Hematopoietic stem cell fate through metabolic control

Mitochondrial quality control in hematopoietic stem cells: mechanisms, implications, and therapeutic opportunities

Mitochondrial quality control (MQC) is a critical mechanism for maintaining mitochondrial function and cellular metabolic homeostasis, playing an essential role in the self-renewal, differentiation, and long-term stability of hematopoietic stem cells (HSCs). Recent research highlights the central importance of MQC in HSC biology, particularly the roles of mitophagy, mitochondrial biogenesis, fission, fusion and mitochondrial transfer in regulating HSC function. Mitophagy ensures the removal of damaged mitochondria, maintaining low levels of reactive oxygen species (ROS) in HSCs, thereby preventing premature aging and functional decline. Concurrently, mitochondrial biogenesis adjusts key metabolic regulators such as mitochondrial transcription factor A (TFAM) and peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α) to meet environmental demands, ensuring the metabolic needs of HSCs are met. Additionally, mitochondrial transfer, as an essential form of intercellular material exchange, facilitates the transfer of functional mitochondria from bone marrow stromal cells to HSCs, contributing to damage repair and metabolic support. Although existing studies have revealed the significance of MQC in maintaining HSC function, the precise molecular mechanisms and interactions among different regulatory pathways remain to be fully elucidated. Furthermore, the potential role of MQC dysfunction in hematopoietic disorders, including its involvement in disease progression and therapeutic resistance, is not yet fully understood. This review discusses the molecular mechanisms of MQC in HSCs, its functions under physiological and pathological conditions, and its potential therapeutic applications. By summarizing the current progress in this field, we aim to provide insights for further research and the development of innovative treatment strategies.

Deciphering the Complexities of Adult Human Steady State and Stress-Induced Hematopoiesis: Progress and Challenges

Human hematopoietic stem cells (HSCs) have traditionally been viewed as self-renewing, multipotent cells with enormous potential in sustaining essential steady state blood and immune cell production throughout life. Indeed, around 86% (1011-1012) of new cells generated daily in a healthy young human adult are of hematopoietic origin. Therapeutically, human HSCs have contributed to over 1.5 million hematopoietic cell transplants (HCTs) globally, making this the most successful regenerative therapy to date. We will commence this review by briefly highlighting selected key achievements (from 1868 to the end of the 20th century) that have contributed to this accomplishment. Much of our knowledge of hematopoiesis is based on small animal models that, despite their enormous importance, do not always recapitulate human hematopoiesis. Given this, we will critically review the progress and challenges faced in identifying adult human HSCs and tracing their lineage differentiation trajectories, referring to murine studies as needed. Moving forward and given that human hematopoiesis is dynamic and can readily adjust to a variety of stressors, we will then discuss recent research advances contributing to understanding (i) which HSPCs maintain daily steady state human hematopoiesis, (ii) where these are located, and (iii) which mechanisms come into play when homeostatic hematopoiesis switches to stress-induced or emergency hematopoiesis.

Targeting Fatty Acid Metabolism Abrogates the Differentiation Blockade in Preleukemic Cells

Metabolism plays a key role in the maintenance of normal hematopoietic stem cells (HSC) and in the development of leukemia. A better understanding of the metabolic characteristics and dependencies of preleukemic cells could help identify potential therapeutic targets to prevent leukemic transformation. As AML1-ETO, one of the most frequent fusion proteins in acute myeloid leukemia that is encoded by a RUNX1::RUNX1T1 fusion gene, is capable of generating preleukemic clones, in this study, we used a conditional Runx1::Runx1t1 knockin mouse model to evaluate preleukemic cell metabolism. AML1-ETO expression resulted in impaired hematopoietic reconstitution and increased self-renewal ability. Oxidative phosphorylation and glycolysis decreased significantly in these preleukemic cells accompanied by increased HSC quiescence and reduced cell cycling. Furthermore, HSCs expressing AML1-ETO exhibited an increased requirement for fatty acids through metabolic flux. Dietary lipid deprivation or loss of the fatty acid transporter FATP3 by targeted deletion using CRISPR/Cas9 partially restored differentiation. These findings reveal the unique metabolic profile of preleukemic cells and propose FATP3 as a potential target for disrupting leukemogenesis. Significance: Fatty acid metabolism is required for maintenance of preleukemic cells but dispensable for normal hematopoiesis, indicating that dietary lipid deprivation or inhibiting fatty acid uptake may serve as potential strategies to prevent leukemogenesis.

Hematopoietic stem cell a reservoir of innate immune memory

Hematopoietic stem cells (HSCs) are a rare, long-lived and multipotent population that give rise to majority of blood cells and some tissue-resident immune cells. There is growing evidence that inflammatory stimuli can trigger persistent reprogramming in HSCs that enhances or inhibits the cellular functions of these HSCs and their progeny in response to subsequent infections. This newly discovered property makes HSCs a reservoir for innate immune memory. The molecular mechanisms underlying innate immune memory in HSCs are similar to those observed in innate immune cells, although their full elucidation is still pending. In this review, we examine the current state of knowledge on how an inflammatory response leads to reprogramming of HSCs. Understanding the full spectrum of consequences of reshaping early hematopoiesis is critical for assessing the potential benefits and risks under physiological and pathological conditions.

A system-level model reveals that transcriptional stochasticity is required for hematopoietic stem cell differentiation

HSCs differentiation has been difficult to study experimentally due to the high number of components and interactions involved, as well as the impact of diverse physiological conditions. From a 200-node network, that was grounded on experimental data, we derived a 21-node regulatory network by collapsing linear pathways and retaining the functional feedback loops. This regulatory network core integrates key nodes and interactions underlying HSCs differentiation, including transcription factors, metabolic, and redox signaling pathways. We used Boolean, continuous, and stochastic dynamic models to simulate the hypoxic conditions of the HSCs niche, as well as the patterns and temporal sequences of HSCs transitions and differentiation. Our findings indicate that HSCs differentiation is a plastic process in which cell fates can transdifferentiate among themselves. Additionally, we found that cell heterogeneity is fundamental for HSCs differentiation. Lastly, we found that oxygen activates ROS production, inhibiting quiescence and promoting growth and differentiation pathways of HSCs.

Met-Flow analyses of the metabolic heterogeneity associated with different stages of cord blood-derived hematopoietic cell differentiation

Background

The differentiation of hematopoietic cells is significantly affected by cell metabolic activity. However, despite increasing interest in this field, there has been no comprehensive investigation of the metabolic functions of human hematopoietic cells during specific phases of differentiation. Thus, this study was conducted to develop a method for comparing hematopoietic cell lineage differentiation based on the metabolic functions of the cell. The metabolic activity of human umbilical cord-derived hematopoietic cells was examined during various phases of differentiation, specifically, hematopoietic stem cells (HSCs), hematopoietic progenitor cells, and differentiated blood cells. This approach was used to develop comprehensive metabolic maps corresponding to the different stages.

Results

HSCs were found to have robust fatty acid (FA) synthesis, FA oxidation, pentose phosphate pathway (PPP) activity, and glucose uptake, shown by their significantly higher expression of ACAC, CPT1A, G6PD, and GLUT1 as compared to differentiated pluripotent progenitor cells, common myeloid progenitors, megakaryocyte erythroid progenitors, lympho-myeloid primed progenitors, and granulocyte-macrophage progenitor cell populations. In monocytic differentiation, higher levels of ACAC, ASS1, ATP5A, CPT1A, G6PD, GLUT1, IDH2, PRDX2, and HK1 protein expression were evident in classical and intermediate monocytes relative to non-classical monocytes, consistent with high anabolic and catabolic levels. Compared with myelocytes and mature cells, the meta-myelocyte and pro-myelocyte populations of granulocytes show significantly elevated levels of ACAC, ASS1, ATP5A, CPT1A, G6PD, IDH2, PRDX2, and HK. In contrast to naïve and regulatory B cells, pro-B cells had higher levels of oxidative phosphorylation, while regulatory B cells showed greater PPP activity, glucose uptake, and tricarboxylic acid cycle activity. The analyses of T cells also indicated significantly higher ACAC, ASS1, ATP5A, CPT1A, G6PD, GLUT1, IDH2, PRDX2, and HK1 expression levels in CD4+ populations compared with CD8+ populations.

