Clonal hematopoiesis, somatic mosaicism, and age-associated disease

Genetic and environmental risks for clonal hematopoiesis and cancer

Somatic variants accumulate in all organs with age, with a positive selection of clonal populations that provide a fitness advantage during times of heightened cellular stress leading to clonal expansion. Easily measured within the hematopoietic compartment, clonal hematopoiesis (CH) is now recognized as a common process in which hematopoietic clones with somatic variants associated with hematopoietic neoplasms exist within the blood or bone marrow of individuals without evidence of malignancy. Most cases of CH involve a limited number of genes, most commonly DNMT3A, TET2, and ASXL1. CH confers risk for solid and hematopoietic malignancies as well as cardiovascular and numerous inflammatory diseases and offers opportunities for cancer prevention. Here, we explore the genetic and environmental factors that predispose individuals to CH with unique variant signatures and discuss how CH drives cancer progression with the goals of improving individual cancer risk stratification, identifying key intervention opportunities, and understanding how CH impacts therapeutic strategies and outcomes.

TET2 mutation in acute myeloid leukemia: biology, clinical significance, and therapeutic insights

TET2 is a critical gene that regulates DNA methylation, encoding a dioxygenase protein that plays a vital role in the regulation of genomic methylation and other epigenetic modifications, as well as in hematopoiesis. Mutations in TET2 are present in 7%-28% of adult acute myeloid leukemia (AML) patients. Despite this, the precise mechanisms by which TET2 mutations contribute to malignant transformation and how these insights can be leveraged to enhance treatment strategies for AML patients with TET2 mutations remain unclear. In this review, we provide an overview of the functions of TET2, the effects of its mutations, its role in clonal hematopoiesis, and the possible mechanisms of leukemogenesis. Additionally, we explore the mutational landscape across different AML subtypes and present recent promising preclinical research findings.

Increased TP53 somatic evolution in peritoneal washes of individuals with BRCA1 germline mutations

BACKGROUND

Individuals with germline BRCA1 and BRCA2 pathogenic variants (BRCA carriers) are at high risk of developing high grade serous ovarian carcinoma (HGSC). HGSC is predominantly driven by TP53 mutations, but mutations in this gene are also commonly found in non-cancerous tissue as a feature of normal human aging. We hypothesized that HGSC predisposition in BRCA carriers may be related to increased TP53 somatic evolution, which could be detectable by ultra-deep sequencing of TP53 mutations in gynecological liquid biopsies.

METHODS

Duplex sequencing was used to identify TP53 mutations with high sensitivity in peritoneal washes and cervical liquid-based cytology (LBC) collected at surgery from 60 individuals including BRCA1 and BRCA2 carriers, and non-carriers. TP53 mutation pathogenicity was compared across groups and with TP53 cancer mutations.

RESULTS

TP53 mutations were more abundant in cervical LBC than in peritoneal washes but increased with age in both sample types. In peritoneal washes, but not in cervical LBC, pathogenic TP53 mutation burden was increased in BRCA1 carriers compared to non-carriers, independently of age. Five individuals shared identical pathogenic TP53 mutations in peritoneal washes and cervical LBC, but not in blood.

CONCLUSIONS

Ultra-deep sequencing of TP53 mutations in peritoneal washes collected at surgery reveals increased burden of pathogenic TP53 mutations in BRCA1 carriers. This excess of pathogenic TP53 mutations might be linked to the elevated risk of HGSC in these individuals. In some patients, concordant TP53 mutations were found in peritoneal washes and cervical LBCs, but the cell of origin remains unknown and deserves further investigation.

Experimental TET2 Clonal Hematopoiesis Predisposes to Renal Hypertension Through an Inflammasome-Mediated Mechanism

BACKGROUND

Hypertension incidence increases with age and represents one of the most prevalent risk factors for cardiovascular disease. Clonal events in the hematopoietic system resulting from somatic mutations in driver genes are prevalent in elderly individuals who lack overt hematologic disorders. This condition is referred to as age-related clonal hematopoiesis (CH), and it is a newly recognized risk factor for cardiovascular disease. It is not known whether CH and hypertension in the elderly are causally related and, if so, what are the mechanistic features.

METHODS

A murine model of adoptive bone marrow transplantation was employed to examine the interplay between Tet2 (ten-eleven translocation methylcytosine dioxygenase 2) clonal hematopoiesis and hypertension.

