Understanding intrinsic hematopoietic stem cell aging

Single-cell profiling unveils a geroprotective role of Procyanidin C1 in hematopoietic immune system via senolytic and senomorphic effects

Aging of hematopoietic and immune system (HIS) leads to cellular senescence and immune dysregulation, contributing to age-related diseases. Here, we show that Procyanidin C1 (PCC1), a compound with both senolytic and senomorphic properties, can counteract aging-related changes in HIS. Using single-cell RNA sequencing and validation experiments, we found that aging induced cellular senescence, inflammation, and immune dysregulation in the bone marrow and spleen tissues of mice. Long-term PCC1 treatment improved key physiological parameters especially the grip strength of aged mice. Further single-cell analysis revealed PCC1's broad geroprotective effects on HIS, including an increase in the proportion of B cells (BCs) and hematopoietic stem cells (HSCs), suppression of senescence-associated markers, and restoration of normal immune processes. Specifically, PCC1 mitigated inflammation and restored immune homeostasis in BCs by suppressing Cebpb expression and age-associated BCs. Moreover, PCC1 reversed aging-induced alterations in HSCs through upregulating Nedd4 and CD62L-Ca2+ axis expression. Finally, we identified senescent cells (SnCs) using machine learning and gene set enrichment analysis, revealing that PCC1 induced apoptosis of SnCs and regulated their metabolic processes, particularly in granulocytes and myeloid cells. The experimental validation further confirmed the senolytic and senomorphic effects of PCC1 both in vivo and in vitro. Overall, PCC1 holds potential as a therapeutic agent for alleviating immune dysfunction and promoting healthy aging via senolytic and senomorphic effects.

Epigenetic ageing clocks: statistical methods and emerging computational challenges

Over the past decade, epigenetic clocks have emerged as powerful machine learning tools, not only to estimate chronological and biological age but also to assess the efficacy of anti-ageing, cellular rejuvenation and disease-preventive interventions. However, many computational and statistical challenges remain that limit our understanding, interpretation and application of epigenetic clocks. Here, we review these computational challenges, focusing on interpretation, cell-type heterogeneity and emerging single-cell methods, aiming to provide guidelines for the rigorous construction of interpretable epigenetic clocks at cell-type and single-cell resolution.

Epithelial Fibronectin meshwork controls skin regeneration

Adult stem cell fate is tightly balanced by the local microenvironment called niche and sustains tissue regeneration. How niche signals are integrated and regulate regeneration remains largely unexplored. Fibronectin (FN) is a major extracellular matrix component and integrin ligand, which role is well characterized during wound healing. Here, using the hair follicle as a mini organ which regenerates, we discovered a previously unreported role for FN in epidermal regeneration. Hair follicle stem cells (HFSCs) undergo long-term self-renewal and multi-lineage differentiation. We show that FN displays a highly specific enrichment in stem cells at the onset of hair follicle regeneration. We reveal FN tracks along the regenerating hair follicles forming a meshwork. FN conditional deletion in HFSC compartments (Lrig1, K19) leads to impaired stem cell location and fate. Loss of this meshwork is accompanied by hair regeneration blocade. Dermal injection of exogenous FN rescues these phenotypes. Analyzing the molecular mechanisms underlying FN function led us to identify integrin-dependent mechanotransduction as the main player in hair follicle regeneration, via YAP/Taz. Thus, in epithelial cells, fibronectin-integrin-mechanotransduction finely tunes adult stem cell fate and tissue regenerative power.

The Role of Aging and Senescence in Bone Marrow Transplantation Outcome

Bone marrow transplantation is considered a cornerstone in the treatment of hematologic malignancies and blood disorders. While it may offer the possibility of a cure through the use of high-dose chemotherapy and radiation, outcomes are significantly impacted by biological and medical factors. Herein, aging is associated with reduced hematopoiesis, immune function, and overall regenerative capacity of tissues. Growth arrest, a crucial property of cellular senescence, inhibits bone marrow function, lowers immune surveillance in aged adults, and reduces the efficiency of bone marrow transplantation. The clinical course for older recipients is further complicated by the presence of prolonged immunosuppression, slower recovery, and higher complication rates, including life-threatening graft-versus-host disease. Accordingly, there is increasing interest in explaining how aging, cellular senescence, and transplant outcomes are interrelated. The current chapter outlines the mechanisms whereby aging and senescence contribute to the immunological dysregulation and poor bone marrow transplantation outcomes observed in elderly cancer patients. The authors' goal is to suggest therapeutic approaches that will enhance the quality of life and survival rates of elderly bone marrow transplant recipients.

Cell polarity: cell type-specific regulators, common pathways, and polarized vesicle transport

Cell polarity, the asymmetric organization of cellular components, is evolutionarily conserved from unicellular and multicellular organisms and is crucial for many biological processes. Polarity is required to maintain cell and tissue integrity by regulating cell division, migration, orientation, cell-cell interactions, and morphogenesis. Impaired polarity leads to dysregulation of cellular functions and is associated with disease. Understanding how polarity is established, maintained, and regulated is thus critical to improving our knowledge of pathologies and devising novel therapies. Here, we explore the various manifestations of cell polarity across different model systems, tissues, and cell types and focus on known polarity mechanisms in hematopoietic stem and progenitor cells. We discuss how cells with vastly different functions utilize conserved molecular complexes to establish cell polarity while adapting polarity proteins to unique cell-type-specific functions. In this discussion, we attempt to extract common themes and concepts to improve our understanding of cell polarity in hematological malignancies and other diseases. Finally, we summarize, compare, and evaluate classical as well as recently developed methods to quantify cell polarity, highlight important advances in imaging and analytical techniques, and suggest critical next steps required to move the field forward.

Global, regional, and national burden of myelodysplastic syndromes and myeloproliferative neoplasms, 1990-2021: an analysis from the global burden of disease study 2021

Objective

To analyze the trends and cross-country inequalities in the burden of Myelodysplastic syndromes (MDS) and myeloproliferative neoplasms (MPN) over the past 30 years and forecast potential changes through 2045.

Methods

Estimates and 95% uncertainty intervals (UIs) for incidence, deaths, and disability-adjusted life-years (DALYs) associated with MDS/MPN were obtained from the Global Burden of Diseases (GBD) 2021 database. We described the epidemiology of MDS/MPN at global, regional, and national levels, analyzed trends in the burden of MDS/MPN from 1990 to 2021 through overall, local, and multidimensional perspectives, decomposed the burden based on population size, age structure, and epidemiological changes, quantified cross-country inequalities in MDS/MPN burden using standard health equity methods recommended by the WHO, and predicted changes of MDS/MPN burden to 2045.

Results

The global incidence of MDS/MPN has shown a marked increase, escalating from 171,132 cases in 1990 to 341,017 cases in 2021. Additionally, the burden was found to be significantly greater in men compared to women. The overall global burden of MDS/MPN exhibited a consistent increase from 1990 to 2021, although the growth rate showed a noticeable slowdown between 2018 and 2021. Decomposition analysis identified population growth as a key factor influencing the variations in the burden of MDS/MPN. An inequality analysis across countries indicated that high Socio-demographic Index (SDI) countries bore a disproportionate share of the MDS/MPN burden, with significant SDI-related disparities remaining evident. Interestingly, while the incidence and deaths of MDS/MPN, along with the age-standardized rate (ASR) for DALYs, are projected to decline annually from 2020 to 2045, the absolute number of cases for these indicators is expected to continue rising. By 2045, the projected numbers are estimated to reach 457,320 cases for incidence, 82,047 cases for deaths, and 1,689,518 cases for DALYs.

Conclusions

As a major public health issue, the global burden of MDS/MPN showed an overall increasing trend from 1990 to 2021, which was primarily driven by population growth and aging. The largest share of the MDS/MPN burden was seen primarily in men, with older demographics. Countries with elevated SDI experienced a significantly higher burden of MDS/MPN. While the burden of MDS/MPN was most pronounced in high SDI quintile, the fastest growth was observed in the low-middle SDI quintile, especially in tropical Latin America. This study highlighted great challenges in the control and management of MDS/MPN, including both growing case number and distributive inequalities worldwide. These findings provide valuable insights for developing more effective public health policies and optimizing the allocation of medical resources.

