Inflammation and Aging of Hematopoietic Stem Cells in Their Niche

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.

Role of chemokines in aging and age-related diseases

Chemokines (chemotactic cytokines) play essential roles in developmental process, immune cell trafficking, inflammation, immunity, angiogenesis, cellular homeostasis, aging, neurodegeneration, and tumorigenesis. Chemokines also modulate response to immunotherapy, and consequently influence the therapeutic outcome. The mechanisms underlying these processes are accomplished by interaction of chemokines with their cognate cell surface G protein-coupled receptors (GPCRs) and subsequent cellular signaling pathways. Chemokines play crucial role in influencing aging process and age-related diseases across various tissues and organs, primarily through inflammatory responses (inflammaging), recruitment of macrophages, and orchestrated trafficking of other immune cells. Chemokines are categorized in four distinct groups based on the position and number of the N-terminal cysteine residues; namely, the CC, CXC, CX3C, and (X)C. They mediate inflammatory responses, and thereby considerably impact aging process across multiple organ-systems. Therefore, understanding the underlying mechanisms mediated by chemokines may be of crucial importance in delaying and/or modulating the aging process and preventing age-related diseases. In this review, we highlight recent progress accomplished towards understanding the role of chemokines and their cellular signaling pathways involved in aging and age-relaed diseases of various organs. Moreover, we explore potential therapeutic strategies involving anti-chemokines and chemokine receptor antagonists aimed at reducing aging and mitigating age-related diseases. One of the modern methods in this direction involves use of chemokine receptor antagonists and anti-chemokines, which suppress the pro-inflammatory response, thereby helping in resolution of inflammation. Considering the wide-spectrum of functional involvements of chemokines in aging and associated diseases, several clinical trials are being conducted to develop therapeutic approaches using anti-chemokine and chemokine receptor antagonists to improve life span and promote healthy aging.

Siwu decoction mitigates radiation-induced immune senescence by attenuating hematopoietic damage

BACKGROUND

To investigate the long term effects of ionizing radiation (IR) on hematopoietic stem/progenitor cells (HSPCs), immune tissues and cells, and the effects of Siwu decoction (SWD) on immune senescence mice.

METHODS

C57BL/6 J mice were exposed to 6.0 Gy 60Co γ irradiation. After 8-weeks of IR, SWD (5, 10, 20 g/kg/d) was administered for 30 days. The changes of HSPCs in bone marrow (BM) and T, B type lymphocyte and natural killer (NK) cells in spleen were detected by flow cytometry. The changes of peripheral blood cells were also examined. Hematoxylin-eosin staining were used to detect the pathological lesions of hippocampus, spleen and thymus tissues. Absolute mouse telomere length quantification qPCR assay kit was used to measure the telomere length of BM cells. The expression of factors associated with inflammation and aging such as p16, β-galactosidase in spleen, thymus and BM was determined.

RESULTS

Administration of SWD could increase the proportion of LSK (Lin-, Sca-1 + , c-Kit-), multipotent progenitor cells and multipotent progenitor cells and decrease the proportion of common myeloid progenitors and granulocyte-macrophage progenitors in BM. The proportion of B cells and NK cells in spleen and the content of white blood cells, red blood cells, hemoglobin, lymphocytes and eosinophils in peripheral blood were increased, at the same time, the proportion of neutrophils and monocytes was reduced by SWD. The pathological lesions of hippocampus, spleen and thymus were improved. The expression of p16 and β-galactosidase in spleen, thymus and BM was reduced and shortening of the telomere of BM cells was inhibited after administration. In addition, SWD could reduce the content of Janus activated kinase (JAK) 1, JAK2 and signal transducer and activator of transcription 3 (STAT3) in BM and spleen.

CONCLUSIONS

SWD could slow down IR-induced immune senescence by improving hematopoietic and immunologic injury. SWD might reduce the inflammation level of BM hematopoietic microenvironment by acting on JAK/STAT signaling pathway, while the immune damage of mice was improved by affecting the differentiation of HSPCs. The remission of hematopoietic and immunologic senescence was further demonstrated at the overall level.

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.