RESULTS

In this model, a subpressor dose of Ang II (angiotensin II) resulted in elevated systolic and diastolic blood pressure as early as 1 day after challenge. These conditions led to the expansion of Tet2-deficient proinflammatory monocytes and bone marrow progenitor populations. Tet2 deficiency promoted renal CCL5 (C-C motif ligand 5) chemokine expression and macrophage infiltration into the kidney. Consistent with macrophage involvement, Tet2 deficiency in myeloid cells promoted hypertension when mice were treated with a subpressor dose of Ang II. The hematopoietic Tet2-/- condition led to sodium retention, renal inflammasome activation, and elevated levels of IL (interleukin)-1β and IL-18. Analysis of the sodium transporters indicated NCC (sodium-chloride symporter) and NKCC2 (Na+-K+-Cl- cotransporter 2) activation at residues Thr53 and Ser105, respectively. Administration of the NLRP3 (NLR family pyrin domain containing 3) inflammasome inhibitor MCC950 reversed the hypertensive state, sodium retention, and renal transporter activation.

CONCLUSIONS

Tet2-mediated CH sensitizes mice to a hypertensive stimulus. Mechanistically, the expansion of hematopoietic Tet2-deficient cells promotes hypertension due to elevated renal immune cell infiltration and activation of the NLRP3 inflammasome, with consequences on sodium retention. These data indicate that carriers of TET2 CH could be at elevated risk for the development of hypertension and that immune modulators could be useful in treating hypertension in this patient population.

Hemostasis and complement in allogeneic hematopoietic stem cell transplantation: clinical significance of two interactive systems

Hematopoietic stem cell transplantation (HCT) represents a curative treatment option for certain malignant and nonmalignant hematological diseases. Conditioning regimens before HCT, the development of graft-versus-host disease (GVHD) in the allogeneic setting, and delayed immune reconstitution contribute to early and late complications by inducing tissue damage or humoral alterations. Hemostasis and/or the complement system are biological regulatory defense systems involving humoral and cellular reactions and are variably involved in these complications after allogeneic HCT. The hemostasis and complement systems have multiple interactions, which have been described both under physiological and pathological conditions. They share common tissue targets, such as the endothelium, which suggests interactions in the pathogenesis of several serious complications in the early or late phase after HCT. Complications in which both systems interfere with each other and thus contribute to disease pathogenesis include transplant-associated thrombotic microangiopathy (HSCT-TMA), sinusoidal obstruction syndrome/veno-occlusive disease (SOS/VOD), and GVHD. Here, we review the current knowledge on changes in hemostasis and complement after allogeneic HCT and how these changes may define clinical impact.

The Clinical Spectrum of Mosaic Genetic Disease

Genetic mosaicism is defined as the presence of two or more cell lineages with different genotypes arising from a single zygote. Mosaicism has been implicated in hundreds of genetic diseases with diverse genetic etiologies affecting every organ system. Mosaic genetic disease (MDG) is a spectrum that, on the extreme ends, enables survival from genetic severe disorders that would be lethal in a non-mosaic form. On the milder end of the spectrum, mosaicism can result in little if any phenotypic effects but increases the risk of transmitting a pathogenic genotype. In the middle of the spectrum, mosaicism has been implicated in reducing the phenotypic severity of genetic disease. In this review will describe the spectrum of mosaic genetic disease whilst discussing the status of the detection and prevalence of mosaic genetic disease.

Association Between Clonal Hematopoiesis and Left Ventricular Reverse Remodeling in Nonischemic Dilated Cardiomyopathy

Although clonal hematopoiesis of indeterminate potential (CHIP) is an adverse prognostic factor for atherosclerotic disease, its impact on nonischemic dilated cardiomyopathy (DCM) is elusive. The authors performed whole-exome sequencing and deep target sequencing among 198 patients with DCM and detected germline mutations in cardiomyopathy-related genes and somatic mutations in CHIP driver genes. Twenty-five CHIP driver mutations were detected in 22 patients with DCM. Ninety-two patients had cardiomyopathy-related pathogenic mutations. Multivariable analysis revealed that CHIP was an independent risk factor of left ventricular reverse remodeling, irrespective of known prognostic factors. CHIP exacerbated cardiac systolic dysfunction and fibrosis in a DCM murine model. The identification of germline and somatic mutations in patients with DCM predicts clinical prognosis.

Clonal hematopoiesis and inflammation in the vasculature: CHIVE, a prospective, longitudinal clonal hematopoiesis cohort and biorepository