How age affects human hematopoietic stem and progenitor cells and the strategies to mitigate aging

Hematopoietic stem cells (HSCs) are central to blood formation and play a pivotal role in hematopoietic and systemic aging. With aging, HSCs undergo significant functional changes, such as an increased stem cell pool, declined homing and reconstitution capacity, and skewed differentiation toward myeloid and megakaryocyte/platelet progenitors. These phenotypic alterations are likely due to the expansion of certain clones, known as clonal hematopoiesis (CH), which leads to disrupted hematopoietic homeostasis, including anemia, impaired immunity, higher risks of hematological malignancies, and even associations with cardiovascular disease, highlighting the broader impact of HSC aging on overall health. HSC aging is driven by a range of mechanisms involving both intrinsic and extrinsic factors, such as DNA damage accumulation, epigenetic remodeling, inflammaging and metabolic regulation. In this review, we summarize the updated understanding of age-related changes in hematopoietic stem and progenitor cells (HSPCs) and the mechanisms underlying the aging process in mammalian models, especially in human study. Additionally, we provide insights into potential therapeutic strategies to counteract aging process and enhance HSC regenerative capacity, which will support therapeutic interventions and promote healthy aging.

Hematopoietic stem cell metabolism within the bone marrow niche - insights and opportunities

Hematopoiesis unfolds within the bone marrow niche where hematopoietic stem cells (HSCs) play a central role in continually replenishing blood cells. The hypoxic bone marrow environment imparts peculiar metabolic characteristics to hematopoietic processes. Here, we discuss the internal metabolism of HSCs and describe external influences exerted on HSC metabolism by the bone marrow niche environment. Importantly, we suggest that the metabolic environment and metabolic cues are intertwined with HSC cell fate, and are crucial for hematopoietic processes. Metabolic dysregulation within the bone marrow niche during acute stress, inflammation, and chronic inflammatory conditions can lead to reduced HSC vitality. Additionally, we raise questions regarding metabolic stresses imposed on HSCs during implementation of stem cell protocols such as allo-SCT and gene therapy, and the potential ramifications. Enhancing our comprehension of metabolic influences on HSCs will expand our understanding of pathophysiology in the bone marrow and improve the application of stem cell therapies.

Immune Aging in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a life-long autoimmune disease caused by the confluence of genetic and environmental variables that lead to loss of self-tolerance and persistent joint inflammation. RA occurs at the highest incidence in individuals >65 years old, implicating the aging process in disease susceptibility. Transformative approaches in molecular immunology and in functional genomics have paved the way for pathway paradigms underlying the replacement of immune homeostasis with autodestructive immunity in affected patients, including the process of immune aging. Patients with RA have a signature of premature immune aging, best understood for CD4+ T cells, which function as pathogenic effectors in this HLA class II-associated disease. Premature immune aging is present in healthy HLA-DRB1*04+ individuals, placing accelerated immune aging before joint inflammation. Aging-related molecular abnormalities directly implicated in turning RA CD4+ T cells into proinflammatory effector cells are linked to malfunction of subcellular organelles, such as mitochondria, lysosomes, lipid droplets, and the endoplasmic reticulum. Resulting changes in T cell behavior include cellular hypermobility, tissue invasiveness, unopposed mammalian target of rapamycin complex (mTORC)1 activation, excessive release of tumor necrosis factor, lysosomal failure, clonal expansion, and immunogenic cell death. Aged and metabolically reprogrammed T cells in patients with RA are accompanied by age-associated B cells, which specialize in autoantibody production. Clonal hematopoiesis drives myeloid cell aging by producing aged monocytes and hypermetabolic macrophages, which sustain the process of inflammaging. Here, we synthesize insights into the relationship of RA risk and immune aging and discuss mechanisms through which immune aging can cause autoimmunity.

Reducing functionally defective old HSCs alleviates aging-related phenotypes in old recipient mice

Aging is a process accompanied by functional decline in tissues and organs with great social and medical consequences. Developing effective anti-aging strategies is of great significance. In this study, we demonstrated that transplantation of young hematopoietic stem cells (HSCs) into old mice can mitigate aging phenotypes, underscoring the crucial role of HSCs in the aging process. Through comprehensive molecular and functional analyses, we identified a subset of HSCs in aged mice that exhibit "younger" molecular profiles and functions, marked by low levels of CD150 expression. Mechanistically, CD150low HSCs from old mice but not their CD150high counterparts can effectively differentiate into downstream lineage cells. Notably, transplantation of old CD150low HSCs attenuates aging phenotypes and prolongs lifespan of elderly mice compared to those transplanted with unselected or CD150high HSCs. Importantly, reducing the dysfunctional CD150high HSCs can alleviate aging phenotypes in old recipient mice. Thus, our study demonstrates the presence of "younger" HSCs in old mice, and that aging-associated functional decline can be mitigated by reducing dysfunctional HSCs.

Cell-type specific epigenetic clocks to quantify biological age at cell-type resolution

The ability to accurately quantify biological age could help monitor and control healthy aging. Epigenetic clocks have emerged as promising tools for estimating biological age, yet they have been developed from heterogeneous bulk tissues, and are thus composites of two aging processes, one reflecting the change of cell-type composition with age and another reflecting the aging of individual cell-types. There is thus a need to dissect and quantify these two components of epigenetic clocks, and to develop epigenetic clocks that can yield biological age estimates at cell-type resolution. Here we demonstrate that in blood and brain, approximately 39% and 12% of an epigenetic clock's accuracy is driven by underlying shifts in lymphocyte and neuronal subsets, respectively. Using brain and liver tissue as prototypes, we build and validate neuron and hepatocyte specific DNA methylation clocks, and demonstrate that these cell-type specific clocks yield improved estimates of chronological age in the corresponding cell and tissue-types. We find that neuron and glia specific clocks display biological age acceleration in Alzheimer's Disease with the effect being strongest for glia in the temporal lobe. Moreover, CpGs from these clocks display a small but significant overlap with the causal DamAge-clock, mapping to key genes implicated in neurodegeneration. The hepatocyte clock is found accelerated in liver under various pathological conditions. In contrast, non-cell-type specific clocks do not display biological age-acceleration, or only do so marginally. In summary, this work highlights the importance of dissecting epigenetic clocks and quantifying biological age at cell-type resolution.

Inflammation in myelodysplastic syndrome pathogenesis

Inflammation is a key driver of the progression of preleukemic myeloid conditions, such as clonal hematopoiesis of indeterminate potential (CHIP) and clonal cytopenia of undetermined significance (CCUS), to myelodysplastic syndromes (MDS). Inflammation is a critical mediator in the complex interplay of the genetic, epigenetic, and microenvironmental factors contributing to clonal evolution. Under inflammatory conditions, somatic mutations in TET2, DNMT3A, and ASXL1, the most frequently mutated genes in CHIP and CCUS, induce a competitive advantage to hematopoietic stem and progenitor cells, which leads to their clonal expansion in the bone marrow. Chronic inflammation also drives metabolic reprogramming and immune system deregulation, further promoting the expansion of malignant clones. This review underscores the urgent need to fully elucidate the role of inflammation in MDS initiation and highlights the potential of the therapeutical targeting of inflammatory pathways as an early intervention in MDS.

Inflammation and DNA methylation in Alzheimer's disease: mechanisms of epigenetic remodelling by immune cell oxidants in the ageing brain

Alzheimer's disease is a neurodegenerative disease involving memory impairment, confusion, and behavioural changes. The disease is characterised by the accumulation of amyloid beta plaques and neurofibrillary tangles in the brain, which disrupt normal neuronal function. There is no known cure for Alzheimer's disease and due to increasing life expectancy, occurrence is projected to rise over the coming decades. The causes of Alzheimer's disease are multifactorial with inflammation, oxidative stress, genetic and epigenetic variation, and cerebrovascular abnormalities among the strongest contributors. We review the current literature surrounding inflammation and epigenetics in Alzheimer's disease, with a focus on how oxidants from infiltrating immune cells have the potential to alter DNA methylation profiles in the ageing brain.

