Epigenomic profiling of young and aged HSCs reveals concerted changes during aging that reinforce self-renewal

Innate immune pathways and inflammation in hematopoietic aging, clonal hematopoiesis, and MDS

With a growing aged population, there is an imminent need to develop new therapeutic strategies to ameliorate disorders of hematopoietic aging, including clonal hematopoiesis and myelodysplastic syndrome (MDS). Cell-intrinsic dysregulation of innate immune- and inflammatory-related pathways as well as systemic inflammation have been implicated in hematopoietic defects associated with aging, clonal hematopoiesis, and MDS. Here, we review and discuss the role of dysregulated innate immune and inflammatory signaling that contribute to the competitive advantage and clonal dominance of preleukemic and MDS-derived hematopoietic cells. We also propose how emerging concepts will further reveal critical biology and novel therapeutic opportunities.

Extracellular Vesicles and Hematopoietic Stem Cell Aging

[Figure: see text].

Aged hematopoietic stem cells are refractory to bloodborne systemic rejuvenation interventions

While young blood can restore many aged tissues, its effects on the aged blood system itself and old hematopoietic stem cells (HSCs) have not been determined. Here, we used transplantation, parabiosis, plasma transfer, exercise, calorie restriction, and aging mutant mice to understand the effects of age-regulated systemic factors on HSCs and their bone marrow (BM) niche. We found that neither exposure to young blood, nor long-term residence in young niches after parabiont separation, nor direct heterochronic transplantation had any observable rejuvenating effects on old HSCs. Likewise, exercise and calorie restriction did not improve old HSC function, nor old BM niches. Conversely, young HSCs were not affected by systemic pro-aging conditions, and HSC function was not impacted by mutations influencing organismal aging in established long-lived or progeroid genetic models. Therefore, the blood system that carries factors with either rejuvenating or pro-aging properties for many other tissues is itself refractory to those factors.

Epigenetic Remodeling in Obesity-Related Vascular Disease

Significance: The prevalence of obesity and cardiometabolic phenotypes is alarmingly increasing across the globe and is associated with atherosclerotic vascular complications and high mortality. In spite of multifactorial interventions, vascular residual risk remains high in this patient population, suggesting the need for breakthrough therapies. The mechanisms underpinning obesity-related vascular disease remain elusive and represent an intense area of investigation. Recent Advances: Epigenetic modifications-defined as environmentally induced chemical changes of DNA and histones that do not affect DNA sequence-are emerging as a potent modulator of gene transcription in the vasculature and might significantly contribute to the development of obesity-induced endothelial dysfunction. DNA methylation and histone post-translational modifications cooperate to build complex epigenetic signals, altering transcriptional networks that are implicated in redox homeostasis, mitochondrial function, vascular inflammation, and perivascular fat homeostasis in patients with cardiometabolic disturbances. Critical Issues: Deciphering the epigenetic landscape in the vasculature is extremely challenging due to the complexity of epigenetic signals and their function in regulating transcription. An overview of the most important epigenetic pathways is required to identify potential molecular targets to treat or prevent obesity-related endothelial dysfunction and atherosclerotic disease. This would enable the employment of precision medicine approaches in this setting. Future Directions: Current and future research efforts in this field entail a better definition of the vascular epigenome in obese patients as well as the unveiling of novel, cell-specific chromatin-modifying drugs that are able to erase specific epigenetic signals that are responsible for maladaptive transcriptional alterations and vascular dysfunction in obese patients. Antioxid. Redox Signal. 34, 1165-1199.

Megakaryocyte progenitor cell function is enhanced upon aging despite the functional decline of aged hematopoietic stem cells

Age-related morbidity is associated with a decline in hematopoietic stem cell (HSC) function, but the mechanisms of HSC aging remain unclear. We performed heterochronic HSC transplants followed by quantitative analysis of cell reconstitution. Although young HSCs outperformed old HSCs in young recipients, young HSCs unexpectedly failed to outcompete the old HSCs of aged recipients. Interestingly, despite substantial enrichment of megakaryocyte progenitors (MkPs) in old mice in situ and reported platelet (Plt) priming with age, transplanted old HSCs were deficient in reconstitution of all lineages, including MkPs and Plts. We therefore performed functional analysis of young and old MkPs. Surprisingly, old MkPs displayed unmistakably greater regenerative capacity compared with young MkPs. Transcriptome analysis revealed putative molecular regulators of old MkP expansion. Collectively, these data demonstrated that aging affects HSCs and megakaryopoiesis in fundamentally different ways: whereas old HSCs functionally decline, MkPs gain expansion capacity upon aging.

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Reconstitution deficit by old HSCs was observed by chimerism and absolute cell numbers

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Young HSCs did not outcompete resident HSCs in aged recipient mice

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Old MkPs display remarkable capacity to engraft, expand, and reconstitute platelets

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Aging is associated with changes in MkP genome-wide expression signatures

Molecular pathogenesis of progression to myeloid leukemia from TET-insufficient status

Loss-of-function mutations in ten-eleven translocation-2 (TET2) are recurrent events in acute myeloid leukemia (AML) as well as in preleukemic hematopoietic stem cells (HSCs) of age-related clonal hematopoiesis. TET3 mutations are infrequent in AML, but the level of TET3 expression in HSCs has been found to decline with age. We examined the impact of gradual decrease of TET function in AML development by generating mice with Tet deficiency at various degrees. Tet2f/f and Tet3f/f mice were crossed with mice expressing Mx1-Cre to generate Tet2f/wtTet3f/fMx-Cre+ (T2ΔT3), Tet2f/fTet3f/wtMx-Cre+ (ΔT2T3), and Tet2f/fTet3f/fMx-Cre+ (ΔT2ΔT3) mice. All ΔT2ΔT3 mice died of aggressive AML at a median survival of 10.7 weeks. By comparison, T2ΔT3 and ΔT2T3 mice developed AML at longer latencies, with a median survival of ∼27 weeks. Remarkably, all 9 T2ΔT3 and 8 ΔT2T3 mice with AML showed inactivation of the remaining nontargeted Tet2 or Tet3 allele, respectively, owing to exonic loss in either gene or stop-gain mutations in Tet3. Recurrent mutations other than Tet3 were not noted in any mice by whole-exome sequencing. Spontaneous inactivation of residual Tet2 or Tet3 alleles is a recurrent genetic event during the development of AML with Tet insufficiency.

