Aging-associated changes in hematopoiesis and leukemogenesis: what's the connection?

Inflammation promotes aging-associated oncogenesis in the lung

Background

Lung cancer is the leading cause of cancer death in the world. While cigarette smoking is the major preventable factor for cancers in general and lung cancer in particular, old age is also a major risk factor. Aging-related chronic, low-level inflammation, termed inflammaging, has been widely documented; however, it remains unclear how inflammaging contributes to increased lung cancer incidence. Aim: To establish connections between aging-associated changes in the lungs and cancer risk.

Methods

We analyzed public databases of gene expression for normal and cancerous human lungs and used mouse models to understand which changes were dependent on inflammation, as well as to assess the impact on oncogenesis.

Results

Analyses of GTEx and TCGA databases comparing gene expression profiles from normal lungs, lung adenocarcinoma, lung squamous cell carcinoma of subjects across age groups revealed upregulated pathways such as inflammatory response, TNFA signaling via NFκB, and interferon-gamma response. Similar pathways were identified comparing the gene expression profiles of young and old mouse lungs. Transgenic expression of alpha 1 antitrypsin (AAT) partially reverses increases in markers of aging-associated inflammation and immune deregulation. Using an orthotopic model of lung cancer using cells derived from EML4-ALK fusion-induced adenomas, we demonstrated an increased tumor outgrowth in lungs of old mice while NLRP3 knockout in old mice decreased tumor volumes, suggesting that inflammation contributes to increased lung cancer development in aging organisms.

Conclusions

These studies reveal how expression of an anti-inflammatory mediator (AAT) can reduce some but not all aging-associated changes in mRNA and protein expression in the lungs. We further show that aging is associated with increased tumor outgrowth in the lungs, which may relate to an increased inflammatory microenvironment.

Circadian immunity from bench to bedside: a practical guide

The immune system is built to counteract unpredictable threats, yet it relies on predictable cycles of activity to function properly. Daily rhythms in immune function are an expanding area of study, and many originate from a genetically based timekeeping mechanism known as the circadian clock. The challenge is how to harness these biological rhythms to improve medical interventions. Here, we review recent literature documenting how circadian clocks organize fundamental innate and adaptive immune activities, the immunologic consequences of circadian rhythm and sleep disruption, and persisting knowledge gaps in the field. We then consider the evidence linking circadian rhythms to vaccination, an important clinical realization of immune function. Finally, we discuss practical steps to translate circadian immunity to the patient's bedside.

Novel insights into IL-37: an anti-inflammatory cytokine with emerging roles in anti-cancer process

Interleukin-37 (IL-37) is a newly discovered member of IL-1 family. The cytokine was proved to have extensive protective effects in infectious diseases, allergic diseases, metabolic diseases, autoimmune diseases and tumors since its discovery. IL-37 was mainly produced by immune and some non-immune cells in response to inflammatory stimulus. The IL-37 precursors can convert into the mature forms after caspase-1 cleavage and activation intracellularly, and then bind to Smad-3 and transfer to the nucleus to inhibit the production and functions of proinflammatory cytokines; extracellularly, IL-37 binds to cell surface receptors to form IL-37/IL-18Rα/IL-1R8 complex to exert immunosuppressive function via inhibiting/activating multiple signal pathways. In addition, IL-37 can attenuate the pro-inflammatory effect of IL-18 through directly or forming an IL-37/IL-18BP/IL-18Rβ complex. Therefore, IL-37 has the ability to suppress innate and acquired immunity of the host, and effectively control inflammatory stimulation, which was considered as a new hallmark of cancer. Specifically, it is concluded that IL-37 can inhibit the growth and migration of tumor cells, prohibit angiogenesis and mediate the immunoregulation in tumor microenvironment, so as to exert effective anti-tumor effects. Importantly, latest studies also showed that IL-37 may be a novel therapeutic target for cancer monitoring. In this review, we summarize the immunoregulation roles and mechanisms of IL-37 in anti-tumor process, and discuss its progress so far and potential as tumor immunotherapy.

Mosaic Chromosomal Alterations and Human Longevity

Mosaic chromosomal alterations (mCAs) are structural alterations associated with aging, cancer, cardiovascular disease, infectious diseases, and mortality. The distribution of mCAs in centenarians and individuals with familial longevity is poorly understood. We used MOsaic CHromosomal Alteration (MoChA) to discover mCAs in 2050 centenarians, offspring, and 248 controls from the New England Centenarian Study (NECS) and in 3 642 subjects with familial longevity and 920 spousal controls from the Long-Life Family Study (LLFS). We analyzed study-specific associations of somatic mCAs with age, familial longevity, the incidence of age-related diseases, and mortality and aggregated the results by meta-analysis. We show that the accumulation of mCAs > 100 KB increased to 102 years and plateaued at older ages. Centenarians and offspring accumulated fewer autosomal mCAs compared with controls (relative risk 0.637, p = .0147). Subjects with the APOE E4 allele had a 35.3% higher risk of accumulating autosomal mCAs (p = .002). Males were at higher risk for mCAs compared to females (male relative risk 1.36, p = 5.15e-05). mCAs were associated with increased hazard for cancer (hazard ratio 1.2) and dementia (hazard ratio 1.259) at a 10% false discovery rate. We observed a borderline significant association between mCAs and risk for mortality (hazard ratio 1.07, p = .0605). Our results show that the prevalence of individuals with mCAs does not continue to increase at ages >102 years and factors promoting familial longevity appear to confer protections from mCAs. These results suggest that limited mCA accumulation could be an important mechanism for extreme human longevity that needs to be investigated.

Immunometabolic reprogramming, another cancer hallmark

Molecular carcinogenesis is a multistep process that involves acquired abnormalities in key biological processes. The complexity of cancer pathogenesis is best illustrated in the six hallmarks of the cancer: (1) the development of self-sufficient growth signals, (2) the emergence of clones that are resistant to apoptosis, (3) resistance to the antigrowth signals, (4) neo-angiogenesis, (5) the invasion of normal tissue or spread to the distant organs, and (6) limitless replicative potential. It also appears that non-resolving inflammation leads to the dysregulation of immune cell metabolism and subsequent cancer progression. The present article delineates immunometabolic reprogramming as a critical hallmark of cancer by linking chronic inflammation and immunosuppression to cancer growth and metastasis. We propose that targeting tumor immunometabolic reprogramming will lead to the design of novel immunotherapeutic approaches to cancer.