Cellular stress and epigenetic regulation in adult stem cells

Stem cells are a unique class of cells that possess the ability to differentiate and self-renew, enabling them to repair and replenish tissues. To protect and maintain the potential of stem cells, the cells and the environment surrounding these cells (stem cell niche) are highly responsive and tightly regulated. However, various stresses can affect the stem cells and their niches. These stresses are both systemic and cellular and can arise from intrinsic or extrinsic factors which would have strong implications on overall aging and certain disease states. Therefore, understanding the breadth of drivers, namely epigenetic alterations, involved in cellular stress is important for the development of interventions aimed at maintaining healthy stem cells and tissue homeostasis. In this review, we summarize published findings of epigenetic responses to replicative, oxidative, mechanical, and inflammatory stress on various types of adult stem cells.

Organoids as Tools for Investigating Skin Aging: Mechanisms, Applications, and Insights

Organoids have emerged as transformative tools in biomedical research, renowned for their ability to replicate the complexity construct of human tissues. Skin aging is a multifaceted biological process, influenced by both intrinsic factors and extrinsic factors. Traditional models for studying skin aging often fall short in capturing the intricate dynamics of human skin. In contrast, skin organoids offer a more physiologically relevant system, reflecting the structural and functional characteristics of native skin. These characteristics make skin organoids highly suitable for studying the mechanisms of skin aging, identifying novel therapeutic targets, and testing anti-aging interventions. Despite their promise, challenges such as limited scalability, reproducibility, and ethical considerations remain. Addressing these hurdles through interdisciplinary research and technological advancements will be essential to maximizing the potential of skin organoids for dermatological research and personalized anti-aging therapies.

Emerging insights into epigenetics and hematopoietic stem cell trafficking in age-related hematological malignancies

BACKGROUND

Hematopoiesis within the bone marrow (BM) is a complex and tightly regulated process predominantly influenced by immune factors. Aging, diabetes, and obesity are significant contributors to BM niche damage, which can alter hematopoiesis and lead to the development of clonal hematopoiesis of intermediate potential (CHIP). Genetic/epigenetic alterations during aging could influence BM niche reorganization for hematopoiesis or clonal hematopoiesis. CHIP is driven by mutations in genes such as Tet2, Dnmt3a, Asxl1, and Jak2, which are associated with age-related hematological malignancies.

OBJECTIVE

This literature review aims to provide an updated exploration of the functional aspects of BM niche cells within the hematopoietic microenvironment in the context of age-related hematological malignancies. The review specifically focuses on how immunological stressors modulate different signaling pathways that impact hematopoiesis.

METHODS

An extensive review of recent studies was conducted, examining the roles of various BM niche cells in hematopoietic stem cell (HSC) trafficking and the development of age-related hematological malignancies. Emphasis was placed on understanding the influence of immunological stressors on these processes.

RESULTS

Recent findings reveal a significant microheterogeneity and temporal stochasticity of niche cells across the BM during hematopoiesis. These studies demonstrate that niche cells, including mesenchymal stem cells, osteoblasts, and endothelial cells, exhibit dynamic interactions with HSCs, significantly influenced by the BM microenvironment as the age increases. Immunosurveillance plays a crucial role in maintaining hematopoietic homeostasis, with alterations in immune signaling pathways contributing to the onset of hematological malignancies. Novel insights into the interaction between niche cells and HSCs under stress/aging conditions highlight the importance of niche plasticity and adaptability.

CONCLUSION

The involvement of age-induced genetic/epigenetic alterations in BM niche cells and immunological stressors in hematopoiesis is crucial for understanding the development of age-related hematological malignancies. This comprehensive review provides new insights into the complex interplay between niche cells and HSCs, emphasizing the potential for novel therapeutic approaches that target niche cell functionality and resilience to improve hematopoietic outcomes in the context of aging and metabolic disorders.

NOVELTY STATEMENT

This review introduces novel concepts regarding the plasticity and adaptability of BM niche cells in response to immunological stressors and epigenetics. It proposes that targeted therapeutic strategies aimed at enhancing niche cell resilience could mitigate the adverse effects of aging, diabetes, and obesity on hematopoiesis and clonal hematopoiesis. Additionally, the review suggests that understanding the precise temporal and spatial dynamics of niche-HSC interactions and epigenetics influence may lead to innovative treatments for age-related hematological malignancies.

A cellular identity crisis? Plasticity changes during aging and rejuvenation

Cellular plasticity in adult multicellular organisms is a protective mechanism that allows certain tissues to regenerate in response to injury. Considering that aging involves exposure to repeated injuries over a lifetime, it is conceivable that cell identity itself is more malleable-and potentially erroneous-with age. In this review, we summarize and critically discuss the available evidence that cells undergo age-related shifts in identity, with an emphasis on those that contribute to age-associated pathologies, including neurodegeneration and cancer. Specifically, we focus on reported instances of programs associated with dedifferentiation, biased differentiation, acquisition of features from alternative lineages, and entry into a preneoplastic state. As some of the most promising approaches to rejuvenate cells reportedly also elicit transient changes to cell identity, we further discuss whether cell state change and rejuvenation can be uncoupled to yield more tractable therapeutic strategies.

The Comparative Effect of Plasma Exosomes of Young and Old People on the Expression of BCL-2 and BAX Genes in Hematopoietic Stem Cells

Apoptosis may disrupt differentiation of hematopoietic stem cells (HSCs), which can affect aging. Thus, the main goal of this study was to compare the effect of plasma exosomes from young and old people on the expression of Bcl-2-associated X (BAX) and B-cell lymphoma 2 (BCL-2) genes in the HSCs. Plasma samples were acquired from four elderly adults and four younger adults, referring to Blood Transfusion Organization of Tehran-Iran during August 2022- September 2022.Then, the exosomes of the samples were extracted and analyzed using DLS, TEM, and CD63 surface marker. HSCs were isolated from umbilical cord blood cells. The MTT test was used to assess the viability of exosomes-treated HSCs at doses of 5 and 10 μg/ml. The expression of BAX and BCL-2 genes in the cells was examined using real-time PCR. A one-way analysis of variance (ANOVA) was performed to examine the distinctions among five groups. The viability of HSCs was not affected by the exosomes from young and old people than the control group (P = 0.453). Exosomes from young people (doses 5 and 10 µg/ml) did not have any significant impacts on BAX (P = 0.746, and P = 0.345, respectively) and BCL-2 (P = 0.773, and P = 0.461, respectively) expression in the HSCs compared to the control group. The BAX gene was significantly upregulated and the BCL-2 gene was significantly downregulated after utilizing the exosomes derived from the plasma of elderly individuals (dose 10 µg/ml) compared to the control (P = 0.001, P = 0.002, respectively). The current research shows that aged people's exosomes can increase BAX/ BCL-2 ratio in umbilical cord blood-derived HSCs compared to control and young groups.

The Influence of Circulating Exosomes Derived From Younger and Older Donors on Hypoxia-Inducible Factor 1 Alpha Gene Expression and P21 Protein in Cord Blood Hematopoietic Stem Cells

Background

Exosomes are a group of extracellular vesicles that are influential in intercellular signaling and can affect aging. Hypoxia-inducible factor 1α (HIF-1α) is the principal mediator in response to hypoxia and can regulate aging. Moreover, P21 is a part of the downstream signaling pathway of hypoxia and is elevated during aging. Therefore, this research was conducted to investigate the effect of plasma exosomes of younger and older individuals on the expression of HIF-1α gene and P21 protein in hematopoietic stem cells (HSCs).

Methods

Plasma exosomes were derived from older and younger men and were characterized. Then, HSCs were isolated from cord blood samples and treated with exosomes of older and younger men. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay was performed to evaluate cell viability. Next, the expression of HIF-1α gene and P21 protein were evaluated by quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot, respectively.