Nicotinamide riboside attenuates age-associated metabolic and functional changes in hematopoietic stem cells

With age, hematopoietic stem cells (HSC) undergo changes in function, including reduced regenerative potential and loss of quiescence, which is accompanied by a significant expansion of the stem cell pool that can lead to haematological disorders. Elevated metabolic activity has been implicated in driving the HSC ageing phenotype. Here we show that nicotinamide riboside (NR), a form of vitamin B3, restores youthful metabolic capacity by modifying mitochondrial function in multiple ways including reduced expression of nuclear encoded metabolic pathway genes, damping of mitochondrial stress and a decrease in mitochondrial mass and network-size. Metabolic restoration is dependent on continuous NR supplementation and accompanied by a shift of the aged transcriptome towards the young HSC state, more youthful bone marrow cellular composition and an improved regenerative capacity in a transplant setting. Consequently, NR administration could support healthy ageing by re-establishing a more youthful hematopoietic system.

Low Plasma Citrate Levels and Specific Transcriptional Signatures Associated with Quiescence of CD34+ Progenitors Predict Azacitidine Therapy Failure in MDS/AML Patients

Simple Summary

Epigenetic drugs, such as azacitidine (AZA), hold promise in the treatment of myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML), however, the mechanisms predicting the patients’ response to AZA is not completely understood. Quiescence of hematopoietic CD34⁺ progenitors has been proposed as a predictive factor for AZA therapy failure in MDS/AML patients, but the interplay between CD34⁺ cell cycle status and their metabolic signature in a predisposition to AZA (non)responsiveness remains unclear. Our data on patients with MDS or AML with myelodysplasia-related changes (AML-MRC) suggest that AZA-responders have actively cycling CD34⁺ cells poised for erythro-myeloid differentiation, with high metabolic activity controlling histone acetylation. Conversely, the patients who progressed early on AZA therapy revealed quiescence signature of their CD34⁺ cells, with signs of reduced metabolically-controlled acetylation of histones needed for transcription-permissive chromatin configuration. Our study delineates plasma citrate levels and CD34⁺ cells’ transcriptional signatures associated with cycling status and metabolic characteristics as factors predicting the response to AZA monotherapy in MDS/AML-MRC patients.

Abstract

To better understand the molecular basis of resistance to azacitidine (AZA) therapy in myelodysplastic syndromes (MDS) and acute myeloid leukemia with myelodysplasia-related changes (AML-MRC), we performed RNA sequencing on pre-treatment CD34⁺ hematopoietic stem/progenitor cells (HSPCs) isolated from 25 MDS/AML-MRC patients of the discovery cohort (10 AZA responders (RD), six stable disease, nine progressive disease (PD) during AZA therapy) and from eight controls. Eleven MDS/AML-MRC samples were also available for analysis of selected metabolites, along with 17 additional samples from an independent validation cohort. Except for two patients, the others did not carry isocitrate dehydrogenase (IDH)1/2 mutations. Transcriptional landscapes of the patients’ HSPCs were comparable to those published previously, including decreased signatures of active cell cycling and DNA damage response in PD compared to RD and controls. In addition, PD-derived HSPCs revealed repressed markers of the tricarboxylic acid cycle, with IDH2 among the top 50 downregulated genes in PD compared to RD. Decreased citrate plasma levels, downregulated expression of the (ATP)-citrate lyase and other transcriptional/metabolic networks indicate metabolism-driven histone modifications in PD HSPCs. Observed histone deacetylation is consistent with transcription-nonpermissive chromatin configuration and quiescence of PD HSPCs. This study highlights the complexity of the molecular network underlying response/resistance to hypomethylating agents.

Heterochromatin and Polycomb as regulators of haematopoiesis

Haematopoiesis is the process by which multipotent haematopoietic stem cells are transformed into each and every type of terminally differentiated blood cell. Epigenetic silencing is critical for this process by regulating the transcription of cell-cycle genes critical for self-renewal and differentiation, as well as restricting alternative fate genes to allow lineage commitment and appropriate differentiation. There are two distinct forms of transcriptionally repressed chromatin: H3K9me3-marked heterochromatin and H3K27me3/H2AK119ub1-marked Polycomb (often referred to as facultative heterochromatin). This review will discuss the role of these distinct epigenetic silencing mechanisms in regulating normal haematopoiesis, how these contribute to age-related haematopoietic dysfunction, and the rationale for therapeutic targeting of these pathways in the treatment of haematological malignancies.

Immune Reconstitution in the Aging Host: Opportunities for Mechanism-Based Therapy in Allogeneic Hematopoietic Cell Transplantation

Older patients with hematologic malignancies are increasingly considered for allogeneic hematopoietic cell transplantation with encouraging outcomes. While aging-related thymic dysfunction remains a major obstacle to optimal and timely immune reconstitution post- transplantation, recent accumulating evidence has suggested that various aging hallmarks such as cellular senescence, inflamm-aging, and hematopoietic stem cell exhaustion, could also impact immune reconstitution post-transplantation in both thymic-dependent and independent manner. Here we review molecular and cellular aspects of immune senescence and immune rejuvenation related to allogeneic hematopoietic cell transplantation among older patients and discuss potential strategies for mechanism-based therapeutic intervention.

A comprehensive transcriptome signature of murine hematopoietic stem cell aging

We surveyed 16 published and unpublished data sets to determine whether a consistent pattern of transcriptional deregulation in aging murine hematopoietic stem cells (HSC) exists. Despite substantial heterogeneity between individual studies, we uncovered a core and robust HSC aging signature. We detected increased transcriptional activation in aged HSCs, further confirmed by chromatin accessibility analysis. Unexpectedly, using two independent computational approaches, we established that deregulated aging genes consist largely of membrane-associated transcripts, including many cell surface molecules previously not associated with HSC biology. We show that Selp, the most consistent deregulated gene, is not merely a marker for aged HSCs but is associated with HSC functional decline. Additionally, single-cell transcriptomics analysis revealed increased heterogeneity of the aged HSC pool. We identify the presence of transcriptionally "young-like" HSCs in aged bone marrow. We share our results as an online resource and demonstrate its utility by confirming that exposure to sympathomimetics, and deletion of Dnmt3a/b, molecularly resembles HSC rejuvenation or aging, respectively.