Conclusions

The results provide comprehensive analytical methods and reference values for future systematic studies into the metabolic functions of various cord blood-derived hematopoietic cell populations in different pathological or physiological conditions. These findings could also contribute to research on the connection between cellular metabolism and cancer or aging.

Dynamically adjusted cell fate decisions and resilience to mutant invasion during steady-state hematopoiesis revealed by an experimentally parameterized mathematical model

A major next step in hematopoietic stem cell (HSC) biology is to enhance our quantitative understanding of cellular and evolutionary dynamics involved in undisturbed hematopoiesis. Mathematical models have been and continue to be key in this respect, and are most powerful when parameterized experimentally and containing sufficient biological complexity. In this paper, we use data from label propagation experiments in mice to parameterize a mathematical model of hematopoiesis that includes homeostatic control mechanisms as well as clonal evolution. We find that nonlinear feedback control can drastically change the interpretation of kinetic estimates at homeostasis. This suggests that short-term HSC and multipotent progenitors can dynamically adjust to sustain themselves temporarily in the absence of long-term HSCs, even if they differentiate more often than they self-renew in undisturbed homeostasis. Additionally, the presence of feedback control in the model renders the system resilient against mutant invasion. Invasion barriers, however, can be overcome by a combination of age-related changes in stem cell differentiation and evolutionary niche construction dynamics based on a mutant-associated inflammatory environment. This helps us understand the evolution of e.g., TET2 or DNMT3A mutants, and how to potentially reduce mutant burden.

OGT and OGA gene-edited human induced pluripotent stem cells for dissecting the functional roles of O-GlcNAcylation in hematopoiesis

Hematopoiesis continues throughout life to produce all types of blood cells from hematopoietic stem cells (HSCs). Metabolic state is a known regulator of HSC self-renewal and differentiation, but whether and how metabolic sensor O-GlcNAcylation, which can be modulated via an inhibition of its cycling enzymes O-GlcNAcase (OGA) and O-GlcNAc transferase (OGT), contributes to hematopoiesis remains largely unknown. Herein, isogenic, single-cell clones of OGA-depleted (OGAi) and OGT-depleted (OGTi) human induced pluripotent stem cells (hiPSCs) were successfully generated from the master hiPSC line MUSIi012-A, which were reprogrammed from CD34+ hematopoietic stem/progenitor cells (HSPCs) containing epigenetic memory. The established OGAi and OGTi hiPSCs exhibiting an increase or decrease in cellular O-GlcNAcylation concomitant with their loss of OGA and OGT, respectively, appeared normal in phenotype and karyotype, and retained pluripotency, although they may favor differentiation toward certain germ lineages. Upon hematopoietic differentiation through mesoderm induction and endothelial-to-hematopoietic transition, we found that OGA inhibition accelerates hiPSC commitment toward HSPCs and that disruption of O-GlcNAc homeostasis affects their commitment toward erythroid lineage. The differentiated HSPCs from all groups were capable of giving rise to all hematopoietic progenitors, thus confirming their functional characteristics. Altogether, the established single-cell clones of OGTi and OGAi hiPSCs represent a valuable platform for further dissecting the roles of O-GlcNAcylation in blood cell development at various stages and lineages of blood cells. The incomplete knockout of OGA and OGT in these hiPSCs makes them susceptible to additional manipulation, i.e., by small molecules, allowing the molecular dynamics studies of O-GlcNAcylation.

KBTBD4-mediated reduction of MYC is critical for hematopoietic stem cell expansion upon UM171 treatment

ABSTRACT

Ex vivo expansion of hematopoietic stem cells (HSCs) is gaining importance for cell and gene therapy, and requires a shift from dormancy state to activation and cycling. However, abnormal or excessive HSC activation results in reduced self-renewal ability and increased propensity for myeloid-biased differentiation. We now report that activation of the E3 ligase complex CRL3KBTBD4 by UM171 not only induces epigenetic changes through CoREST1 degradation but also controls chromatin-bound master regulator of cell cycle entry and proliferative metabolism (MYC) levels to prevent excessive activation and maintain lympho-myeloid potential of expanded populations. Furthermore, reconstitution activity and multipotency of UM171-treated HSCs are specifically compromised when MYC levels are experimentally increased despite degradation of CoREST1.

A mitochondrial NADPH-cholesterol axis regulates extracellular vesicle biogenesis to support hematopoietic stem cell fate

Mitochondrial fatty acid oxidation (FAO) is essential for hematopoietic stem cell (HSC) self-renewal; however, the mechanism by which mitochondrial metabolism controls HSC fate remains unknown. Here, we show that within the hematopoietic lineage, HSCs have the largest mitochondrial NADPH pools, which are required for proper HSC cell fate and homeostasis. Bioinformatic analysis of the HSC transcriptome, biochemical assays, and genetic inactivation of FAO all indicate that FAO-generated NADPH fuels cholesterol synthesis in HSCs. Interference with FAO disturbs the segregation of mitochondrial NADPH toward corresponding daughter cells upon single HSC division. Importantly, we have found that the FAO-NADPH-cholesterol axis drives extracellular vesicle (EV) biogenesis and release in HSCs, while inhibition of EV signaling impairs HSC self-renewal. These data reveal the existence of a mitochondrial NADPH-cholesterol axis for EV biogenesis that is required for hematopoietic homeostasis and highlight the non-stochastic nature of HSC fate determination.

A metabolic perspective of the neutrophil life cycle: new avenues in immunometabolism

Neutrophils are the most abundant innate immune cells. Multiple mechanisms allow them to engage a wide range of metabolic pathways for biosynthesis and bioenergetics for mediating biological processes such as development in the bone marrow and antimicrobial activity such as ROS production and NET formation, inflammation and tissue repair. We first discuss recent work on neutrophil development and functions and the metabolic processes to regulate granulopoiesis, neutrophil migration and trafficking as well as effector functions. We then discuss metabolic syndromes with impaired neutrophil functions that are influenced by genetic and environmental factors of nutrient availability and usage. Here, we particularly focus on the role of specific macronutrients, such as glucose, fatty acids, and protein, as well as micronutrients such as vitamin B3, in regulating neutrophil biology and how this regulation impacts host health. A special section of this review primarily discusses that the ways nutrient deficiencies could impact neutrophil biology and increase infection susceptibility. We emphasize biochemical approaches to explore neutrophil metabolism in relation to development and functions. Lastly, we discuss opportunities and challenges to neutrophil-centered therapeutic approaches in immune-driven diseases and highlight unanswered questions to guide future discoveries.

GPRC5C drives branched-chain amino acid metabolism in leukemogenesis

Leukemia stem cells (LSCs) share numerous features with healthy hematopoietic stem cells (HSCs). G-protein coupled receptor family C group 5 member C (GPRC5C) is a regulator of HSC dormancy. However, GPRC5C functionality in acute myeloid leukemia (AML) is yet to be determined. Within patient AML cohorts, high GPRC5C levels correlated with poorer survival. Ectopic Gprc5c expression increased AML aggression through the activation of NF-κB, which resulted in an altered metabolic state with increased levels of intracellular branched-chain amino acids (BCAAs). This onco-metabolic profile was reversed upon loss of Gprc5c, which also abrogated the leukemia-initiating potential. Targeting the BCAA transporter SLC7A5 with JPH203 inhibited oxidative phosphorylation and elicited strong antileukemia effects, specifically in mouse and patient AML samples while sparing healthy bone marrow cells. This antileukemia effect was strengthened in the presence of venetoclax and azacitidine. Our results indicate that the GPRC5C-NF-κB-SLC7A5-BCAAs axis is a therapeutic target that can compromise leukemia stem cell function in AML.