ABSTRACT

Clonal hematopoiesis (CH) is an age-associated phenomenon leading to an increased risk of both hematologic malignancy and nonmalignant organ dysfunction. Increasingly available genetic testing has made the incidental discovery of CH clinically common yet evidence-based guidelines and effective management strategies to prevent adverse CH health outcomes are lacking. To address this gap, the prospective CHIVE (clonal hematopoiesis and inflammation in the vasculature) registry and biorepository was created to identify and monitor individuals at risk, support multidisciplinary CH clinics, and refine taxonomy and standards of practice for CH risk mitigation. Data from the first 181 patients enrolled in this prospective registry recapitulate the molecular epidemiology of CH from biobank-scale retrospective studies, with DNMT3A, TET2, ASXL1, and TP53 as the most commonly mutated genes. Blood counts across all hematopoietic lineages trended lower in patients with CH. In addition, patients with CH had higher rates of end organ dysfunction, in particular chronic kidney disease. Among patients with CH, variant allele frequency was independently associated with the presence of cytopenias and progression to hematologic malignancy, whereas other common high-risk CH clone features were not clear. Notably, accumulation of multiple distinct high-risk clone features was also associated with cytopenias and hematologic malignancy progression, supporting a recently published CH risk score. Surprisingly, ∼30% of patients enrolled in CHIVE from CH clinics were adjudicated as not having clonal hematopoiesis of indeterminate potential, highlighting the need for molecular standards and purpose-built assays in this field. Maintenance of this well-annotated cohort and continued expansion of CHIVE to multiple institutions are underway and will be critical to understanding how to thoughtfully care for this patient population.

TP53 somatic evolution in cervical liquid-based cytology and blood from individuals with and without ovarian cancer and BRCA1 or BRCA2 germline mutations

Somatic TP53 mutations are prevalent in normal tissue but little is known about their association with cancer risk. Cervical liquid-based cytology (LBC), commonly known as Pap test, provides an accessible gynecological sample to test the value of TP53 somatic mutations as a biomarker for high-grade serous ovarian cancer (HGSC), a cancer type mostly driven by TP53 mutations. We used ultra-deep duplex sequencing to analyze TP53 mutations in LBC and blood samples from 70 individuals (30 with and 40 without HGSC) undergoing gynecologic surgery, 30 carrying BRCA1 or BRCA2 germline pathogenic variants (BRCApv). Only 30% of the tumor mutations were found in LBC samples. However, TP53 pathogenic mutations were identified in nearly all LBC and blood samples, with only 5.4% of mutations in LBC (20/368) also found in the corresponding blood sample. TP53 mutations were more abundant in LBC than in blood and increased with age in both sample types. BRCApv carriers with HGSC had more TP53 clonal expansions in LBC than BRCApv carriers without cancer. Our results show that, while not useful for direct cancer detection, LBC samples capture TP53 mutation burden in the gynecological tract, presenting potential value for cancer risk assessment in individuals at higher hereditary risk for ovarian cancer.

Association of Mosaic Chromosomal Alterations and Genetic Factors with the Risk of Cirrhosis

Background and Aims

Age-related mosaic chromosomal alterations (mCAs) detected from genotyping of blood-derived DNA are structural somatic variants that indicate clonal hematopoiesis. This study aimed to investigate whether mCAs contribute to the risk of cirrhosis and modify the effect of a polygenic risk score (PRS) on cirrhosis risk prediction.

Methods

mCA call sets of individuals with European ancestry were obtained from the UK Biobank. The PRS was constructed based on 12 susceptible single-nucleotide polymorphisms for cirrhosis. Cox proportional hazard models were applied to evaluate the associations between mCAs and cirrhosis risk.

Results

Among 448,645 individuals with a median follow-up of 12.5 years, we identified 2,681 cases of cirrhosis, 1,775 cases of compensated cirrhosis, and 1,706 cases of decompensated cirrhosis. Compared to non-carriers, individuals with copy-neutral loss of heterozygosity mCAs had a significantly increased risk of cirrhosis (hazard ratio (HR) 1.42, 95% confidence interval (CI) 1.12-1.81). This risk was higher in patients with expanded cell fractions of mCAs (cell fractions ≥10% vs. cell fractions <10%), especially for the risk of decompensated cirrhosis (HR 2.03 [95% CI 1.09-3.78] vs. 1.14 [0.80-1.64]). In comparison to non-carriers of mCAs with low genetic risk, individuals with expanded copy-neutral loss of heterozygosity and high genetic risk showed the highest cirrhosis risk (HR 5.39 [95% CI 2.41-12.07]).

Conclusions

The presence of mCAs is associated with increased susceptibility to cirrhosis risk and could be combined with PRS for personalized cirrhosis risk stratification.

James German and the Quest to Understand Human RECQ Helicase Deficiencies

James German's work to establish the natural history and cancer risk associated with Bloom syndrome (BS) has had a strong influence on the generation of scientists and clinicians working to understand other RECQ deficiencies and heritable cancer predisposition syndromes. I summarize work by us and others below, inspired by James German's precedents with BS, to understand and compare BS with the other heritable RECQ deficiency syndromes with a focus on Werner syndrome (WS). What we know, unanswered questions and new opportunities are discussed, as are potential ways to treat or modify WS-associated disease mechanisms and pathways.

