Distribution of hematopoietic stem cells in the bone marrow according to regional hypoxia

Hypoxia Promotes the Stemness of Mesangiogenic Progenitor Cells and Prevents Osteogenic but not Angiogenic Differentiation

The stem cell niche in the bone marrow is a hypoxic environment, where the low oxygen tension preserves the pluripotency of stem cells. We have identified mesangiogenic progenitor cells (MPC) exhibiting angiogenic and mesenchymal differentiation capabilities in vitro. The effect of hypoxia on MPC has not been previously explored. In this study, MPCs were isolated from volunteers' bone marrow and cultured under both normoxic and hypoxic conditions (3% O2). MPCs maintained their characteristic morphology and surface marker expression (CD18 + CD31 + CD90-CD73-) under hypoxia. However, hypoxic conditions led to reduced MPC proliferation in primary cultures and hindered their differentiation into mesenchymal stem cells (MSCs) upon exposure to differentiative medium. First passage MSCs derived from MPC appeared unaffected by hypoxia, exhibiting no discernible differences in proliferative potential or cell cycle. However, hypoxia impeded the subsequent osteogenic differentiation of MSCs, as evidenced by decreased hydroxyapatite deposition. Conversely, hypoxia did not impact the angiogenic differentiation potential of MPCs, as demonstrated by spheroid-based assays revealing comparable angiogenic sprouting and tube-like formation capabilities under both hypoxic and normoxic conditions. These findings indicate that hypoxia preserves the stemness phenotype of MPCs, inhibits their differentiation into MSCs, and hampers their osteogenic maturation while leaving their angiogenic potential unaffected. Our study sheds light on the intricate effects of hypoxia on bone marrow-derived MPCs and their differentiation pathways.

Tissue mosaicism following stem cell aging: blood as an exemplar

Loss of stem cell regenerative potential underlies aging of all tissues. Somatic mosaicism, the emergence of cellular patchworks within tissues, increases with age and has been observed in every organ yet examined. In the hematopoietic system, as in most tissues, stem cell aging through a variety of mechanisms occurs in lockstep with the emergence of somatic mosaicism. Here, we draw on insights from aging hematopoiesis to illustrate fundamental principles of stem cell aging and somatic mosaicism. We describe the generalizable changes intrinsic to aged stem cells and their milieu that provide the backdrop for somatic mosaicism to emerge. We discuss genetic and nongenetic mechanisms that can result in tissue somatic mosaicism and existing methodologies to detect such clonal outgrowths. Finally, we propose potential avenues to modify mosaicism during aging, with the ultimate aim of increasing tissue resiliency.

Metabolic regulation of the hallmarks of stem cell biology

Stem cells perform many different functions, each of which requires specific metabolic adaptations. Over the past decades, studies of pluripotent and tissue stem cells have uncovered a range of metabolic preferences and strategies that correlate with or exert control over specific cell states. This review aims to describe the common themes that emerge from the study of stem cell metabolism: (1) metabolic pathways supporting stem cell proliferation, (2) metabolic pathways maintaining stem cell quiescence, (3) metabolic control of cellular stress responses and cell death, (4) metabolic regulation of stem cell identity, and (5) metabolic requirements of the stem cell niche.

tRNA-derived small RNA changes in bone marrow stem cells under hypoxia and osteogenic conduction

BACKGROUND

Tissue engineering using bone mesenchymal stem cells (BMSCs) transplantation is a promising therapeutic for bone regeneration. However, the effect of bone regeneration remains unsatisfactory due to the BMSCs' functional abnormality influenced by hypoxia. In this study, we attempt to explore the mechanism of osteogenic differentiation of BMSCs under hypoxic conditions from the perspective of non-coding RNA regulation.

METHODS

The study employed BMSCs obtained from healthy donors and simulated hypoxia using CoCl2 stimulation. High-throughput sequencing technique was used to identify differential expression profiles of tRNA-derived small RNA (tsRNA) in three experimental groups: BMSCs-0d, BMSCs-7d and BMSCs-0d-CoCl2 . TargetScan and miRanda algorithms were used to determine tsRNA target genes, while Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analysis were employed for the prediction of biological functions. Real-time reverse transcriptase-polymerase chain reaction (Real-time RT-PCR) was carried out on four selected differentially expressed tsRNAs.

RESULTS

After the osteogenic induction and CoCl2 stimulated separately, there were 19 tsRNAs differentially expressed in BMSCs, including 14 upregulated and five downregulated. According to the analysis of biological information, these tsRNAs may regulate 311 potential target genes and mainly enrich the pathways such as metabolic pathways, Wnt signalling pathway, osteoclast differentiation, cellular senescence and mTOR signalling pathway. The results of Real-time RT-PCR for 3'tiRNA-41-GlnTTG-6, 3'tiRNA-42-LysTTT-8, 5'tiRNA-35-CysACA-1 and tRF3a-AsnGTT-9 were consistent with small RNA sequencing data.

CONCLUSION

We discovered the tsRNA that changes the process of osteogenesis and hypoxia, which provides new targets for promoting survival and regeneration functions after BMSCs transplantation.

Hypoxia activates SREBP2 through Golgi disassembly in bone marrow-derived monocytes for enhanced tumor growth

Bone marrow-derived cells (BMDCs) infiltrate hypoxic tumors at a pre-angiogenic state and differentiate into mature macrophages, thereby inducing pro-tumorigenic immunity. A critical factor regulating this differentiation is activation of SREBP2-a well-known transcription factor participating in tumorigenesis progression-through unknown cellular mechanisms. Here, we show that hypoxia-induced Golgi disassembly and Golgi-ER fusion in monocytic myeloid cells result in nuclear translocation and activation of SREBP2 in a SCAP-independent manner. Notably, hypoxia-induced SREBP2 activation was only observed in an immature lineage of bone marrow-derived cells. Single-cell RNA-seq analysis revealed that SREBP2-mediated cholesterol biosynthesis was upregulated in HSCs and monocytes but not in macrophages in the hypoxic bone marrow niche. Moreover, inhibition of cholesterol biosynthesis impaired tumor growth through suppression of pro-tumorigenic immunity and angiogenesis. Thus, our findings indicate that Golgi-ER fusion regulates SREBP2-mediated metabolic alteration in lineage-specific BMDCs under hypoxia for tumor progression.

Role of IL8 in myeloid malignancies

Aberrant overexpression of Interleukin-8 (IL8) has been reported in Myelodysplastic Syndromes (MDS), Acute Myeloid Leukemia (AML), Myeloproliferative Neoplasms (MPNs) and other myeloid malignancies. IL8 (CXCL8) is a CXC chemokine that is secreted by aberrant hematopoietic stem and progenitors as well as other cells in the tumor microenvironment. IL8 can bind to CXCR1/CXCR2 receptors and activate oncogenic signaling pathways, and also increase the recruitment of myeloid derived suppressor cells to the tumor microenvironment. IL8/CXCR1/2 overexpression has been associated with poorer prognosis in MDS and AML and increased bone marrow fibrosis in Myelofibrosis. Preclinical studies have demonstrated benefit of inhibiting the IL8/CXCR1/2 pathways via restricting the growth of leukemic stem cells as well as normalizing the immunosuppressive microenvironment in tumors. Targeting the IL8-CXCR1/2 pathway is a potential therapeutic strategy in myeloid neoplasms and is being evaluated with small molecule inhibitors as well as monoclonal antibodies in ongoing clinical trials. We review the role of IL8 signaling pathway in myeloid cancers and discuss future directions on therapeutic targeting of IL8 in these diseases.