Conservation of Aging and Cancer Epigenetic Signatures across Human and Mouse

Aging and cancer are two interrelated processes, with aging being a major risk factor for the development of cancer. Parallel epigenetic alterations have been described for both, although differences, especially within the DNA hypomethylation scenario, have also been recently reported. Although many of these observations arise from the use of mouse models, there is a lack of systematic comparisons of human and mouse epigenetic patterns in the context of disease. However, such comparisons are significant as they allow to establish the extent to which some of the observed similarities or differences arise from pre-existing species-specific epigenetic traits. Here, we have used reduced representation bisulfite sequencing to profile the brain methylomes of young and old, tumoral and nontumoral brain samples from human and mouse. We first characterized the baseline epigenomic patterns of the species and subsequently focused on the DNA methylation alterations associated with cancer and aging. Next, we described the functional genomic and epigenomic context associated with the alterations, and finally, we integrated our data to study interspecies DNA methylation levels at orthologous CpG sites. Globally, we found considerable differences between the characteristics of DNA methylation alterations in cancer and aging in both species. Moreover, we describe robust evidence for the conservation of the specific cancer and aging epigenomic signatures in human and mouse. Our observations point toward the preservation of the functional consequences of these alterations at multiple levels of genomic regulation. Finally, our analyses reveal a role for the genomic context in explaining disease- and species-specific epigenetic traits.

Attrition of X Chromosome Inactivation in Aged Hematopoietic Stem Cells

During X chromosome inactivation (XCI), the inactive X chromosome (Xi) is recruited to the nuclear lamina at the nuclear periphery. Beside X chromosome reactivation resulting in a highly penetrant aging-like hematopoietic malignancy, little is known about XCI in aged hematopoietic stem cells (HSCs). Here, we demonstrate that LaminA/C defines a distinct repressive nuclear compartment for XCI in young HSCs, and its reduction in aged HSCs correlates with an impairment in the overall control of XCI. Integrated omics analyses reveal higher variation in gene expression, global hypomethylation, and significantly increased chromatin accessibility on the X chromosome (Chr X) in aged HSCs. In summary, our data support the role of LaminA/C in the establishment of a special repressive compartment for XCI in HSCs, which is impaired upon aging.

Cellular aging beyond cellular senescence: Markers of senescence prior to cell cycle arrest in vitro and in vivo

The field of research on cellular senescence experienced a rapid expansion from being primarily focused on in vitro aspects of aging to the vast territories of animal and clinical research. Cellular senescence is defined by a set of markers, many of which are present and accumulate in a gradual manner prior to senescence induction or are found outside of the context of cellular senescence. These markers are now used to measure the impact of cellular senescence on aging and disease as well as outcomes of anti-senescence interventions, many of which are at the stage of clinical trials. It is thus of primary importance to discuss their specificity as well as their role in the establishment of senescence. Here, the presence and role of senescence markers are described in cells prior to cell cycle arrest, especially in the context of replicative aging and in vivo conditions. Specifically, this review article seeks to describe the process of "cellular aging": the progression of internal changes occurring in primary cells leading to the induction of cellular senescence and culminating in cell death. Phenotypic changes associated with aging prior to senescence induction will be characterized, as well as their effect on the induction of cell senescence and the final fate of cells reviewed. Using published datasets on assessments of senescence markers in vivo, it will be described how disparities between quantifications can be explained by the concept of cellular aging. Finally, throughout the article the applicational value of broadening cellular senescence paradigm will be discussed.

A ride through the epigenetic landscape: aging reversal by reprogramming

Aging has become one of the fastest-growing research topics in biology. However, exactly how the aging process occurs remains unknown. Epigenetics plays a significant role, and several epigenetic interventions can modulate lifespan. This review will explore the interplay between epigenetics and aging, and how epigenetic reprogramming can be harnessed for age reversal. In vivo partial reprogramming holds great promise as a possible therapy, but several limitations remain. Rejuvenation by reprogramming is a young but rapidly expanding subfield in the biology of aging.

Monocytes in the Tumor Microenvironment

Immunotherapy has revolutionized cancer treatment over the past decade. Nonetheless, prolonged survival is limited to relatively few patients. Cancers enforce a multifaceted immune-suppressive network whose nature is progressively shaped by systemic and local cues during tumor development. Monocytes bridge innate and adaptive immune responses and can affect the tumor microenvironment through various mechanisms that induce immune tolerance, angiogenesis, and increased dissemination of tumor cells. Yet monocytes can also give rise to antitumor effectors and activate antigen-presenting cells. This yin-yang activity relies on the plasticity of monocytes in response to environmental stimuli. In this review, we summarize current knowledge of the ontogeny, heterogeneity, and functions of monocytes and monocyte-derived cells in cancer, pinpointing the main pathways that are important for modeling the immunosuppressive tumor microenvironment.

Age-related changes in polycomb gene regulation disrupt lineage fidelity in intestinal stem cells

Tissue homeostasis requires long-term lineage fidelity of somatic stem cells. Whether and how age-related changes in somatic stem cells impact the faithful execution of lineage decisions remains largely unknown. Here, we address this question using genome-wide chromatin accessibility and transcriptome analysis as well as single-cell RNA-seq to explore stem-cell-intrinsic changes in the aging Drosophila intestine. These studies indicate that in stem cells of old flies, promoters of Polycomb (Pc) target genes become differentially accessible, resulting in the increased expression of enteroendocrine (EE) cell specification genes. Consistently, we find age-related changes in the composition of the EE progenitor cell population in aging intestines, as well as a significant increase in the proportion of EE-specified intestinal stem cells (ISCs) and progenitors in aging flies. We further confirm that Pc-mediated chromatin regulation is a critical determinant of EE cell specification in the Drosophila intestine. Pc is required to maintain expression of stem cell genes while ensuring repression of differentiation and specification genes. Our results identify Pc group proteins as central regulators of lineage identity in the intestinal epithelium and highlight the impact of age-related decline in chromatin regulation on tissue homeostasis.

Functional genomics of inflamm-aging and immunosenescence

The aging population is at a higher risk for age-related diseases and infections. This observation could be due to immunosenescence: the decline in immune efficacy of both the innate and the adaptive immune systems. Age-related immune decline also links to the concept of 'inflamm-aging,' whereby aging is accompanied by sterile chronic inflammation. Along with a decline in immune function, aging is accompanied by a widespread of 'omics' remodeling. Transcriptional landscape changes linked to key pathways of immune function have been identified across studies, such as macrophages having decreased expression of genes associated to phagocytosis, a major function of macrophages. Therefore, a key mechanism underlying innate immune cell dysfunction during aging may stem from dysregulation of youthful genomic networks. In this review, we discuss both molecular and cellular phenotypes of innate immune cells that contribute to age-related inflammation.