Severity of effect considerations regarding the use of mutation as a toxicological endpoint for risk assessment: A report from the 8th International Workshop on Genotoxicity Testing (IWGT)

Exposure levels without appreciable human health risk may be determined by dividing a point of departure on a dose-response curve (e.g., benchmark dose) by a composite adjustment factor (AF). An "effect severity" AF (ESAF) is employed in some regulatory contexts. An ESAF of 10 may be incorporated in the derivation of a health-based guidance value (HBGV) when a "severe" toxicological endpoint, such as teratogenicity, irreversible reproductive effects, neurotoxicity, or cancer was observed in the reference study. Although mutation data have been used historically for hazard identification, this endpoint is suitable for quantitative dose-response modeling and risk assessment. As part of the 8th International Workshops on Genotoxicity Testing, a sub-group of the Quantitative Analysis Work Group (WG) explored how the concept of effect severity could be applied to mutation. To approach this question, the WG reviewed the prevailing regulatory guidance on how an ESAF is incorporated into risk assessments, evaluated current knowledge of associations between germline or somatic mutation and severe disease risk, and mined available data on the fraction of human germline mutations expected to cause severe disease. Based on this review and given that mutations are irreversible and some cause severe human disease, in regulatory settings where an ESAF is used, a majority of the WG recommends applying an ESAF value between 2 and 10 when deriving a HBGV from mutation data. This recommendation may need to be revisited in the future if direct measurement of disease-causing mutations by error-corrected next generation sequencing clarifies selection of ESAF values.

Association Between Rheumatoid Arthritis and Clonal Hematopoiesis: A Mendelian Randomization Study

Immunity activation and inflammation are the main characteristics of rheumatoid arthritis and clonal hematopoiesis. However, it remains unclear whether rheumatoid arthritis increase the risk of clonal hematopoiesis. Here, a Mendelian randomization (MR) analysis was conduct to explore the causal effects of rheumatoid arthritis on clonal hematopoiesis. Summary statistics data of rheumatoid arthritis (13,838 cases and 33,742 controls) and clonal hematopoiesis (10,203 cases and 173,918 controls) derived from a genomewide association study were selected to analyze. We selected inverse-variance weighted, MR-Egger, weighted median, simple mode, and weighted mode to evaluate the causal effect of rheumatoid arthritis on clonal hematopoiesis. The two-sample MR analysis suggested a strong causal relationship between rheumatoid arthritis and clonal hematopoiesis by inverse-variance weighted (OR = 1.002311673, 95% CI [1.000110757, 1.004517433], p = .039706) and weighted median (OR = 1.002311673, 95% CI [1.000110757, 1.004517433], p = .039518447) methods. No significant pleiotropy or heterogeneity was found in the sensitivity analysis. These results supported a potentially causal relationship between rheumatoid arthritis and clonal hematopoiesis, and the exposure of rheumatoid arthritis increased the risks of clonal hematopoiesis. Our findings highlight the importance of how chronic inflammation and immune activation induced rheumatoid arthritis enhances the risks of clonal hematopoiesis, and that early intervention with rheumatoid arthritis patients might reduce the clonal hematopoiesis risks in rheumatoid arthritis patients. Moreover, our study provides clues for prediction of risk factors and potential mechanisms of clonal hematopoiesis.

Cell Tree Rings: the structure of somatic evolution as a human aging timer

Biological age is typically estimated using biomarkers whose states have been observed to correlate with chronological age. A persistent limitation of such aging clocks is that it is difficult to establish how the biomarker states are related to the mechanisms of aging. Somatic mutations could potentially form the basis for a more fundamental aging clock since the mutations are both markers and drivers of aging and have a natural timescale. Cell lineage trees inferred from these mutations reflect the somatic evolutionary process, and thus, it has been conjectured, the aging status of the body. Such a timer has been impractical thus far, however, because detection of somatic variants in single cells presents a significant technological challenge. Here, we show that somatic mutations detected using single-cell RNA sequencing (scRNA-seq) from thousands of cells can be used to construct a cell lineage tree whose structure correlates with chronological age. De novo single-nucleotide variants (SNVs) are detected in human peripheral blood mononuclear cells using a modified protocol. A default model based on penalized multiple regression of chronological age on 31 metrics characterizing the phylogenetic tree gives a Pearson correlation of 0.81 and a median absolute error of ~4 years between predicted and chronological ages. Testing of the model on a public scRNA-seq dataset yields a Pearson correlation of 0.85. In addition, cell tree age predictions are found to be better predictors of certain clinical biomarkers than chronological age alone, for instance glucose, albumin levels, and leukocyte count. The geometry of the cell lineage tree records the structure of somatic evolution in the individual and represents a new modality of aging timer. In addition to providing a numerical estimate of "cell tree age," it unveils a temporal history of the aging process, revealing how clonal structure evolves over life span. Cell Tree Rings complements existing aging clocks and may help reduce the current uncertainty in the assessment of geroprotective trials.