Aging drives Tet2+/- clonal hematopoiesis via IL-1 signaling

Clonal hematopoiesis of indeterminate potential (CHIP), also referred to as aging-related clonal hematopoiesis, is defined as an asymptomatic clonal expansion of mutant mature hematopoietic cells in ≥4% of blood leukocytes. CHIP associates with advanced age and increased risk for hematological malignancy, cardiovascular disease, and all-cause mortality. Loss-of-function somatic mutations in TET2 are frequent drivers of CHIP. However, the contribution of aging-associated cooperating cell-extrinsic drivers, like inflammation, remains underexplored. Using bone marrow (BM) transplantation and newly developed genetic mosaicism (HSC-SCL-Cre-ERT; Tet2+/flox; R26+/tm6[CAG-ZsGreen1]Hze) mouse models of Tet2+/-driven CHIP, we observed an association between increased Tet2+/- clonal expansion and higher BM levels of the inflammatory cytokine interleukin-1 (IL-1) upon aging. Administration of IL-1 to mice carrying CHIP led to an IL-1 receptor 1 (IL-1R1)-dependent expansion of Tet2+/- hematopoietic stem and progenitor cells (HSPCs) and mature blood cells. This expansion was caused by increased Tet2+/- HSPC cell cycle progression, increased multilineage differentiation, and higher repopulation capacity compared with their wild-type counterparts. In agreement, IL-1α-treated Tet2+/- hematopoietic stem cells showed increased DNA replication and repair transcriptomic signatures and reduced susceptibility to IL-1α-mediated downregulation of self-renewal genes. More important, genetic deletion of IL-1R1 in Tet2+/- HPSCs or pharmacologic inhibition of IL-1 signaling impaired Tet2+/- clonal expansion, establishing the IL-1 pathway as a relevant and therapeutically targetable driver of Tet2+/- CHIP progression during aging.

International expert group collaboration for developing an adverse outcome pathway for radiation induced leukaemia

PURPOSE

The concept of the adverse outcome pathway (AOP) has recently gained significant attention as to its potential for incorporation of mechanistic biological information into the assessment of adverse health outcomes following ionizing radiation (IR) exposure. This work is an account of the activities of an international expert group formed specifically to develop an AOP for IR-induced leukaemia. Group discussions were held during dedicated sessions at the international AOP workshop jointly organized by the MELODI (Multidisciplinary European Low Dose Initiative) and the ALLIANCE (European Radioecology Alliance) associations to consolidate knowledge into a number of biological key events causally linked by key event relationships and connecting a molecular initiating event with the adverse outcome. Further knowledge review to generate a weight of evidence support for the Key Event Relationships (KERs) was undertaken using a systematic review approach.

CONCLUSIONS

An AOP for IR-induced acute myeloid leukaemia was proposed and submitted for review to the OECD-curated AOP-wiki (aopwiki.org). The systematic review identified over 500 studies that link IR, as a stressor, to leukaemia, as an adverse outcome. Knowledge gap identification, although requiring a substantial effort via systematic review of literature, appears to be one of the major added values of the AOP concept. Further work, both within this leukaemia AOP working group and other similar working groups, is warranted and is anticipated to produce highly demanded products for the radiation protection research community.

Somatic Mutations of Hematopoietic Cells Are an Additional Mechanism of Body Aging, Conducive to Comorbidity and Increasing Chronification of Inflammation

It is known that the development of foci of chronic inflammation usually accompanies body aging. In these foci, senescent cells appear with a pro-inflammatory phenotype that helps maintain inflammation. Their removal with the help of senolytics significantly improves the general condition of the body and, according to many indicators, contributes to rejuvenation. The cells of the immune system participate in the initiation, development, and resolution of inflammation. With age, the human body accumulates mutations, including the cells of the bone marrow, giving rise to the cells of the immune system. We assume that a number of such mutations formed with age can lead to the appearance of “naive” cells with an initially pro-inflammatory phenotype, the migration of which to preexisting foci of inflammation contributes not to the resolution of inflammation but its chronicity. One of such cell variants are monocytes carrying mitochondrial mutations, which may be responsible for comorbidity and deterioration in the prognosis of the course of pathologies associated with aging, such as atherosclerosis, arthritis, osteoporosis, and neurodegenerative diseases.

JAK-STAT in Early Hematopoiesis and Leukemia

Hematopoietic stem cells (HSCs) produce all the terminally differentiated blood cells and are controlled by extracellular signals from the microenvironment, the bone marrow (BM) niche, as well as intrinsic cell signals. Intrinsic signals include the tightly controlled action of signaling pathways, as the Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway. Activation of JAK-STAT leads to phosphorylation of members of the STAT family to regulate proliferation, survival, and self-renewal of HSCs. Mutations in components of the JAK-STAT pathway are linked with defects in HSCs and hematologic malignancies. Accumulating mutations in HSCs and aging contribute to leukemia transformation. Here an overview of hematopoiesis, and the role of the JAK-STAT pathway in HSCs and in the promotion of leukemic transformation is presented. Therapeutic targeting of JAK-STAT and clinical implications of the existing research findings are also discussed.

Interleukin-37 improves T-cell-mediated immunity and chimeric antigen receptor T-cell therapy in aged backgrounds

Aging‐associated declines in innate and adaptive immune responses are well documented and pose a risk for the growing aging population, which is predicted to comprise greater than 40 percent of the world's population by 2050. Efforts have been made to improve immunity in aged populations; however, safe and effective protocols to accomplish this goal have not been universally established. Aging‐associated chronic inflammation is postulated to compromise immunity in aged mice and humans. Interleukin‐37 (IL‐37) is a potent anti‐inflammatory cytokine, and we present data demonstrating that IL‐37 gene expression levels in human monocytes significantly decline with age. Furthermore, we demonstrate that transgenic expression of interleukin‐37 (IL‐37) in aged mice reduces or prevents aging‐associated chronic inflammation, splenomegaly, and accumulation of myeloid cells (macrophages and dendritic cells) in the bone marrow and spleen. Additionally, we show that IL‐37 expression decreases the surface expression of programmed cell death protein 1 (PD‐1) and augments cytokine production from aged T‐cells. Improved T‐cell function coincided with a youthful restoration of Pdcd1, Lat, and Stat4 gene expression levels in CD4⁺ T‐cells and Lat in CD8⁺ T‐cells when aged mice were treated with recombinant IL‐37 (rIL‐37) but not control immunoglobin (Control Ig). Importantly, IL‐37‐mediated rejuvenation of aged endogenous T‐cells was also observed in aged chimeric antigen receptor (CAR) T‐cells, where improved function significantly extended the survival of mice transplanted with leukemia cells. Collectively, these data demonstrate the potency of IL‐37 in boosting the function of aged T‐cells and highlight its therapeutic potential to overcome aging‐associated immunosenescence.