Limited rejuvenation of aged hematopoietic stem cells in young bone marrow niche

Hematopoietic stem cells (HSCs) exhibit functional alterations, such as reduced regenerative capacity and myeloid-biased differentiation, with age. The HSC niche, which is essential for the maintenance of HSCs, also undergoes marked changes with aging. However, it has been technically challenging to directly evaluate the contribution of niche aging to age-associated HSC alterations without niche-damaging myeloablation in HSC transplantation assays. We herein transplanted an excess of aged HSCs into young mice without preconditioning. Although aged HSCs successfully engrafted in the intact young bone marrow niche, they poorly regenerated downstream progenitors and exhibited persistent myeloid-biased differentiation, resulting in no significant functional rejuvenation. Transcriptome and methylome analyses revealed that the young niche largely restored the transcriptional profile of aged HSCs, but not their DNA methylation profiles. Therefore, the restoration of the young niche is insufficient for rejuvenating HSC functions, highlighting a key role for age-associated cell-intrinsic defects in HSC aging.

Ectopic humanized mesenchymal niche in mice enables robust engraftment of myelodysplastic stem cells

Myelodysplastic syndrome (MDS) are clonal stem cell diseases characterized mainly by ineffective hematopoiesis. Here, we present an approach that enables robust long-term engraftment of primary MDS stem cells (MDS-SCs) in mice by implantation of human mesenchymal cell-seeded scaffolds. Critically for modelling MDS, where patient sample material is limiting, mononuclear bone marrow cells containing as few as 104 CD34+ cells can be engrafted and expanded by this approach with the maintenance of the genetic make-up seen in the patients. Non-invasive high-resolution ultrasound imaging shows that these scaffolds are fully perfused. Our data shows that human microenvironment but not mouse is essential to MDS-SCs homing and engraftment. Notably, the alternative niche provided by healthy donor MSCs enhanced engraftment of MDS-SCs. This study characterizes a new tool to model MDS human disease with the level of engraftment previously unattainable in mice, and offers insights into human-specific determinants of MDS-SC microenvironment.

Altered microRNA expression links IL6 and TNF-induced inflammaging with myeloid malignancy in humans and mice

Aging is associated with significant changes in the hematopoietic system, including increased inflammation, impaired hematopoietic stem cell (HSC) function, and increased incidence of myeloid malignancy. Inflammation of aging ("inflammaging") has been proposed as a driver of age-related changes in HSC function and myeloid malignancy, but mechanisms linking these phenomena remain poorly defined. We identified loss of miR-146a as driving aging-associated inflammation in AML patients. miR-146a expression declined in old wild-type mice, and loss of miR-146a promoted premature HSC aging and inflammation in young miR-146a-null mice, preceding development of aging-associated myeloid malignancy. Using single-cell assays of HSC quiescence, stemness, differentiation potential, and epigenetic state to probe HSC function and population structure, we found that loss of miR-146a depleted a subpopulation of primitive, quiescent HSCs. DNA methylation and transcriptome profiling implicated NF-κB, IL6, and TNF as potential drivers of HSC dysfunction, activating an inflammatory signaling relay promoting IL6 and TNF secretion from mature miR-146a-/- myeloid and lymphoid cells. Reducing inflammation by targeting Il6 or Tnf was sufficient to restore single-cell measures of miR-146a-/- HSC function and subpopulation structure and reduced the incidence of hematological malignancy in miR-146a-/- mice. miR-146a-/- HSCs exhibited enhanced sensitivity to IL6 stimulation, indicating that loss of miR-146a affects HSC function via both cell-extrinsic inflammatory signals and increased cell-intrinsic sensitivity to inflammation. Thus, loss of miR-146a regulates cell-extrinsic and -intrinsic mechanisms linking HSC inflammaging to the development of myeloid malignancy.

Sirtuins and the prevention of immunosenescence

Aging of hematopoietic stem cells (HSCs) has been largely described as one underlying cause of senescence of the immune-hematopoietic system (immunosenescence). A set of well-defined hallmarks characterizes aged HSCs contributing to unbalanced hematopoiesis and aging-associated functional alterations of both branches of the immune system. In this chapter, the contribution of sirtuins, a family of conserved NAD⁺ dependent deacetylases with key roles in metabolism, genome integrity, aging and lifespan, to immunosenescence, will be addressed. In particular, the role of SIRT6 will be deeply analyzed highlighting a multifaceted part of this deacetylase in HSCs aging as well as in the immunosenescence of dendritic cells (DCs). These and other emerging data are currently paving the way for future design and development of rejuvenation means aiming at rescuing age-related changes in immune function in the elderly and combating age-associated hematopoietic diseases.

Splicing alterations in healthy aging and disease

Alternative RNA splicing is a key step in gene expression that allows generation of numerous messenger RNA transcripts encoding proteins of varied functions from the same gene. It is thus a rich source of proteomic and functional diversity. Alterations in alternative RNA splicing are observed both during healthy aging and in a number of human diseases, several of which display premature aging phenotypes or increased incidence with age. Age-associated splicing alterations include differential splicing of genes associated with hallmarks of aging, as well as changes in the levels of core spliceosomal genes and regulatory splicing factors. Here, we review the current known links between alternative RNA splicing, its regulators, healthy biological aging, and diseases associated with aging or aging-like phenotypes. This article is categorized under: RNA in Disease and Development > RNA in Disease RNA Processing > Splicing Regulation/Alternative Splicing.

Epigenetic signatures in cancer: proper controls, current challenges and the potential for clinical translation

Epigenetic alterations are associated with normal biological processes such as aging or differentiation. Changes in global epigenetic signatures, together with genetic alterations, are driving events in several diseases including cancer. Comparative studies of cancer and healthy tissues found alterations in patterns of DNA methylation, histone posttranslational modifications, and changes in chromatin accessibility. Driven by sophisticated, next-generation sequencing-based technologies, recent studies discovered cancer epigenomes to be dominated by epigenetic patterns already present in the cell-of-origin, which transformed into a neoplastic cell. Tumor-specific epigenetic changes therefore need to be redefined and factors influencing epigenetic patterns need to be studied to unmask truly disease-specific alterations. The underlying mechanisms inducing cancer-associated epigenetic alterations are poorly understood. Studies of mutated epigenetic modifiers, enzymes that write, read, or edit epigenetic patterns, or mutated chromatin components, for example oncohistones, help to provide functional insights on how cancer epigenomes arise. In this review, we highlight the importance and define challenges of proper control tissues and cell populations to exploit cancer epigenomes. We summarize recent advances describing mechanisms leading to epigenetic changes in tumorigenesis and briefly discuss advances in investigating their translational potential.