RNA modification in normal hematopoiesis and hematologic malignancies

N6-methyladenosine (m6A) is the most abundant RNA modification in eukaryotic cells. Previous studies have shown that m6A plays a critical role under both normal physiological and pathological conditions. Hematopoiesis and differentiation are highly regulated processes, and recent studies on m6A mRNA methylation have revealed how this modification controls cell fate in both normal and malignant hematopoietic states. However, despite these insights, a comprehensive understanding of its complex roles between normal hematopoietic development and malignant hematopoietic diseases remains elusive. This review first provides an overview of the components and biological functions of m6A modification regulators. Additionally, it highlights the origin, differentiation process, biological characteristics, and regulatory mechanisms of hematopoietic stem cells, as well as the features, immune properties, and self-renewal pathways of leukemia stem cells. Last, the article systematically reviews the latest research advancements on the roles and mechanisms of m6A regulatory factors in normal hematopoiesis and related malignant diseases. More importantly, this review explores how targeting m6A regulators and various signaling pathways could effectively intervene in the development of leukemia, providing new insights and potential therapeutic targets. Targeting m6A modification may hold promise for achieving more precise and effective leukemia treatments.

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.

Linker histone regulates the myeloid versus lymphoid bifurcation of multipotent hematopoietic stem and progenitors

Myeloid-biased differentiation of multipotent hematopoietic stem and progenitor cells (HSPCs) occurs with aging or exhaustion. The molecular mechanism(s) responsible for this fate bias remain unclear. Here we report that linker histone regulates HSPC fate choice at the lymphoid versus myeloid bifurcation. HSPCs expressing H1.0 from a doxycycline (dox) inducible transgene favor the lymphoid fate, display strengthened nucleosome organization and reduced chromatin accessibility at genomic regions hosting key myeloid fate drivers. The transcription factor Hlf is located in one of such regions, where chromatin accessibility and gene expression is reduced in H1.0 high HSPCs. Furthermore, H1.0 protein in HSPCs decreases in an aspartyl protease dependent manner, a process enhanced in response to interferon alpha (IFNα) signaling. Aspartyl protease inhibitors preserve endogenous H1.0 levels and promote the lymphoid fate of wild type HSPCs. Thus, our work uncovers a point of intervention to mitigate myeloid skewed hematopoiesis.

Treatment of post-allogeneic hematopoietic stem cell transplant cytopenias with sequential doses of multipotent mesenchymal stromal/stem cells

BACKGROUND AIMS

Cytopenias after allogeneic stem cell transplantation (allo-SCT) are a common complication, the underlying pathogenic mechanisms of which remain incompletely understood. Multipotent mesenchymal stromal/stem cell (MSC) therapy has been successfully employed in the treatment of immune-related disorders and can aid in the restoration of the hematopoietic niche.

METHODS

A phase II clinical trial to assess the efficacy and safety of administering four sequential doses of ex-vivo expanded bone marrow MSCs from a third-party donor to patients with persistent severe cytopenias after allo-SCT was performed.

RESULTS

The overall response rate on day 90 was 75% among the 27 evaluable patients (comprising 12 complete responses, 8 partial responses, and 7 with no response). The median time to respond was 14.5 days. Responses were observed across different profiles, including single or multiple affected lineages, primary or secondary timing, and potential immune-mediated or post-infectious pathophysiology versus idiopathic origin. With a median follow-up for surviving patients of 85 months after MSC infusion, 53% of patients are alive. Notably, no adverse events related to MSC therapy were reported.

CONCLUSIONS

In summary, the sequential infusion of third-party MSCs emerges as a viable and safe therapeutic option, exhibiting potential benefits for patients experiencing cytopenias following allo-SCT.

Variation in mesenchymal KITL/SCF and IGF1 expression in middle age underlies steady-state hematopoietic stem cell aging

ABSTRACT

Intrinsic molecular programs and extrinsic factors including proinflammatory molecules are understood to regulate hematopoietic aging. This is based on foundational studies using genetic perturbation to evaluate causality. However, individual organisms exhibit natural variation in the hematopoietic aging phenotypes and the molecular basis of this heterogeneity is poorly understood. Here, we generated individual single-cell transcriptomic profiles of hematopoietic and nonhematopoietic cell types in 5 young adult and 9 middle-aged C57BL/6J female mice, providing a web-accessible transcriptomic resource for the field. Among all assessed cell types, hematopoietic stem cells (HSCs) exhibited the greatest phenotypic variation in expansion among individual middle-aged mice. We computationally pooled samples to define modules representing the molecular signatures of middle-aged HSCs and interrogated, which extrinsic regulatory cell types and factors would predict the variance in these signatures between individual middle-aged mice. Decline in signaling mediated by adiponectin, kit ligand (KITL) and insulin-like growth factor 1 (IGF1) from mesenchymal stromal cells (MSCs) was predicted to have the greatest transcriptional impact on middle-aged HSCs, as opposed to signaling mediated by endothelial cells or mature hematopoietic cell types. In individual middle-aged mice, lower expression of Kitl and Igf1 in MSCs was highly correlated with reduced lymphoid lineage commitment of HSCs and increased signatures of differentiation-inactive HSCs. These signatures were independent of expression of aging-associated proinflammatory cytokines including interleukin-1β (IL-1β), IL-6, tumor necrosis factor α and RANTES. In sum, we find that Kitl and Igf1 expression are coregulated and variable between individual mice at the middle age and expression of these factors is predictive of HSC activation and lymphoid commitment independently of inflammation.