The multifaceted role of mitochondria in HSC fate decisions: energy and beyond

Hematopoietic stem cells (HSCs) have the properties to self-renew and/or differentiate into all-mature blood cell lineages. The fate decisions to generate progeny that retain stemness properties or that commit to differentiation is a fundamental process to maintain tissue homeostasis and must be tightly regulated to prevent HSC overgrowth or exhaustion. HSC fate decisions are inherently coupled to cell division. The transition from quiescence to activation is accompanied by major metabolic and mitochondrial changes that are important for cell cycle entry and for balanced decisions between self-renewal and differentiation. In this review, we discuss the current understanding of the role of mitochondrial metabolism in HSC transition from quiescence to activation and fate decisions.

Elucidating the cell metabolic heterogeneity during hematopoietic lineage differentiation based on Met-Flow

Cell metabolism is critically involved in the differentiation of the hematopoietic lineage and, therefore, has attracted the attention of researchers, however, in-depth studies on cellular metabolic activity of hematopoietic cells (HCs) require attention. This investigation compared the metabolic activity of HCs at critical lineage differentiation stages, including hematopoietic stem cells (HSCs), hematopoietic progenitor cells (HPCs), and differentiated blood cells, via multiple methods and basic reference values. Primary metabolic processes of HCs, including anabolism, catabolism, phosphate, and glucose metabolism, were analyzed, and their maps were drawn. The data revealed that GLUT1 expression in HSCs was substantially higher than in all progenitor cells and mature myeloid blood cells, indicating their strong glucose uptake capacity. In myeloid differentiation, the ACAC expression of HPC2 was markedly higher than in neutrophils and monocytes. The ACAC, ASS1, ATP5A, and PRDX2 of HPC2 expression in lymphoid differentiation was substantially greater than in B and Natural-killer cells. CLP, CMP, GMP, MEP, and HPC1 inherit increased glucose uptake stem cell properties. In lymphocyte subsets, the expression of ACAC, ASS1, ATP5A, CPT1A, and PRDX2 in CD4+ T subgroups (naive and memory CD4+ T and nTreg) were elevated than in B subgroups (pro-, pre-, immature and mature Bs) and CD8+ T subgroups. Furthermore, leukemia stem cells (LSCs) had increased levels of ACAC, CPT1A, G6PD, IDH2, and PRDX2 than leukemia cells, indicating a stronger metabolic capacity of LSCs than differentiated leukemia cells.

Unraveling Heterogeneity in the Aging Hematopoietic Stem Cell Compartment: An Insight From Single-cell Approaches

Specific cell types and, therefore, organs respond differently during aging. This is also true for the hematopoietic system, where it has been demonstrated that hematopoietic stem cells alter a variety of features, such as their metabolism, and accumulate DNA damage, which can lead to clonal outgrowth over time. In addition, profound changes in the bone marrow microenvironment upon aging lead to senescence in certain cell types such as mesenchymal stem cells and result in increased inflammation. This heterogeneity makes it difficult to pinpoint the molecular drivers of organismal aging gained from bulk approaches, such as RNA sequencing. A better understanding of the heterogeneity underlying the aging process in the hematopoietic compartment is, therefore, needed. With the advances of single-cell technologies in recent years, it is now possible to address fundamental questions of aging. In this review, we discuss how single-cell approaches can and indeed are already being used to understand changes observed during aging in the hematopoietic compartment. We will touch on established and novel methods for flow cytometric detection, single-cell culture approaches, and single-cell omics.

Mesenchymal loss of p53 alters stem cell capacity and models human soft tissue sarcoma traits

Soft tissue sarcomas (STSs) are a heterogeneous group of tumors that originate from mesenchymal cells. p53 is frequently mutated in human STS. In this study, we found that the loss of p53 in mesenchymal stem cells (MSCs) mainly causes adult undifferentiated soft tissue sarcoma (USTS). MSCs lacking p53 show changes in stem cell properties, including differentiation, cell cycle progression, and metabolism. The transcriptomic changes and genetic mutations in murine p53-deficient USTS mimic those seen in human STS. Furthermore, single-cell RNA sequencing revealed that MSCs undergo transcriptomic alterations with aging-a risk factor for certain types of USTS-and that p53 signaling decreases simultaneously. Moreover, we found that human STS can be transcriptomically classified into six clusters with different prognoses, different from the current histopathological classification. This study paves the way for understanding MSC-mediated tumorigenesis and provides an efficient mouse model for sarcoma studies.

Extracellular Matrix-Mimetic Peptide Scaffolds Prolonged the Hypothermic Preservation of Stem Cells for Storage and Transportation

Encouraging advances in both regenerative medicine and tissue engineering with stem cells require a short-term preservation protocol to provide enough time for quality control or the transportation of cell products from manufacturing facilities to clinical destinations. The hypothermic preservation of stem cells under refrigerated conditions (2-8 °C) in their specific culture medium provides an alternative and low-cost method for cryopreservation or commercial preservation fluid for short-term storage. However, most stem cells are vulnerable to hypothermia, which might result in cell damage from the cooling process and the lack of extracellular matrix (ECM). Herein, we report a peptide scaffold cell-culture-medium additive for mimicking in vivo ECM to enhance the storage efficiency of mesenchymal stem cells (MSCs) under hypothermic preservation. Peptide scaffolds exhibit protective effects against hypothermic injury by maintaining the viability, proliferation, migration, and differentiation capabilities of cells. The mechanistic study showed that the peptide scaffold was conducive to maintain mitochondrial function by retaining mitochondrial respiration, mitochondrial membrane potential (ΔΨm), and mass to alleviate intracellular and mitochondrial reactive oxygen species (ROS) production. Moreover, the peptide scaffold also prolonged the survival and retained the multipotency of hematopoietic stem and progenitor cells (HSPCs) under hypothermic conditions. In conclusion, these results demonstrate a feasible and convenient preservation system for stem cells that has the potential to promote the clinical application of hematopoietic stem cell therapy.

Hematopoietic Stem Cells and Metabolic Deterioration in Alström Syndrome, a Rare Genetic Model of the Metabolic Syndrome

Alström syndrome (AS) is a rare genetic disease caused by ALMS1 mutations, characterized by short stature, and vision and hearing loss. Patients with AS develop the metabolic syndrome, long-term organ complications, and die prematurely. We explored the association between AS and a shortage of hematopoietic stem/progenitor cells (HSPCs), which is linked to metabolic diseases and predicts diabetic complications. We included patients with AS at a national referral center. We measured HSPCs with flow cytometry at baseline and follow-up. We followed patients up to January 2022 for metabolic worsening and end-organ damage. We evaluated HSPC levels and mobilization as well as bone marrow histology in a murine model of AS. In 23 patients with AS, we found significantly lower circulating HSPCs than in healthy blood donors (-40%; P = .002) and age/sex-matched patients (-25%; P = .022). Longitudinally, HSPCs significantly declined by a further 20% in patients with AS over a median of 36 months (interquartile range 30-44). Patients with AS who displayed metabolic deterioration over 5.3 years had lower levels of HSPCs, both at baseline and at last observation, than those who did not deteriorate. Alms1-mutated mice were obese and insulin resistant and displayed significantly reduced circulating HSPCs, despite no overt hematological abnormality. Contrary to what was observed in diabetic mice, HSPC mobilization and bone marrow structure were unaffected. We found depletion of HSPCs in patients with AS, which was recapitulated in Alms1-mutated mice. Larger and longer studies will be needed to establish HSPCs shortage as a driver of metabolic deterioration leading to end-organ damage in AS.