Splicing alterations in healthy aging and disease

Alternative RNA splicing is a key step in gene expression that allows generation of numerous messenger RNA transcripts encoding proteins of varied functions from the same gene. It is thus a rich source of proteomic and functional diversity. Alterations in alternative RNA splicing are observed both during healthy aging and in a number of human diseases, several of which display premature aging phenotypes or increased incidence with age. Age-associated splicing alterations include differential splicing of genes associated with hallmarks of aging, as well as changes in the levels of core spliceosomal genes and regulatory splicing factors. Here, we review the current known links between alternative RNA splicing, its regulators, healthy biological aging, and diseases associated with aging or aging-like phenotypes. This article is categorized under: RNA in Disease and Development > RNA in Disease RNA Processing > Splicing Regulation/Alternative Splicing.

Stem cell quiescence: the challenging path to activation

Quiescence is a cellular state in which a cell remains out of the cell cycle but retains the capacity to divide. The unique ability of adult stem cells to maintain quiescence is crucial for life-long tissue homeostasis and regenerative capacity. Quiescence has long been viewed as an inactive state but recent studies have shown that it is in fact an actively regulated process and that adult stem cells are highly reactive to extrinsic stimuli. This has fuelled hopes of boosting the reactivation potential of adult stem cells to improve tissue function during ageing. In this Review, we provide a perspective of the quiescent state and discuss how quiescent adult stem cells transition into the cell cycle. We also discuss current challenges in the field, highlighting recent technical advances that could help overcome some of these challenges.

Single-cell RNA-seq reveals a concomitant delay in differentiation and cell cycle of aged hematopoietic stem cells

BACKGROUND

Hematopoietic stem cells (HSCs) are the guarantor of the proper functioning of hematopoiesis due to their incredible diversity of potential. During aging, heterogeneity of HSCs changes, contributing to the deterioration of the immune system. In this study, we revisited mouse HSC compartment and its transcriptional plasticity during aging at unicellular scale.

RESULTS

Through the analysis of 15,000 young and aged transcriptomes, we identified 15 groups of HSCs revealing rare and new specific HSC abilities that change with age. The implantation of new trajectories complemented with the analysis of transcription factor activities pointed consecutive states of HSC differentiation that were delayed by aging and explained the bias in differentiation of older HSCs. Moreover, reassigning cell cycle phases for each HSC clearly highlighted an imbalance of the cell cycle regulators of very immature aged HSCs that may contribute to their accumulation in an undifferentiated state.

CONCLUSIONS

Our results establish a new reference map of HSC differentiation in young and aged mice and reveal a potential mechanism that delays the differentiation of aged HSCs and could promote the emergence of age-related hematologic diseases.

Niche derived netrin-1 regulates hematopoietic stem cell dormancy via its receptor neogenin-1

Haematopoietic stem cells (HSCs) are characterized by their self-renewal potential associated to dormancy. Here we identify the cell surface receptor neogenin-1 as specifically expressed in dormant HSCs. Loss of neogenin-1 initially leads to increased HSC expansion but subsequently to loss of self-renewal and premature exhaustion in vivo. Its ligand netrin-1 induces Egr1 expression and maintains quiescence and function of cultured HSCs in a Neo1 dependent manner. Produced by arteriolar endothelial and periarteriolar stromal cells, conditional netrin-1 deletion in the bone marrow niche reduces HSC numbers, quiescence and self-renewal, while overexpression increases quiescence in vivo. Ageing associated bone marrow remodelling leads to the decline of netrin-1 expression in niches and a compensatory but reversible upregulation of neogenin-1 on HSCs. Our study suggests that niche produced netrin-1 preserves HSC quiescence and self-renewal via neogenin-1 function. Decline of netrin-1 production during ageing leads to the gradual decrease of Neo1 mediated HSC self-renewal.

Haematopoietic ageing through the lens of single-cell technologies

Human lifespan is now longer than ever and, as a result, modern society is getting older. Despite that, the detailed mechanisms behind the ageing process and its impact on various tissues and organs remain obscure. In general, changes in DNA, RNA and protein structure throughout life impair their function. Haematopoietic ageing refers to the age-related changes affecting a haematopoietic system. Aged blood cells display different functional aberrations depending on their cell type, which might lead to the development of haematologic disorders, including leukaemias, anaemia or declining immunity. In contrast to traditional bulk assays, which are not suitable to dissect cell-to-cell variation, single-cell-level analysis provides unprecedented insight into the dynamics of age-associated changes in blood. In this Review, we summarise recent studies that dissect haematopoietic ageing at the single-cell level. We discuss what cellular changes occur during haematopoietic ageing at the genomic, transcriptomic, epigenomic and metabolomic level, and provide an overview of the benefits of investigating those changes with single-cell precision. We conclude by considering the potential clinical applications of single-cell techniques in geriatric haematology, focusing on the impact on haematopoietic stem cell transplantation in the elderly and infection studies, including recent COVID-19 research.

DNA Damage and the Aging Epigenome

In mammals, genome instability and aging are intimately linked as illustrated by the growing list of patients with progeroid and animal models with inborn DNA repair defects. Until recently, DNA damage was thought to drive aging by compromising transcription or DNA replication, thereby leading to age-related cellular malfunction and somatic mutations triggering cancer. However, recent evidence suggests that DNA lesions also elicit widespread epigenetic alterations that threaten cell homeostasis as a function of age. In this review, we discuss the functional links of persistent DNA damage with the epigenome in the context of aging and age-related diseases.