Results

HIF-1α gene expression was considerably increased in HSCs treated with 10 µg/mL of exosomes isolated from younger men (Y10-Exo) compared to the untreated group (P = 0.002). Moreover, HIF-1α gene expression was remarkably decreased in HSCs treated with 10 µg/mL of exosomes obtained from older men (O10-Exo) in comparison with the untreated group (P < 0.001). Additionally, the expression of P21 protein was significantly increased in HSCs treated with 5 µg/mL of exosomes derived from older individuals (O5-Exo) and O10-Exo compared to the untreated group (P = 0.000 and P = 0.002, respectively).

Conclusions

Our findings showed that exosomes isolated from younger participants cause elevation in HIF-1α and may lead to delayed aging in HSCs. In addition, exosomes isolated from older participants can probably lead to aging through the reduction in HIF-1α and elevation in P21.

CD38 and the mitochondrial calcium uniporter contribute to age-related hematopoietic stem cell dysfunction

Hematopoietic stem cells (HSCs) are the multipotent progenitors of all immune cells. During aging, their regenerative capacity decreases for reasons that are not well understood. Recently, Song et al investigated the roles of two metabolic proteins in age-related HSC dysfunction: CD38 (a membrane-bound NADase) and the mitochondrial calcium uniporter that transports calcium into the mitochondrial matrix. They found that the interplay between these proteins is deranged in aged HSCs, contributing to their diminished renewal capacity. These findings implicate compromised nicotinamide adenine dinucleotide metabolism as underlying HSC dysfunction in aging.

Unveiling aging dynamics in the hematopoietic system insights from single-cell technologies

As the demographic structure shifts towards an aging society, strategies aimed at slowing down or reversing the aging process become increasingly essential. Aging is a major predisposing factor for many chronic diseases in humans. The hematopoietic system, comprising blood cells and their associated bone marrow microenvironment, intricately participates in hematopoiesis, coagulation, immune regulation and other physiological phenomena. The aging process triggers various alterations within the hematopoietic system, serving as a spectrum of risk factors for hematopoietic disorders, including clonal hematopoiesis, immune senescence, myeloproliferative neoplasms and leukemia. The emerging single-cell technologies provide novel insights into age-related changes in the hematopoietic system. In this review, we summarize recent studies dissecting hematopoietic system aging using single-cell technologies. We discuss cellular changes occurring during aging in the hematopoietic system at the levels of the genomics, transcriptomics, epigenomics, proteomics, metabolomics and spatial multi-omics. Finally, we contemplate the future prospects of single-cell technologies, emphasizing the impact they may bring to the field of hematopoietic system aging research.

CHIP: a clonal odyssey of the bone marrow niche

Clonal hematopoiesis of indeterminate potential (CHIP) is characterized by the selective expansion of hematopoietic stem and progenitor cells (HSPCs) carrying somatic mutations. While CHIP is typically asymptomatic, it has garnered substantial attention due to its association with the pathogenesis of multiple disease conditions, including cardiovascular disease (CVD) and hematological malignancies. In this Review, we will discuss seminal and recent studies that have advanced our understanding of mechanisms that drive selection for mutant HSPCs in the BM niche. Next, we will address recent studies evaluating potential relationships between the clonal dynamics of CHIP and hematopoietic development across the lifespan. Next, we will examine the roles of systemic factors that can influence hematopoietic stem cell (HSC) fitness, including inflammation, and exposures to cytotoxic agents in driving selection for CHIP clones. Furthermore, we will consider how - through their impact on the BM niche - lifestyle factors, including diet, exercise, and psychosocial stressors, might contribute to the process of somatic evolution in the BM that culminates in CHIP. Finally, we will review the role of old age as a major driver of selection in CHIP.

Hematopoietic Stem Cells and Their Niche in Bone Marrow

Extensive research has explored the functional correlation between stem cells and progenitor cells, particularly in blood. Hematopoietic stem cells (HSCs) can self-renew and regenerate tissues within the bone marrow, while stromal cells regulate tissue function. Recent studies have validated the role of mammalian stem cells within specific environments, providing initial empirical proof of this functional phenomenon. The interaction between bone and blood has always been vital to the function of the human body. It was initially proposed that during evolution, mammalian stem cells formed a complex relationship with the surrounding microenvironment, known as the niche. Researchers are currently debating the significance of molecular-level data to identify individual stromal cell types due to incomplete stromal cell mapping. Obtaining these data can help determine the specific activities of HSCs in bone marrow. This review summarizes key topics from previous studies on HSCs and their environment, discussing current and developing concepts related to HSCs and their niche in the bone marrow.

Hyperexpression of tumor necrosis factor receptor 2 inhibits differentiation of myeloid-derived suppressor cells by instigating apolarity during ageing

During the ageing process, TNF-α can promote the expansion of myeloid-derived suppressor cells (MDSCs). However, it remains unclear which receptor(s) of TNF-α are involved in and how they modulate this process. Here, we report that TNFR2 hyperexpression induced by either TNF-α or IL-6, two proinflammatory factors of senescence-associated secretory phenotype (SASP), causes cellular apolarity and differentiation inhibition in aged MDSCs. Ex vivo overexpression of TNFR2 in young MDSCs inhibited their polarity and differentiation, whereas in vivo depletion of Tnfr2 in aged MDSCs promotes their differentiation. Consequently, the age-dependent increase of TNFR2 versus unaltered TNFR1 expression in aged MDSCs significantly shifts the balance of TNF-α signaling toward the TNFR2-JNK axis, which accounts for JNK-induced impairment of cell polarity and differentiation failure of aged MDSCs. Consistently, inhibiting JNK attenuates apolarity and partially restores the differentiation capacity of aged MDSCs, suggesting that upregulated TNFR2/JNK signaling is a key factor limiting MDSC differentiation during organismal ageing. Therefore, abnormal hyperexpression of TNFR2 represents a general mechanism by which extrinsic SASP signals disrupt intrinsic cell polarity behavior, thereby arresting mature differentiation of MDSCs with ageing, suggesting that TNFR2 could be a potential therapeutic target for intervention of ageing through rejuvenation of aged MDSCs.

Age-specific induction of mutant p53 drives clonal hematopoiesis and acute myeloid leukemia in adult mice

The investigation of the mechanisms behind p53 mutations in acute myeloid leukemia (AML) has been limited by the lack of suitable mouse models, which historically have resulted in lymphoma rather than leukemia. This study introduces two new AML mouse models. One model induces mutant p53 and Mdm2 haploinsufficiency in early development, showing the role of Mdm2 in myeloid-biased hematopoiesis and AML predisposition, independent of p53. The second model mimics clonal hematopoiesis by inducing mutant p53 in adult hematopoietic stem cells, demonstrating that the timing of p53 mutation determines AML vs. lymphoma development. In this context, age-related changes in hematopoietic stem cells (HSCs) collaborate with mutant p53 to predispose toward myeloid transformation rather than lymphoma development. Our study unveils new insights into the cooperative impact of HSC age, Trp53 mutations, and Mdm2 haploinsufficiency on clonal hematopoiesis and the development of myeloid malignancies.