Mitochondria Dictate Function and Fate of HSCs and T Cells

Hematopoietic stem cells (HSC) and T cells are intimately related, lineage-dependent cell populations that are extensively used as therapeutic products for the treatment of hematologic malignancies and certain types of solid tumors. These cellular therapies can be life-saving treatments; however, their efficacies are often limited by factors influencing their activity and cellular properties. Among these factors is mitochondrial metabolism, which influences the function and fate commitment of both HSCs and T cells. Mitochondria, besides being the "cellular powerhouse," provide metabolic intermediates that are used as substrates for epigenetic modifications and chromatin remodeling, thus, driving cell fate decisions during differentiation. Moreover, mitochondrial fitness and mitochondrial quality control mechanisms are closely related to cellular function, and impairment of these mitochondrial properties associates with cellular dysfunction due to factors such as T-cell exhaustion and aging. Here, we give an overview of the role of mitochondria in shaping the behavior of these lineage-related cell populations. Moreover, we discuss the potential of novel mitochondria-targeting strategies for enhancing HSC- and T cell-based cancer immunotherapies and highlight how design and application of such approaches requires consideration of the metabolic similarities and differences between HSCs and T cells. See related article on p. 1302.

Effect of hypoxia on HIF-1α and NOS3 expressions in CD34+ cells of JAK2V617F-positive myeloproliferative neoplasms

PURPOSE

Myeloproliferative neoplasms (MPN) are a heterogeneous group of hematopoietic stem-cell diseases with excessive proliferation of one or more blood cell lines. In this study, we evaluated the effect of different oxygen concentrations on HIF-1α and NOS3 gene expression to determine the effect of the bone marrow microenvironment on JAK2V617F positive Philadelphia chromosome negative (Ph-) MPNs.

PATIENTS AND METHODS

Peripheral blood mononuclear cells (MNC) of 12 patients with Ph- MPN were collected. The presence of JAK2V617F allele status was determined with allele-specific nested PCR analysis. MPN CD34+ and CD34depleted populations were isolated from MNC by magnetic beads. Separate cell cultures of CD34+/depleted populations were managed at different oxygen concentrations including anoxia (∼0%), hypoxia (∼3%), and normoxia (∼20%) conditions for 24 ​h. HIF-1α and NOS3 gene expression changes were examined in each population related to JAK2V617F status with real time RT-PCR.

RESULT

It was revealed that relative HIF-1α and NOS3 expressions were significantly increased in response to decreased oxygen concentration in all samples. Relative HIF-1α and NOS3 expressions were found to be higher especially in CD34+ and CD34depleted populations carrying JAK2V617F mutations compared to MPN patients carrying wild-type JAK2.

CONCLUSION

JAK2V617F might have specific role in HIF-1α and NOS3 regulations with respect to low oxygen concentrations in Ph- MPN. Further evaluations might reveal the effect of JAK2V617F on Ph- MPN pathogenesis in bone marrow microenvironment.

Hematopoiesis and Mast Cell Development

Hematopoietic stem cells (HSCs) are defined based on their capacity to replenish themselves (self-renewal) and give rise to all mature hematopoietic cell types (multi-lineage differentiation) over their lifetime. HSCs are mainly distributed in the bone marrow during adult life, harboring HSC populations and a hierarchy of different kinds of cells contributing to the "niche" that supports HSC regulation, myelopoiesis, and lymphopoiesis. In addition, HSC-like progenitors, innate immune cell precursors such as macrophages, mast cells, natural killer cells, innate lymphoid cells, and megakaryocytes and erythrocyte progenitor cells are connected by a series of complex ontogenic relationships. The first source of mast cells is the extraembryonic yolk sac, on embryonic day 7. Mast cell progenitors circulate and enter peripheral tissues where they complete their differentiation. Embryonic mast cell populations are gradually replaced by definitive stem cell-derived progenitor cells. Thereafter, mast cells originate from the bone marrow, developing from the hematopoietic stem cells via multipotent progenitors, common myeloid progenitors, and granulocyte/monocyte progenitors. In this review article, we summarize the knowledge on mast cell sources, particularly focusing on the complex and multifaceted mechanisms intervening between the hematopoietic process and the development of mast cells.

Further Characterization of Multi-Organ DEARE and Protection by 16,16 Dimethyl Prostaglandin E2 in a Mouse Model of the Hematopoietic Acute Radiation Syndrome

Survivors of acute radiation exposure suffer from the delayed effects of acute radiation exposure (DEARE), a chronic condition affecting multiple organs, including lung, kidney, heart, gastrointestinal tract, eyes, and brain, and often causing cancer. While effective medical countermeasures (MCM) for the hematopoietic-acute radiation syndrome (H-ARS) have been identified and approved by the FDA, development of MCM for DEARE has not yet been successful. We previously documented residual bone marrow damage (RBMD) and progressive renal and cardiovascular DEARE in murine survivors of H-ARS, and significant survival efficacy of 16,16-dimethyl prostaglandin E2 (dmPGE2) given as a radioprotectant or radiomitigator for H-ARS. We now describe additional DEARE (physiological and neural function, progressive fur graying, ocular inflammation, and malignancy) developing after sub-threshold doses in our H-ARS model, and detailed analysis of the effects of dmPGE2 administered before (PGE-pre) or after (PGE-post) lethal total-body irradiation (TBI) on these DEARE. Administration of PGE-pre normalized the twofold reduction of white blood cells (WBC) and lymphocytes seen in vehicle-treated survivors (Veh), and increased the number of bone marrow (BM) cells, splenocytes, thymocytes, and phenotypically defined hematopoietic progenitor cells (HPC) and hematopoietic stem cells (HSC) to levels equivalent to those in non-irradiated age-matched controls. PGE-pre significantly protected HPC colony formation ex vivo by >twofold, long term-HSC in vivo engraftment potential up to ninefold, and significantly blunted TBI-induced myeloid skewing. Secondary transplantation documented continued production of LT-HSC with normal lineage differentiation. PGE-pre reduced development of DEARE cardiovascular pathologies and renal damage; prevented coronary artery rarefication, blunted progressive loss of coronary artery endothelia, reduced inflammation and coronary early senescence, and blunted radiation-induced increase in blood urea nitrogen (BUN). Ocular monocytes were significantly lower in PGE-pre mice, as was TBI-induced fur graying. Increased body weight and decreased frailty in male mice, and reduced incidence of thymic lymphoma were documented in PGE-pre mice. In assays measuring behavioral and cognitive functions, PGE-pre reduced anxiety in females, significantly blunted shock flinch response, and increased exploratory behavior in males. No effect of TBI was observed on memory in any group. PGE-post, despite significantly increasing 30-day survival in H-ARS and WBC and hematopoietic recovery, was not effective in reducing TBI-induced RBMD or any other DEARE. In summary, dmPGE2 administered as an H-ARS MCM before lethal TBI significantly increased 30-day survival and ameliorated RBMD and multi-organ and cognitive/behavioral DEARE to at least 12 months after TBI, whereas given after TBI, dmPGE2 enhances survival from H-ARS but has little impact on RBMD or other DEARE.

Novel differential calcium regulation of hematopoietic stem and progenitor cells under physiological low oxygen conditions

Low oxygen bone marrow (BM) niches (~1%-4% low O₂ ) provide critical signals for hematopoietic stem/progenitor cells (HSC/HSPCs). Our presented data are the first to investigate live, sorted HSC/HSPCs in their native low O₂ conditions. Transcriptional and proteomic analysis uncovered differential Ca²⁺ regulation that correlated with overlapping phenotypic populations consisting of robust increases of cytosolic and mitochondrial Ca²⁺ , ABC transporter (ABCG2) expression and sodium/hydrogen exchanger (NHE1) expression in live, HSC/HSPCs remaining in constant low O_2. We identified a novel Ca²⁺ high population in HSPCs predominantly detected in low O₂ that displayed enhanced frequency of phenotypic LSK/LSKCD150 in low O₂ replating assays compared to Ca²⁺ low populations. Inhibition of the Ca²⁺ regulator NHE1 (Cariporide) resulted in attenuation of both the low O₂ induced Ca²⁺ high population and subsequent enhanced maintenance of phenotypic LSK and LSKCD150 during low O₂ replating. These data reveal multiple levels of differential Ca²⁺ regulation in low O₂ resulting in phenotypic, signaling, and functional consequences in HSC/HSPCs.