BML-260 promotes the growth of cord blood and mobilized peripheral blood hematopoietic stem and progenitor cells with improved reconstitution ability

Hematopoietic stem cells (HSCs), which are multipotent and have the ability to self-renew, are frequently used in the treatment of hematological diseases and cancer. Small molecules that target HSC quiescence regulators could be used for ex vivo expansion of both mobilized peripheral blood (mPB) and umbilical cord blood (UCB) hematopoietic stem and progenitor cells (HSPC). We identified and investigated 35 small molecules that target HSC quiescence factors. We looked at how they affected HSC activity, such as expansion, quiescence, multilineage capacity, cycling ability, metabolism, cytotoxicity, and genotoxicity. A transplantation study was carried out on immunocompromised mice to assess the expanded cells' repopulation and engraftment abilities. 4-[(5Z)-5-benzylidene-4-oxo-2-sulfanylidene-1,3-thiazolidin-3-yl]benzoic acid (BML)-260 and tosyl-l-arginine methyl ester (TAME) significantly increased both mPB and UCB-HSPC content and activated HSC re-entry into the cell cycle. The improved multilineage capacity was confirmed by the colony forming unit (CFU) assay. Furthermore, gene expression analysis revealed that BML-260 and TAME molecules aided HSC expansion by modulating cell cycle kinetics, such as p27, SKP2, and CDH1. In addition to these in vitro findings, we discovered that BML-260-expanded HSCs had a high hematopoietic reconstitution capacity with increased immune cell content after xenotransplantation into immunocompromised mice. In addition to the BML-260 molecule, a comparison study of serum-containing and serum-free chemically defined media, including various supplements, was performed. These in vitro and xenotransplantation results show that BML-260 molecules can be used for human HSC expansion and regulation of function. Furthermore, the medium composition discovered may be a novel platform for human HSPC expansion that could be used in clinical trials.

Acly Deficiency Enhances Myelopoiesis through Acetyl Coenzyme A and Metabolic-Epigenetic Cross-Talk

Hematopoiesis integrates cytokine signaling, metabolism, and epigenetic modifications to regulate blood cell generation. These processes are linked, as metabolites provide essential substrates for epigenetic marks. In this study, we demonstrate that ATP citrate lyase (Acly), which metabolizes citrate to generate cytosolic acetyl-CoA and is of clinical interest, can regulate chromatin accessibility to limit myeloid differentiation. Acly was tested for a role in murine hematopoiesis by small-molecule inhibition or genetic deletion in lineage-depleted, c-Kit-enriched hematopoietic stem and progenitor cells from Mus musculus. Treatments increased the abundance of cell populations that expressed the myeloid integrin CD11b and other markers of myeloid differentiation. When single-cell RNA sequencing was performed, we found that Acly inhibitor-treated hematopoietic stem and progenitor cells exhibited greater gene expression signatures for macrophages and enrichment of these populations. Similarly, the single-cell assay for transposase-accessible chromatin sequencing showed increased chromatin accessibility at genes associated with myeloid differentiation, including CD11b, CD11c, and IRF8. Mechanistically, Acly deficiency altered chromatin accessibility and expression of multiple C/EBP family transcription factors known to regulate myeloid differentiation and cell metabolism, with increased Cebpe and decreased Cebpa and Cebpb. This effect of Acly deficiency was accompanied by altered mitochondrial metabolism with decreased mitochondrial polarization but increased mitochondrial content and production of reactive oxygen species. The bias to myeloid differentiation appeared due to insufficient generation of acetyl-CoA, as exogenous acetate to support alternate compensatory pathways to produce acetyl-CoA reversed this phenotype. Acly inhibition thus can promote myelopoiesis through deprivation of acetyl-CoA and altered histone acetylome to regulate C/EBP transcription factor family activity for myeloid differentiation.

Loss of sphingosine kinase 2 promotes the expansion of hematopoietic stem cells by improving their metabolic fitness

Hematopoietic stem cells (HSCs) have reduced capacities to properly maintain and replenish the hematopoietic system during myelosuppressive injury or aging. Expanding and rejuvenating HSCs for therapeutic purposes has been a long-sought goal with limited progress. Here, we show that the enzyme Sphk2 (sphingosine kinase 2), which generates the lipid metabolite sphingosine-1-phosphate, is highly expressed in HSCs. The deletion of Sphk2 markedly promotes self-renewal and increases the regenerative potential of HSCs. More importantly, Sphk2 deletion globally preserves the young HSC gene expression pattern, improves the function, and sustains the multilineage potential of HSCs during aging. Mechanistically, Sphk2 interacts with prolyl hydroxylase 2 and the Von Hippel-Lindau protein to facilitate HIF1α ubiquitination in the nucleus independent of the Sphk2 catalytic activity. Deletion of Sphk2 increases hypoxic responses by stabilizing the HIF1α protein to upregulate PDK3, a glycolysis checkpoint protein for HSC quiescence, which subsequently enhances the function of HSCs by improving their metabolic fitness; specifically, it enhances anaerobic glycolysis but suppresses mitochondrial oxidative phosphorylation and generation of reactive oxygen species. Overall, targeting Sphk2 to enhance the metabolic fitness of HSCs is a promising strategy to expand and rejuvenate functional HSCs.

Central gene transcriptional regulatory networks shaping monocyte development in bone marrow

The development of monocytes in bone marrow is a complex process with multiple steps. We used RNA-seq data to analyze the transcriptome profiles in developing stages of monocytes, including hematopoietic stem cells (HSCs), common myeloid progenitors (CMPs), granulocyte-monocyte progenitors (GMPs), and monocytes. We found that genes related to potassium and other cation transmembrane activities and ion binding were upregulated during the differentiation of HSCs into CMPs. Protein transport and membrane surface functional molecules were significantly upregulated in the GMP stage. The CD42RAC and proteasome pathways are significantly upregulated during the development of HSCs into monocytes. Transcription factors Ank1, Runx2, Hmga2, Klf1, Nfia, and Bmyc were upregulated during the differentiation of HSCs into CMPs; Gfi1 and Hmgn2 were highly expressed during the differentiation of CMPs into GMPs; Seventeen transcription factors including Foxo1, Cdkn2d, Foxo3, Ep300, Pias1, Nfkb1, Creb1, Bcl6, Ppp3cb, Stat5b, Nfatc4, Mef2a, Stat6, Ifnar2, Irf7, Irf5, and Cebpb were identified as potentially involved in the development of GMPs into monocytes in mice and humans. In metabolism pathway regulation, HSCs have high glucose, lipid, and nucleic acid metabolism activities; CMPs mainly up regulate the TCA cycle related genes; and GMPs have extremely active metabolisms, with significantly elevated pentose phosphate pathway, TCA cycle, histidine metabolism, and purine metabolism. In the monocyte phase, the tricarboxylic acid (TCA) cycle is reduced, and the anaerobic glycolysis process becomes dominated. Overall, our studies offer the kinetics and maps of gene transcriptional expressions and cell metabolisms during monocyte development in bone marrow.