Toward Heart-Healthy and Sustainable Cities: A Policy Statement From the American Heart Association

Nearly 56% of the global population lives in cities, with this number expected to increase to 6.6 billion or >70% of the world's population by 2050. Given that cardiometabolic diseases are the leading causes of morbidity and mortality in people living in urban areas, transforming cities and urban provisioning systems (or urban systems) toward health, equity, and economic productivity can enable the dual attainment of climate and health goals. Seven urban provisioning systems that provide food, energy, mobility-connectivity, housing, green infrastructure, water management, and waste management lie at the core of human health, well-being, and sustainability. These provisioning systems transcend city boundaries (eg, demand for food, water, or energy is met by transboundary supply); thus, transforming the entire system is a larger construct than local urban environments. Poorly designed urban provisioning systems are starkly evident worldwide, resulting in unprecedented exposures to adverse cardiometabolic risk factors, including limited physical activity, lack of access to heart-healthy diets, and reduced access to greenery and beneficial social interactions. Transforming urban systems with a cardiometabolic health-first approach could be accomplished through integrated spatial planning, along with addressing current gaps in key urban provisioning systems. Such an approach will help mitigate undesirable environmental exposures and improve cardiovascular and metabolic health while improving planetary health. The purposes of this American Heart Association policy statement are to present a conceptual framework, summarize the evidence base, and outline policy principles for transforming key urban provisioning systems to heart-health and sustainability outcomes.

Tumor Predisposing Post-Zygotic Chromosomal Alterations in Bladder Cancer-Insights from Histologically Normal Urothelium

Bladder urothelial carcinoma (BLCA) is the 10th most common cancer with a low survival rate and strong male bias. We studied the field cancerization in BLCA using multi-sample- and multi-tissue-per-patient protocol for sensitive detection of autosomal post-zygotic chromosomal alterations and loss of chromosome Y (LOY). We analysed 277 samples of histologically normal urothelium, 145 tumors and 63 blood samples from 52 males and 15 females, using the in-house adapted Mosaic Chromosomal Alterations (MoChA) pipeline. This approach allows identification of the early aberrations in urothelium from BLCA patients. Overall, 45% of patients exhibited at least one alteration in at least one normal urothelium sample. Recurrence analysis resulted in 16 hotspots composed of either gains and copy number neutral loss of heterozygosity (CN-LOH) or deletions and CN-LOH, encompassing well-known and new BLCA cancer driver genes. Conservative assessment of LOY showed 29%, 27% and 18% of LOY-cells in tumors, blood and normal urothelium, respectively. We provide a proof of principle that our approach can characterize the earliest alterations preconditioning normal urothelium to BLCA development. Frequent LOY in blood and urothelium-derived tissues suggest its involvement in BLCA.

Autoimmunity and Autoinflammation: Relapsing Polychondritis and VEXAS Syndrome Challenge

Relapsing polychondritis is a chronic autoimmune inflammatory condition characterized by recurrent episodes of inflammation at the level of cartilaginous structures and tissues rich in proteoglycans. The pathogenesis of the disease is complex and still incompletely elucidated. The data support the important role of a particular genetic predisposition, with HLA-DR4 being considered an allele that confers a major risk of disease occurrence. Environmental factors, mechanical, chemical or infectious, act as triggers in the development of clinical manifestations, causing the degradation of proteins and the release of cryptic cartilage antigens. Both humoral and cellular immunity play essential roles in the occurrence and perpetuation of autoimmunity and inflammation. Autoantibodies anti-type II, IX and XI collagens, anti-matrilin-1 and anti-COMPs (cartilage oligomeric matrix proteins) have been highlighted in increased titers, being correlated with disease activity and considered prognostic factors. Innate immunity cells, neutrophils, monocytes, macrophages, natural killer lymphocytes and eosinophils have been found in the perichondrium and cartilage, together with activated antigen-presenting cells, C3 deposits and immunoglobulins. Also, T cells play a decisive role in the pathogenesis of the disease, with relapsing polychondritis being considered a TH1-mediated condition. Thus, increased secretions of interferon γ, interleukin (IL)-12 and IL-2 have been highlighted. The "inflammatory storm" formed by a complex network of pro-inflammatory cytokines and chemokines actively modulates the recruitment and infiltration of various cells, with cartilage being a source of antigens. Along with RP, VEXAS syndrome, another systemic autoimmune disease with genetic determinism, has an etiopathogenesis that is still incompletely known, and it involves the activation of the innate immune system through different pathways and the appearance of the cytokine storm. The clinical manifestations of VEXAS syndrome include an inflammatory phenotype often similar to that of RP, which raises diagnostic problems. The management of RP and VEXAS syndrome includes common immunosuppressive therapies whose main goal is to control systemic inflammatory manifestations. The objective of this paper is to detail the main etiopathogenetic mechanisms of a rare disease, summarizing the latest data and presenting the distinct features of these mechanisms.