Functions and regulatory mechanisms of resting hematopoietic stem cells: a promising targeted therapeutic strategy

Hematopoietic stem cells (HSCs) are the common and essential precursors of all blood cells, including immune cells, and they are responsible for the lifelong maintenance and damage repair of blood tissue homeostasis. The vast majority (> 95%) of HSCs are in a resting state under physiological conditions and are only activated to play a functional role under stress conditions. This resting state affects their long-term survival and is also closely related to the lifelong maintenance of hematopoietic function; however, abnormal changes may also be an important factor leading to the decline of immune function in the body and the occurrence of diseases in various systems. While the importance of resting HSCs has attracted increasing research attention, our current understanding of this topic remains insufficient, and the direction of clinical targeted treatments is unclear. Here, we describe the functions of HSCs, analyze the regulatory mechanisms that affect their resting state, and discuss the relationship between resting HSCs and different diseases, with a view to providing guidance for the future clinical implementation of related targeted treatments.

Vitamin B5 and succinyl-CoA improve ineffective erythropoiesis in SF3B1-mutated myelodysplasia

Patients with myelodysplastic syndrome and ring sideroblasts (MDS-RS) present with symptomatic anemia due to ineffective erythropoiesis that impedes their quality of life and increases morbidity. More than 80% of patients with MDS-RS harbor splicing factor 3B subunit 1 (SF3B1) mutations, the founder aberration driving MDS-RS disease. Here, we report how mis-splicing of coenzyme A synthase (COASY), induced by mutations in SF3B1, affects heme biosynthesis and erythropoiesis. Our data revealed that COASY was up-regulated during normal erythroid differentiation, and its silencing prevented the formation of erythroid colonies, impeded erythroid differentiation, and precluded heme accumulation. In patients with MDS-RS, loss of protein due to COASY mis-splicing led to depletion of both CoA and succinyl-CoA. Supplementation with COASY substrate (vitamin B5) rescued CoA and succinyl-CoA concentrations in SF3B1mut cells and mended erythropoiesis differentiation defects in MDS-RS primary patient cells. Our findings reveal a key role of the COASY pathway in erythroid maturation and identify upstream and downstream metabolites of COASY as a potential treatment for anemia in patients with MDS-RS.

Selenium Improves Bone Microenvironment-Related Hematopoiesis and Immunity in T-2 Toxin-Exposed Mice

The T-2 toxin is one of the most frequent contaminants in the environment and agricultural production globally. It exerts a wide range of toxic effects. Selenium (Se), as an antioxidant, has the potential to be widely used to antagonize mycotoxin toxicity. To investigate the protective effects of Se on bone microenvironment (BM)-related hematopoiesis and immunity after T-2 toxin exposure, 36 male mice were treated with the T-2 toxin (1 mg/kg) and/or Se (0.2 mg/kg) by intragastric administration for 28 days. The results showed that Se alleviated T-2 toxin-induced cytopenia and splenic extramedullary hematopoiesis. Se also significantly relieved T-2 toxin-induced immunosuppression, as assessed by immune factors and lymphocytes. Furthermore, Se also attenuated oxidative stress and apoptosis and improved the BM in T-2 toxin-exposed mice. Therefore, Se improves BM-related hematopoiesis and immunity after T-2 toxin exposure. This study provides references for identifying the toxic mechanism and screening potential therapeutic drugs of the T-2 toxin.

Leukemic stem cells and therapy resistance in acute myeloid leukemia

A major obstacle in the treatment of acute myeloid leukemia (AML) is refractory disease or relapse after achieving remission. The latter arises from a few therapy-resistant cells within minimal residual disease (MRD). Resistant cells with long-term self-renewal capacity that drive clonal outgrowth are referred to as leukemic stem cells (LSC). The cancer stem cell concept considers LSC as relapse-initiating cells residing at the top of each genetically defined AML subclone forming epigenetically controlled downstream hierarchies. LSC display significant phenotypic and epigenetic plasticity, particularly in response to therapy stress, which results in various mechanisms mediating treatment resistance. Given the inherent chemotherapy resistance of LSC, targeted strategies must be incorporated into first-line regimens to prevent LSC-mediated AML relapse. The combination of venetoclax and azacitidine is a promising current strategy for the treatment of AML LSC. Nevertheless, the selection of patients who would benefit either from standard chemotherapy or venetoclax + azacitidine treatment in first-line therapy has yet to be established and the mechanisms of resistance still need to be discovered and overcome. Clinical trials are currently underway that investigate LSC susceptibility to first-line therapies. The era of single-cell multi-omics has begun to uncover the complex clonal and cellular architectures and associated biological networks. This should lead to a better understanding of the highly heterogeneous AML at the inter- and intra-patient level and identify resistance mechanisms by longitudinal analysis of patients' samples. This review discusses LSC biology and associated resistance mechanisms, potential therapeutic LSC vulnerabilities and current clinical trial activities.

Metabolism in Hematopoiesis and Its Malignancy

Hematopoietic stem cells (HSCs) are multipotent stem cells that can self-renew and generate all blood cells of different lineages. The system is under tight control in order to maintain a precise equilibrium of the HSC pool and the effective production of mature blood cells to support various biological activities. Cell metabolism can regulate different molecular activities, such as epigenetic modification and cell cycle regulation, and subsequently affects the function and maintenance of HSC. Upon malignant transformation, oncogenic drivers in malignant hematopoietic cells can remodel the metabolic pathways for supporting the oncogenic growth. The dysregulation of metabolism results in oncogene addiction, implying the development of malignancy-specific metabolism-targeted therapy. In this chapter, we will discuss the significance of different metabolic pathways in hematopoiesis, specifically, the distinctive metabolic dependency in hematopoietic malignancies and potential metabolic therapy.

Hematopoietic Stem Cells in Wound Healing Response

Significance: Emerging evidence has shown a link between the status of hematopoietic stem cells (HSCs) and wound healing responses. Thus, better understanding HSCs will contribute to further advances in wound healing research. Recent Advances: Myeloid cells such as neutrophils and monocyte-derived macrophages are critical players in the process of wound healing. HSCs actively respond to wound injury and other tissue insults, including infection and produce the effector myeloid cells, and a failing of the HSC response can result in impaired wound healing. Technological advances such as transcriptome at single-cell resolution, epigenetics, three-dimensional imaging, transgenic animals, and animal models, have provided novel concepts of myeloid generation (myelopoiesis) from HSCs, and have revealed cell-intrinsic and -extrinsic mechanisms that can impact HSC functions in the context of health conditions. Critical Issues: The newer concepts include-the programmed cellular fate at a differentiation stage that is used to be considered as the multilineage, the signaling pathways that can activate HSCs directly and indirectly, the mechanisms that can deteriorate HSCs, the roles and remodeling of the surrounding environment for HSCs and their progenitors (the niche). Future Directions: The researches on HSCs, which produce blood cells, should contribute to the development of blood biomarkers predicting a risk of chronic wounds, which may transform clinical practice of wound care with precision medicine for patients at high risk of poor healing.