Context-dependent modification of PFKFB3 in hematopoietic stem cells promotes anaerobic glycolysis and ensures stress hematopoiesis

Metabolic pathways are plastic and rapidly change in response to stress or perturbation. Current metabolic profiling techniques require lysis of many cells, complicating the tracking of metabolic changes over time after stress in rare cells such as hematopoietic stem cells (HSCs). Here, we aimed to identify the key metabolic enzymes that define differences in glycolytic metabolism between steady-state and stress conditions in murine HSCs and elucidate their regulatory mechanisms. Through quantitative 13C metabolic flux analysis of glucose metabolism using high-sensitivity glucose tracing and mathematical modeling, we found that HSCs activate the glycolytic rate-limiting enzyme phosphofructokinase (PFK) during proliferation and oxidative phosphorylation (OXPHOS) inhibition. Real-time measurement of ATP levels in single HSCs demonstrated that proliferative stress or OXPHOS inhibition led to accelerated glycolysis via increased activity of PFKFB3, the enzyme regulating an allosteric PFK activator, within seconds to meet ATP requirements. Furthermore, varying stresses differentially activated PFKFB3 via PRMT1-dependent methylation during proliferative stress and via AMPK-dependent phosphorylation during OXPHOS inhibition. Overexpression of Pfkfb3 induced HSC proliferation and promoted differentiated cell production, whereas inhibition or loss of Pfkfb3 suppressed them. This study reveals the flexible and multilayered regulation of HSC glycolytic metabolism to sustain hematopoiesis under stress and provides techniques to better understand the physiological metabolism of rare hematopoietic cells.

Differential Effects of Endurance Exercise on Musculoskeletal and Hematopoietic Modulation in Old Mice

One of the most important strategies for successful aging is exercise. However, the effect of exercise can differ among individuals, even with exercise of the same type and intensity. Therefore, this study aims to confirm whether endurance training (ETR) has the same health-promoting effects on the musculoskeletal and hematopoietic systems regardless of age. Ten weeks of ETR improved endurance exercise capacity, with increased skeletal muscle mitochondrial enzymes in both young and old mice. In addition, age-related deterioration of muscle fiber size and bone microstructure was improved. The expression levels of myostatin, muscle RING-finger protein-1, and muscle atrophy F-box in skeletal muscle and peroxisome proliferator-activated receptor-γ in the femur increased with age but decreased after ETR. ETR differentially modulated hematopoietic stem cells (HSCs) depending on age; ETR induced HSC quiescence in young mice but caused HSC senescence in old mice. ETR has differential effects on modulation of the musculoskeletal and hematopoietic systems in old mice. In other words, endurance exercise is a double-edged sword for successful aging, and great effort is required to establish exercise strategies for healthy aging.

Deep learning-based predictive classification of functional subpopulations of hematopoietic stem cells and multipotent progenitors

BACKGROUND

Hematopoietic stem cells (HSCs) and multipotent progenitors (MPPs) play a pivotal role in maintaining lifelong hematopoiesis. The distinction between stem cells and other progenitors, as well as the assessment of their functions, has long been a central focus in stem cell research. In recent years, deep learning has emerged as a powerful tool for cell image analysis and classification/prediction.

METHODS

In this study, we explored the feasibility of employing deep learning techniques to differentiate murine HSCs and MPPs based solely on their morphology, as observed through light microscopy (DIC) images.

RESULTS

After rigorous training and validation using extensive image datasets, we successfully developed a three-class classifier, referred to as the LSM model, capable of reliably distinguishing long-term HSCs, short-term HSCs, and MPPs. The LSM model extracts intrinsic morphological features unique to different cell types, irrespective of the methods used for cell identification and isolation, such as surface markers or intracellular GFP markers. Furthermore, employing the same deep learning framework, we created a two-class classifier that effectively discriminates between aged HSCs and young HSCs. This discovery is particularly significant as both cell types share identical surface markers yet serve distinct functions. This classifier holds the potential to offer a novel, rapid, and efficient means of assessing the functional states of HSCs, thus obviating the need for time-consuming transplantation experiments.

CONCLUSION

Our study represents the pioneering use of deep learning to differentiate HSCs and MPPs under steady-state conditions. This novel and robust deep learning-based platform will provide a basis for the future development of a new generation stem cell identification and separation system. It may also provide new insight into the molecular mechanisms underlying stem cell self-renewal.

Aging and comprehensive molecular profiling in acute myeloid leukemia

Acute myeloid leukemia (AML) is an aging-related and heterogeneous hematopoietic malignancy. In this study, a total of 1,474 newly diagnosed AML patients with RNA sequencing data were enrolled, and targeted or whole exome sequencing data were obtained in 94% cases. The correlation of aging-related factors including age and clonal hematopoiesis (CH), gender, and genomic/transcriptomic profiles (gene fusions, genetic mutations, and gene expression networks or pathways) was systematically analyzed. Overall, AML patients aged 60 y and older showed an apparently dismal prognosis. Alongside age, the frequency of gene fusions defined in the World Health Organization classification decreased, while the positive rate of gene mutations, especially CH-related ones, increased. Additionally, the number of genetic mutations was higher in gene fusion-negative (GF-) patients than those with GF. Based on the status of CH- and myelodysplastic syndromes (MDS)-related mutations, three mutant subgroups were identified among the GF- AML cohort, namely, CH-AML, CH-MDS-AML, and other GF- AML. Notably, CH-MDS-AML demonstrated a predominance of elderly and male cases, cytopenia, and significantly adverse clinical outcomes. Besides, gene expression networks including HOXA/B, platelet factors, and inflammatory responses were most striking features associated with aging and poor prognosis in AML. Our work has thus unraveled the intricate regulatory circuitry of interactions among different age, gender, and molecular groups of AML.

Differentiation of regulatory myeloid and T-cells from adult human hematopoietic stem cells after allogeneic stimulation

Introduction

Donor hematopoietic stem cell (DHSC) infusions are increasingly being studied in transplant patients for tolerance induction.

Methods

To analyze the fate of infused DHSCs in patients, we developed an in vitro culture system utilizing CD34+DHSCs stimulated with irradiated allogeneic cells in cytokine supplemented medium long-term.

Results

Flow cytometric analyses revealed loss of the CD34 marker and an increase in CD33+ myeloid and CD3+ T-cell proportion by 10.4% and 72.7%, respectively, after 21 days in culture. T-cells primarily expressed TcR-αβ and were of both CD4+ and CD8+ subsets. Approximately 80% of CD3+ T cells lacked expression of the co-stimulatory receptor CD28. The CD4+ compartment was predominated by CD4+CD25+CD127-FOXP3+ Tregs (>50% CD4+CD127- compartment) with <1% of all leukocytes exhibiting a CD4+CD127+ phenotype. Molecular analyses for T-cell receptor excision circles showed recent and increased numbers of TcR rearrangements in generated T cells over time suggesting de novo differentiation from DHSCs. CD33+ myeloid cells mostly expressed HLA-DR, but lacked expression of co-stimulatory receptors CD80 and CD83. When studied as modulators in primary mixed lymphocyte reactions where the cells used to stimulate the DHSC were used as responders, the DHSC-lines and their purified CD8+, CD4+, CD33+ and linage negative subsets inhibited the responses in a dose-dependent and non-specific fashion. The CD8+ cell-mediated inhibition was due to direct lysis of responder cells.

Discussion

Extrapolation of these results into the clinical situation would suggest that DHSC infusions into transplant recipients may generate multiple subsets of donor "chimeric" cells and promote recipient Treg development that could regulate the anti-donor immune response in the periphery. These studies have also indicated that T cell maturation can occur in vitro in response to allogeneic stimulation without the pre-requisite of a thymic-like environment or NOTCH signaling stimulatory cell line.

Analyzing somatic mutations by single-cell whole-genome sequencing

Somatic mutations are the cause of cancer and have been implicated in other, noncancerous diseases and aging. While clonally expanded mutations can be studied by deep sequencing of bulk DNA, very few somatic mutations expand clonally, and most are unique to each cell. We describe a detailed protocol for single-cell whole-genome sequencing to discover and analyze somatic mutations in tissues and organs. The protocol comprises single-cell multiple displacement amplification (SCMDA), which ensures efficiency and high fidelity in amplification, and the SCcaller software tool to call single-nucleotide variations and small insertions and deletions from the sequencing data by filtering out amplification artifacts. With SCMDA and SCcaller at its core, this protocol describes a complete procedure for the comprehensive analysis of somatic mutations in a single cell, covering (1) single-cell or nucleus isolation, (2) single-cell or nucleus whole-genome amplification, (3) library preparation and sequencing, and (4) computational analyses, including alignment, variant calling, and mutation burden estimation. Methods are also provided for mutation annotation, hotspot discovery and signature analysis. The protocol takes 12-15 h from single-cell isolation to library preparation and 3-7 d of data processing. Compared with other single-cell amplification methods or single-molecular sequencing, it provides high genomic coverage, high accuracy in single-nucleotide variation and small insertions and deletion calling from the same single-cell genome, and fewer processing steps. SCMDA and SCcaller require basic experience in molecular biology and bioinformatics. The protocol can be utilized for studying mutagenesis and genome mosaicism in normal and diseased human and animal tissues under various conditions.