Lysosomes and Their Role in Regulating the Metabolism of Hematopoietic Stem Cells

Hematopoietic stem cells (HSCs) have the capacity to renew blood cells at all stages of life and are largely quiescent at a steady state. It is essential to understand the processes that govern quiescence in HSCs to enhance bone marrow transplantation. It is hypothesized that in their quiescent state, HSCs primarily use glycolysis for energy production rather than mitochondrial oxidative phosphorylation (OXPHOS). In addition, the HSC switch from quiescence to activation occurs along a continuous developmental path that is driven by metabolism. Specifying the metabolic regulation pathway of HSC quiescence will provide insights into HSC homeostasis for therapeutic application. Therefore, understanding the metabolic demands of HSCs at a steady state is key to developing innovative hematological therapeutics. Lysosomes are the major degradative organelle in eukaryotic cells. Catabolic, anabolic, and lysosomal function abnormalities are connected to an expanding list of diseases. In recent years, lysosomes have emerged as control centers of cellular metabolism, particularly in HSC quiescence, and essential regulators of cell signaling have been found on the lysosomal membrane. In addition to autophagic processes, lysosomal activities have been shown to be crucial in sustaining quiescence by restricting HSCs access to a nutritional reserve essential for their activation into the cell cycle. Lysosomal activity may preserve HSC quiescence by altering glycolysis-mitochondrial biogenesis. The understanding of HSC metabolism has significantly expanded over the decade, revealing previously unknown requirements of HSCs in both their dividing (active) and quiescent states. Therefore, understanding the role of lysosomes in HSCs will allow for the development of innovative treatment methods based on HSCs to fight clonal hematopoiesis and HSC aging.

Role of pyroptosis in inflammation and cancer

Pyroptosis is a form of programmed cell death mediated by gasdermin and is a product of continuous cell expansion until the cytomembrane ruptures, resulting in the release of cellular contents that can activate strong inflammatory and immune responses. Pyroptosis, an innate immune response, can be triggered by the activation of inflammasomes by various influencing factors. Activation of these inflammasomes can induce the maturation of caspase-1 or caspase-4/5/11, both of which cleave gasdermin D to release its N-terminal domain, which can bind membrane lipids and perforate the cell membrane. Here, we review the latest advancements in research on the mechanisms of pyroptosis, newly discovered influencing factors, antitumoral properties, and applications in various diseases. Moreover, this review also provides updates on potential targeted therapies for inflammation and cancers, methods for clinical prevention, and finally challenges and future directions in the field.

Zeb1 sustains hematopoietic stem cell functions by suppressing mitofusin-2-mediated mitochondrial fusion

Metabolic status is essential in maintaining normal functions of hematopoietic stem cells (HSCs). However, how the dynamic of the mitochondrion, as a central organelle in metabolism, is molecularly regulated to orchestrate metabolism and HSC stemness remains to be elucidated. Here, we focus on the role of Zeb1, a well-characterized epithelial-to-mesenchymal transition (EMT) inducer which has been demonstrated to confer stem-cell-like characteristics in multiple cancer types in stemness regulation of HSCs. Using a Zeb1-tdTomato reporter mouse model, we find that Zeb1⁺Lin^-Sca-1⁺c-Kit⁺ cells (Zeb1⁺-LSKs) represent a subset of functional long-term HSCs. Zeb1⁺LSKs exhibit a reduced reactive oxygen species (ROS) level, low mitochondrial mass, low mitochondrial membrane potential (MMP), and particularly small, round fragmented mitochondria. Of note, ectopic expression of Zeb1 leads to a fragmented mitochondrial morphology with a low mitochondrial metabolic status in EML cells. In addition, Zeb1-knockout (Zeb1-KO) LSKs from fetal liver display an exhausted stem-cell activity. Zeb1 deficiency results in elongated and tubulated mitochondria with increased mitochondrial mass, elevated MMP, and higher ROS production. Mechanistically, Zeb1 acts as a transcriptional suppressor on the key mitochondrial-fusion protein Mitofusin-2 (encoded by Mfn2). We highlight an important role of Zeb1 in the regulation of mitochondrial morphology in HSC and the metabolic control of HSC stemness by repressing Mfn2-mediated mitochondrial fusion.

UHPLC/MS-Based Serum Metabolomics Reveals the Mechanism of Radiation-Induced Thrombocytopenia in Mice

Radiation-induced thrombocytopenia is a common and life-threatening side effect of ionizing radiation (IR) therapy. However, the underlying pathological mechanisms remain unclear. In the present study, irradiation was demonstrated to significantly reduce platelet levels, inhibit megakaryocyte differentiation, and promote the apoptosis of bone marrow (BM) cells. A metabolomics approach and a UHPLC-QTOF MS system were subsequently employed for the comprehensive analysis of serum metabolic profiles of normal and irradiated mice. A total of 66 metabolites were significantly altered, of which 56 were up-regulated and 10 were down-regulated in irradiated mice compared to normal mice on day 11 after irradiation. Pathway analysis revealed that disorders in glycerophospholipid metabolism, nicotinate and nicotinamide metabolism, sphingolipid metabolism, inositol phosphate metabolism, and tryptophan metabolism were involved in radiation-induced thrombocytopenia. In addition, three important differential metabolites, namely L-tryptophan, LysoPC (17:0), and D-sphinganine, which were up-regulated in irradiated mice, significantly induced the apoptosis of K562 cells. L-tryptophan inhibited megakaryocyte differentiation of K562 cells. Finally, serum metabolomics was performed on day 30 (i.e., when the platelet levels in irradiated mice recovered to normal levels). The contents of L-tryptophan, LysoPC (17:0), and D-sphinganine in normal and irradiated mice did not significantly differ on day 30 after irradiation. In conclusion, radiation can cause metabolic disorders, which are highly correlated with the apoptosis of hematopoietic cells and inhibition of megakaryocyte differentiation, ultimately resulting in thrombocytopenia. Further, the metabolites, L-tryptophan, LysoPC (17:0), and D-sphinganine can serve as biomarkers for radiation-induced thrombocytopenia.

The new metabolic needs of hematopoietic stem cells

PURPOSE OF REVIEW

Hematopoietic stem cells (HSCs) are endowed with high regenerative potential to supply mature blood cells throughout life, under steady state or stress conditions. HSCs are thought to rely on glycolysis when in a quiescent state and to switch to oxidative phosphorylation to meet their metabolic needs during activation. Recently, a series of important studies reveals a higher degree of complexity that goes well beyond the dichotomy between glycolysis and oxidative phosphorylation. The purpose of this review is to summarize the recent findings highlighting the multifaceted metabolic requirements of HSC homeostasis.

RECENT FINDINGS

Emerging evidence points to the importance of lysosomal catabolic activity and noncanonical retinoic acid pathway in maintaining HSC quiescence and stemness. HSC activation into cycle seems to be accompanied by a switch to glycolysis-mitochondrial coupling and to anabolic pathways, including Myc, aspartate-mediated purine synthesis.

SUMMARY

Knowledge of metabolism of HSCs has dramatically increased in the past 2 years and reveals unexpected needs of HSCs during both their quiescent and activated state. Understanding how HSCs use metabolism for their functions will offer new opportunity for HSC-based therapies.

Molecular regulation of hematopoietic stem cell quiescence

Hematopoietic stem cells (HSCs) are primarily dormant in a cell-cycle quiescence state to preserve their self-renewal capacity and long-term maintenance, which is essential for the homeostasis of hematopoietic system. Dysregulation of quiescence causes HSC dysfunction and may result in aberrant hematopoiesis (e.g., myelodysplastic syndrome and bone marrow failure syndromes) and leukemia transformation. Accumulating evidence indicates that both intrinsic molecular networks and extrinsic signals regulate HSC quiescence, including cell-cycle regulators, transcription factors, epigenetic factors, and niche factors. Further, the transition between quiescence and activation of HSCs is a continuous developmental path driven by cell metabolism (e.g., protein synthesis, glycolysis, oxidative phosphorylation, and autophagy). Elucidating the complex regulatory networks of HSC quiescence will expand the knowledge of HSC hemostasis and benefit for clinical HSC use. Here, we review the current understanding and progression on the molecular and metabolic regulation of HSC quiescence, providing a more complete picture regarding the mechanisms of HSC quiescence maintenance.