Hypoxic stress and hypoxia-inducible factors in leukemias

To cope with hypoxic stress, ancient organisms have developed evolutionally conserved programs centered on hypoxia-inducible transcriptional factors (HIFs). HIFs and their regulatory proteins have evolved as rheostats to adapt cellular metabolism to atmospheric oxygen fluctuations, but the amplitude of their transcriptional programs has tremendously increased along evolution to include a wide spectrum of physiological and pathological processes. The bone marrow represents a notable example of an organ that is physiologically exposed to low oxygen levels and where basal activation of hypoxia signaling appears to be intrinsically wired within normal and neoplastic hematopoietic cells. HIF-mediated responses are mainly piloted by the oxygen-labile α subunits HIF1α and HIF2α, and current literature suggests that these genes have a functional specification that remains to be fully defined. Since their identification in the mid 90s, HIF factors have been extensively studied in solid tumors, while their implication in leukemia has lagged behind. In the last decades however, many laboratories have addressed the function of hypoxia signaling in leukemia and obtained somewhat contradictory results. Suppression of HIFs expression in different types of leukemia has unveiled common leukemia-promoting functions such as stimulation of bone marrow neoangiogenesis, maintenance of leukemia stem cells and chemoresistance. However, genetic studies are revealing that a definition of HIF factors as bona fide tumor promoters is overly simplistic, and, depending on the leukemia subtype, the specific oncogenic event, or the stage of leukemia development, activation of hypoxia-inducible genes may lead to opposite consequences. With this article we will provide an updated summary of the studies describing the regulation and function of HIF1α and HIF2α in blood malignancies, spanning from acute to chronic, lymphoid to myeloid leukemias. In discussing these data, we will attempt to provide plausible explanations to contradictory findings and point at what we believe are areas of weakness in which further investigations are urgently needed. Gaining additional knowledge into the role of hypoxia signaling in leukemia appears especially timely nowadays, as new inhibitors of HIF factors are entering the clinical arena for specific types of solid tumors but their utility for patients with leukemia is yet to be determined.

Novel Germline PHD2 Variant in a Metastatic Pheochromocytoma and Chronic Myeloid Leukemia, but in the Absence of Polycythemia

Background: Pheochromocytoma (Pheo) and paraganglioma (PGL) are rare tumors, mostly resulting from pathogenic variants of predisposing genes, with a genetic contribution that now stands at around 70%. Germline variants account for approximately 40%, while the remaining 30% is attributable to somatic variants. Objective: This study aimed to describe a new PHD2 (EGLN1) variant in a patient affected by metastatic Pheo and chronic myeloid leukemia (CML) without polycythemia and to emphasize the need to adopt a comprehensive next-generation sequencing (NGS) panel. Methods: Genetic analysis was carried out by NGS. This analysis was initially performed using a panel of genes known for tumor predisposition (EGLN1, EPAS1, FH, KIF1Bβ, MAX, NF1, RET, SDHA, SDHAF2, SDHB, SDHC, SDHD, TMEM127, and VHL), followed initially by SNP-CGH array, to exclude the presence of the pathogenic Copy Number Variants (CNVs) and the loss of heterozygosity (LOH) and subsequently by whole exome sequencing (WES) comparative sequence analysis of the DNA extracted from tumor fragments and peripheral blood. Results: We found a novel germline PHD2 (EGLN1) gene variant, c.153G>A, p.W51*, in a patient affected by metastatic Pheo and chronic myeloid leukemia (CML) in the absence of polycythemia. Conclusions: According to the latest guidelines, it is mandatory to perform genetic analysis in all Pheo/PGL cases regardless of phenotype. In patients with metastatic disease and no evidence of polycythemia, we propose testing for PHD2 (EGLN1) gene variants. A possible correlation between PHD2 (EGLN1) pathogenic variants and CML clinical course should be considered.

Hypoxia and hypoxia-inducible factor signals regulate the development, metabolism, and function of B cells

Hypoxia is a common hallmark of healthy tissues in physiological states or chronically inflamed tissues in pathological states. Mammalian cells sense and adapt to hypoxia mainly through hypoxia-inducible factor (HIF) signaling. Many studies have shown that hypoxia and HIF signaling play an important regulatory role in development and function of innate immune cells and T cells, but their role in B cell biology is still controversial. B cells experience a complex life cycle (including hematopoietic stem cells, pro-B cells, pre-B cells, immature B cells, mature naïve B cells, activated B cells, plasma cells, and memory B cells), and the partial pressure of oxygen (PO₂) in the corresponding developmental niche of stage-specific B cells is highly dynamic, which suggests that hypoxia and HIF signaling may play an indispensable role in B cell biology. Based on the fact that hypoxia niches exist in the B cell life cycle, this review focuses on recent discoveries about how hypoxia and HIF signaling regulate the development, metabolism, and function of B cells, to facilitate a deep understanding of the role of hypoxia in B cell-mediated adaptive immunity and to provide novel strategies for vaccine adjuvant research and the treatment of immunity-related or infectious diseases.

Modelling acute myeloid leukemia (AML): What's new? A transition from the classical to the modern

Acute myeloid leukemia (AML) is a heterogeneous malignancy affecting myeloid cells in the bone marrow (BM) but can spread giving rise to impaired hematopoiesis. AML incidence increases with age and is associated with poor prognostic outcomes. There has been a disconnect between the success of novel drug compounds observed in preclinical studies of hematological malignancy and less than exceptional therapeutic responses in clinical trials. This review aims to provide a state-of-the-art overview on the different preclinical models of AML available to expand insights into disease pathology and as preclinical screening tools. Deciphering the complex physiological and pathological processes and developing predictive preclinical models are key to understanding disease progression and fundamental in the development and testing of new effective drug treatments. Standard scaffold-free suspension models fail to recapitulate the complex environment where AML occurs. To this end, we review advances in scaffold/matrix-based 3D models and outline the most recent advances in on-chip technology. We also provide an overview of clinically relevant animal models and review the expanding use of patient-derived samples, which offer the prospect to create more "patient specific" screening tools either in the guise of 3D matrix models, microphysiological "organ-on-chip" tools or xenograft models and discuss representative examples.

Liver Regeneration by Hematopoietic Stem Cells: Have We Reached the End of the Road?

The liver is the organ with the highest regenerative capacity in the human body. However, various insults, including viral infections, alcohol or drug abuse, and metabolic overload, may cause chronic inflammation and fibrosis, leading to irreversible liver dysfunction. Despite advances in surgery and pharmacological treatments, liver diseases remain a leading cause of death worldwide. To address the shortage of donor liver organs for orthotopic liver transplantation, cell therapy in liver disease has emerged as a promising regenerative treatment. Sources include primary hepatocytes or functional hepatocytes generated from the reprogramming of induced pluripotent stem cells (iPSC). Different types of stem cells have also been employed for transplantation to trigger regeneration, including hematopoietic stem cells (HSCs), mesenchymal stromal cells (MSCs), endothelial progenitor cells (EPCs) as well as adult and fetal liver progenitor cells. HSCs, usually defined by the expression of CD34 and CD133, and MSCs, defined by the expression of CD105, CD73, and CD90, are attractive sources due to their autologous nature, ease of isolation and cryopreservation. The present review focuses on the use of bone marrow HSCs for liver regeneration, presenting evidence for an ongoing crosstalk between the hematopoietic and the hepatic system. This relationship commences during embryogenesis when the fetal liver emerges as the crossroads between the two systems converging the presence of different origins of cells (mesoderm and endoderm) in the same organ. Ample evidence indicates that the fetal liver supports the maturation and expansion of HSCs during development but also later on in life. Moreover, the fact that the adult liver remains one of the few sites for extramedullary hematopoiesis—albeit pathological—suggests that this relationship between the two systems is ongoing. Can, however, the hematopoietic system offer similar support to the liver? The majority of clinical studies using hematopoietic cell transplantation in patients with liver disease report favourable observations. The underlying mechanism—whether paracrine, fusion or transdifferentiation or a combination of the three—remains to be confirmed.

Development and clinical translation considerations for the next wave of gene modified hematopoietic stem and progenitor cells therapies

INTRODUCTION

Consistent and reliable manufacture of gene modified hematopoietic stem and progenitor cell (HPSC) therapies will be of the utmost importance as they become more mainstream and address larger populations. Robust development campaigns will be needed to ensure that these products will be delivered to patients with the highest quality standards.

AREAS COVERED

Through publicly available manuscripts, press releases, and news articles - this review touches on aspects related to HSPC therapy, development, and manufacturing.