Aging-disturbed FUS phase transition impairs hematopoietic stem cells by altering chromatin structure

ABSTRACT

Aged hematopoietic stem cells (HSCs) exhibit compromised reconstitution capacity. The molecular mechanisms behind this phenomenon are not fully understood. Here, we observed that the expression of FUS is increased in aged HSCs, and enforced FUS recapitulates the phenotype of aged HSCs through arginine-glycine-glycine-mediated aberrant FUS phase transition. By using Fus-gfp mice, we observed that FUShigh HSCs exhibit compromised FUS mobility and resemble aged HSCs both functionally and transcriptionally. The percentage of FUShigh HSCs is increased upon physiological aging and replication stress, and FUSlow HSCs of aged mice exhibit youthful function. Mechanistically, FUShigh HSCs exhibit a different global chromatin organization compared with FUSlow HSCs, which is observed in aged HSCs. Many topologically associating domains (TADs) are merged in aged HSCs because of the compromised binding of CCCTC-binding factor with chromatin, which is invoked by aberrant FUS condensates. It is notable that the transcriptional alteration between FUShigh and FUSlow HSCs originates from the merged TADs and is enriched in HSC aging-related genes. Collectively, this study reveals for the first time that aberrant FUS mobility promotes HSC aging by altering chromatin structure.

CD61 identifies a superior population of aged murine HSCs and is required to preserve quiescence and self-renewal

ABSTRACT

Aging leads to a decline in function of hematopoietic stem cells (HSCs) and increases susceptibility to hematological disease. We found CD61 to be highly expressed in aged murine HSCs. Here, we investigate the role of CD61 in identifying distinct subpopulations of aged HSCs and assess how expression of CD61 affects stem cell function. We show that HSCs with high expression of CD61 are functionality superior and retain self-renewal capacity in serial transplantations. In primary transplantations, aged CD61High HSCs function similarly to young HSCs. CD61High HSCs are more quiescent than their CD61Low counterparts. We also show that in aged bone marrow, CD61High and CD61Low HSCs are transcriptomically distinct populations. Collectively, our research identifies CD61 as a key player in maintaining stem cell quiescence, ensuring the preservation of their functional integrity and potential during aging. Moreover, CD61 emerges as a marker to prospectively isolate a superior, highly dormant population of young and aged HSCs, making it a valuable tool both in fundamental and clinical research.

Deep learning-based predictive classification of functional subpopulations of hematopoietic stem cells and multipotent progenitors

Background

Hematopoietic stem cells (HSCs) and multipotent progenitors (MPPs) play a pivotal role in maintaining lifelong hematopoiesis. The distinction between stem cells and other progenitors, as well as the assessment of their functions, has long been a central focus in stem cell research. In recent years, deep learning has emerged as a powerful tool for cell image analysis and classification/prediction.

Methods

In this study, we explored the feasibility of employing deep learning techniques to differentiate murine HSCs and MPPs based solely on their morphology, as observed through light microscopy (DIC) images.

Results

After rigorous training and validation using extensive image datasets, we successfully developed a three-class classifier, referred to as the LSM model, capable of reliably distinguishing long-term HSCs (LT-HSCs), short-term HSCs (ST-HSCs), and MPPs. The LSM model extracts intrinsic morphological features unique to different cell types, irrespective of the methods used for cell identification and isolation, such as surface markers or intracellular GFP markers. Furthermore, employing the same deep learning framework, we created a two-class classifier that effectively discriminates between aged HSCs and young HSCs. This discovery is particularly significant as both cell types share identical surface markers yet serve distinct functions. This classifier holds the potential to offer a novel, rapid, and efficient means of assessing the functional states of HSCs, thus obviating the need for time-consuming transplantation experiments.

Conclusion

Our study represents the pioneering use of deep learning to differentiate HSCs and MPPs under steady-state conditions. With ongoing advancements in model algorithms and their integration into various imaging systems, deep learning stands poised to become an invaluable tool, significantly impacting stem cell research.

Non-Genomic Hallmarks of Aging-The Review

Aging is a natural, gradual, and inevitable process associated with a series of changes at the molecular, cellular, and tissue levels that can lead to an increased risk of many diseases, including cancer. The most significant changes at the genomic level (DNA damage, telomere shortening, epigenetic changes) and non-genomic changes are referred to as hallmarks of aging. The hallmarks of aging and cancer are intertwined. Many studies have focused on genomic hallmarks, but non-genomic hallmarks are also important and may additionally cause genomic damage and increase the expression of genomic hallmarks. Understanding the non-genomic hallmarks of aging and cancer, and how they are intertwined, may lead to the development of approaches that could influence these hallmarks and thus function not only to slow aging but also to prevent cancer. In this review, we focus on non-genomic changes. We discuss cell senescence, disruption of proteostasis, deregualation of nutrient sensing, dysregulation of immune system function, intercellular communication, mitochondrial dysfunction, stem cell exhaustion and dysbiosis.

Aging and Age-Related Epigenetic Drift in the Pathogenesis of Leukemia and Lymphomas: New Therapeutic Targets

One of the traits of cancer cells is abnormal DNA methylation patterns. The idea that age-related epigenetic changes may partially explain the increased risk of cancer in the elderly is based on the observation that aging is also accompanied by comparable changes in epigenetic patterns. Lineage bias and decreased stem cell function are signs of hematopoietic stem cell compartment aging. Additionally, aging in the hematopoietic system and the stem cell niche have a role in hematopoietic stem cell phenotypes linked with age, such as leukemia and lymphoma. Understanding these changes will open up promising pathways for therapies against age-related disorders because epigenetic mechanisms are reversible. Additionally, the development of high-throughput epigenome mapping technologies will make it possible to identify the "epigenomic identity card" of every hematological disease as well as every patient, opening up the possibility of finding novel molecular biomarkers that can be used for diagnosis, prediction, and prognosis.

Chronic inflammation and the hallmarks of aging

BACKGROUND

Recently, the hallmarks of aging were updated to include dysbiosis, disabled macroautophagy, and chronic inflammation. In particular, the low-grade chronic inflammation during aging, without overt infection, is defined as "inflammaging," which is associated with increased morbidity and mortality in the aging population. Emerging evidence suggests a bidirectional and cyclical relationship between chronic inflammation and the development of age-related conditions, such as cardiovascular diseases, neurodegeneration, cancer, and frailty. How the crosstalk between chronic inflammation and other hallmarks of aging underlies biological mechanisms of aging and age-related disease is thus of particular interest to the current geroscience research.

SCOPE OF REVIEW

This review integrates the cellular and molecular mechanisms of age-associated chronic inflammation with the other eleven hallmarks of aging. Extra discussion is dedicated to the hallmark of "altered nutrient sensing," given the scope of Molecular Metabolism. The deregulation of hallmark processes during aging disrupts the delicate balance between pro-inflammatory and anti-inflammatory signaling, leading to a persistent inflammatory state. The resultant chronic inflammation, in turn, further aggravates the dysfunction of each hallmark, thereby driving the progression of aging and age-related diseases.

MAIN CONCLUSIONS

The crosstalk between chronic inflammation and other hallmarks of aging results in a vicious cycle that exacerbates the decline in cellular functions and promotes aging. Understanding this complex interplay will provide new insights into the mechanisms of aging and the development of potential anti-aging interventions. Given their interconnectedness and ability to accentuate the primary elements of aging, drivers of chronic inflammation may be an ideal target with high translational potential to address the pathological conditions associated with aging.