Mitochondrial calcium homeostasis in hematopoietic stem cell: Molecular regulation of quiescence, function, and differentiation

Hematopoiesis is based on the existence of hematopoietic stem cells (HSC) with the capacity to self-proliferate and self-renew or to differentiate into specialized cells. The hematopoietic niche is the essential microenvironment where stem cells reside and integrate various stimuli to determine their fate. Recent studies have identified niche containing high level of calcium (Ca²⁺) suggesting that HSCs are sensitive to Ca²⁺. This is a highly versatile and ubiquitous second messenger that regulates a wide variety of cellular functions. Advanced methods for measuring its concentrations, genetic experiments, cell fate tracing data, single-cell imaging, and transcriptomics studies provide information into its specific roles to integrate signaling into an array of mechanisms that determine HSC identity, lineage potential, maintenance, and self-renewal. Accumulating and contrasting evidence, are revealing Ca²⁺ as a previously unacknowledged feature of HSC, involved in functional maintenance, by regulating multiple actors including transcription and epigenetic factors, Ca²⁺-dependent kinases and mitochondrial physiology. Mitochondria are significant participants in HSC functions and their responsiveness to cellular demands is controlled to a significant extent via Ca²⁺ signals. Recent reports indicate that mitochondrial Ca²⁺ uptake also controls HSC fate. These observations reveal a physiological feature of hematopoietic stem cells that can be harnessed to improve HSC-related disease. In this review, we discuss the current knowledge Ca²⁺ in hematopoietic stem cell focusing on its potential involvement in proliferation, self-renewal and maintenance of HSC and discuss future research directions.

Mitochondrial metabolism as a potential therapeutic target in myeloid leukaemia

While the understanding of the genomic aberrations that underpin chronic and acute myeloid leukaemia (CML and AML) has allowed the development of therapies for these diseases, limitations remain. These become apparent when looking at the frequency of treatment resistance leading to disease relapse in leukaemia patients. Key questions regarding the fundamental biology of the leukaemic cells, such as their metabolic dependencies, are still unresolved. Even though a majority of leukaemic cells are killed during initial treatment, persistent leukaemic stem cells (LSCs) and therapy-resistant cells are still not eradicated with current treatments, due to various mechanisms that may contribute to therapy resistance, including cellular metabolic adaptations. In fact, recent studies have shown that LSCs and treatment-resistant cells are dependent on mitochondrial metabolism, hence rendering them sensitive to inhibition of mitochondrial oxidative phosphorylation (OXPHOS). As a result, rewired energy metabolism in leukaemic cells is now considered an attractive therapeutic target and the significance of this process is increasingly being recognised in various haematological malignancies. Therefore, identifying and targeting aberrant metabolism in drug-resistant leukaemic cells is an imperative and a relevant strategy for the development of new therapeutic options in leukaemia. In this review, we present a detailed overview of the most recent studies that present experimental evidence on how leukaemic cells can metabolically rewire, more specifically the importance of OXPHOS in LSCs and treatment-resistant cells, and the current drugs available to target this process. We highlight that uncovering specific energy metabolism dependencies will guide the identification of new and more targeted therapeutic strategies for myeloid leukaemia.

Oxidative Stress and X-ray Exposure Levels-Dependent Survival and Metabolic Changes in Murine HSPCs

Haematopoietic bone marrow cells are amongst the most sensitive to ionizing radiation (IR), initially resulting in cell death or genotoxicity that may later lead to leukaemia development, most frequently Acute Myeloid Leukaemia (AML). The target cells for radiation-induced Acute Myeloid Leukaemia (rAML) are believed to lie in the haematopoietic stem and progenitor cell (HSPC) compartment. Using the inbred strain CBA/Ca as a murine model of rAML, progress has been made in understanding the underlying mechanisms, characterisation of target cell population and responses to IR. Complex regulatory systems maintain haematopoietic homeostasis which may act to modulate the risk of rAML. However, little is currently known about the role of metabolic factors and diet in these regulatory systems and modification of the risk of AML development. This study characterises cellular proliferative and clonogenic potential as well as metabolic changes within murine HSPCs under oxidative stress and X-ray exposure. Ambient oxygen (normoxia; 20.8% O2) levels were found to increase irradiated HSPC-stress, stimulating proliferative activity compared to low oxygen (3% O2) levels. IR exposure has a negative influence on the proliferative capability of HSPCs in a dose-dependent manner (0-2 Gy) and this is more pronounced under a normoxic state. One Gy x-irradiated HSPCs cultured under normoxic conditions displayed a significant increase in oxygen consumption compared to those cultured under low O2 conditions and to unirradiated HSPCs. Furthermore, mitochondrial analyses revealed a significant increase in mitochondrial DNA (mtDNA) content, mitochondrial mass and membrane potential in a dose-dependent manner under normoxic conditions. Our results demonstrate that both IR and normoxia act as stressors for HSPCs, leading to significant metabolic deregulation and mitochondrial dysfunctionality which may affect long term risks such as leukaemia.

Role of GM-CSF in regulating metabolism and mitochondrial functions critical to macrophage proliferation

Granulocyte-macrophage colony-stimulating factor (GM-CSF) exerts pleiotropic effects on macrophages and is required for self-renewal but the mechanisms responsible are unknown. Using mouse models with disrupted GM-CSF signaling, we show GM-CSF is critical for mitochondrial turnover, functions, and integrity. GM-CSF signaling is essential for fatty acid β-oxidation and markedly increased tricarboxylic acid cycle activity, oxidative phosphorylation, and ATP production. GM-CSF also regulated cytosolic pathways including glycolysis, pentose phosphate pathway, and amino acid synthesis. We conclude that GM-CSF regulates macrophages in part through a critical role in maintaining mitochondria, which are necessary for cellular metabolism as well as proliferation and self-renewal.

Inflammatory Modulation of Hematopoiesis: Linking Trained Immunity and Clonal Hematopoiesis with Chronic Disorders

Inflammation-adapted hematopoietic stem and progenitor cells (HSPCs) have long been appreciated as key drivers of emergency myelopoiesis, thereby enabling the bone marrow to meet the elevated demand for myeloid cell generation under various stress conditions, such as systemic infection, inflammation, or myelosuppressive insults. In recent years, HSPC adaptations were associated with potential involvement in the induction of long-lived trained immunity and the emergence of clonal hematopoiesis of indeterminate potential (CHIP). Whereas trained immunity has context-dependent effects, protective in infections and tumors but potentially detrimental in chronic inflammatory diseases, CHIP increases the risk for hematological neoplastic disorders and cardiometabolic pathologies. This review focuses on the inflammatory regulation of HSPCs in the aforementioned processes and discusses how modulation of HSPC function could lead to novel therapeutic interventions. Expected final online publication date for the Annual Review of Physiology, Volume 84 is February 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Unique metabolic phenotype and its transition during maturation of juvenile male germ cells

Human male reproductive development has a prolonged prepubertal period characterized by juvenile quiescence of germ cells with immature spermatogonial stem cell (SSC) precursors (gonocytes) present in the testis for an extended period of time. The metabolism of gonocytes is not defined. We demonstrate with mitochondrial ultrastructure studies via TEM and IHC and metabolic flux studies with UHPLC-MS that a distinct metabolic transition occurs during the maturation to SSCs. The mitochondrial ultrastructure of prepubertal human spermatogonia is shared with prepubertal pig spermatogonia. The metabolism of early prepubertal porcine spermatogonia (gonocytes) is characterized by the reliance on OXPHOS fuelled by oxidative decarboxylation of pyruvate. Interestingly, at the same time, a high amount of the consumed pyruvate is also reduced and excreted as lactate. With maturation, prepubertal spermatogonia show a metabolic shift with decreased OXHPOS and upregulation of the anaerobic metabolism-associated uncoupling protein 2 (UCP2). This shift is accompanied with stem cell specific promyelocytic leukemia zinc finger protein (PLZF) protein expression and glial cell-derived neurotropic factor (GDNF) pathway activation. Our results demonstrate that gonocytes differently from mature spermatogonia exhibit unique metabolic demands that must be attained to enable their maintenance and growth in vitro.