EXPERT OPINION

Recent advances in genome modification technology coupled with the longstanding clinical success of HSPCs warrants great optimism for the next generation of engineered HSPC-based therapies. Treatments for some diseases that have thus far been intractable now appear within reach. Reproducible manufacturing will be of critical importance in delivering these therapies but will be challenging due to the need for bespoke materials and methods in combination with the lack of off-the-shelf solutions. Continued progress in the field will manifest in the form of industrialization which currently requires attention and resources directed toward the custom reagents, a focus on closed and automated processes, and safer and more precise genome modification technologies that will enable broader, faster, and safer access to these life-changing therapies.

MIF/CXCR4 signaling axis contributes to survival, invasion, and drug resistance of metastatic neuroblastoma cells in the bone marrow microenvironment

BACKGROUND

The bone marrow (BM) is the most common site of dissemination in patients with aggressive, metastatic neuroblastoma (NB). However, the molecular mechanisms underlying the aggressive behavior of NB cells in the BM niche are still greatly unknown. In the present study, we explored biological mechanisms that play a critical role in NB cell survival and progression in the BM and investigated potential therapeutic targets.

METHODS

Patient-derived bone marrow (BM) primary cultures were generated using fresh BM aspirates obtained from NB patients. NB cell lines were cultured in the presence of BM conditioned media containing cell-secreted factors, and under low oxygen levels (1% O₂) to mimic specific features of the BM microenvironment of high-risk NB patients. The BM niche was explored using cytokine profiling assays, cell migration-invasion and viability assays, flow cytometry and analysis of RNA-sequencing data. Selective pharmacological inhibition of factors identified as potential mediators of NB progression within the BM niche was performed in vitro and in vivo.

RESULTS

We identified macrophage migration inhibitory factor (MIF) as a key inflammatory cytokine involved in BM infiltration. Cytokine profiling and RNA-sequencing data analysis revealed NB cells as the main source of MIF in the BM, suggesting a potential role of MIF in tumor invasion. Exposure of NB cells to BM-conditions increased NB cell-surface expression of the MIF receptor CXCR4, which was associated with increased cell viability, enhanced migration-invasion, and activation of PI3K/AKT and MAPK/ERK signaling pathways. Moreover, subcutaneous co-injection of NB and BM cells enhanced tumor engraftment in mice. MIF inhibition with 4-IPP impaired in vitro NB aggressiveness, and improved drug response while delayed NB growth, improving survival of the NB xenograft model.

CONCLUSIONS

Our findings suggest that BM infiltration by NB cells may be mediated, in part, by MIF-CXCR4 signaling. We demonstrate the antitumor efficacy of MIF targeting in vitro and in vivo that could represent a novel therapeutic target for patients with disseminated high-risk NB.

Quiescence regulation by normal haematopoietic stem cells and leukaemia stem cells

The haematopoietic system is maintained by rare haematopoietic stem cells (HSCs), which are quiescent most of the time and only divide occasionally to self-renew and/or to undergo commitment to clonal expansion via the generation of highly proliferative progenitor cells. The latter is responsible for the generation of all mature cells of the system through subsequent lineage commitment and terminal differentiation. Cells with similar properties also exist in leukaemias and are known as leukaemia stem cells (LSCs). Quiescence provides essential protection for both HSC and LSC from cytotoxic stress and DNA damage and, in the case of LSCs, likely causes therapy resistance and disease relapse in leukaemia patients. Specific inhibition of LSC quiescence has been considered a promising strategy for eliminating LSCs and curing leukaemias. Although the understanding of mechanisms responsible for quiescence maintenance in these cells remains limited, particularly for LSCs, recent studies have suggested potential differences in their dependency on certain pathways and their levels of stress and DNA damage caused by increased cycling. Such differences likely stem from oncogenic mutations in LSCs and could be specifically exploited for the elimination of LSCs while sparing normal HSCs in the future.

Human acute myeloid leukemia stem cells: evolution of concept

The history of human acute myeloid leukemia stem cells (AMLSCs) began in a seminal study performed by Lapidot and Dick, proving that only CD34+CD38- human primary acute myeloid leukemia (AML) cells can repopulate in severe combined immunodeficient mice. The concept of leukemic stem cells (LSCs) has impeded a huge change in the treatment strategy against AML from killing proliferating leukemic cells to eradicating quiescent/dormant LSCs. As next-generation sequencing technologies have developed, multiple and recurrent genetic mutations have been discovered in large cohorts of patients with AML, and the updated understanding of leukemogenesis has improved the old concept of LSC to a revised version of a serial developmental model of LSC; that is, pre-LSCs are generated as seeds by the first hit on epigenetic regulators, and then, leukemia-initiating LSCs emerge from seeds by the second hits on genes involved in transcription and signaling. Dreams for universal and targetable AMLSC biomarker sparing healthy hematopoietic stem cells have weakened after the confrontation of significant heterogeneity of AMLSCs from genomic and immunophenotypic viewpoints. However, there is still hope for effective targets for AMLSCs since there is evidence that grouped gene signatures, such as 17-gene LSC score, and common epigenetic signatures, such as HOXA clusters, independent of various gene mutations, exist. Recently, the LSC niche in the bone marrow has been actively investigated and has expanded our knowledge of the physiology and vulnerability of AMLSCs. Presently, an applicable treatment that always works in AMLSCs is lacking. However, we will find a way, we always have.

Bone Marrow Niches of Hematopoietic Stem and Progenitor Cells

The mammalian hematopoietic system is remarkably efficient in meeting an organism’s vital needs, yet is highly sensitive and exquisitely regulated. Much of the organismal control over hematopoiesis comes from the regulation of hematopoietic stem cells (HSCs) by specific microenvironments called niches in bone marrow (BM), where HSCs reside. The experimental studies of the last two decades using the most sophisticated and advanced techniques have provided important data on the identity of the niche cells controlling HSCs functions and some mechanisms underlying niche-HSC interactions. In this review we discuss various aspects of organization and functioning of the HSC cell niche in bone marrow. In particular, we review the anatomy of BM niches, various cell types composing the niche, niches for more differentiated cells, metabolism of HSCs in relation to the niche, niche aging, leukemic transformation of the niche, and the current state of HSC niche modeling in vitro.

Deletion of Vhl in Dmp1-Expressing Cells Causes Microenvironmental Impairment of B Cell Lymphopoiesis

The contributions of skeletal cells to the processes of B cell development in the bone marrow (BM) have not been completely described. The von-Hippel Lindau protein (VHL) plays a key role in cellular responses to hypoxia. Previous work showed that Dmp1-Cre;Vhl conditional knockout mice (VhlcKO), which deletes Vhl in subsets of mesenchymal stem cells, late osteoblasts and osteocytes, display dysregulated bone growth and reduction in B cells. Here, we investigated the mechanisms underlying the B cell defects using flow cytometry and high-resolution imaging. In the VhlcKO BM, B cell progenitors were increased in frequency and number, whereas Hardy Fractions B-F were decreased. VhlcKO Fractions B-C cells showed increased apoptosis and quiescence. Reciprocal BM chimeras confirmed a B cell-extrinsic source of the VhlcKO B cell defects. In support of this, VhlcKO BM supernatant contained reduced CXCL12 and elevated EPO levels. Intravital and ex vivo imaging revealed VhlcKO BM blood vessels with increased diameter, volume, and a diminished blood-BM barrier. Staining of VhlcKO B cells with an intracellular hypoxic marker indicated the natural existence of distinct B cell microenvironments that differ in local oxygen tensions and that the B cell developmental defects in VhlcKO BM are not initiated by hypoxia. Our studies identify novel mechanisms linking altered bone homeostasis with drastic BM microenvironmental changes that dysregulate B cell development.