The Role of Inflammation in the Initiation and Progression of Myeloid Neoplasms

Myeloid malignancies are devastating hematologic cancers with limited therapeutic options. Inflammation is emerging as a novel driver of myeloid malignancy, with important implications for tumor composition, immune response, therapeutic options, and patient survival. Here, we discuss the role of inflammation in normal and malignant hematopoiesis, from clonal hematopoiesis to full-blown myeloid leukemia. We discuss how inflammation shapes clonal output from hematopoietic stem cells, how inflammation alters the immune microenvironment in the bone marrow, and novel therapies aimed at targeting inflammation in myeloid disease.

SIGNIFICANCE

Inflammation is emerging as an important factor in myeloid malignancies. Understanding the role of inflammation in myeloid transformation, and the interplay between inflammation and other drivers of leukemogenesis, may yield novel avenues for therapy.

Biomarkers of aging

Aging biomarkers are a combination of biological parameters to (i) assess age-related changes, (ii) track the physiological aging process, and (iii) predict the transition into a pathological status. Although a broad spectrum of aging biomarkers has been developed, their potential uses and limitations remain poorly characterized. An immediate goal of biomarkers is to help us answer the following three fundamental questions in aging research: How old are we? Why do we get old? And how can we age slower? This review aims to address this need. Here, we summarize our current knowledge of biomarkers developed for cellular, organ, and organismal levels of aging, comprising six pillars: physiological characteristics, medical imaging, histological features, cellular alterations, molecular changes, and secretory factors. To fulfill all these requisites, we propose that aging biomarkers should qualify for being specific, systemic, and clinically relevant.

Gene regulatory network inference with popInfer reveals dynamic regulation of hematopoietic stem cell quiescence upon diet restriction and aging

Inference of gene regulatory networks (GRNs) can reveal cell state transitions from single-cell genomics data. However, obstacles to temporal inference from snapshot data are difficult to overcome. Single-nuclei multiomics data offer means to bridge this gap and derive temporal information from snapshot data using joint measurements of gene expression and chromatin accessibility in the same single cells. We developed popInfer to infer networks that characterize lineage-specific dynamic cell state transitions from joint gene expression and chromatin accessibility data. Benchmarking against alternative methods for GRN inference, we showed that popInfer achieves higher accuracy in the GRNs inferred. popInfer was applied to study single-cell multiomics data characterizing hematopoietic stem cells (HSCs) and the transition from HSC to a multipotent progenitor cell state during murine hematopoiesis across age and dietary conditions. From networks predicted by popInfer, we discovered gene interactions controlling entry to/exit from HSC quiescence that are perturbed in response to diet or aging.

MYB insufficiency disrupts proteostasis in hematopoietic stem cells, leading to age-related neoplasia

MYB plays a key role in gene regulation throughout the hematopoietic hierarchy and is critical for the maintenance of normal hematopoietic stem cells (HSC). Acquired genetic dysregulation of MYB is involved in the etiology of a number of leukemias, although inherited noncoding variants of the MYB gene are a susceptibility factor for many hematological conditions, including myeloproliferative neoplasms (MPN). The mechanisms that connect variations in MYB levels to disease predisposition, especially concerning age dependency in disease initiation, are completely unknown. Here, we describe a model of Myb insufficiency in mice that leads to MPN, myelodysplasia, and leukemia in later life, mirroring the age profile of equivalent human diseases. We show that this age dependency is intrinsic to HSC, involving a combination of an initial defective cellular state resulting from small effects on the expression of multiple genes and a progressive accumulation of further subtle changes. Similar to previous studies showing the importance of proteostasis in HSC maintenance, we observed altered proteasomal activity and elevated proliferation indicators, followed by elevated ribosome activity in young Myb-insufficient mice. We propose that these alterations combine to cause an imbalance in proteostasis, potentially creating a cellular milieu favoring disease initiation.

The essential roles of small non-coding RNAs and RNA modifications in normal and malignant hematopoiesis

Hematopoietic stem cells (HSCs) developing from mesoderm during embryogenesis are important for the blood circulatory system and immune system. Many factors such as genetic factors, chemical exposure, physical radiation, and viral infection, can lead to the dysfunction of HSCs. Hematological malignancies (involving leukemia, lymphoma, and myeloma) were diagnosed in more than 1.3 million people globally in 2021, taking up 7% of total newly-diagnosed cancer patients. Although many treatments like chemotherapy, bone marrow transplantation, and stem cell transplantation have been applied in clinical therapeutics, the average 5-year survival rate for leukemia, lymphoma, and myeloma is about 65%, 72%, and 54% respectively. Small non-coding RNAs play key roles in a variety of biological processes, including cell division and proliferation, immunological response and cell death. With the development of technologies in high-throughput sequencing and bioinformatic analysis, there is emerging research about modifications on small non-coding RNAs, as well as their functions in hematopoiesis and related diseases. In this study, we summarize the updated information of small non-coding RNAs and RNA modifications in normal and malignant hematopoiesis, which sheds lights into the future application of HSCs into the treatment of blood diseases.

Hematopoietic Stem Cells and the Immune System in Development and Aging

Hematopoietic stem cells (HSCs) support haematopoiesis throughout life and give rise to the whole variety of cells of the immune system. Developing in the early embryo, passing through the precursor stage, and maturing into the first HSCs, they undergo a fairly large number of divisions while maintaining a high regenerative potential due to high repair activity. This potential is greatly reduced in adult HSCs. They go into a state of dormancy and anaerobic metabolism to maintain their stemness throughout life. However, with age, changes occur in the pool of HSCs that negatively affect haematopoiesis and the effectiveness of immunity. Niche aging and accumulation of mutations with age reduces the ability of HSCs to self-renew and changes their differentiation potential. This is accompanied by a decrease in clonal diversity and a disturbance of lymphopoiesis (decrease in the formation of naive T- and B-cells) and the predominance of myeloid haematopoiesis. Aging also affects mature cells, regardless of HSC, therefore, phagocytic activity and the intensity of the oxidative burst decrease, and the efficiency of processing and presentation of antigens by myeloid cells is impaired. Aging cells of innate and adaptive immunity produce factors that form a chronic inflammatory background. All these processes have a serious negative impact on the protective properties of the immune system, increasing inflammation, the risk of developing autoimmune, oncological, and cardiovascular diseases with age. Understanding the mechanisms of reducing the regenerative potential in a comparative analysis of embryonic and aging HSCs, the features of inflammatory aging will allow us to get closer to deciphering the programs for the development, aging, regeneration and rejuvenation of HSCs and the immune system.

Establishing a human bone marrow single cell reference atlas to study ageing and diseases

Introduction

Ageing in the human bone marrow is associated with immune function decline that results in the elderly being vulnerable to illnesses. A comprehensive healthy bone marrow consensus atlas can serve as a reference to study the immunological changes associated with ageing, and to identify and study abnormal cell states.

Methods

We collected publicly available single cell transcriptomic data of 145 healthy samples encompassing a wide spectrum of ages ranging from 2 to 84 years old to construct our human bone marrow atlas. The final atlas has 673,750 cells and 54 annotated cell types.

Results

We first characterised the changes in cell population sizes with respect to age and the corresponding changes in gene expression and pathways. Overall, we found significant age-associated changes in the lymphoid lineage cells. The naïve CD8+ T cell population showed significant shrinkage with ageing while the effector/memory CD4+ T cells increased in proportion. We also found an age-correlated decline in the common lymphoid progenitor population, in line with the commonly observed myeloid skew in haematopoiesis among the elderly. We then employed our cell type-specific ageing gene signatures to develop a machine learning model that predicts the biological age of bone marrow samples, which we then applied to healthy individuals and those with blood diseases. Finally, we demonstrated how to identify abnormal cell states by mapping disease samples onto the atlas. We accurately identified abnormal plasma cells and erythroblasts in multiple myeloma samples, and abnormal cells in acute myeloid leukaemia samples.

