostasis by maintaining a minimal threshold level of IKKβ/NF-κB signaling.

Histone demethylase LSD1 regulates hematopoietic stem cells homeostasis and protects from death by endotoxic shock

Hematopoietic stem cells (HSCs) maintain a quiescent state during homeostasis, but with acute infection, they exit the quiescent state to increase the output of immune cells, the so-called "emergency hematopoiesis." However, HSCs' response to severe infection during septic shock and the pathological impact remain poorly elucidated. Here, we report that the histone demethylase KDM1A/LSD1, serving as a critical regulator of mammalian hematopoiesis, is a negative regulator of the response to inflammation in HSCs during endotoxic shock typically observed during acute bacterial or viral infection. Inflammation-induced LSD1 deficiency results in an acute expansion of a pathological population of hyperproliferative and hyperinflammatory myeloid progenitors, resulting in a septic shock phenotype and acute death. Unexpectedly, in vivo administration of bacterial lipopolysaccharide (LPS) to wild-type mice results in acute suppression of LSD1 in HSCs with a septic shock phenotype that resembles that observed following induced deletion of LSD1 The suppression of LSD1 in HSCs is caused, at least in large part, by a cohort of inflammation-induced microRNAs. Significantly, reconstitution of mice with bone marrow progenitor cells expressing inhibitors of these inflammation-induced microRNAs blocked the suppression of LSD1 in vivo following acute LPS administration and prevented mortality from endotoxic shock. Our results indicate that LSD1 activators or miRNA antagonists could serve as a therapeutic approach for life-threatening septic shock characterized by dysfunction of HSCs.

Impairment in the Mesenchymal Bone-Marrow Niche of Beta-Thalassemia Patients and Association with Prolonged Iron Exposure

Bone marrow (BM) contains a population of mesenchymal stromal cells (MSC) that, together with endothelial cells and osteoblasts, provide a specific microenvironment to support hematopoietic stem cell homeostasis. Beta-thalassemia (BT) is an hereditary blood disorder characterized by reduced or absent synthesis of hemoglobin beta-chains. Data on the mesenchymal compartment in BT patients are scarce. We isolated and characterized MSCs from BT and healthy donor (HD) BM samples. BT-MSCs showed a reduced clonogenic capacity, delay in colony formation, lower numbers of CFU-Fs and longer population doubling time. Similarly, we observed an altered differentiation capacity into adipocytes and osteoblasts. Both HD- and BT-MSCs express the canonical mesenchymal markers. On the contrary, the expression of CD146 and CD271 was extremely reduced in BT-MSCs, indicating a pauperization of the most primitive stem cell pool. We analyzed the expression of genes involved in the crosstalk between MSCs and HSCs and found a reduced expression of Cxcl12, SCF and Angp1 in BT-MSCs. Several genes relevant for MSC functionality were also downregulated in BT-MSCs. We demonstrated that MSCs are able to uptake and store iron. ROS levels were increased in BT-MSCs possibly due to altered anti-oxidant response and iron overload associated with blood transfusions. Importantly, higher level of ROS and reduced expression of primitive markers were observed in HD-MSCs cultured in presence of iron, underlying the importance of iron level for normal MSC function. In conclusion, we showed an impairment in the mesenchymal niche of BT-BM possibly associated with prolonged iron exposure. DisclosuresMarktel:GSK: Other: B-thalassemia gene therapy was developed by Fondazione Telethon and Ospedale San Raffaele and has been inlicenced by GSK that provides funding for the clinical trial, Research Funding. Ciceri:GSK: Other: B-thalassemia gene therapy was developed by Fondazione Telethon and Ospedale San Raffaele and has been inlicenced by GSK that provides funding for the clinical trial, Research Funding.