Effect of Cellular Senescence in Disease Progression and Transplantation: Immune Cells and Solid Organs

Aging of the world population significantly impacts healthcare globally and specifically, the field of transplantation. Together with end-organ dysfunction and prolonged immunosuppression, age increases the frequency of comorbid chronic diseases in transplant candidates and recipients, contributing to inferior outcomes. Although the frequency of death increases with age, limited use of organs from older deceased donors reflects the concerns about organ durability and inadequate function. Cellular senescence (CS) is a hallmark of aging, which occurs in response to a myriad of cellular stressors, leading to activation of signaling cascades that stably arrest cell cycle progression to prevent tumorigenesis. In aging and chronic conditions, senescent cells accumulate as the immune system's ability to clear them wanes, which is causally implicated in the progression of chronic diseases, immune dysfunction, organ damage, decreased regenerative capacity, and aging itself. The intimate interplay between senescent cells, their proinflammatory secretome, and immune cells results in a positive feedback loop, propagating chronic sterile inflammation and the spread of CS. Hence, senescent cells in organs from older donors trigger the recipient's alloimmune response, resulting in the increased risk of graft loss. Eliminating senescent cells or attenuating their inflammatory phenotype is a novel, potential therapeutic target to improve transplant outcomes and expand utilization of organs from older donors. This review focuses on the current knowledge about the impact of CS on circulating immune cells in the context of organ damage and disease progression, discusses the impact of CS on abdominal solid organs that are commonly transplanted, and reviews emerging therapies that target CS.

Hematopoietic aging: Cellular, molecular, and related mechanisms

ABSTRACT

Aging is accompanied by significant inhibition of hematopoietic and immune system function and disruption of bone marrow structure. Aging-related alterations in the inflammatory response, immunity, and stem cell niches are at the root of hematopoietic aging. Understanding the molecular mechanisms underlying hematopoietic and bone marrow aging can aid the clinical treatment of aging-related diseases. In particular, it is unknown how the niche reprograms hematopoietic stem cells (HSCs) in an age-dependent manner to maintain normal hematopoiesis in elderly individuals. Recently, specific inhibitors and blood exchange methods have been shown to reshape the hematopoietic niche and reverse hematopoietic aging. Here, we present the latest scientific discoveries related to hematopoietic aging and hematopoietic system rejuvenation, discuss the relationships between hematopoietic niche aging and HSC aging, and describe related studies on stem cell-mediated regulation of hematopoietic aging, aiming to provide new ideas for further study.

Depleting myeloid-biased haematopoietic stem cells rejuvenates aged immunity

Ageing of the immune system is characterized by decreased lymphopoiesis and adaptive immunity, and increased inflammation and myeloid pathologies1,2. Age-related changes in populations of self-renewing haematopoietic stem cells (HSCs) are thought to underlie these phenomena3. During youth, HSCs with balanced output of lymphoid and myeloid cells (bal-HSCs) predominate over HSCs with myeloid-biased output (my-HSCs), thereby promoting the lymphopoiesis required for initiating adaptive immune responses, while limiting the production of myeloid cells, which can be pro-inflammatory4. Ageing is associated with increased proportions of my-HSCs, resulting in decreased lymphopoiesis and increased myelopoiesis3,5,6. Transfer of bal-HSCs results in abundant lymphoid and myeloid cells, a stable phenotype that is retained after secondary transfer; my-HSCs also retain their patterns of production after secondary transfer5. The origin and potential interconversion of these two subsets is still unclear. If they are separate subsets postnatally, it might be possible to reverse the ageing phenotype by eliminating my-HSCs in aged mice. Here we demonstrate that antibody-mediated depletion of my-HSCs in aged mice restores characteristic features of a more youthful immune system, including increasing common lymphocyte progenitors, naive T cells and B cells, while decreasing age-related markers of immune decline. Depletion of my-HSCs in aged mice improves primary and secondary adaptive immune responses to viral infection. These findings may have relevance to the understanding and intervention of diseases exacerbated or caused by dominance of the haematopoietic system by my-HSCs.