Impact of Diabetes Mellitus on the Potential of Autologous Stem Cells and Stem Cell-Derived Microvesicles to Repair the Ischemic Heart

Ischemic heart disease remains the leading cause of morbidity and mortality worldwide. Despite the advances in medical management and catheter-based therapy, mortality remains high, as does the risk of developing heart failure. Regenerative therapies have been widely used as an alternative option to repair the damaged heart mainly because of their paracrine-related beneficial effects. Although cell-based therapy has been demonstrated as feasible and safe, randomized controlled trials and meta-analyses show little consistent benefit from treatments with adult-derived stem cells. Mounting evidence from our group and others supports that cardiovascular risk factors and comorbidities impair stem cell potential thus hampering their autologous use. This review aims to better understand the influence of diabetes on stem cell potential. For this purpose, we will first discuss the most recent advances in the mechanistic understanding of the effects of diabetes on stem cell phenotype, function, and molecular fingerprint to further elaborate on diabetes-induced alterations in stem cell extracellular vesicle profile. Although we acknowledge that multiple sources of stem or progenitor cells are used for regenerative purposes, we will focus on bone marrow hematopoietic stem/progenitor cells, mesenchymal stem cells residing in the bone marrow, and adipose tissue and briefly discuss endothelial colony-forming cells.

Lipid metabolism in focus: how the build-up and breakdown of lipids affects stem cells

Cellular metabolism has recently emerged as a key regulator of stem cell behavior. Various studies have suggested that metabolic regulatory mechanisms are conserved in different stem cell niches, suggesting a common level of stem cell regulation across tissues. Although the balance between glycolysis and oxidative phosphorylation has been shown to be distinct in stem cells and their differentiated progeny, much less is known about lipid metabolism in stem cell regulation. In this Review, we focus on how stem cells are affected by two major lipid metabolic pathways: the build-up of lipids, called de novo lipogenesis, and the breakdown of lipids, called fatty acid beta-oxidation. We cover the recent literature on hematopoietic stem cells, intestinal stem cells, neural stem/progenitor cells and cancer stem cells, where these two lipid pathways have been studied in more depth.

Alternative Polyadenylation in Stem Cell Self-Renewal and Differentiation

Cellular function is shaped by transcriptional and post-transcriptional mechanisms, including alternative polyadenylation (APA). By directly controlling 3'- untranslated region (UTR) length and the selection of the last exon, APA regulates up to 70% of all cellular transcripts influencing RNA stability, output, and protein isoform expression. Cell-state-dependent 3'-UTR shortening has been identified as a hallmark of cellular proliferation. Hence, quiescent/dormant stem cells are characterized by long 3'-UTRs, whereas proliferative stem/progenitor cells exhibit 3'-UTR shortening. Here, the latest studies analyzing the role of APA in regulating stem cell state, self-renewal, differentiation, and metabolism are reviewed. The new role of APA in controlling stem cell fate opens novel potential therapeutic avenues in the field of regenerative medicine.

Nuclear DEK preserves hematopoietic stem cells potential via NCoR1/HDAC3-Akt1/2-mTOR axis

The oncogene DEK is found fused with the NUP214 gene creating oncoprotein DEK-NUP214 that induces acute myeloid leukemia (AML) in patients, and secreted DEK protein functions as a hematopoietic cytokine to regulate hematopoiesis; however, the intrinsic role of nuclear DEK in hematopoietic stem cells (HSCs) remains largely unknown. Here, we show that HSCs lacking DEK display defects in long-term self-renew capacity, eventually resulting in impaired hematopoiesis. DEK deficiency reduces quiescence and accelerates mitochondrial metabolism in HSCs, in part, dependent upon activating mTOR signaling. At the molecular level, DEK recruits the corepressor NCoR1 to repress acetylation of histone 3 at lysine 27 (H3K27ac) and restricts the chromatin accessibility of HSCs, governing the expression of quiescence-associated genes (e.g., Akt1/2, Ccnb2, and p21). Inhibition of mTOR activity largely restores the maintenance and potential of Dek-cKO HSCs. These findings highlight the crucial role of nuclear DEK in preserving HSC potential, uncovering a new link between chromatin remodelers and HSC homeostasis, and have clinical implications.

Mitochondria Turnover and Lysosomal Function in Hematopoietic Stem Cell Metabolism

Hematopoietic stem cells (HSCs) reside in a hypoxic microenvironment that enables glycolysis-fueled metabolism and reduces oxidative stress. Nonetheless, metabolic regulation in organelles such as the mitochondria and lysosomes as well as autophagic processes have been implicated as essential for the determination of HSC cell fate. This review encompasses the current understanding of anaerobic metabolism in HSCs as well as the emerging roles of mitochondrial metabolism and lysosomal regulation for hematopoietic homeostasis.

A single-cell resolution developmental atlas of hematopoietic stem and progenitor cell expansion in zebrafish

The caudal hematopoietic tissue (CHT) is characterized as a hematopoietic organ for fetal hematopoietic stem and progenitor cell (HSPC) expansion in zebrafish. In this study, we used scRNA-seq combined with functional assays to decode the developing CHT. First, we resolved fetal HSPC heterogeneity, manifested as lineage priming and metabolic gene signatures. We further analyzed the cellular interactions among nonhematopoietic niche components and HSPCs and identified an endothelial cell-specific factor, Gpr182, followed by experimental validation of its role in promoting HSPC expansion. Finally, we uncovered the conservation and divergence of developmental hematopoiesis between human fetal liver and zebrafish CHT. Our study provides a valuable resource for fetal HSPC development and clues to establish a supportive niche for HSPC expansion in vitro.

During vertebrate embryogenesis, fetal hematopoietic stem and progenitor cells (HSPCs) exhibit expansion and differentiation properties in a supportive hematopoietic niche. To profile the developmental landscape of fetal HSPCs and their local niche, here, using single-cell RNA-sequencing, we deciphered a dynamic atlas covering 28,777 cells and 9 major cell types (23 clusters) of zebrafish caudal hematopoietic tissue (CHT). We characterized four heterogeneous HSPCs with distinct lineage priming and metabolic gene signatures. Furthermore, we investigated the regulatory mechanism of CHT niche components for HSPC development, with a focus on the transcription factors and ligand–receptor networks involved in HSPC expansion. Importantly, we identified an endothelial cell-specific G protein–coupled receptor 182, followed by in vivo and in vitro functional validation of its evolutionally conserved role in supporting HSPC expansion in zebrafish and mice. Finally, comparison between zebrafish CHT and human fetal liver highlighted the conservation and divergence across evolution. These findings enhance our understanding of the regulatory mechanism underlying hematopoietic niche for HSPC expansion in vivo and provide insights into improving protocols for HSPC expansion in vitro.

Autophagy in Viral Development and Progression of Cancer

Autophagy is a complex degradative process by which eukaryotic cells capture cytoplasmic components for subsequent degradation through lysosomal hydrolases. Although this catabolic process can be triggered by a great variety of stimuli, action in cells varies according to cellular context. Autophagy has been previously linked to disease development modulation, including cancer. Autophagy helps suppress cancer cell advancement in tumor transformation early stages, while promoting proliferation and metastasis in advanced settings. Oncoviruses are a particular type of virus that directly contribute to cell transformation and tumor development. Extensive molecular studies have revealed complex ways in which autophagy can suppress or improve oncovirus fitness while still regulating viral replication and determining host cell fate. This review includes recent advances in autophagic cellular function and emphasizes its antagonistic role in cancer cells.