EBF1 As a Novel Regulator of Bone Marrow Mesenchymal Stromal Progenitors

Hematopoietic stem and progenitor cells (HSPC) are in daily demand worldwide because of their ability to replenish entire blood system. However, the in vitro expansion of HSPC is still a major challenge since the cues from bone marrow microenvironment remain largely elusive. Signals coming from the bone marrow niche, and specifically mesenchymal stem and progenitor cells (MSPC), orchestrate maintenance, trafficking and stage specific differentiation of HSPCs. Although, it is generally accepted that MSPCs are essential for hematopoietic homeostasis and generating multiple types of stromal cells, the exact transcriptional networks regulating MSPCs are not well established. Early B-cell factor 1 (Ebf1) has been discovered as lineage-specific transcription factor governing B lymphopoiesis. Additionally, it has been shown to play important role in differentiation of adipocytes, which are a niche component supporting hematopoietic regeneration. Thus, in this study we seek to examine if Ebf1 has an alternative function in non-hematopoietic compartment of bone marrow, specifically in mesenchymal stromal cells that maintain proper hematopoiesis.Here, we identified Ebf1 as new transcription regulator of MSPCs activity. Mesenchymal progenitors isolated from Ebf1-/- mice show diminished capacity to form fibroblasticcolonies (CFU-F) indicating reduced self-renewal. Moreover, cells expanded from these colonies display impaired in vitro differentiation towards osteoblasts, chondrocytes and adipocytes. In order to test how this defective MSPCs influence maintenance of HSPCs, we performed long-term culture-initiating cell assay (LTC-IC). After 5 weeks of co-culture of Ebf1-deficient stromal cells with wild type HSPCs we could observe significantly decreased number of cobblestone and CFU colonies formed by primitive HSPCs, in comparison to co-cultures with control stromal cells. Furthermore, in vivo adoptive transfers of wild type HSPCs to Ebf1+/- recipient mice showed a decrease in the absolute numbers of HSPCs in primary recipients and reduced donor chimerism within the HSCP compartment in competitive secondary transplant experiments. Additionally, Prx1-Cre-mediated deletion of Ebf1 specifically in MSPCs of mice leads to reduced frequency and numbers of HSPCs and myeloid cells in the bone marrow. These results confirm that mesenchymal stromal cells lacking Ebf1 render insufficient support for HSPCs to sustain proper hematopoiesis. Interestingly, we also observed a reduced ability of HSPCs sorted from Prx1CreEbf1fl/fl mice to form colonies in methylcellulose, suggesting not only impaired maintenance but also hindered function of these cells. Moreover, HSPCs exposed to Ebf1-deficient niche exhibit changes in chromatin accessibility with reduced occupancy of AP-1, ETS, Runx and IRF motifs, which is consistent with decreased myeloid output seen in Prx1CreEbf1fl/fl mice. These results support the hypothesis that defective niche can cause epigenetic reprograming of HSPCs. Finally, single cell and bulk transcriptome analysis of MSPCs lacking Ebf1 revealed differences in the niche composition and decreased expression of lineage-instructive signals for myeloid cells. Thus, our study establishes Ebf1 as a novel regulator of MSPCs playing a crucial role in the maintenance and differentiation of HSPCs. DisclosuresNo relevant conflicts of interest to declare.

Atad3a suppresses Pink1-dependent mitophagy to maintain homeostasis of hematopoietic progenitor cells.

Although deletion of certain autophagy-related genes has been associated with defects in hematopoiesis, it remains unclear whether hyperactivated mitophagy affects the maintenance and differentiation of hematopoietic stem cells (HSCs) and committed progenitor cells. Here we report that targeted deletion of the gene encoding the AAA+-ATPase Atad3a hyperactivated mitophagy in mouse hematopoietic cells. Affected mice showed reduced survival, severely decreased bone-marrow cellularity, erythroid anemia and B cell lymphopenia. Those phenotypes were associated with skewed differentiation of stem and progenitor cells and an enlarged HSC pool. Mechanistically, Atad3a interacted with the mitochondrial channel components Tom40 and Tim23 and served as a bridging factor to facilitate appropriate transportation and processing of the mitophagy protein Pink1. Loss of Atad3a caused accumulation of Pink1 and activated mitophagy. Notably, deletion of Pink1 in Atad3a-deficient mice significantly 'rescued' the mitophagy defect, which resulted in restoration of the progenitor and HSC pools. Our data indicate that Atad3a suppresses Pink1-dependent mitophagy and thereby serves a key role in hematopoietic homeostasis.

Alleviation of ginsenoside Rg1 on hematopoietic homeostasis defects caused by lead-acetate

The hematopoietic system is one of the potential targets of lead intoxication. Recognition of the lead-related deleterious outcomes promotes us to explore the potential therapeutic intervention. Here, we show that ginsenoside Rg1 (Rg1), extracted from the Chinese herb Panax ginseng, remarkably ameliorates the lead acetate-caused hematological index distortion as well as advanced hematopoietic stem cells (HSCs) aging and aging associated inflammation response. Specifically, Rg1 administration alleviated the increment of aging associated p53-p21-Rb signaling in aged HSCs induced by lead acetate. It also led a reduction of the lead acetate-induced increased inflammation level in blood plasma, which also partly contribute the aged HSCs rejuvenation. In conclusion, our results indicate that ginsenoside Rg1 therapeutically alleviated the essential blood deficits and advanced HSCs aging by lead acetate exposure, by which it could be viewed as a potential candidate for lead acetate-caused blood toxicity treatment.

The presence of anaemia negatively influences survival in patients with POLG disease.

Mitochondria play an important role in iron metabolism and haematopoietic cell homeostasis. Recent studies in mice showed that a mutation in the catalytic subunit of polymerase gamma (POLG) was associated with haematopoietic dysfunction including anaemia. The aim of this study was to analyse the frequency of anaemia in a large cohort of patients with POLG related disease. We conducted a multi-national, retrospective study of 61 patients with confirmed, pathogenic biallelic POLG mutations from six centres, four in Norway and two in the United Kingdom. Clinical, laboratory and genetic data were collected using a structured questionnaire. Anaemia was defined as an abnormally low haemoglobin value adjusted for age and sex. Univariate survival analysis was performed using log-rank test to compare differences in survival time between categories. Anaemia occurred in 67% (41/61) of patients and in 23% (14/61) it was already present at clinical presentation. The frequency of anaemia in patients with early onset disease including Alpers syndrome and myocerebrohepatopathy spectrum (MCHS) was high (72%) and 35% (8/23) of these had anaemia at presentation. Survival analysis showed that the presence of anaemia was associated with a significantly worse survival (P=0.004). Our study reveals that anaemia can be a feature of POLG-related disease. Further, we show that its presence is associated with significantly worse prognosis either because anaemia itself is impacting survival or because it reflects the presence of more serious disease. In either case, our data suggests anaemia is a marker for negative prognosis.