Time-series analysis of hematopoietic stem cells

This study aimed to investigate the molecular mechanisms underlying the aging of hematopoietic stem cells (HSCs). Gene expression profile GSE32719 was downloaded from the Gene Expression Omnibus database, including 14 young, 5 middle, and 8 old HSCs. Differential expression analysis, short time-series expression miner analysis, and weighted co-expression network analysis were conducted to screen for hub genes whose expression changed over time during HSC aging. Subsequently, functional enrichment and multiple regulatory network analyses of the hub genes were performed. A total of 124 intersecting time-dependent differentially expressed and module genes were obtained, which were considered hub genes whose expression changed over time during HSC aging. Hub genes were significantly enriched in pathways such as the Hippo and AMP-activated protein kinase (AMPK) signaling pathways. Moreover, AP-1 Transcription Factor Subunit (FOS) and sirtuin 1 (SIRT1) had higher degrees in the protein-protein interaction network, were regulated by more transcription factors (TFs), such as Sp1 transcription factor (SP1) and BRCA1 DNA repair-associated (BRCA1), in the TF-mRNA-miRNA network, were associated with more diseases in the disease-gene network, and could be targeted by more drugs in the drug-gene network. Furthermore, SIRT1 was targeted by miR-9-5p in the TF-mRNA-miRNA network. Hub genes such as FOS and SIRT1 and key pathways such as the Hippo and AMPK signaling pathways may play crucial roles in HSC aging. Moreover, FOS and SIRT1 were regulated by SP1 and BRCA1, respectively, during HSC aging. Furthermore, miR-9-5p may modulate HSC aging by targeting SIRT1. Thus, FOS and SIRT1 may be potential therapeutic targets for age-related hematopoietic dysfunction.

Haematopoietic stem cell health in sickle cell disease and its implications for stem cell therapies and secondary haematological disorders

Gene modification of haematopoietic stem cells (HSCs) is a potentially curative approach to sickle cell disease (SCD) and offers hope for patients who are not eligible for allogeneic HSC transplantation. Current approaches require in vitro manipulation of healthy autologous HSC prior to their transplantation. However, the health and integrity of HSCs may be compromised by a variety of disease processes in SCD, and challenges have emerged in the clinical trials of gene therapy. There is also concern about increased susceptibility to haematological malignancies during long-term follow up of patients, and this raises questions about genomic stability in the stem cell compartment. In this review, we evaluate the evidence for HSC deficits in SCD and then discuss their potential causation. Finally, we suggest several questions which need to be addressed in order to progress with successful HSC manipulation for gene therapy in SCD.

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.

Adipocytes control hematopoiesis and inflammation through CD40 signaling

The co-stimulatory CD40-CD40L dyad plays an important role in chronic inflammatory diseases associated with aging. Although CD40 is mainly expressed by immune cells, CD40 is also present on adipocytes. We aimed to delineate the role of adipocyte CD40 in the aging hematopoietic system and evaluated the effects of adipocyte CD40 deficiency on cardiometabolic diseases. Adult adipocyte CD40-deficient mice (AdiCD40KO) mice had a decrease in bone marrow hematopoietic stem cells (Lin-Sca+cKit+, LSK) and common lymphoid progenitors, which was associated with increased bone marrow adiposity and T-cell activation, along with elevated plasma corticosterone levels, a phenotype that became more pronounced with age. Atherosclerotic AdiCD40koApoE-/- (CD40AKO) mice also displayed changes in the LSK population, showing increased myeloid and lymphoid multipotent progenitors, and augmented corticosterone levels. Increased T-cell activation could be observed in bone marrow, spleen, and adipose tissue, while the numbers of B cells were decreased. Although atherosclerosis was reduced in CD40AKO mice, plaques contained more activated T cells and larger necrotic cores. Analysis of peripheral adipose tissue in a diet-induced model of obesity revealed that obese AdiCD40KO mice had increased T-cell activation in adipose tissue and lymphoid organs, but decreased weight gain and improved insulin sensitivity, along with increased fat oxidation. In conclusion, adipocyte CD40 plays an important role in maintaining immune cell homeostasis in bone marrow during aging and chronic inflammatory diseases, particularly of the lymphoid populations. Although adipocyte CD40 deficiency reduces atherosclerosis burden and ameliorates diet-induced obesity, the accompanying T-cell activation may eventually aggravate cardiometabolic diseases.