Aging and immunotherapies: New horizons for the golden ages

The life expectancy of the world’s elderly population (65 and older) continues to reach new milestones with older individuals currently comprising greater than 8.5% (617 million) of the world’s population. This percentage is predicted to approach 20% of the world’s population by 2050 (representing 1.6 billion people). Despite this amazing feat, many healthcare systems are not equipped to handle the multitude of diseases that commonly manifest with age, including most types of cancers. As the world’s aging population grows, cancer treatments continue to evolve. Immunotherapies are a new drug class that has revolutionized our ability to treat previously intractable cancers; however, their efficacy in patients with compromised immune systems remains unclear. In this review, we will discuss how aging-associated losses in immune homeostasis impact the efficacy and safety of immunotherapy treatment in preclinical models of aging. We will also discuss how these findings translate to elderly patients receiving immunotherapy treatment for refractory and relapsed cancers, as well as, strategies that could be explored to improve the efficacy of immunotherapies in aged patients.

The role of clonal haematopoiesis in cardiovascular diseases: epidemiology and experimental studies

Clonal haematopoiesis results from acquired mutations in haematopoietic stem and progenitor cells (HSPCs). These mutations can confer the HSPC with a competitive advantage, leading to their clonal expansion within the limiting bone marrow niche. This process is often insufficient to produce a haematologic malignancy; however, the expanding HSPC clones increasingly give rise to progeny leucocytes whose phenotypes can be altered by the somatic mutations that they harbour. Key findings from multiple human studies have shown that clonal haematopoiesis in the absence of overt haematologic alterations is common amongst the ageing population and associated with mortality and cardiovascular disease. Key findings from experimental studies have provided evidence for a causative role for clonal haematopoiesis in cardiovascular diseases, and aspects of these mechanisms have been elucidated. Whilst our understanding of the impact and biology of clonal haematopoiesis is in its infancy, analyses of some of the most commonly mutated driver genes suggest promising clinical scenarios involving the development of personalized therapies with immunomodulatory drugs that exploit the perturbation caused by the particular mutation. Herein, we review the accumulating epidemiological and experimental evidence, and summarize our current understanding of the importance of clonal haematopoiesis as a new causal risk factor for atherosclerotic cardiovascular disease and heart failure.

Human adipose-derived stromal vascular fraction: characterization, safety and therapeutic potential in an experimental mouse model of articular injury

Due to their capacity to self-renew, proliferate and generate multi-lineage cells, adult-derived stem cells offer great potential in regenerative therapies to treat maladies such as diabetes, cardiac disease, neurological disorders and orthopedic injuries. Commonly derived from adipose tissue, the stromal vascular fraction (SVF), a heterogeneous cell population enriched with mesenchymal stem cells (MSCs), has garnered interest as a cellular therapy due to ease of accessibility as an autologous, point-of-care application. However, the heterogeneous cell population within SVF is not historically taken into consideration when injecting into patients. Here, we characterized SVF, determined its safety and verify its therapeutic effects in a NOD/scid mouse model of articular injury. SVF were isolated from lipoaspirates utilizing a commercially available system (InGeneron Inc.), while MSCs were isolated from SVF via cell culture. Flow cytometry showed that neither age nor BMI affects the frequency of progenitor cells-like (CD31+CD34+), immune cells-like (CD4+) T cells, (CD14+) monocytes and total number of cells obtained. However, there was a negative correlation between donor BMI and MSC frequency within the SVF. ELISAs showed that following LPS activation in SVF, there were low levels of TNF-α and high levels of IL-10 secreted. However, T cell activation with anti-CD3 or anti-CD3+ anti-CD28, while leading to expected high levels of IFN-γ, did not lead to significant levels of TGF-β. PCR analysis showed no significant numbers of cells outside the joint 1-hour post injection, moreover, no engraftment or abnormal growth in other organs 60-days post injection. Finally, both cell populations were able to ameliorate disease progression, as confirmed by the increase in movement of treated groups compared to injured groups. Noteworthy, the histological analysis indicated that there was no cartilage growth, suggesting an alternative therapeutic mechanism to cartilage regeneration.

Clonal Hematopoiesis of Indeterminate Potential Reshapes Age-Related CVD: JACC Review Topic of the Week

The incidence of cardiovascular diseases increases with age and is also correlated with increased inflammatory burden. Recently, human genetics provided a new paradigm linking aging, inflammation, and atherosclerotic cardiovascular disease (ASCVD). Next-generation genetic sequencing of whole blood-derived DNA in humans showed that clonal expansion of hematopoietic cells with somatic mutations in leukemogenic genes was associated with age and correlated with increased mortality. This phenomenon, termed clonal hematopoiesis of indeterminate potential (CHIP), was associated with hematologic malignancy as well as ASCVD independently of age and other traditional risk factors. Because the implication of CHIP with ASCVD, genetic loss-of-function studies of Tet2 and Dnmt3a in murine models have supported a mechanistic role for CHIP in promoting vascular disease. Despite the potential contribution of CHIP to myriad cardiovascular and aging-related diseases, the epidemiology and biology surrounding this phenomenon remains incompletely appreciated and understood, especially as applied to clinical practice and prognostication. Here, the authors review this emerging key risk factor, defining its discovery, relationship to cardiovascular diseases, preclinical evidence for causality, and implications for risk prediction and mitigation.

Cardiovascular Disease, Aging, and Clonal Hematopoiesis

Traditional risk factors are incompletely predictive of cardiovascular disease development, a leading cause of death in the elderly. Recent epidemiological studies have shown that human aging is associated with an increased frequency of somatic mutations in the hematopoietic system, which provide a competitive advantage to a mutant cell, thus allowing for its clonal expansion, a phenomenon known as clonal hematopoiesis. Unexpectedly, these mutations have been associated with a higher incidence of cardiovascular disease, suggesting a previously unrecognized connection between somatic mutations in hematopoietic cells and cardiovascular disease. Here, we provide an up-to-date review of clonal hematopoiesis and its association with aging and cardiovascular disease. We also give a detailed report of the experimental studies that have been instrumental in understanding the relationship between clonal hematopoiesis and cardiovascular disease and have shed light on the mechanisms by which hematopoietic somatic mutations contribute to disease pathology.

A mathematical solution to Peto's paradox using Polya's urn model: implications for the aetiology of cancer in general

Ageing is the leading risk factor for the emergence of cancer in humans. Accumulation of pro-carcinogenic events throughout life is believed to explain this observation; however, the lack of direct correlation between the number of cells in an organism and cancer incidence, known as Peto's Paradox, is at odds with this assumption. Finding the events responsible for this discrepancy can unveil mechanisms with potential uses in prevention and treatment of cancer in humans. On the other hand, the immune system is important in preventing the development of clinically relevant tumours by maintaining a fine equilibrium between reactive and suppressive lymphocyte clones. It is suggested here that the loss of this equilibrium is what ultimately leads to increased risk of cancer and to propose a mechanism for the changes in clonal proportions based on decreased proliferative capacity of lymphocyte clones as a natural phenomenon of ageing. This mechanism, being a function of the number of cells, provides an explanation for Peto's Paradox.