Autophagy in Viral Development and Progression of Cancer

Autophagy is a complex degradative process by which eukaryotic cells capture cytoplasmic components for subsequent degradation through lysosomal hydrolases. Although this catabolic process can be triggered by a great variety of stimuli, action in cells varies according to cellular context. Autophagy has been previously linked to disease development modulation, including cancer. Autophagy helps suppress cancer cell advancement in tumor transformation early stages, while promoting proliferation and metastasis in advanced settings. Oncoviruses are a particular type of virus that directly contribute to cell transformation and tumor development. Extensive molecular studies have revealed complex ways in which autophagy can suppress or improve oncovirus fitness while still regulating viral replication and determining host cell fate. This review includes recent advances in autophagic cellular function and emphasizes its antagonistic role in cancer cells.

Biomechanical Regulation of Hematopoietic Stem Cells in the Developing Embryo

PURPOSE OF REVIEW

The contribution of biomechanical forces to hematopoietic stem cell (HSC) development in the embryo is a relatively nascent area of research. Herein, we address the biomechanics of the endothelial-to-hematopoietic transition (EHT), impact of force on organelles, and signaling triggered by extrinsic forces within the aorta-gonad-mesonephros (AGM), the primary site of HSC emergence.

RECENT FINDINGS

Hemogenic endothelial cells undergo carefully orchestrated morphological adaptations during EHT. Moreover, expansion of the stem cell pool during embryogenesis requires HSC extravasation into the circulatory system and transit to the fetal liver, which is regulated by forces generated by blood flow. Findings from other cell types also suggest that forces external to the cell are sensed by the nucleus and mitochondria. Interactions between these organelles and the actin cytoskeleton dictate processes such as cell polarization, extrusion, division, survival, and differentiation.

SUMMARY

Despite challenges of measuring and modeling biophysical cues in the embryonic HSC niche, the past decade has revealed critical roles for mechanotransduction in governing HSC fate decisions. Lessons learned from the study of the embryonic hematopoietic niche promise to provide critical insights that could be leveraged for improvement in HSC generation and expansion ex vivo.

Metabolic sensor O-GlcNAcylation regulates megakaryopoiesis and thrombopoiesis through c-Myc stabilization and integrin perturbation

Metabolic state of hematopoietic stem cells (HSCs) is an important regulator of self‐renewal and lineage‐specific differentiation. Posttranslational modification of proteins via O‐GlcNAcylation is an ideal metabolic sensor, but how it contributes to megakaryopoiesis and thrombopoiesis remains unknown. Here, we reveal for the first time that cellular O‐GlcNAcylation levels decline along the course of megakaryocyte (MK) differentiation from human‐derived hematopoietic stem and progenitor cells (HSPCs). Inhibition of O‐GlcNAc transferase (OGT) that catalyzes O‐GlcNAcylation prolongedly decreases O‐GlcNAcylation and induces the acquisition of CD34⁺CD41a⁺ MK‐like progenitors and its progeny CD34⁻CD41a⁺/CD42b⁺ megakaryoblasts (MBs)/MKs from HSPCs, consequently resulting in increased CD41a⁺ and CD42b⁺ platelets. Using correlation and co‐immunoprecipitation analyses, we further identify c‐Myc as a direct downstream target of O‐GlcNAcylation in MBs/MKs and provide compelling evidence on the regulation of platelets by novel O‐GlcNAc/c‐Myc axis. Our data indicate that O‐GlcNAcylation posttranslationally regulates c‐Myc stability by interfering with its ubiquitin‐mediated proteasomal degradation. Depletion of c‐Myc upon inhibition of OGT promotes platelet formation in part through the perturbation of cell adhesion molecules, that is, integrin‐α4 and integrin‐β7, as advised by gene ontology and enrichment analysis for RNA sequencing and validated herein. Together, our findings provide a novel basic knowledge on the regulatory role of O‐GlcNAcylation in megakaryopoiesis and thrombopoiesis that could be important in understanding hematologic disorders whose etiology are related to impaired platelet production and may have clinical applications toward an ex vivo platelet production for transfusion.

Targeting Lactate Metabolism by Inhibiting MCT1 or MCT4 Impairs Leukemic Cell Proliferation, Induces Two Different Related Death-Pathways and Increases Chemotherapeutic Sensitivity of Acute Myeloid Leukemia Cells

Metabolism in acute myeloid leukemia (AML) cells is dependent primarily on oxidative phosphorylation. However, in order to sustain their high proliferation rate and metabolic demand, leukemic blasts use a number of metabolic strategies, including glycolytic metabolism. Understanding whether monocarboxylate transporters MCT1 and MCT4, which remove the excess of lactate produced by cancer cells, represent new hematological targets, and whether their respective inhibitors, AR-C155858 and syrosingopine, can be useful in leukemia therapy, may reveal a novel treatment strategy for patients with AML. We analyzed MCT1 and MCT4 expression and function in hematopoietic progenitor cells from healthy cord blood, in several leukemic cell lines and in primary leukemic blasts from patients with AML, and investigated the effects of AR-C155858 and syrosingopine, used alone or in combination with arabinosylcytosine, on leukemic cell proliferation. We found an inverse correlation between MCT1 and MCT4 expression levels in leukemic cells, and showed that MCT4 overexpression is associated with poor prognosis in AML patients. We also found that AR-C155858 and syrosingopine inhibit leukemic cell proliferation by activating two different cell-death related pathways, i.e., necrosis for AR-C155858 treatment and autophagy for syrosingopine, and showed that AR-C155858 and syrosingopine exert an anti-proliferative effect, additive to chemotherapy, by enhancing leukemic cells sensitivity to chemotherapeutic agents. Altogether, our study shows that inhibition of MCT1 or MCT4 impairs leukemic cell proliferation, suggesting that targeting lactate metabolism may be a new therapeutic strategy for AML, and points to MCT4 as a potential therapeutic target in AML patients and to syrosingopine as a new anti-proliferative drug and inducer of autophagy to be used in combination with conventional chemotherapeutic agents in AML treatment.

Understanding the "SMART" features of hematopoietic stem cells and beyond

Since the huge success of bone marrow transplantation technology in clinical practice, hematopoietic stem cells (HSCs) have become the gold standard for defining the properties of adult stem cells (ASCs). Here, we describe the "self-renewal, multi-lineage differentiation, apoptosis, rest, and trafficking" or "SMART" model, which has been developed based on data derived from studies of HSCs as the most well-characterized stem cell type. Given the potential therapeutic applications of ASCs, we delineate the key characteristics of HSCs using this model and speculate on the physiological relevance of stem cells identified in other tissues. Great strides are being made in understanding the biology of ASCs, and efforts are now underway to develop safe and effective ASC-based therapies in this emerging area.

Immunometabolic control of hematopoiesis

Hematopoietic stem cells (HSC) lie at the center of the hematopoiesis process, as they bear capacity to self-renew and generate all hematopoietic lineages, hence, all mature blood cells. The ability of HSCs to recognize systemic infection or inflammation or other forms of peripheral stress, such as blood loss, is essential for demand-adapted hematopoiesis. Also of critical importance for HSC function, specific metabolic cues (e.g., associated with changes in energy or O₂ levels) can regulate HSC function and fate decisions. In this regard, the metabolic adaptation of HSCs facilitates their switching between different states, namely quiescence, self-renewal, proliferation and differentiation. Specific metabolic alterations in hematopoietic stem and progenitor cells (HSPCs) have been linked with the induction of trained myelopoiesis in the bone marrow as well as with HSPC dysfunction in aging and clonal hematopoiesis of indeterminate potential (CHIP). Thus, HSPC function is regulated by both immunologic/inflammatory and metabolic cues. The immunometabolic control of HSPCs and of hematopoiesis is discussed in this review along with the translational implications thereof, that is, how metabolic pathways can be therapeutically manipulated to prevent or reverse HSPC dysfunction or to enhance or attenuate trained myelopoiesis according to the needs of the host.