Megakaryocyte Secreted Factors Regulate Bone Marrow Niche Cells During Skeletal Homeostasis, Aging, and Disease

The bone marrow microenvironment contains a diverse array of cell types under extensive regulatory control and provides for a novel and complex mechanism for bone regulation. Megakaryocytes (MKs) are one such cell type that potentially acts as a master regulator of the bone marrow microenvironment due to its effects on hematopoiesis, osteoblastogenesis, and osteoclastogenesis. While several of these processes are induced/inhibited through MK secreted factors, others are primarily regulated by direct cell-cell contact. Notably, the regulatory effects that MKs exert on these different cell populations has been found to change with aging and disease states. Overall, MKs are a critical component of the bone marrow that should be considered when examining regulation of the skeletal microenvironment. An increased understanding of the role of MKs in these physiological processes may provide insight into novel therapies that can be used to target specific pathways important in hematopoietic and skeletal disorders.

Targeting lymphoid-derived IL-17 signaling to delay skin aging

Skin aging is characterized by structural and functional changes that contribute to age-associated frailty. This probably depends on synergy between alterations in the local niche and stem cell-intrinsic changes, underscored by proinflammatory microenvironments that drive pleotropic changes. The nature of these age-associated inflammatory cues, or how they affect tissue aging, is unknown. Based on single-cell RNA sequencing of the dermal compartment of mouse skin, we show a skew towards an IL-17-expressing phenotype of T helper cells, γδ T cells and innate lymphoid cells in aged skin. Importantly, in vivo blockade of IL-17 signaling during aging reduces the proinflammatory state of the skin, delaying the appearance of age-related traits. Mechanistically, aberrant IL-17 signals through NF-κB in epidermal cells to impair homeostatic functions while promoting an inflammatory state. Our results indicate that aged skin shows signs of chronic inflammation and that increased IL-17 signaling could be targeted to prevent age-associated skin ailments.

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.

Telomeres and Telomerase in the Control of Stem Cells

Stem cells serve as a source of cellular material in embryogenesis and postnatal growth and regeneration. This requires significant proliferative potential ensured by sufficient telomere length. Telomere attrition in the stem cells and their niche cells can result in the exhaustion of the regenerative potential of high-turnover organs, causing or contributing to the onset of age-related diseases. In this review, stem cells are examined in the context of the current telomere-centric theory of cell aging, which assumes that telomere shortening depends not just on the number of cell doublings (mitotic clock) but also on the influence of various internal and external factors. The influence of the telomerase and telomere length on the functional activity of different stem cell types, as well as on their aging and prospects of use in cell therapy applications, is discussed.

The parasitic worm product ES-62 protects the osteoimmunology axis in a mouse model of obesity-accelerated ageing

Despite significant increases in human lifespan over the last century, adoption of high calorie diets (HCD) has driven global increases in type-2 diabetes, obesity and cardiovascular disease, disorders precluding corresponding improvements in healthspan. Reflecting that such conditions are associated with chronic systemic inflammation, evidence is emerging that infection with parasitic helminths might protect against obesity-accelerated ageing, by virtue of their evolution of survival-promoting anti-inflammatory molecules. Indeed, ES-62, an anti-inflammatory secreted product of the filarial nematode Acanthocheilonema viteae, improves the healthspan of both male and female C57BL/6J mice undergoing obesity-accelerated ageing and also extends median lifespan in male animals, by positively impacting on inflammatory, adipose metabolic and gut microbiome parameters of ageing. We therefore explored whether ES-62 affects the osteoimmunology axis that integrates environmental signals, such as diet and the gut microbiome to homeostatically regulate haematopoiesis and training of immune responses, which become dysregulated during (obesity-accelerated) ageing. Of note, we find sexual dimorphisms in the decline in bone health, and associated dysregulation of haematopoiesis and consequent peripheral immune responses, during obesity-accelerated ageing, highlighting the importance of developing sex-specific anti-ageing strategies. Related to this, ES-62 protects trabecular bone structure, maintaining bone marrow (BM) niches that counter the ageing-associated decline in haematopoietic stem cell (HSC) functionality highlighted by a bias towards myeloid lineages, in male but not female, HCD-fed mice. This is evidenced by the ability of ES-62 to suppress the adipocyte and megakaryocyte bias and correspondingly promote increases in B lymphocytes in the BM. Furthermore, the consequent prevention of ageing-associated myeloid/lymphoid skewing is associated with reduced accumulation of inflammatory CD11c+ macrophages and IL-1β in adipose tissue, disrupting the perpetuation of inflammation-driven dysregulation of haematopoiesis during obesity-accelerated ageing in male HCD-fed mice. Finally, we report the ability of small drug-like molecule analogues of ES-62 to mimic some of its key actions, particularly in strongly protecting trabecular bone structure, highlighting the translational potential of these studies.