Impact of age and sex on myelopoiesis and inflammation during myocardial infarction

Of all the different risk factors known to cause cardiovascular disease (CVD), age and sex are considered to play a crucial role. Aging follows a continuum from birth to death, and therefore it inevitably acts as a risk for CVD. Along with age, sex differences have also been shown to demonstrate variations in immune system responses to pathological insults. It has been widely perceived that females are protected against myocardial infarction (MI) and the protection is quite apparent in young vs. old women. Acute MI leads to changes in the population of myeloid and lymphoid cells at the injury site with myeloid bias being observed in the initial inflammation and the lymphoid in the late-resolution phases of the pathology. Multiple evidence demonstrates that aging enhances damage to various cellular processes through inflamm-aging, an inflammatory process identified to increase pro-inflammatory markers in circulation and tissues. Following MI, marked changes were observed in different sub-sets of major myeloid cell types viz., neutrophils, monocytes, and macrophages. There is a paucity of information regarding the tissue and site-specific functions of these sub-sets. In this review, we highlight the importance of age and sex as crucial risk factors by discussing their role during MI-induced myelopoiesis while emphasizing the current status of myeloid cell sub-sets. We further put forth the need for designing and executing age and sex interaction studies aimed to determine the appropriate age and sex to develop personalized therapeutic strategies post-MI.

DNMT3A clonal hematopoiesis-driver mutations induce cardiac fibrosis by paracrine activation of fibroblasts

Hematopoietic mutations in epigenetic regulators like DNA methyltransferase 3 alpha (DNMT3A), play a pivotal role in driving clonal hematopoiesis of indeterminate potential (CHIP), and are associated with unfavorable outcomes in patients suffering from heart failure (HF). However, the precise interactions between CHIP-mutated cells and other cardiac cell types remain unknown. Here, we identify fibroblasts as potential partners in interactions with CHIP-mutated monocytes. We used combined transcriptomic data derived from peripheral blood mononuclear cells of HF patients, both with and without CHIP, and cardiac tissue. We demonstrate that inactivation of DNMT3A in macrophages intensifies interactions with cardiac fibroblasts and increases cardiac fibrosis. DNMT3A inactivation amplifies the release of heparin-binding epidermal growth factor-like growth factor, thereby facilitating activation of cardiac fibroblasts. These findings identify a potential pathway of DNMT3A CHIP-driver mutations to the initiation and progression of HF and may also provide a compelling basis for the development of innovative anti-fibrotic strategies.

Regulators of clonal hematopoiesis and physiological consequences of this condition

Clonal hematopoiesis (CH) is a prevalent condition that results from somatic mutations in hematopoietic stem cells. When these mutations occur in "driver" genes, they can potentially confer fitness advantages to the affected cells, leading to a clonal expansion. While most clonal expansions of mutant cells are generally considered to be asymptomatic since they do not impact overall blood cell numbers, CH carriers face long-term risks of all-cause mortality and age-associated diseases, including cardiovascular disease and hematological malignancies. While considerable research has focused on understanding the association between CH and these diseases, less attention has been given to exploring the regulatory factors that contribute to the expansion of the driver gene clone. This review focuses on the association between environmental stressors and inherited genetic risk factors in the context of CH development. A better understanding of how these stressors impact CH development will facilitate mechanistic studies and potentially lead to new therapeutic avenues to treat individuals with this condition.

Clonal Hematopoiesis in Clinical and Experimental Heart Failure With Preserved Ejection Fraction

BACKGROUND

Clonal hematopoiesis (CH), which results from an array of nonmalignant driver gene mutations, can lead to altered immune cell function and chronic disease, and has been associated with worse outcomes in patients with heart failure (HF) with reduced ejection fraction. However, the role of CH in the prognosis of HF with preserved ejection fraction (HFpEF) has been understudied. This study aimed to characterize CH in patients with HFpEF and elucidate its causal role in a murine model.

METHODS

Using a panel of 20 candidate CH driver genes and a variant allele fraction cutoff of 0.5%, ultradeep error-corrected sequencing identified CH in a cohort of 81 patients with HFpEF (mean age, 71±6 years; ejection fraction, 63±5%) and 36 controls without a diagnosis of HFpEF (mean age, 74±7 years; ejection fraction, 61.5±8%). CH was also evaluated in a replication cohort of 59 individuals with HFpEF.