The Epigenome in Atherosclerosis

Emerging evidence suggests the growing importance of "nongenetic factors" in the pathogenesis of atherosclerotic vascular disease. Indeed, the inherited genome determines only part of the risk profile as genomic approaches do not take into account additional layers of biological regulation by "epi"-genetic changes. Epigenetic modifications are defined as plastic chemical changes of DNA/histone complexes which critically affect gene activity without altering the DNA sequence. These modifications include DNA methylation, histone posttranslational modifications, and non-coding RNAs and have the ability to modulate gene expression at both transcriptional and posttranscriptional level. Notably, epigenetic signals are mainly induced by environmental factors (i.e., pollution, smoking, noise) and, once acquired, may be transmitted to the offspring. The inheritance of adverse epigenetic changes may lead to premature deregulation of pathways involved in vascular damage and endothelial dysfunction. Here, we describe the emerging role of epigenetic modifications as fine-tuners of gene transcription in atherosclerosis. Specifically, the following aspects are described in detail: (1) discovery and impact of the epigenome in cardiovascular disease, (2) the epigenetic landscape in atherosclerosis; (3) inheritance of epigenetic signals and premature vascular disease; (4) epigenetic control of lipid metabolism, vascular oxidative stress, inflammation, autophagy, and apoptosis; (5) epigenetic biomarkers in patients with atherosclerosis; (6) novel therapeutic strategies to modulate epigenetic marks. Understanding the individual epigenetic profile may pave the way for new approaches to determine cardiovascular risk and to develop personalized therapies to treat atherosclerosis and its complications.

Human hematopoiesis: aging and leukemogenic risk

PURPOSE OF REVIEW

Our understanding of the effects of aging on human hematopoiesis has advanced significantly in recent years, yet the full ramifications of these findings are not fully understood. This review summarizes these findings and discusses their implication as they relate to malignant hematopoiesis.

RECENT FINDINGS

With human aging there is an impaired immune response, loss of hematopoietic stem cell (HSC) function, increase in clonal hematopoiesis, and higher frequency of myeloid malignancies. Although murine models have implicated abnormalities in DNA damage repair, autophagy, metabolism, and epigenetics, studies in primary human specimens are more limited. The development of age-related clonal hematopoiesis and the risk associated with this is one of the major findings in the field of recent years. This is accompanied by changes in bone marrow stem and progenitor composition, changes in the epigenetic program of stem cells and an inflammatory milieu in the bone marrow. The precise consequences of these changes for the development of age-related malignancies are still unclear.

SUMMARY

Advances in the field have begun to reveal the mechanisms driving human HSC loss of function with age. It will be critical to delineate between normal and malignant aging in order to better prevent age-associated myeloid malignancies.

The effects of early-life growth hormone intervention on tissue specific histone H3 modifications in long-lived Ames dwarf mice

Histone modifications, specifically in the lysine residues of histone H3, have been implicated in lifespan regulation in several model organisms. Our previous studies showed that growth hormone (GH) treatment during early life can dramatically influence lifespan in long-lived Ames dwarf mice. However, the effects of this hormonal intervention on epigenetic modifications have never been examined. In this study, we sought to compare tissue-specific histone H3 lysine methylation and acetylation markers in Ames dwarf and wild type (WT) mice and to determine how these markers are affected by early-life GH intervention. Ames dwarf mice exhibited suppressed H3K4me in both hepatic and brain tissues, while showing elevated H3K27me in the brain. Early-life GH intervention significantly altered the histone H3 markers in those tissues. Furthermore, early GH intervention increased expression of histone H3 acetylation at multiple lysine residues in a tissue-specific manner. This included changes in H3K14ac and H3K18ac in the liver and brain, H3K18ac in visceral adipose tissue and H3K9ac, H3K14ac and H3K27ac in subcutaneous adipose tissue. This study serves as an initial, but important step in elucidating the epigenetic mechanisms by which hormonal signals during early life can influence aging and longevity in mammals.

Fate of Hematopoiesis During Aging. What Do We Really Know, and What are its Implications?

There is an ongoing shift in demographics such that older persons will outnumber young persons in the coming years, and with it age-associated tissue attrition and increased diseases and disorders. There has been increased information on the association of the aging process with dysregulation of hematopoietic stem (HSC) and progenitor (HPC) cells, and hematopoiesis. This review provides an extensive up-to date summary on the literature of aged hematopoiesis and HSCs placed in context of potential artifacts of the collection and processing procedure, that may not be totally representative of the status of HSCs in their in vivo bone marrow microenvironment, and what the implications of this are for understanding aged hematopoiesis. This review covers a number of interactive areas, many of which have not been adequately explored. There are still many unknowns and mechanistic insights to be elucidated to better understand effects of aging on the hematopoietic system, efforts that will take multidisciplinary approaches, and that could lead to means to ameliorate at least some of the dysregulation of HSCs and HPCs associated with the aging process. Graphical Abstract.

Molecular and cellular mechanisms of aging in hematopoietic stem cells and their niches

Aging drives the genetic and epigenetic changes that result in a decline in hematopoietic stem cell (HSC) functioning. Such changes lead to aging-related hematopoietic/immune impairments and hematopoietic disorders. Understanding how such changes are initiated and how they progress will help in the development of medications that could improve the quality life for the elderly and to treat and possibly prevent aging-related hematopoietic diseases. Here, we review the most recent advances in research into HSC aging and discuss the role of HSC-intrinsic events, as well as those that relate to the aging bone marrow niche microenvironment in the overall processes of HSC aging. In addition, we discuss the potential mechanisms by which HSC aging is regulated.

TET2: A cornerstone in normal and malignant hematopoiesis

Regulation of genome‐wide DNA methylation is fundamental for a variety of biological processes such as mammalian development, stem cell function, cellular proliferation/differentiation, and oncogenesis. Among the regulators of DNA methylation, ten‐eleven translocation 2 (TET2) is one of the most frequently mutated genes in clonal hematopoiesis of indeterminate potential and in various hematological malignancies, underscoring a pivotal role for TET2 in blood homeostasis and hematopoietic transformation. TET2 oxidizes methylated cytosines to further modify cytosines, which behave as intermediates in active/passive DNA demethylation processes. TET2 itself associates with histone modifiers, thereby regulating histone modifications and expression of target genes. A number of studies have reported pleiotropic effects of TET2 on hematopoietic stem cell self‐renewal, hematopoietic differentiation, genome instability and inflammatory response. Recent single‐cell genomics studies have identified gene promoters as well as transcription factor binding sites as TET2‐targeted genetic loci in which disruption of DNA methylation can fundamentally modify hematopoietic differentiation and promote leukemogenesis. TET2 mutations show convergent cooperativity with other disease alleles in signaling molecules, epigenetic modifiers, and spliceosome factors in hematopoietic transformation. Future studies focusing on the molecular basis of stem cell and immune regulation by TET2 loss will further deepen our understanding of the entire landscape of pathophysiology and molecular vulnerabilities of TET2‐mutated hematological malignancies.