Isolation, Maintenance and Expansion of Adult Hematopoietic Stem/Progenitor Cells and Leukemic Stem Cells

Simple Summary

Transplantation of adult hematopoietic stem cells is an important therapeutic tool to help patients suffering from diverse hematological disorders. All types of blood cells can develop from a single hematopoietic stem cell underlining their enormous potential. Intense efforts are ongoing to generate “engraftable” human hematopoietic stem cells to treat hematopoietic diseases and to understand the molecular machinery driving them. Leukemic stem cells represent a low frequency subpopulation of leukemia cells that possess stem cell properties. They can instigate, maintain, and serially propagate leukemia in vivo, while they retain the capacity to differentiate into committed progenitors. Leukemic stem cells are unaffected by many therapeutic strategies and represent the major cause of relapse. We here describe all methods to maintain and expand murine and human hematopoietic cells in culture and describe their specific advantages. These methods are also employed to understand the biology of leukemic stem cells and to identify novel therapeutic strategies.

Abstract

Hematopoietic stem cells (HSCs) are rare, self-renewing cells that perch on top of the hematopoietic tree. The HSCs ensure the constant supply of mature blood cells in a tightly regulated process producing peripheral blood cells. Intense efforts are ongoing to optimize HSC engraftment as therapeutic strategy to treat patients suffering from hematopoietic diseases. Preclinical research paves the way by developing methods to maintain, manipulate and expand HSCs ex vivo to understand their regulation and molecular make-up. The generation of a sufficient number of transplantable HSCs is the Holy Grail for clinical therapy. Leukemia stem cells (LSCs) are characterized by their acquired stem cell characteristics and are responsible for disease initiation, progression, and relapse. We summarize efforts, that have been undertaken to increase the number of long-term (LT)-HSCs and to prevent differentiation towards committed progenitors in ex vivo culture. We provide an overview and compare methods currently available to isolate, maintain and enrich HSC subsets, progenitors and LSCs and discuss their individual advantages and drawbacks.

Fusion of Normoxic- and Hypoxic-Preconditioned Myoblasts Leads to Increased Hypertrophy

Injuries, high altitude, and endurance exercise lead to hypoxic conditions in skeletal muscle and sometimes to hypoxia-induced local tissue damage. Thus, regenerative myoblasts/satellite cells are exposed to different levels and durations of partial oxygen pressure depending on the spatial distance from the blood vessels. To date, it is unclear how hypoxia affects myoblasts proliferation, differentiation, and particularly fusion with normoxic myoblasts. To study this, we investigated how 21% and 2% oxygen affects C2C12 myoblast morphology, proliferation, and myogenic differentiation and evaluated the fusion of normoxic- or hypoxic-preconditioned C2C12 cells in 21% or 2% oxygen in vitro. Out data show that the long-term hypoxic culture condition does not affect the proliferation of C2C12 cells but leads to rounder cells and reduced myotube formation when compared with myoblasts exposed to normoxia. However, when normoxic- and hypoxic-preconditioned myoblasts were differentiated together, the resultant myotubes were significantly larger than the control myotubes. Whole transcriptome sequencing analysis revealed several novel candidate genes that are differentially regulated during the differentiation under normoxia and hypoxia in mixed culture conditions and may thus be involved in the increase in myotube size. Taken together, oxygen-dependent adaption and interaction of myoblasts may represent a novel approach for the development of innovative therapeutic targets.

The Role of Nitric Oxide in Stem Cell Biology

Nitric oxide (NO) is a gaseous biomolecule endogenously synthesized with an essential role in embryonic development and several physiological functions, such as regulating mitochondrial respiration and modulation of the immune response. The dual role of NO in embryonic stem cells (ESCs) has been previously reported, preserving pluripotency and cell survival or inducing differentiation with a dose-dependent pattern. In this line, high doses of NO have been used in vitro cultures to induce focused differentiation toward different cell lineages being a key molecule in the regenerative medicine field. Moreover, optimal conditions to promote pluripotency in vitro are essential for their use in advanced therapies. In this sense, the molecular mechanisms underlying stemness regulation by NO have been studied intensively over the current years. Recently, we have reported the role of low NO as a hypoxia-like inducer in pluripotent stem cells (PSCs), which supports using this molecule to maintain pluripotency under normoxic conditions. In this review, we stress the role of NO levels on stem cells (SCs) fate as a new approach for potential cell therapy strategies. Furthermore, we highlight the recent uses of NO in regenerative medicine due to their properties regulating SCs biology.

Metabolic regulation of somatic stem cells in vivo

Metabolism has been studied mainly in cultured cells or at the level of whole tissues or whole organisms in vivo. Consequently, our understanding of metabolic heterogeneity among cells within tissues is limited, particularly when it comes to rare cells with biologically distinct properties, such as stem cells. Stem cell function, tissue regeneration and cancer suppression are all metabolically regulated, although it is not yet clear whether there are metabolic mechanisms unique to stem cells that regulate their activity and function. Recent work has, however, provided evidence that stem cells do have a metabolic signature that is distinct from that of restricted progenitors and that metabolic changes influence tissue homeostasis and regeneration. Stem cell maintenance throughout life in many tissues depends upon minimizing anabolic pathway activation and cell division. Consequently, stem cell activation by tissue injury is associated with changes in mitochondrial function, lysosome activity and lipid metabolism, potentially at the cost of eroding self-renewal potential. Stem cell metabolism is also regulated by the environment: stem cells metabolically interact with other cells in their niches and are able to sense and adapt to dietary changes. The accelerating understanding of stem cell metabolism is revealing new aspects of tissue homeostasis with the potential to promote tissue regeneration and cancer suppression.

Current Understanding of Hypoxia in Glioblastoma Multiforme and Its Response to Immunotherapy

Simple Summary

Glioblastoma multiforme (GBM) is the most aggressive tumor type in the central nervous system. Hypoxia, defined as a lack of sufficient oxygen in tissues, is the most detrimental factor for the survival of GBM patients, promoting drug resistance, and invasion and inhibition of immune responses. Traditionally, tumor hypoxia has been studied from a narrow viewpoint, excluding the immune system and focusing primarily on the effect of hypoxia on blood vessels and tumor cells. More recently, however, evidence highlighting the important role of immunosurveillance has been uncovered for multiple tumors, including GBM. Thus, connecting the knowledge gained from traditional hypoxia studies with findings from recent immunological studies is urgently needed to better understand the role of hypoxia in cancer.

Abstract

Hypoxia is a hallmark of glioblastoma multiforme (GBM), the most aggressive cancer of the central nervous system, and is associated with multiple aspects of tumor pathogenesis. For example, hypoxia induces resistance to conventional cancer therapies and inhibits antitumor immune responses. Thus, targeting hypoxia is an attractive strategy for GBM therapy. However, traditional studies on hypoxia have largely excluded the immune system. Recently, the critical role of the immune system in the defense against multiple tumors has become apparent, leading to the development of effective immunotherapies targeting numerous cancer types. Critically, however, GBM is classified as a “cold tumor” due to poor immune responses. Thus, to improve GBM responsiveness against immunotherapies, an improved understanding of both immune function in GBM and the role of hypoxia in mediating immune responses within the GBM microenvironment is needed. In this review, we discuss the role of hypoxia in GBM from a clinical, pathological, and immunological perspective.

Hif-1a suppresses ROS-induced proliferation of cardiac fibroblasts following myocardial infarction

We report that cardiac fibroblasts (CFs) and mesenchymal progenitors are more hypoxic than other cardiac interstitial populations, express more hypoxia-inducible factor 1α (HIF-1α), and exhibit increased glycolytic metabolism. CF-specific deletion of Hif-1a resulted in decreased HIF-1 target gene expression and increased mesenchymal progenitors in uninjured hearts and increased CF activation without proliferation following sham injury, as demonstrated using single-cell RNA sequencing (scRNA-seq). After myocardial infarction (MI), however, there was ∼50% increased CF proliferation and excessive scarring and contractile dysfunction, a scenario replicated in 3D engineered cardiac microtissues. CF proliferation was associated with higher reactive oxygen species (ROS) as occurred also in wild-type mice treated with the mitochondrial ROS generator MitoParaquat (MitoPQ). The mitochondrial-targeted antioxidant MitoTEMPO rescued Hif-1a mutant phenotypes. Thus, HIF-1α in CFs provides a critical braking mechanism against excessive post-ischemic CF activation and proliferation through regulation of mitochondrial ROS. CFs are potential cellular targets for designer antioxidant therapies in cardiovascular disease.