Discussion

The bone marrow is the site of haematopoiesis, a highly important bodily process. We believe that our healthy bone marrow atlas is a valuable reference for studying bone marrow processes and bone marrow-related diseases. It can be mined for novel discoveries, as well as serve as a reference scaffold for mapping samples to identify and investigate abnormal cells.

Clonal hematopoiesis, somatic mosaicism, and age-associated disease

Somatic mosaicism, the occurrence of multiple genetically distinct cell clones within the same tissue, is an evitable consequence of human aging. The hematopoietic system is no exception to this, where studies have revealed the presence of expanded blood cell clones carrying mutations in preleukemic driver genes and/or genetic alterations in chromosomes. This phenomenon is referred to as clonal hematopoiesis and is remarkably prevalent in elderly individuals. While clonal hematopoiesis represents an early step toward a hematological malignancy, most individuals will never develop blood cancer. Somewhat unexpectedly, epidemiological studies have found that clonal hematopoiesis is associated with an increase in the risk of all-cause mortality and age-related disease, particularly in the cardiovascular system. Studies using murine models of clonal hematopoiesis have begun to shed light on this relationship, suggesting that driver mutations in mature blood cells can causally contribute to aging and disease by augmenting inflammatory processes. Here we provide an up-to-date review of clonal hematopoiesis within the context of somatic mosaicism and aging and describe recent epidemiological studies that have reported associations with age-related disease. We will also discuss the experimental studies that have provided important mechanistic insight into how driver mutations promote age-related disease and how this knowledge could be leveraged to treat individuals with clonal hematopoiesis.

Haematopoietic stem cell quiescence exposed using mitochondrial membrane potential

PURPOSE OF REVIEW

Quiescence is a fundamental property of haematopoietic stem cells (HSCs). Despite the importance of quiescence in predicting the potency of HSCs, tools that measure routinely the degree of quiescence or select for quiescent HSCs have been lacking. This Commentary discusses recent findings that address this fundamental gap in the HSC toolbox.

RECENT FINDINGS

Highly purified, phenotypically-defined HSCs are heterogeneous in their mitochondrial membrane potential (MMP). The lowest MMP subsets are enriched in greatly quiescent HSCs with the highest potency within the purified HSC population. MMP provides an intrinsic probe to select HSC subsets with unique cell cycle properties and distinct stem cell potential. Using this approach, new and unanticipated metabolic properties of quiescent HSCs' exit have been discovered. This methodology may improve the mechanistic understanding, of HSCs' exit from and entry to, quiescence.

SUMMARY

Selecting HSCs using MMP is likely to lead to discoveries of new HSC properties, may improve the ex vivo maintenance of HSCs and has implications for the clinic, including for improving HSC transplantations.

A Comprehensive Study on the Anti-cancer Effects of Quercetin and Its Epigenetic Modifications in Arresting Progression of Colon Cancer Cell Proliferation

Colon cancer etiology involves a wide spectrum of genetic and epigenetic alterations, finding it challenging to find effective therapeutic strategies. Quercetin exhibits potent anti-proliferative/apoptotic properties. In the present study, we aimed to elucidate the anti-cancer and anti-aging effect of quercetin in colon cancer cell lines. The anti-proliferative effect of quercetin was assessed in vitro by CCK-8 in normal and colon cancer cell lines. To check the anti-aging potential of quercetin, collagenase, elastase, and hyaluronidase inhibitory activity assays were performed. The epigenetic and DNA damage assays were performed using the human NAD-dependent deacetylase Sirtuin-6, proteasome 20S, Klotho, Cytochrome-C, and telomerase ELISA kits. Furthermore, the aging-associated miRNA expression profiling was performed on colon cancer cells. The treatment with quercetin inhibited cell proliferation of colon cancer cells in a dose-dependent manner. Quercetin arrested colon cancer cell growth by modulating expression of aging proteins including Sirtuin-6 and Klotho and also by inhibiting telomerase activity to restrict the telomere length which is evident from qPCR analysis. Quercetin also exhibited DNA damage protection by reducing proteasome 20S levels. The miRNA expression profiling results displayed differential expression of miRNA in colon cancer cell, and in addition, the highly upregulated miRNA was involved in the regulation of cell cycle, proliferation, and transcription. Our data suggest that quercetin treatment inhibited cell proliferation in colon cancer cells through regulating the anti-aging protein expression and provides better understanding for quercetin's potential use in colon cancer treatment.

The landscape of aging

Aging is characterized by a progressive deterioration of physiological integrity, leading to impaired functional ability and ultimately increased susceptibility to death. It is a major risk factor for chronic human diseases, including cardiovascular disease, diabetes, neurological degeneration, and cancer. Therefore, the growing emphasis on "healthy aging" raises a series of important questions in life and social sciences. In recent years, there has been unprecedented progress in aging research, particularly the discovery that the rate of aging is at least partly controlled by evolutionarily conserved genetic pathways and biological processes. In an attempt to bring full-fledged understanding to both the aging process and age-associated diseases, we review the descriptive, conceptual, and interventive aspects of the landscape of aging composed of a number of layers at the cellular, tissue, organ, organ system, and organismal levels.

Pathogenesis of giant cell arteritis with focus on cellular populations

Giant cell arteritis (GCA), the most common non-infectious vasculitis, mainly affects elderly individuals. The disease usually affects the aorta and its main supra-aortic branches causing both general symptoms of inflammation and specific ischemic symptoms because of the limited blood flow due to arterial structural changes in the inflamed arteries. The pathogenesis of the GCA is complex and includes a dysregulated immune response that affects both the innate and the adaptive immunity. During the last two decades several studies have investigated interactions among antigen-presenting cells and lymphocytes, which contribute to the formation of the inflammatory infiltrate in the affected arteries. Toll-like receptor signaling and interactions through the VEGF-Notch-Jagged1 pathway are emerging as crucial events of the aberrant inflammatory response, facilitating among others the migration of inflammatory cells to the inflamed arteries and their interactions with the local stromal milieu. The increased use of checkpoint inhibitors in cancer immunotherapy and their immune-related adverse events has fed interest in the role of checkpoint dysfunction in GCA, and recent studies suggest a dysregulated check point system which is unable to suppress the inflammation in the previously immune-privileged arteries, leading to vasculitis. The role of B-cells is currently reevaluated because of new reports of considerable numbers of plasma cells in inflamed arteries as well as the formation of artery tertiary lymphoid organs. There is emerging evidence on previously less studied cell populations, such as the neutrophils, CD8+ T-cells, T regulatory cells and tissue residing memory cells as well as for stromal cells which were previously considered as innocent bystanders. The aim of this review is to summarize the evidence in the literature regarding the cell populations involved in the pathogenesis of GCA and especially in the context of an aged, immune system.

Aging, inflammaging and immunosenescence as risk factors of severe COVID-19

Coronavirus disease 2019 (COVID-19) is a respiratory infectious disease caused by the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). COVID-19 is characterized by having a heterogeneous disease course, ranging from asymptomatic and mild symptoms to more severe and critical cases. In most cases the severity of COVID-19 is related to host factors, especially deregulation of the immune response in patients. Even if COVID-19 indiscriminately affects individuals of different age group, ethnicity and economic status; most severe cases and disproportional mortality occur in elderly individuals. This point out that aging is one risk factor for unfavourable clinical outcomes among COVID-19 patients. The biology of aging is a complex process; Aging can alter the structure and function of cells, tissues, and organs resulting in impaired response to stress. Alongside with other systems, the immune system is also affected with the aging process. Immunosenescence is an age associated change in the immune system that affects the overall response to immunological challenges in the elderly. Similarly, apart from the normal inflammatory process, aging is associated with a low grade, sterile, chronic inflammation which is termed as inflammaging. We hypothesized that inflammaging and immunosenescence could play an important role in SARS-CoV-2 pathogenesis and poor recovery from COVID-19 in elderly individuals. This review summarizes the changes in the immune system with age and how these changes play part in the pathogenesis of SARS-CoV-2 and clinical outcome of COVID-19 which could add to the understanding of age associated targeted immunotherapy in the elderly.