Polyamines Control eIF5A Hypusination, TFEB Translation, and Autophagy to Reverse B Cell Senescence

Failure to make adaptive immune responses is a hallmark of aging. Reduced B cell function leads to poor vaccination efficacy and a high prevalence of infections in the elderly. Here we show that reduced autophagy is a central molecular mechanism underlying immune senescence. Autophagy levels are specifically reduced in mature lymphocytes, leading to compromised memory B cell responses in old individuals. Spermidine, an endogenous polyamine metabolite, induces autophagy in vivo and rejuvenates memory B cell responses. Mechanistically, spermidine post-translationally modifies the translation factor eIF5A, which is essential for the synthesis of the autophagy transcription factor TFEB. Spermidine is depleted in the elderly, leading to reduced TFEB expression and autophagy. Spermidine supplementation restored this pathway and improved the responses of old human B cells. Taken together, our results reveal an unexpected autophagy regulatory mechanism mediated by eIF5A at the translational level, which can be harnessed to reverse immune senescence in humans.

Rejuvenating Strategies of Tissue-specific Stem Cells for Healthy Aging

Although aging is a physiological process, it has raised interest in the science of aging and rejuvenation because of the increasing burden on the rapidly aging global population. With advanced age, there is a decline in homeostatic maintenance and regenerative responsiveness to the injury of various tissues, thereby contributing to the incidence of age-related diseases. The primary cause of the functional declines that occur along with aging is considered to be the exhaustion of stem cell functions in their corresponding tissues. Age-related changes in the systemic environment, the niche, and stem cells contribute to this loss. Thus, the reversal of stem cell aging at the cellular level might lead to the rejuvenation of the animal at an organismic level and the prevention of aging, which would be critical for developing new therapies for age-related dysfunction and diseases. Here, we will explore the effects of aging on stem cells in different tissues. The focus of this discussion is on pro-youth interventions that target intrinsic stem cell properties, environmental niche component, systemic factors, and senescent cellular clearance, which are promising for developing strategies related to the reversal of aged stem cell function and optimizing tissue repair processes.

Hematopoietic Stem Cell Dynamics Are Regulated by Progenitor Demand: Lessons from a Quantitative Modeling Approach

The prevailing view on murine hematopoiesis and on hematopoietic stem cells (HSCs) in particular derives from experiments that are related to regeneration after irradiation and HSC transplantation. However, over the past years, different experimental techniques have been developed to investigate hematopoiesis under homeostatic conditions, thereby providing access to proliferation and differentiation rates of hematopoietic stem and progenitor cells in the unperturbed situation. Moreover, it has become clear that hematopoiesis undergoes distinct changes during aging with large effects on HSC abundance, lineage contribution, asymmetry of division, and self-renewal potential. However, it is currently not fully resolved how stem and progenitor cells interact to respond to varying demands and how this balance is altered by an aging-induced shift in HSC polarity. Aiming toward a conceptual understanding, we introduce a novel in silico model to investigate the dynamics of HSC response to varying demand. By introducing an internal feedback within a heterogeneous HSC population, the model is suited to consistently describe both hematopoietic homeostasis and regeneration, including the limited regulation of HSCs in the homeostatic situation. The model further explains the age-dependent increase in phenotypic HSCs as a consequence of the cells' inability to preserve divisional asymmetry. Our model suggests a dynamically regulated population of intrinsically asymmetrically dividing HSCs as suitable control mechanism that adheres with many qualitative and quantitative findings on hematopoietic recovery after stress and aging. The modeling approach thereby illustrates how a mathematical formalism can support both the conceptual and the quantitative understanding of regulatory principles in HSC biology.

Metabolic underpinnings of leukemia pathology and treatment

BACKGROUND

Carcinogenic transformation of white blood cells during hematopoiesis leads to the development of leukemia, a cancer characterized by incompetent immune cells and a disruption of normal bone marrow function. Leukemias are diverse in type, affected population, prognosis, and treatment regimen, yet a common theme in leukemia is the dysregulated metabolism of leukemic cells and leukemic stem cells with respect to their noncancerous counterparts.

RECENT FINDINGS

In this review, we highlight current findings that elucidate metabolic traits unique to the four major types of leukemia, which confer carcinogenic survival but can be potentially exploited for therapeutic intervention. These metabolic features can work in conjunction with or be independent of unique aspects of the bone marrow microenvironment that can also influence cell survival and proliferation, thus sustaining carcinogenesis.

CONCLUSION

Deepening our understanding of the interactions of leukemias with their niche environments in vivo will inform future treatments for leukemia, particularly for those that are refractive to tyrosine kinase inhibitors and other therapeutic mainstays.

The relationship of mammal survivorship and body mass modeled by metabolic and vitality theories

A model describes the relationship between mammal body mass and survivorship by combining replicative senescence theory postulating a cellular basis of aging, metabolic theory relating metabolism to body mass, and vitality theory relating survival to vitality loss and extrinsic mortality. In the combined framework, intrinsic mortality results from replicative senescence of the hematopoietic stem cells and extrinsic mortality results from environmental challenges. Because the model expresses the intrinsic and extrinsic rates with different powers of body mass, across the spectrum of mammals, survivorship changes from Type I to Type II curve shapes with decreasing body mass. Fitting the model to body mass and maximum lifespan data of 494 nonvolant mammals yields allometric relationships of body mass to the vitality parameters, from which full survivorship profiles were generated from body mass alone. Because maximum lifespan data is predominantly derived from captive populations, the generated survivorship curves were dominated by intrinsic mortality. Comparison of the mass-derived and observed survivorship curves provides insights into how specific populations deviate from the aggregate of populations observed under captivity.

Clonal Hematopoiesis in Aging

Purpose of Review

Clonal hematopoiesis of indeterminate potential (CHIP) is a common, age-associated condition characterized by the acquisition of somatic mutations. This concise review explores our current understanding of the mechanisms that influence the development of clonality with aging and its potential malignant and non-malignant clinical implications.

Recent Findings

Aging of the hematopoietic system results in phenotypic changes that favor clonal dominance. Cell-extrinsic factors provide additional selective pressures that further shape clonal architecture. Even so, small clones with candidate driver mutations appear to be ubiquitous with age and largely benign in the absence of strong selective pressures. Benign clonal expansion may compensate for the loss of regenerative HSC capacity as we age.

Summary

CHIP is a marker of aging that reflects the biologic interplay between HSC aging and cell-extrinsic factors. The clinical significance of CHIP is highly variable and dependent on clinical context. Distinguishing the causal relationships and confounding factors that regulate clonal behavior will be essential to define the mechanistic role of CHIP in aging and potentially mitigate its clinical consequences.