RESULTS

Compared with controls, there was an enrichment of TET2-mediated CH in the HFpEF patient cohort (12% versus 0%, respectively; P=0.02). In the HFpEF cohort, patients with CH exhibited exacerbated diastolic dysfunction in terms of E/e' (14.9 versus 11.7, respectively; P=0.0096) and E/A (1.69 versus 0.89, respectively; P=0.0206) compared with those without CH. The association of CH with exacerbated diastolic dysfunction was corroborated in a validation cohort of individuals with HFpEF. In accordance, patients with HFpEF, an age ≥70 years, and CH exhibited worse prognosis in terms of 5-year cardiovascular-related hospitalization rate (hazard ratio, 5.06; P=0.042) compared with patients with HFpEF and an age ≥70 years without CH. To investigate the causal role of CH in HFpEF, nonconditioned mice underwent adoptive transfer with Tet2-wild-type or Tet2-deficient bone marrow and were subsequently subjected to a high-fat diet/L-NAME (Nω-nitro-l-arginine methyl ester) combination treatment to induce features of HFpEF. This model of Tet2-CH exacerbated cardiac hypertrophy by heart weight/tibia length and cardiomyocyte size, diastolic dysfunction by E/e' and left ventricular end-diastolic pressure, and cardiac fibrosis compared with the Tet2-wild-type condition.

CONCLUSIONS

CH is associated with worse heart function and prognosis in patients with HFpEF, and a murine experimental model of Tet2-mediated CH displays greater features of HFpEF.

Clones of aging: When better fitness can be dangerous

The biological and clinical significance of aberrant clonal expansions in aged tissues is being intensely discussed. Evidence is accruing that these clones often result from the normal dynamics of cell turnover in our tissues. The aged tissue microenvironment is prone to favour the emergence of specific clones with higher fitness partly because of an overall decline in cell intrinsic regenerative potential of surrounding counterparts. Thus, expanding clones in aged tissues need not to be mechanistically associated with the development of cancer, albeit this is a possibility. We suggest that growth pattern is a critical phenotypic attribute that impacts on the fate of such clonal proliferations. The acquisition of a better proliferative fitness, coupled with a defect in tissue pattern formation, could represent a dangerous mix setting the stage for their evolution towards neoplasia.

VEXAS syndrome: Current clinical, diagnostic and treatment approaches

VEXAS syndrome, is a hemato-inflammatory chronic disease characterized with predominantly rheumatic and hematologic systemic involvement. It was first described in 2020 by a group of researchers in the United States. VEXAS syndrome is a rare condition that primarily affects adult males and is caused by a mutation in the UBA1 gene located on the X chromosome. Its pathogenesis is related to the somatic mutation affecting methionine-41 (p.Met41) in UBA1, the major E1 enzyme that initiates ubiquitylation. Mutant gene lead to decreased ubiquitination and activated innate immune pathways and systemic inflammation occur. The specific mechanism by which the UBA1 mutation leads to the clinical features of VEXAS syndrome is not yet fully understood. VEXAS is a newly define adult-onset inflammatory syndrome manifested with treatment-refractory fevers, arthritis, chondritis, vasculitis, cytopenias, typical vacuoles in hematopetic precursor cells, neutrophilic cutaneous and pulmonary inflammation. Diagnosing VEXAS syndrome can be challenging due to its rarity and the overlap of symptoms with other inflammatory conditions. Genetic testing to identify the UBA1 gene mutation is essential for definitive diagnosis. Currently, there is no known cure for VEXAS syndrome, and treatment mainly focuses on managing the symptoms. This may involve the use of anti-inflammatory medications, immunosuppressive drugs, and supportive therapies tailored to the individual patient's needs. Due to the recent discovery of VEXAS syndrome, ongoing research is being conducted to better understand its pathogenesis, clinical features, and potential treatment options. In this review article, the clinical, diagnostic and treatment approaches of VEXAS syndrome were evaluated in the light of the latest literature data.

Unraveling Heterogeneity in the Aging Hematopoietic Stem Cell Compartment: An Insight From Single-cell Approaches

Specific cell types and, therefore, organs respond differently during aging. This is also true for the hematopoietic system, where it has been demonstrated that hematopoietic stem cells alter a variety of features, such as their metabolism, and accumulate DNA damage, which can lead to clonal outgrowth over time. In addition, profound changes in the bone marrow microenvironment upon aging lead to senescence in certain cell types such as mesenchymal stem cells and result in increased inflammation. This heterogeneity makes it difficult to pinpoint the molecular drivers of organismal aging gained from bulk approaches, such as RNA sequencing. A better understanding of the heterogeneity underlying the aging process in the hematopoietic compartment is, therefore, needed. With the advances of single-cell technologies in recent years, it is now possible to address fundamental questions of aging. In this review, we discuss how single-cell approaches can and indeed are already being used to understand changes observed during aging in the hematopoietic compartment. We will touch on established and novel methods for flow cytometric detection, single-cell culture approaches, and single-cell omics.