Cadmium exposure reprograms energy metabolism of hematopoietic stem cells to promote myelopoiesis at the expense of lymphopoiesis in mice

Cadmium (Cd) is a highly toxic heavy metal in our living environment. Hematopoietic stem cells (HSC) are ancestors for all blood cells. Therefore understanding the impact of Cd on HSC is significant for public health. The aim of this study was to investigate the impact of Cd²⁺ on energy metabolism of HSC and its involvement in hematopoiesis. Wild-type C57BL/6 mice were treated with 10 ppm of Cd²⁺ via drinking water for 3 months, and thereafter glycolysis and mitochondrial (MT) oxidative phosphorylation (OXPHOS) of HSC in the bone marrow (BM) and their impact on hematopoiesis were evaluated. After Cd²⁺ treatment, HSC had reduced lactate dehydrogenase (LDH) activity and lactate production while having increased pyruvate dehydrogenase (PDH) activity, MT membrane potential, ATP production, oxygen (O₂) consumption and reactive oxygen species (ROS), indicating that Cd²⁺ switched the pattern of energy metabolism from glycolysis to OXPHOS in HSC. Moreover, Cd²⁺ switch of HSC energy metabolism was critically dependent on Wnt5a/Cdc42/calcium (Ca²⁺) signaling triggered by a direct action of Cd²⁺ on HSC. To test the biological significance of Cd²⁺ impact on HSC energy metabolism, HSC were intervened for Ca²⁺, OXPHOS, or ROS in vitro, and thereafter the HSC were transplanted into lethally irradiated recipients to reconstitute the immune system; the transplantation assay indicated that Ca²⁺-dependent MT OXPHOS dominated the skewed myelopoiesis of HSC by Cd²⁺ exposure. Collectively, we revealed that Cd²⁺ exposure activated Wnt5a/Cdc42/Ca²⁺ signaling to reprogram the energy metabolism of HSC to drive myelopoiesis at the expense of lymphopoiesis.

Multi-Omics Profiling Identifies Pathways Associated With CD8+ T-Cell Activation in Severe Aplastic Anemia

Severe aplastic anemia (SAA) is an autoimmune disease characterized by immune-mediated destruction of hematopoietic stem and progenitor cells. Autoreactive CD8⁺ T cells have been reported as the effector cells; however, the mechanisms regulating their cell activation in SAA remain largely unknown. Here, we performed proteomics and metabolomics analyses of plasma and bone marrow supernatant, together with transcriptional analysis of CD8⁺ T cells from SAA patients and healthy donors, to find key pathways that are involved in pathogenic CD8⁺ T-cell activation. We identified 21 differential proteins and 50 differential metabolites in SAA patients that were mainly involved in energy metabolism, complement and coagulation cascades, and HIF-1α signaling pathways. Interestingly, we found that these pathways are also enriched in T cells from SAA patients by analyzing available single-cell RNA sequencing data. Moreover, CD8⁺ T cells from SAA patients contain a highly activated CD38⁺ subset, which was increased in the bone marrow of SAA patients and a murine model of SAA. This subset presented enriched genes associated with the glycolysis or gluconeogenesis pathway, HIF-1α signaling pathway, and complement associated pathways, all of which were of importance in T-cell activation. In conclusion, our study reveals new pathways that may regulate CD8⁺ T-cell activation in SAA patients and provides potential therapeutic targets for SAA treatment.

Cadaveric Stem Cells: Their Research Potential and Limitations

In the era of growing interest in stem cells, the availability of donors for transplantation has become a problem. The isolation of embryonic and fetal cells raises ethical controversies, and the number of adult donors is deficient. Stem cells isolated from deceased donors, known as cadaveric stem cells (CaSCs), may alleviate this problem. So far, it was possible to isolate from deceased donors mesenchymal stem cells (MSCs), adipose delivered stem cells (ADSCs), neural stem cells (NSCs), retinal progenitor cells (RPCs), induced pluripotent stem cells (iPSCs), and hematopoietic stem cells (HSCs). Recent studies have shown that it is possible to collect and use CaSCs from cadavers, even these with an extended postmortem interval (PMI) provided proper storage conditions (like cadaver heparinization or liquid nitrogen storage) are maintained. The presented review summarizes the latest research on CaSCs and their current therapeutic applications. It describes the developments in thanatotranscriptome and scaffolding for cadaver cells, summarizes their potential applications in regenerative medicine, and lists their limitations, such as donor’s unknown medical condition in criminal cases, limited differentiation potential, higher risk of carcinogenesis, or changing DNA quality. Finally, the review underlines the need to develop procedures determining the safe CaSCs harvesting and use.

Thorny ground, rocky soil: Tissue-specific mechanisms of tumor dormancy and relapse

Disseminated tumor cells (DTCs) spread systemically yet distinct patterns of metastasis indicate a range of tissue susceptibility to metastatic colonization. Distinctions between permissive and suppressive tissues are still being elucidated at cellular and molecular levels. Although there is a growing appreciation for the role of the microenvironment in regulating metastatic success, we have a limited understanding of how diverse tissues regulate DTC dormancy, the state of reversible quiescence and subsequent awakening thought to contribute to delayed relapse. Several themes of microenvironmental regulation of dormancy are beginning to emerge, including vascular association, co-option of pre-existing niches, metabolic adaptation, and immune evasion, with tissue-specific nuances. Conversely, DTC awakening is often associated with injury or inflammation-induced activation of the stroma, promoting a proliferative environment with DTCs following suit. We review what is known about tissue-specific regulation of tumor dormancy on a tissue-by-tissue basis, profiling major metastatic organs including the bone, lung, brain, liver, and lymph node. An aerial view of the barriers to metastatic growth may reveal common targets and dependencies to inform the therapeutic prevention of relapse.

The Proliferation and Stemness of Peripheral Blood-Derived Mesenchymal Stromal Cells Were Enhanced by Hypoxia

This study aimed to address the dilemma of low peripheral blood-derived mesenchymal stromal cell (PBMSC) activity and reduced phenotype in bone or cartilage tissue engineering. Rat PBMSCs (rPBMSCs) were obtained by density gradient centrifugation, and stromal cell characteristics were confirmed by flow cytometry (FCM) and multi-differentiation potential induction experiments. Cell growth curve, viability experiments, and clone formation experiments were performed by [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium] (MTS) and cell counting, and the cell cycle was confirmed by cell FCM. The proliferation signal pathway and stemness-related proteins were detected by molecular methods including Western blot and real-time polymerase chain reaction. CD73, CD90, and CD105 were highly expressed, and CD14, CD19, CD34, CD45, and HLA-DR were barely expressed in rPBMSCs. rPBMSCs possessed the potential to differentiate into chondrocytes, adipocytes, and osteoblasts under their respective induction conditions. Cell growth curve and viability experiments were performed under hypoxic conditions: 19% O₂, 5% O₂, and 1% O₂. Specifically, 5% O₂ accelerated the proliferation and expression of the stemness of PBMSCs. Cycle experiments proved that hypoxia promoted the cell transition from the G1 phase to the S phase. Molecular experiments confirmed that 5% O₂ hypoxia significantly elevated the expressions of hypoxia-inducible factor 1α and β-catenin and simultaneously the expressions of cycle-related genes including CyclinE/CDK2 and stemness-related genes including Nanog and SOX2. The appropriate concentration of hypoxia (i.e., 5% O₂) enhanced the proliferation and stemness of rPBMSCs and increased the multidirectional differentiation potential of stromal cells. The proposed culture method could improve the viability and maintain the phenotype of rPBMSCs in cartilage or bone tissue engineering.

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.