Microenvironmental Features Driving Immune Evasion in Myelodysplastic Syndromes and Acute Myeloid Leukemia

Bone marrow, besides the known functions of hematopoiesis, is an active organ of the immune system, functioning as a sanctuary for several mature immune cells. Moreover, evidence suggests that hematopoietic stem cells (the bone marrow’s functional unit) are capable of directly sensing and responding to an array of exogenous stimuli. This chronic immune stimulation is harmful to normal hematopoietic stem cells, while essential for the propagation of myeloid diseases, which show a dysregulated immune microenvironment. The bone marrow microenvironment in myelodysplastic syndromes (MDS) is characterized by chronic inflammatory activity and immune dysfunction, that drive excessive cellular death and through immune evasion assist in cancer cell expansion. Acute myeloid leukemia (AML) is another example of immune response failure, with features that augment immune evasion and suppression. In this review, we will outline some of the functions of the bone marrow with immunological significance and describe the alterations in the immune landscape of MDS and AML that drive disease progression.

Resident Self-Tissue of Proinflammatory Cytokines Rather than Their Systemic Levels Correlates with Development of Myelofibrosis in Gata1low Mice

Serum levels of inflammatory cytokines are currently investigated as prognosis markers in myelofibrosis, the most severe Philadelphia-negative myeloproliferative neoplasm. We tested this hypothesis in the Gata1low model of myelofibrosis. Gata1low mice, and age-matched wild-type littermates, were analyzed before and after disease onset. We assessed cytokine serum levels by Luminex-bead-assay and ELISA, frequency and cytokine content of stromal cells by flow cytometry, and immunohistochemistry and bone marrow (BM) localization of GFP-tagged hematopoietic stem cells (HSC) by confocal microscopy. Differences in serum levels of 32 inflammatory-cytokines between prefibrotic and fibrotic Gata1low mice and their wild-type littermates were modest. However, BM from fibrotic Gata1low mice contained higher levels of lipocalin-2, CXCL1, and TGF-β1 than wild-type BM. Although frequencies of endothelial cells, mesenchymal cells, osteoblasts, and megakaryocytes were higher than normal in Gata1low BM, the cells which expressed these cytokines the most were malignant megakaryocytes. This increased bioavailability of proinflammatory cytokines was associated with altered HSC localization: Gata1low HSC were localized in the femur diaphysis in areas surrounded by microvessels, neo-bones, and megakaryocytes, while wild-type HSC were localized in the femur epiphysis around adipocytes. In conclusion, bioavailability of inflammatory cytokines in BM, rather than blood levels, possibly by reshaping the HSC niche, correlates with myelofibrosis in Gata1low mice.

Self-Control of Inflammation during Tail Regeneration of Lizards

Lizards can spontaneously regenerate their lost tail without evoking excessive inflammation at the damaged site. In contrast, tissue/organ injury of its mammalian counterparts results in wound healing with a formation of a fibrotic scar due to uncontrolled activation of inflammatory responses. Unveiling the mechanism of self-limited inflammation occurring in the regeneration of a lizard tail will provide clues for a therapeutic alternative to tissue injury. The present review provides an overview of aspects of rapid wound healing and roles of antibacterial peptides, effects of leukocytes on the tail regeneration, self-blocking of the inflammatory activation in leukocytes, as well as inflammatory resistance of blastemal cells or immature somatic cells during lizard tail regeneration. These mechanistic insights of self-control of inflammation during lizard tail regeneration may lead in the future to the development of therapeutic strategies to fight injury-induced inflammation.