Inflammasomes and Atherosclerosis: a Mixed Picture

The CANTOS (Canakinumab Anti-inflammatory Thrombosis Outcome Study) and colchicine trials suggest an important role of inflammasomes and their major product IL-1β (interleukin 1β) in human atherosclerotic cardiovascular disease. Moreover, studies in mouse models indicate a causal role of inflammasomes and IL-1β in atherosclerosis. However, recent studies have led to a more granular view of the role of inflammasomes in atherosclerosis. Studies in hyperlipidemic mouse models suggest that prominent activation of the NLRP3 inflammasome requires a second hit such as defective cholesterol efflux, defective DNA repair, clonal hematopoiesis or diabetes. Similarly in humans some mutations promoting clonal hematopoiesis increase coronary artery disease risk in part by promoting inflammasome activation. Recent studies in mice and humans point to a wider role of the AIM2 (absent in melanoma 2) inflammasome in promoting cardiovascular disease including in some forms of clonal hematopoiesis and diabetes. These developments suggest a precision medicine approach in which treatments targeting inflammasomes or IL-1β might be best employed in clinical settings involving increased inflammasome activation.

Clonal hematopoiesis: the nonhereditary genetics of age-associated cardiovascular disease

PURPOSE OF REVIEW

Somatic mutations, described as noninherited changes in DNA that arise and are passed on to descendant cells, are well known to cause cancers; however, it is increasingly appreciated that the propagation of somatic mutations within a tissue may have a role in causing nonneoplastic disorders and abnormalities in elderly individuals. The nonmalignant clonal expansion of somatic mutations in the hematopoietic system is termed clonal hematopoiesis. This review will briefly discuss how this condition has been linked to various age-related diseases outside the hematopoietic system.

RECENT FINDINGS

Clonal hematopoiesis, resulting from leukemic driver gene mutations or mosaic loss of the Y chromosome in leukocytes, is associated with the development of various forms of cardiovascular disease, including atherosclerosis and heart failure, in a mutation-dependent manner.

SUMMARY

Accumulating evidence shows that clonal hematopoiesis represents a new mechanism for cardiovascular disease and a new risk factor that is as prevalent and consequential as the traditional risk factors that have been studied for decades.

Single-cell multi-scale footprinting reveals the modular organization of DNA regulatory elements

Cis-regulatory elements control gene expression and are dynamic in their structure, reflecting changes to the composition of diverse effector proteins over time1-3. Here we sought to connect the structural changes at cis-regulatory elements to alterations in cellular fate and function. To do this we developed PRINT, a computational method that uses deep learning to correct sequence bias in chromatin accessibility data and identifies multi-scale footprints of DNA-protein interactions. We find that multi-scale footprints enable more accurate inference of TF and nucleosome binding. Using PRINT with single-cell multi-omics, we discover wide-spread changes to the structure and function of candidate cis-regulatory elements (cCREs) across hematopoiesis, wherein nucleosomes slide, expose DNA for TF binding, and promote gene expression. Activity segmentation using the co-variance across cell states identifies "sub-cCREs" as modular cCRE subunits of regulatory DNA. We apply this single-cell and PRINT approach to characterize the age-associated alterations to cCREs within hematopoietic stem cells (HSCs). Remarkably, we find a spectrum of aging alterations among HSCs corresponding to a global gain of sub-cCRE activity while preserving cCRE accessibility. Collectively, we reveal the functional importance of cCRE structure across cell states, highlighting changes to gene regulation at single-cell and single-base-pair resolution.

Hematopoietic Stem Cells and the Immune System in Development and Aging

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

Clonal Hematopoiesis: Connecting Aging and Inflammation in Atherosclerosis

PURPOSE OF REVIEW

Clonal hematopoiesis (CH) is a prevalent condition that results from the acquisition of somatic mutations in hematopoietic stem cells. When these mutations occur in "driver" genes, they can potentially confer fitness advantages to the cell, leading to a clonal expansion. While most clonal expansions of mutant cells are generally considered to be asymptomatic since they do not impact overall blood cell numbers, CH carriers display long-term risks of all-cause mortality and age-associated diseases including cardiovascular disease (CVD). This review summarizes recent findings in CH related to aging, atherosclerotic CVD, and inflammation, emphasizing epidemiological and mechanistic studies, and potential therapeutic options to treat CVDs that are promoted by CH.

RECENT FINDINGS

Epidemiological studies have revealed associations between CH and CVDs. Experimental studies with CH models employing the Tet2- and Jak2-mutant mouse lines display inflammasome activation and a chronic inflammatory state that leads to accelerated atherosclerotic lesion growth. A body of evidence suggests that CH represents a new causal risk factor for CVD. Studies also indicate that understanding an individual's CH status could provide guidance for personalized approaches to treat atherosclerosis and other CVDs with anti-inflammatory drugs.