Total Body Irradiation in Haematopoietic Stem Cell Transplantation for Paediatric Acute Lymphoblastic Leukaemia: Review of the Literature and Future Directions

Total body irradiation (TBI) has been a pivotal component of the conditioning regimen for allogeneic myeloablative haematopoietic stem cell transplantation (HSCT) in very-high-risk acute lymphoblastic leukaemia (ALL) for decades, especially in children and young adults. The myeloablative conditioning regimen has two aims: (1) to eradicate leukaemic cells, and (2) to prevent rejection of the graft through suppression of the recipient's immune system. Radiotherapy has the advantage of achieving an adequate dose effect in sanctuary sites and in areas with poor blood supply. However, radiotherapy is subject to radiobiological trade-offs between ALL cell destruction, immune and haematopoietic stem cell survival, and various adverse effects in normal tissue. To diminish toxicity, a shift from single-fraction to fractionated TBI has taken place. However, HSCT and TBI are still associated with multiple late sequelae, leaving room for improvement. This review discusses the past developments of TBI and considerations for dose, fractionation and dose-rate, as well as issues regarding TBI setup performance, limitations and possibilities for improvement. TBI is typically delivered using conventional irradiation techniques and centres have locally developed heterogeneous treatment methods and ways to achieve reduced doses in several organs. There are, however, limitations in options to shield organs at risk without compromising the anti-leukaemic and immunosuppressive effects of conventional TBI. Technological improvements in radiotherapy planning and delivery with highly conformal TBI or total marrow irradiation (TMI), and total marrow and lymphoid irradiation (TMLI) have opened the way to investigate the potential reduction of radiotherapy-related toxicities without jeopardising efficacy. The demonstration of the superiority of TBI compared with chemotherapy-only conditioning regimens for event-free and overall survival in the randomised For Omitting Radiation Under Majority age (FORUM) trial in children with high-risk ALL makes exploration of the optimal use of TBI delivery mandatory. Standardisation and comprehensive reporting of conventional TBI techniques as well as cooperation between radiotherapy centres may help to increase the ratio between treatment outcomes and toxicity, and future studies must determine potential added benefit of innovative conformal techniques to ultimately improve quality of life for paediatric ALL patients receiving TBI-conditioned HSCT.

Restoring Tumour Selectivity of the Bioreductive Prodrug PR-104 by Developing an Analogue Resistant to Aerobic Metabolism by Human Aldo-Keto Reductase 1C3

PR-104 is a phosphate ester pre-prodrug that is converted in vivo to its cognate alcohol, PR-104A, a latent alkylator which forms potent cytotoxins upon bioreduction. Hypoxia selectivity results from one-electron nitro reduction of PR-104A, in which cytochrome P450 oxidoreductase (POR) plays an important role. However, PR-104A also undergoes ‘off-target’ two-electron reduction by human aldo-keto reductase 1C3 (AKR1C3), resulting in activation in oxygenated tissues. AKR1C3 expression in human myeloid progenitor cells probably accounts for the dose-limiting myelotoxicity of PR-104 documented in clinical trials, resulting in human PR-104A plasma exposure levels 3.4- to 9.6-fold lower than can be achieved in murine models. Structure-based design to eliminate AKR1C3 activation thus represents a strategy for restoring the therapeutic window of this class of agent in humans. Here, we identified SN29176, a PR-104A analogue resistant to human AKR1C3 activation. SN29176 retains hypoxia selectivity in vitro with aerobic/hypoxic IC50 ratios of 9 to 145, remains a substrate for POR and triggers γH2AX induction and cell cycle arrest in a comparable manner to PR-104A. SN35141, the soluble phosphate pre-prodrug of SN29176, exhibited superior hypoxic tumour log cell kill (>4.0) to PR-104 (2.5–3.7) in vivo at doses predicted to be achievable in humans. Orthologues of human AKR1C3 from mouse, rat and dog were incapable of reducing PR-104A, thus identifying an underlying cause for the discrepancy in PR-104 tolerance in pre-clinical models versus humans. In contrast, the macaque AKR1C3 gene orthologue was able to metabolise PR-104A, indicating that this species may be suitable for evaluating the toxicokinetics of PR-104 analogues for clinical development. We confirmed that SN29176 was not a substrate for AKR1C3 orthologues across all four pre-clinical species, demonstrating that this prodrug analogue class is suitable for further development. Based on these findings, a prodrug candidate was subsequently identified for clinical trials.

Hematopoietic Stem Cells and Regeneration

Hematopoietic stem cell (HSC) regeneration is the remarkable process by which extremely rare, normally inactive cells of the bone marrow can replace an entire organ if called to do so by injury or harnessed by transplantation. HSC research is arguably the first quantitative single-cell science and the foundation of adult stem cell biology. Bone marrow transplant is the oldest and most refined technique of regenerative medicine. Here we review the intertwined history of the discovery of HSCs and bone marrow transplant, the molecular and cellular mechanisms of HSC self-renewal, and the use of HSCs and their derivatives for cell therapy.

Loss of Atg2b and Gskip impairs the maintenance of the hematopoietic stem cell pool size

A germ line copy number duplication of chromosome 14q32, which contains ATG2B and GSKIP, was identified in families with myeloproliferative neoplasm (MPN). Here, we show that mice lacking both Atg2b and Gskip, but not either alone, exhibited decreased hematopoiesis, resulting in death in utero accompanied by anemia. In marked contrast to MPN patients with duplication of ATG2B and GSKIP, the number of hematopoietic stem cells (HSCs), in particular long-term HSCs, in double-knockout fetal livers was significantly decreased due to increased cell death. Although the remaining HSCs still had the ability to differentiate into hematopoietic progenitor cells, the differentiation efficiency was quite low. Remarkably, mice with knockout of Atg2b or Gskip alone did not show any hematopoietic abnormality. Mechanistically, while loss of both genes had no effect on autophagy, it increased the expression of genes encoding enzymes involved in oxidative phosphorylation. Taken together, our results indicate that Atg2b and Gskip play a synergistic effect in maintaining the pool size of HSCs.

NOTCH-mediated ex vivo expansion of human hematopoietic stem and progenitor cells by culture under hypoxia

Activation of NOTCH signaling in human hematopoietic stem/progenitor cells (HSPCs) by treatment with an engineered Delta-like ligand (DELTA1^ext-IgG [DXI]) has enabled ex vivo expansion of short-term HSPCs, but the effect on long-term repopulating hematopoietic stem cells (LTR-HSCs) remains uncertain. Here, we demonstrate that ex vivo culture of human adult HSPCs with DXI under low oxygen tension limits ER stress in LTR-HSCs and lineage-committed progenitors compared with normoxic cultures. A distinct HSC gene signature was upregulated in cells cultured with DXI in hypoxia and, after 21 days of culture, the frequency of LTR-HSCs increased 4.9-fold relative to uncultured cells and 4.2-fold compared with the normoxia + DXI group. NOTCH and hypoxia pathways intersected to maintain undifferentiated phenotypes in cultured HSPCs. Our work underscores the importance of mitigating ER stress perturbations to preserve functional LTR-HSCs in extended cultures and offers a clinically feasible platform for the expansion of human HSPCs.

Dietary interventions as regulators of stem cell behavior in homeostasis and disease

Stem cells maintain tissues by balancing self-renewal with differentiation. A stem cell's local microenvironment, or niche, informs stem cell behavior and receives inputs at multiple levels. Increasingly, it is becoming clear that the overall metabolic status of an organism or metabolites themselves can function as integral members of the niche to alter stem cell fate. Macroscopic dietary interventions such as caloric restriction, the ketogenic diet, and a high-fat diet systemically alter an organism's metabolic state in different ways. Intriguingly, however, they all converge on a propensity to enhance self-renewal. Here, we highlight our current knowledge on how dietary changes feed into stem cell behavior across a wide variety of tissues and illuminate possible explanations for why diverse interventions can result in similar stem cell phenotypes. In so doing, we hope to inspire new avenues of inquiry into the importance of metabolism in stem cell homeostasis and disease.