Aging- and Senescence-associated Changes of Mesenchymal Stromal Cells in Myelodysplastic Syndromes

Hematopoietic stem and progenitor cells reside within the bone marrow (BM) microenvironment. By a well-balanced interplay between self-renewal and differentiation, they ensure a lifelong supply of mature blood cells. Physiologically, multiple different cell types contribute to the regulation of stem and progenitor cells in the BM microenvironment by cell-extrinsic and cell-intrinsic mechanisms. During the last decades, mesenchymal stromal cells (MSCs) have been identified as one of the main cellular components of the BM microenvironment holding an indispensable role for normal hematopoiesis. During aging, MSCs diminish their functional and regenerative capacities and in some cases encounter replicative senescence, promoting inflammation and cancer progression. It is now evident that alterations in specific stromal cells that comprise the BM microenvironment can contribute to hematologic malignancies, and there is growing interest regarding the contribution of MSCs to the pathogenesis of myelodysplastic syndromes (MDSs), a clonal hematological disorder, occurring mostly in the elderly, characterized by ineffective hematopoiesis and increased tendency to acute myeloid leukemia evolution. The pathogenesis of MDS has been associated with specific genetic and epigenetic events occurring both in hematopoietic stem cells (HSCs) and in the whole BM microenvironment with an aberrant cross talk between hematopoietic elements and stromal compartment. This review highlights the role of MSCs in MDS showing functional and molecular alterations such as altered cell-cycle regulation with impaired proliferative potential, dysregulated cytokine secretion, and an abnormal gene expression profile. Here, the current knowledge of impaired functional properties of both aged MSCs and MSCs in MDS have been described with a special focus on inflammation and senescence induced changes in the BM microenvironment. Furthermore, a better understanding of aberrant BM microenvironment could improve future potential therapies.

When nature's robots go rogue: exploring protein homeostasis dysfunction and the implications for understanding human aging disease pathologies

INTRODUCTION

Proteins have been historically regarded as 'nature's robots': Molecular machines that are essential to cellular/extracellular physical mechanical properties and catalyze key reactions for cell/system viability. However, these robots are kept in check by other protein-based machinery to preserve proteome integrity and stability. During aging, protein homeostasis is challenged by oxidation, decreased synthesis, and increasingly inefficient mechanisms responsible for repairing or degrading damaged proteins. In addition, disruptions to protein homeostasis are hallmarks of many neurodegenerative diseases and diseases disproportionately affecting the elderly. Areas covered: Here we summarize age- and disease-related changes to the protein machinery responsible for preserving proteostasis and describe how both aging and disease can each exacerbate damage initiated by the other. We focus on alteration of proteostasis as an etiological or phenomenological factor in neurodegenerative diseases such as Alzheimer's, Parkinson's, and Huntington's, along with Down syndrome, ophthalmic pathologies, and cancer. Expert commentary: Understanding the mechanisms of proteostasis and their dysregulation in health and disease will represent an essential breakthrough in the treatment of many (senescence-associated) pathologies. Strides in this field are currently underway and largely attributable to the introduction of high-throughput omics technologies and their combination with novel approaches to explore structural and cross-link biochemistry.

Do human B-lymphocytes avoid aging until 60 years?

Broad changes in human innate and adaptive immunity are associated with advanced age. The age-related alteration of gene expression was reported for both T and B lymphocytes. We analysed the genome-wide expression profiles (n=20) of naive and whole B cell populations from young and early aged healthy donors under 60 years. We revealed large homogeneity of all analysed genome-wide expression profiles but did not identified any significant gene deregulation between young (30-45 years) and early aged healthy donors (50-60 years). We argue that B cells avoid the aging program on molecular level until 60 years of age. Our results demonstrate the potential of hematopoietic stem cells to generate uncompromised lymphocytes in early elderly. These are very encouraging findings for the general health and the immunity maintenance would not need any intervention to naive B cells. Rather, a suitable immune stimulation in healthy body environment warrants further research into aging of older elderly.

Aging promotes neoplastic disease through effects on the tissue microenvironment

A better understanding of the complex relationship between aging and cancer will provide important tools for the prevention and treatment of neoplasia. In these studies, the hypothesis was tested that aging may fuel carcinogenesis via alterations imposed in the tissue microenvironment. Preneoplastic hepatocytes isolated from liver nodules were orthotopically injected into either young or old syngeneic rats and their fate was followed over time using the dipeptidyl-peptidase type IV (DPPIV) system to track donor-derived-cells. At 3 months post-Tx, the mean size of donor-derived clusters was 11±3 cells in young vs. 42±8 in old recipients. At 8 months post-Tx, no visible lesion were detected in any of 21 young recipients, while 17/18 animals transplanted at old age displayed hepatic nodules, including 7 large tumors. All tumors expressed the DPPIV marker enzyme, indicating that they originated from transplanted cells. Expression of senescence-associated β-galactosidase was common in liver of 18-month old animals, while it was a rare finding in young controls. Finally, both mRNA and IL6 protein were found to be increased in the liver of aged rats compared to young controls. These results are interpreted to indicate that the microenvironment of the aged liver promotes the growth of pre-neoplastic hepatocytes.

Understanding the molecular basis of acute myeloid leukemias: where are we now?

Although the treatment modalities for acute myeloid leukemia (AML) have not changed much over the past 40 years, distinct progress has been made in deciphering the basic biology underlying the pathogenesis of this group of hematological disorders. Studies show that AML development is a multicause, multistep and multipathway process. Accordingly, AMLs constitute a heterogeneous group of diseases. The thorough understanding of the molecular basis of AML is paving the way for better therapeutic approaches. Multiple novel drugs are being introduced and new, more efficient and less toxic formulations of conventional therapeutics are becoming available. Here, we review the recent advances in the comprehension of the molecular processes that lead to the onset of AML and its translation into clinical practice.

Pathobiology of the 129:Stat1 -/- mouse model of human age-related ER-positive breast cancer with an immune infiltrate-excluded phenotype

Background

Stat1 gene-targeted knockout mice (129S6/SvEvTac-Stat1^tm1Rds) develop estrogen receptor-positive (ER⁺), luminal-type mammary carcinomas at an advanced age. There is evidence for both host environment as well as tumor cell-intrinsic mechanisms to initiate tumorigenesis in this model. In this report, we summarize details of the systemic and mammary pathology at preneoplastic and tumor-bearing time points. In addition, we investigate tumor progression in the 129:Stat1^−/− host compared with wild-type 129/SvEv, and we describe the immune cell reaction to the tumors.