New Insights into the Role of Histone Changes in Aging

Aging is the progressive decline or loss of function at the cellular, tissue, and organismal levels that ultimately leads to death. A number of external and internal factors, including diet, exercise, metabolic dysfunction, genome instability, and epigenetic imbalance, affect the lifespan of an organism. These aging factors regulate transcriptome changes related to the aging process through chromatin remodeling. Many epigenetic regulators, such as histone modification, histone variants, and ATP-dependent chromatin remodeling factors, play roles in chromatin reorganization. The key to understanding the role of gene regulatory networks in aging lies in characterizing the epigenetic regulators responsible for reorganizing and potentiating particular chromatin structures. This review covers epigenetic studies on aging, discusses the impact of epigenetic modifications on gene expression, and provides future directions in this area.

Therapeutic strategies targeting somatic stem cells: Chemical approaches

Therapeutic modulation of fate and behavior of somatic stem cells can generate safe and functional cells ex vivo for cell-based therapy, or to repair and regenerate damaged tissues in vivo. Chemical approaches involving small molecules have provided promising approaches for modulating cellular fate and function. These strategies offer opportunities that support regenerative medicine. Here, we discuss strategies targeting somatic stem cells through chemical approaches, highlighting their progression as well as future prospects.

Epigenetic Regulators as the Gatekeepers of Hematopoiesis

Hematopoiesis is the process by which both fetal and adult organisms derive the full repertoire of blood cells from a single multipotent progenitor cell type, the hematopoietic stem cells (HSCs). Correct enactment of this process relies on a synergistic interplay between genetically encoded differentiation programs and a host of cell-intrinsic and cell-extrinsic factors. These include the influence of the HSC niche microenvironment, action of specific transcription factors, and alterations in intracellular metabolic state. The consolidation of these inputs with the genetically encoded program into a coherent differentiation program for each lineage is thought to rely on epigenetic modifiers. Recent work has delineated the precise contributions of different classes of epigenetic modifiers to HSC self-renewal as well as lineage specification and differentiation into various cell types. Here, we bring together what is currently known about chromatin status and the development of cells in the hematopoietic system under normal and abnormal conditions.

Opportunistic screening and survival prediction of digestive cancers by the combination of blood mSEPT9 with protein markers

Background:

The early detection of digestive cancers and precancerous diseases remains a significant challenge. This study aimed to investigate the performance of the blood methylated SEPT9 (mSEPT9) assay, and the combination of this assay with serum protein markers, in hospital-based opportunistic screening strategies for digestive cancers.

Methods:

Opportunistic screening was performed in the participating hospitals on outpatients and inpatients who met specific inclusion criteria. We recruited a total of 2030 subjects, including 764 cancer patients [291 colorectal cancer (CRC), 239 gastric cancer (GC), 106 esophageal cancer (EC), and 128 hepatocellular carcinoma (HCC)], 423 subjects with precancerous diseases, and 843 normal subjects. All samples were transported to an authenticated clinical laboratory where the mSEPT9 tests were performed.

Results:

When used separately, the mSEPT9 detected CRC, GC, EC, and HCC, with a sensitivity of 76.6% [area under the receiver operating characteristic curve (AUC) = 0.86)], 47.7% (AUC = 0.76), 42.6% (AUC = 0.69), and 76.7% (AUC = 0.85) and a specificity of 94.6%, 92.3%, 92.5%, and 87.7%, respectively. The mSEPT9 assay also had potent ability to discriminate cancer from non-cancer subjects. The combination of mSEPT9 with CEA, CA724, SNCG, or AFP significantly enhanced the sensitivity for CRC, GC, EC, and HCC to 86.4% (AUC = 0.99, specificity = 92.8%), 63.6% (AUC = 0.86, specificity = 91.1%), 71.3% (AUC = 0.81, specificity = 82.1%), and 83.3% (AUC = 0.93, specificity = 85.1%), respectively. The performance of the mSEPT9 assay was influenced by cancer stage, patient age, pathological types, and the location of cancer. We also identified that mSEPT9 was an independent risk factor and was a valuable predictor for the long-term survival of digestive cancer patients, with a hazard ratio of 2.84, 2.07, 1.88, and 2.45, for CRC, GC, EC, and HCC, respectively.

Conclusion:

The blood mSEPT9 assay, whether used alone or in combination with serum protein markers, is effective for the opportunistic screening of digestive cancers. Furthermore, mSEPT9 is an independent risk factor and a predictive marker for the long-term survival of digestive cancer patients.

SUV39H1 regulates the progression of MLL-AF9-induced acute myeloid leukemia

Epigenetic regulations play crucial roles in leukemogenesis and leukemia progression. SUV39H1 is the dominant H3K9 methyltransferase in the hematopoietic system, and its expression declines with aging. However, the role of SUV39H1 via its-mediated repressive modification H3K9me3 in leukemogenesis/leukemia progression remains to be explored. We found that SUV39H1 was down-regulated in a variety of leukemias, including MLL-r AML, as compared with normal individuals. Decreased levels of Suv39h1 expression and genomic H3K9me3 occupancy were observed in LSCs from MLL-r-induced AML mouse models in comparison with that of hematopoietic stem/progenitor cells. Suv39h1 overexpression increased leukemia latency and decreased the frequency of LSCs in MLL-r AML mouse models, while Suv39h1 knockdown accelerated disease progression with increased number of LSCs. Increased Suv39h1 expression led to the inactivation of Hoxb13 and Six1, as well as reversion of Hoxa9/Meis1 downstream target genes, which in turn decelerated leukemia progression. Interestingly, Hoxb13 expression is up-regulated in MLL-AF9-induced AML cells, while knockdown of Hoxb13 in MLL-AF9 leukemic cells significantly prolonged the survival of leukemic mice with reduced LSC frequencies. Our data revealed that SUV39H1 functions as a tumor suppressor in MLL-AF9-induced AML progression. These findings provide the direct link of SUV39H1 to AML development and progression.

Identification of differentially expressed subpathways via a bilevel consensus scoring of network topology and gene expression

Identifying differentially expressed subpathways connected to the emergence of a disease that can be considered as candidates for pharmacological intervention, with minimal off-target effects, is a daunting task. In this direction, we present a bilevel subpathway analysis method to identify differentially expressed subpathways that are connected with an experimental condition, while taking into account potential crosstalks between subpathways which arise due to their connectivity in a combined multi-pathway network. The efficacy of the method is demonstrated on a hematopoietic stem cell aging dataset, with findings corroborated using recent literature.