Methods

Mice housed and treated according to National Institutes of Health guidelines and Institutional Animal Care and Use Committee-approved methods were evaluated by histopathology, and their tissues were subjected to immunohistochemistry with computer-assisted quantitative image analysis. Tumor cell culture and conditioned media from cell culture were used to perform macrophage (RAW264.7) cell migration assays, including the 129:Stat1^−/−-derived SSM2 cells as well as control Met1 and NDL tumor cells and EpH4 normal cells.

Results

Tumorigenesis in 129:Stat1^−/− originates from a population of FoxA1⁺ large oval pale cells that initially appear and accumulate along the mammary ducts in segments or regions of the gland prior to giving rise to mammary intraepithelial neoplasias. Progression to invasive carcinoma is accompanied by a marked local stromal and immune cell response composed predominantly of T cells and macrophages. In conditioned media experiments, cells derived from 129:Stat1^−/− tumors secrete both chemoattractant and chemoinhibitory factors, with greater attraction in the extracellular vesicular fraction and inhibition in the soluble fraction. The result appears to be recruitment of the immune reaction to the periphery of the tumor, with exclusion of immune cell infiltration into the tumor.

Conclusions

129:Stat1^−/− is a unique model for studying the critical origins and risk reduction strategies in age-related ER⁺ breast cancer. In addition, it can be used in preclinical trials of hormonal and targeted therapies as well as immunotherapies.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-017-0892-8) contains supplementary material, which is available to authorized users.

Exploring donor and product factors and their impact on red cell post-transfusion outcomes

The impact of donor characteristics, red cell age, and red cell processing methods on recipient outcomes is an emerging area of research. Knowledge generated from exploring this transfusion continuum has the potential to change the way donors are selected and how donations are processed and stored with important clinical and operational impact. Recently, donor characteristics including age, gender, donation frequency, genetics, and ethnicity have been shown to affect product quality and possibly recipient outcomes. The structural, biochemical and immunological changes that occur with red cell storage appear to not cause harm to blood recipients after 14 randomized clinical trials. However, both in vitro and clinical data are now beginning to question the safety of blood stored for a shorter duration. Whole blood filtration, a method of blood processing, has been linked to inferior recipient outcomes when compared to red cell filtration. Collectively, this emerging body of literature suggests that pre-transfusion parameters impact product quality and recipient outcomes and that no 2 units of red cells are quite the same. This review will summarize both the pre-clinical and clinical studies evaluating these associations.

Immunological aspects of age-related diseases

The proportion of elderly people rises in the developed countries. The increased susceptibility of the elderly to infectious diseases is caused by immune dysfunction, especially T cell functional decline. Age-related hematopoietic stem cells deviate from lymphoid lineage to myeloid lineage. Thymus shrinks early in life, which is followed by the decline of naïve T cells. T-cell receptor repertoire diversity declines by aging, which is caused by cytomegalovirus-driven T cell clonal expansion. Functional decline of B cell induces antibody affinity declines by aging. Many effector functions including phagocytosis of myeloid cells are down regulated by aging. The studies of aging of myeloid cells have some controversial results. Although M1 macrophages have been shown to be replaced by anti-inflammatory (M2) macrophages by advanced age, many human studies showed that pro-inflammatory cytokines are elevated in older human. To solve this discrepancy here we divide age-related pathological changes into two categories. One is an aging of immune cell itself. Second is involvement of immune cells to age-related pathological changes. Cellular senescence and damaged cells in aged tissue recruit pro-inflammatory M1 macrophages, which produce pro-inflammatory cytokines and proceed to age-related diseases. Underlying biochemical and metabolic studies will open nutritional treatment.

Aging-associated inflammation promotes selection for adaptive oncogenic events in B cell progenitors

The incidence of cancer is higher in the elderly; however, many of the underlying mechanisms for this association remain unexplored. Here, we have shown that B cell progenitors in old mice exhibit marked signaling, gene expression, and metabolic defects. Moreover, B cell progenitors that developed from hematopoietic stem cells (HSCs) transferred from young mice into aged animals exhibited similar fitness defects. We further demonstrated that ectopic expression of the oncogenes BCR-ABL, NRAS(V12), or Myc restored B cell progenitor fitness, leading to selection for oncogenically initiated cells and leukemogenesis specifically in the context of an aged hematopoietic system. Aging was associated with increased inflammation in the BM microenvironment, and induction of inflammation in young mice phenocopied aging-associated B lymphopoiesis. Conversely, a reduction of inflammation in aged mice via transgenic expression of α-1-antitrypsin or IL-37 preserved the function of B cell progenitors and prevented NRAS(V12)-mediated oncogenesis. We conclude that chronic inflammatory microenvironments in old age lead to reductions in the fitness of B cell progenitor populations. This reduced progenitor pool fitness engenders selection for cells harboring oncogenic mutations, in part due to their ability to correct aging-associated functional defects. Thus, modulation of inflammation--a common feature of aging--has the potential to limit aging-associated oncogenesis.

The MicroRNA-132 and MicroRNA-212 Cluster Regulates Hematopoietic Stem Cell Maintenance and Survival with Age by Buffering FOXO3 Expression

MicroRNAs are critical post-transcriptional regulators of hematopoietic cell-fate decisions, though little remains known about their role in aging hematopoietic stem cells (HSCs). We found that the microRNA-212/132 cluster (Mirc19) is enriched in HSCs and is upregulated during aging. Both overexpression and deletion of microRNAs in this cluster leads to inappropriate hematopoiesis with age. Enforced expression of miR-132 in the bone marrow of mice led to rapid HSC cycling and depletion. A genetic deletion of Mirc19 in mice resulted in HSCs that had altered cycling, function, and survival in response to growth factor starvation. We found that miR-132 exerted its effect on aging HSCs by targeting the transcription factor FOXO3, a known aging associated gene. Our data demonstrate that Mirc19 plays a role in maintaining balanced hematopoietic output by buffering FOXO3 expression. We have thus identified it as a potential target that might play a role in age-related hematopoietic defects.

The Intricate Interplay between Mechanisms Underlying Aging and Cancer

Age is the major risk factor in the incidence of cancer, a hyperplastic disease associated with aging. Here, we discuss the complex interplay between mechanisms underlying aging and cancer as a reciprocal relationship. This relationship progresses with organismal age, follows the history of cell proliferation and senescence, is driven by common or antagonistic causes underlying aging and cancer in an age-dependent fashion, and is maintained via age-related convergent and divergent mechanisms. We summarize our knowledge of these mechanisms, outline the most important unanswered questions and suggest directions for future research.