Disentangling the epigenetic landscape in cardiovascular patients: a path toward personalized medicine

Despite significant advances in our understanding of cardiovascular disease (CVD) we are still far from having developed breakthrough strategies to combat coronary atherosclerosis and heart failure, which account for most of CV deaths worldwide. Available cardiovascular therapies have failed to show to be equally effective in all patients, suggesting that inter-individual diversity is an important factor when it comes to conceive and deliver effective personalized treatments. Genome mapping has proved useful in identifying patients who could benefit more from specific drugs depending on genetic variances; however, our genetic make-up determines only a limited part of an individual's risk profile. Recent studies have demonstrated that epigenetic changes - defined as dynamic changes of DNA and histones which do not affect DNA sequence - are key players in the pathophysiology of cardiovascular disease and may participate to delineate cardiovascular risk trajectories over the lifetime. Epigenetic modifications include changes in DNA methylation, histone modifications and non-coding RNAs and these epigenetic signals have shown to cooperate in modulating chromatin accessibility to transcription factors and gene expression. Environmental factors such as air pollution, smoking, psychosocial context, and unhealthy diet regimens have shown to significantly modify the epigenome thus leading to altered transcriptional programs and CVD phenotypes. Therefore, the integration of genetic and epigenetic information might be invaluable to build individual maps of cardiovascular risk and hence, could be employed for the design of customized diagnostic and therapeutic strategies. In the present review, we discuss the growing importance of epigenetic information and its putative implications in cardiovascular precision medicine.

Proliferation: Driver of HSC aging phenotypes?

The decline of stem cell performance with age is a potential paramount mechanism of aging. Hematopoietic stem cells (HSCs) are perhaps the most studied and best characterized tissue-specific somatic stem cells. As such, HSCs offer an excellent research model of how aging affects stem cell performance, and vice versa. Studies from recent years have elucidated major aging phenotypes of HSCs including a decline in reconstitution potential, altered differentiation predisposition, an increase in number, accumulation of DNA damage/mutations and several others. However, what drives these changes, and exactly how they translate to pathology is poorly understood. Recent studies point to proliferative stress of HSCs as a potential driver of their aging and the resulting pathologies. Here we discuss the recent discoveries and suggest the context in which aging phenotypes could be driven, and the relevant mechanisms by which HSCs could be affected.

Global Transcriptomic Profiling of the Bone Marrow Stromal Microenvironment during Postnatal Development, Aging, and Inflammation

Bone marrow (BM) stromal cells provide the regulatory framework for hematopoiesis and contribute to developmental stage-specific niches, such as those preserving hematopoietic stem cells. Despite advances in our understanding of stromal function, little is known about the transcriptional changes that this compartment undergoes throughout lifespan and during adaptation to stress. Using RNA sequencing, we perform transcriptional analyses of four principal stromal subsets, namely CXCL12-abundant reticular, platelet-derived growth factor receptor (PDGFR)-α⁺Sca1⁺, sinusoidal, and arterial endothelial cells, from early postnatal, adult, and aged mice. Our data reveal (1) molecular fingerprints defining cell-specific anatomical and functional features, (2) a radical reprogramming of pro-hematopoietic, immune, and matrisomic transcriptional programs during the transition from juvenile stages to adulthood, and (3) the aging-driven progressive upregulation of pro-inflammatory gene expression in stroma. We further demonstrate that transcriptomic pathways elicited in vivo by prototypic microbial molecules are largely recapitulated during aging, thereby supporting the inflammatory basis of age-related adaptations of BM hematopoietic function.

Hand in hand: intrinsic and extrinsic drivers of aging and clonal hematopoiesis

Over the past 25 years, the importance of hematopoietic stem cell (HSC) aging in overall hematopoietic and immune system health span has been appreciated. Much work has been done in model organisms to understand the intrinsic dysregulation that occurs in HSCs during aging, with the goal of identifying modifiable mechanisms that represent the proverbial "fountain of youth." Much more recently, the discovery of somatic mutations that are found to provide a selective advantage to HSCs and accumulate in the hematopoietic system during aging, termed clonal hematopoiesis (CH), inspires revisiting many of these previously defined drivers of HSC aging in the context of these somatic mutations. To truly understand these processes and develop a holistic picture of HSC aging, ongoing and future studies must include investigation of the critical changes that occur in the HSC niche or bone marrow microenvironment with aging, as increasing evidence supports that these HSC-extrinsic alterations provide necessary inflammation, signaling pathway activation or repression, and other selective pressures to favor HSC aging-associated phenotypes and CH. Here, we provide our perspectives based on the past 8 years of our own laboratory's investigations into these mechanisms and chart a path for integrative studies that, in our opinion, will provide an ideal opportunity to discover HSC and hematopoietic health span-extending interventions. This path includes examining when and how aging-associated HSC-intrinsic and HSC-extrinsic changes accumulate over time in different individuals and developing new models to track and test relevant HSC-extrinsic changes, complementary to innovative HSC lineage tracing systems that have recently been developed.

p53 involvement in clonal hematopoiesis of indeterminate potential

PURPOSE OF REVIEW

Clonal hematopoiesis of indeterminate potential (CHIP) increases with age and occurs when a single mutant hematopoietic stem cell (HSC) contributes to a significant clonal proportion of mature blood lineages. Somatic mutations in the TP53 gene, which encodes the tumor suppressor protein p53, rank in the top five among genes that were mutated in CHIP. This review focuses on mechanisms by which mutant p53 promotes CHIP progression and drives the pathogenesis of hematological malignancies, including myelodysplastic syndromes, and acute myeloid leukemia.

RECENT FINDINGS

TP53 was frequently mutated in individuals with CHIP. Although clinical studies suggest that expansion of HSCs with TP53 mutations predisposes the elderly to hematological neoplasms, there is a significant gap in knowledge regarding the mechanisms by which TP53 mutations promote HSC expansion. Recent findings suggest that several cellular stressors, including hematopoietic transplantation, genotoxic stress, and inflammation, promote the expansion of HSCs with TP53 mutations. Further, TP53 mutations identified in CHIP cooperate with genetic and/or epigenetic changes in leukemogenesis.

SUMMARY

TP53 mutations identified in CHIP are associated with increased risks of de novo and therapy-related hematological neoplasms. Thus, targeting mutant p53 and related pathways holds great potential in preventing CHIP progression and treating hematological malignancies.