Tif1γ regulates the TGF-β1 receptor and promotes physiological aging of hematopoietic stem cells

The hematopoietic system declines with age. Myeloid-biased differentiation and increased incidence of myeloid malignancies feature aging of hematopoietic stem cells (HSCs), but the mechanisms involved remain uncertain. Here, we report that 4-mo-old mice deleted for transcription intermediary factor 1γ (Tif1γ) in HSCs developed an accelerated aging phenotype. To reinforce this result, we also show that Tif1γ is down-regulated in HSCs during aging in 20-mo-old wild-type mice. We established that Tif1γ controls TGF-β1 receptor (Tgfbr1) turnover. Compared with young HSCs, Tif1γ(-/-) and old HSCs are more sensitive to TGF-β signaling. Importantly, we identified two populations of HSCs specifically discriminated by Tgfbr1 expression level and provided evidence of the capture of myeloid-biased (Tgfbr1(hi)) and myeloid-lymphoid-balanced (Tgfbr1(lo)) HSCs. In conclusion, our data provide a new paradigm for Tif1γ in regulating the balance between lymphoid- and myeloid-derived HSCs through TGF-β signaling, leading to HSC aging.

Age-related dysfunction in mechanotransduction impairs differentiation of human mammary epithelial progenitors

Dysfunctional progenitor and luminal cells with acquired basal cell properties accumulate during human mammary epithelial aging for reasons not understood. Multipotent progenitors from women aged <30 years were exposed to a physiologically relevant range of matrix elastic modulus (stiffness). Increased stiffness causes a differentiation bias towards myoepithelial cells while reducing production of luminal cells and progenitor maintenance. Lineage representation in progenitors from women >55 years is unaffected by physiological stiffness changes. Efficient activation of Hippo pathway transducers YAP and TAZ is required for the modulus-dependent myoepithelial/basal bias in younger progenitors. In older progenitors, YAP and TAZ are activated only when stressed with extraphysiologically stiff matrices, which bias differentiation towards luminal-like phenotypes. In vivo YAP is primarily active in myoepithelia of younger breasts, but localization and activity increases in luminal cells with age. Thus, aging phenotypes of mammary epithelia may arise partly because alterations in Hippo pathway activation impair microenvironment-directed differentiation and lineage specificity.

Hematopoietic stem cell aging

Aging is organized in a hierarchy, in which aging of cells results in aged tissues, ultimately limiting lifespan. For organ systems that also in the adult depend on stem cells for tissue homeostasis like the hematopoietic system that forms immune cells, it is believed that aging of the stem cells strongly contributes to aging-associated dysfunction. In this review, we summarize current aspects on cellular and molecular mechanisms that are associated with aging of hematopoietic stem cells, the role of the stem cell niche for stem cell aging as well as novel and encouraging experimental approaches to attenuate aging of hematopoietic stem cells to target immunosenescence.

Changes in the frequencies of human hematopoietic stem and progenitor cells with age and site

This study enumerated CD45(hi)/CD34(+) and CD45(hi)/CD133(+) human hematopoietic stem cells (HSCs) and progenitor granulocyte-macrophage colony forming cells (GM-CFCs) in blood and trochanteric and femoral bone marrow in 233 individuals. Stem cell frequencies were determined with multiparameter flow cytometry and using an internal control to determine the intrinsic variance of the assays. Progenitor cell frequency was determined using a standard colony assay technique. The frequency of outliers from undetermined methodological causes was highest for blood, but less than 5% for all values. The frequency of CD45(hi)/CD133(+) cells correlated highly with the frequency of CD45(hi)/CD34(+) cells in trochanteric and femoral bone marrow. The frequency of these HSC populations in trochanteric and femoral bone marrow rose significantly with age. In contrast, there was no significant trend of either of these cell populations with age in the blood. Trochanteric marrow progenitor GM-CFCs showed no significant trends with age, but femoral marrow GM-CFCs trended downward with age, potentially because of the reported conversion of red marrow at this site to fat with age. Hematopoietic stem and progenitor cells exhibited changes in frequencies with age that differed between blood and bone marrow. We previously reported that side population (SP) multipotential HSC, which includes the precursors of CD45(hi)/CD133(+) and CD45(hi)/CD34(+), decline with age. Potentially the increases in stem cell frequencies in the intermediate compartment between SP and GM progenitor cells observed in this study represent a compensatory increase for the loss of more potent members of the HSC hierarchy.

Rapamycin extends life- and health span because it slows aging

Making headlines, a thought-provocative paper by Neff, Ehninger and coworkers claims that rapamycin extends life span but has limited effects on aging. How is that possibly possible? And what is aging if not an increase of the probability of death with age. I discuss that the JCI paper actually shows that rapamycin slows aging and also extends lifespan regardless of its direct anti-cancer activities. Aging is, in part, MTOR-driven: a purposeless continuation of developmental growth. Rapamycin affects the same processes in young and old animals: young animals' traits and phenotypes, which continuations become hyperfunctional, harmful and lethal later in life.

Klotho deficiency disrupts hematopoietic stem cell development and erythropoiesis

Klotho deficiency is a characteristic feature of chronic kidney disease in which anemia and cardiovascular complications are prevalent. Disruption of the Klotho gene in mice results in hypervitaminosis D and a syndrome resembling accelerated aging that includes osteopenia and vascular calcifications. Given that the bone microenvironment and its cellular components considerably influence hematopoiesis, in the present study, we addressed the in vivo role of klotho in blood cell formation and differentiation. Herein, we report that genetic ablation of Klotho in mice results in a significant increase in erythropoiesis and a decrease in the hematopoietic stem cell pool size in the bone marrow, leading to impaired hematopoietic stem cell homing in vivo. Our data also suggest that high vitamin D levels are only partially responsible for these hematopoietic changes in Klotho(-/-) mice. Importantly, we found similar hematopoietic abnormalities in Klotho(-/-) fetal liver cells, suggesting that the effects of klotho in hematopoietic stem cell development are independent of the bone microenvironment. Finally, injection of klotho protein results in hematopoietic changes opposite to the ones observed in Klotho(-/-) mice. These observations unveil a novel role for the antiaging hormone klotho in the regulation of prenatal and postnatal hematopoiesis and provide new insights for the development of therapeutic strategies targeting klotho to treat hematopoietic disorders associated with aging.

Aged mice are unable to mount an effective myeloid response to sepsis

The elderly have increased morbidity and mortality following sepsis; however, the cause(s) remains unclear. We hypothesized that these poor outcomes are due in part to defects in innate immunity, rather than to an exaggerated early inflammatory response. Young (6-12 wk) or aged (20-24 mo) mice underwent polymicrobial sepsis, and subsequently, the aged mice had increased mortality and defective peritoneal bacterial clearance compared with young mice. No differences were found in the magnitude of the plasma cytokine responses. Although septic aged mice displayed equivalent or increased numbers of circulating, splenic, and bone marrow myeloid cells, some of these cells exhibited decreased phagocytosis, reactive oxygen species production, and chemotaxis. Blood leukocyte gene expression was less altered in aged versus young mice 1 d after sepsis. Aged mice had a relative inability to upregulate gene expression of pathways related to neutrophil-mediated protective immunity, chemokine/chemokine receptor binding, and responses to exogenous molecules. Expression of most MHC genes remained more downregulated in aged mice at day 3. Despite their increased myeloid response to sepsis, the increased susceptibility of aged mice to sepsis appears not to be due to an exaggerated inflammatory response, but rather, a failure to mount an effective innate immune response.

Selective anti-cancer agents as anti-aging drugs

Recent groundbreaking discoveries have revealed that IGF-1, Ras, MEK, AMPK, TSC1/2, FOXO, PI3K, mTOR, S6K, and NFκB are involved in the aging process. This is remarkable because the same signaling molecules, oncoproteins and tumor suppressors, are well-known targets for cancer therapy. Furthermore, anti-cancer drugs aimed at some of these targets have been already developed. This arsenal could be potentially employed for anti-aging interventions (given that similar signaling molecules are involved in both cancer and aging). In cancer, intrinsic and acquired resistance, tumor heterogeneity, adaptation, and genetic instability of cancer cells all hinder cancer-directed therapy. But for anti-aging applications, these hurdles are irrelevant. For example, since anti-aging interventions should be aimed at normal postmitotic cells, no selection for resistance is expected. At low doses, certain agents may decelerate aging and age-related diseases. Importantly, deceleration of aging can in turn postpone cancer, which is an age-related disease.

Immunosuppressants in cancer prevention and therapy

Rapalogs such as rapamycin (sirolimus), everolimus, temserolimus, and deforolimus are indicated for the treatment of some malignancies. Rapamycin is the most effective cancer-preventive agent currently known, at least in mice, dramatically delaying carcinogenesis in both normal and cancer-prone murine strains. In addition, rapamycin and everolimus decrease the risk of cancer in patients receiving these drugs in the context of immunosuppressive regimens. In general, the main concern about the use of immunosuppressants in humans is an increased risk of cancer. Given that rapalogs are useful in cancer prevention and therapy, should they be viewed as immunosuppressants or immunostimulators? Or should we reconsider the role of immunity in cancer altogether? In addition to its anti-viral, anti-inflammatory, anti-angiogenic and anti-proliferative effects, rapamycin operates as a gerosuppressant, meaning that it inhibits the cellular conversion to a senescent state (the so-called geroconversion), a fundamental process involved in aging and age-related pathologies including cancer.

Dysregulation of the mTOR pathway in p53-deficient mice

Mammalian or mechanistic target of rapamycin (mTOR) is involved in growth, aging, and age-related diseases including cancer. There is an extensive cross talk between p53 and mTOR. In cell culture, p53 inhibits the mTOR pathway in a cell type-dependent manner. p53-deficient mice develop pro-inflammation and cancer. We have shown that rapamycin delayed cancer and extended lifespan, thus partially substituting for p53. Here we show that a marker of mTOR activity, phosphorylated S6 (p-S6), is increased in the hearts of p53-deficient mice. Furthermore, cardiac p-S6 correlated with body weight. Also, p53(-/-) mice were slightly hyperinsulinemic with a tendency to elevated IGF-1. Radiation exacerbated the difference between IGF-1 levels in normal and p53(-/-) mice. Noteworthy, radiation induced Thr-308 Akt phosphorylation in the livers (but not in the hearts) of both p53(+/+) and p53(-/-) mice. Simultaneously, radiation decreased p-S6 in the livers of normal mice, consistent with the negative effect of p53 on mTOR. Our data indicate that the activity of mTOR is increased in some but not all tissues of p53(-/-) mice, associated with the tendency to increased insulin and IGF-1 levels. Therefore, the absence of p53 may create oncophilic microenvironment, favoring cancer.

Tissue resident stem cells: till death do us part

Aging is accompanied by reduced regenerative capacity of all tissues and organs and dysfunction of adult stem cells. Notably, these age-related alterations contribute to distinct pathophysiological characteristics depending on the tissue of origin and function and thus require special attention in a type by type manner. In this paper, we review the current understanding of the mechanisms leading to tissue-specific adult stem cell dysfunction and reduced regenerative capacity with age. A comprehensive investigation of the hematopoietic, the neural, the mesenchymal, and the skeletal stem cells in age-related research highlights that distinct mechanisms are associated with the different types of tissue stem cells. The link between age-related stem cell dysfunction and human pathologies is discussed along with the challenges and the future perspectives in stem cell-based therapies in age-related diseases.

Increased ID2 levels in adult precursor B cells as compared with children is associated with impaired Ig locus contraction and decreased bone marrow output

Precursor B cell production from bone marrow in mice and humans declines with age. Because the mechanisms behind are still unknown, we studied five precursor B cell subsets (ProB, PreBI, PreBII large, PreBII small, immature B) and their differentiation-stage characteristic gene expression profiles in healthy individual toddlers and middle-aged adults. Notably, the composition of the precursor B cell compartment did not change with age. The expression levels of several transcripts encoding V(D)J recombination factors were decreased in adults as compared with children: RAG1 expression was significantly reduced in ProB cells, and DNA-PKcs, Ku80, and XRCC4 were decreased in PreBI cells. In contrast, TdT was 3-fold upregulated in immature B cells of adults. Still, N-nucleotides, P-nucleotides, and deletions were similar for IGH and IGK junctions between children and adults. PreBII large cells in adults, but not in children, showed highly upregulated expression of the differentiation inhibitor, inhibitor of DNA binding 2 (ID2), in absence of changes in expression of the ID2-binding partner E2A. Further, we identified impaired Ig locus contraction in adult precursor B cells as a likely mechanism by which ID2-mediated blocking of E2A function results in reduced bone marrow B cell output in adults. The reduced B cell production was not compensated by increased proliferation in adult immature B cells, despite increased Ki67 expression. These findings demonstrate distinct regulatory mechanisms in B cell differentiation between adults and children with a central role for transcriptional regulation of ID2.

The changing balance between osteoblastogenesis and adipogenesis in aging and its impact on hematopoiesis

Osteoblasts (OBs) and adipocytes (APs) share a common mesenchymal ancestor. It is now clear that mesenchymal stem cell (MSC) maturation along the OB lineage comes at the expense of adipogenesis and vice versa. During aging, this balance increasingly favors the formation of APs. Hematopoiesis also slowly declines during the aging process. The role of OB lineage cells in hematopoiesis has been studied, but less is known about how APs regulate hematopoiesis. A few studies have demonstrated a negative relationship between APs and hematopoiesis; however, there is also evidence that brown adipose tissue (BAT) may promote hematopoiesis. This review will examine the current knowledge of how adipogenesis and osteogenesis change with aging and the implications of this changing environment on hematopoeisis.