Dnmt3a-mutated clonal hematopoiesis promotes osteoporosis

Tissue-specific roles of de novo DNA methyltransferases

DNA methylation, catalyzed by DNA methyltransferases (DNMT), plays pivotal role in regulating embryonic development, gene expression, adaption to environmental stress, and maintaining genome integrity. DNMT family consists of DNMT1, DNMT3A, DNMT3B, and the enzymatically inactive DNMT3L. DNMT3A and DNMT3B establish novel methylation patterns maintained by DNMT1 during replication. Genetic variants of DNMT3A and DNMT3B cause rare diseases such as Tatton-Brown-Rahman and ICF syndromes. Additionally, somatic mutations cause common conditions such as osteoarthritis, osteoporosis, clonal hematopoiesis of indeterminate potential (CHIP), hematologic malignancies, and cancer. While DNMTs have been extensively studied in vitro, in early development and in disease, their detailed physiologic roles remain less understood as in vivo investigations are hindered by the embryonic or perinatal lethality of the knockout mice. To circumvent this problem, tissue-specific Dnmt3a and Dnmt3b knockouts were engineered. This review explores their diverse molecular roles across various organs and cell types and characterizes the phenotype of the knockout mice. We provide a comprehensive collection of over forty tissue-specific knockout models generated by cre recombinase. We highlight the distinct functions of DNMT3A and DNMT3B in germ cells, early development, uterus, hematopoietic differentiation, musculoskeletal development, visceral organs, and nervous system. Our findings indicate that DNMT3A primarily regulates hematopoietic differentiation, while DNMT3B is crucial for cartilage homeostasis and ossification. We emphasize the context-dependent roles of DNMT3A and DNMT3B and demonstrate that they also complement DNMT1 maintenance methyltransferase activity. Overall, the expression patterns of DNMTs across tissues provide insights into potential therapeutic applications for treating neurologic diseases, cancer, and osteoporosis.

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.

Clinical Challenges of Emerging Acquired Autoinflammatory Diseases, Including VEXAS Syndrome

Vacuoles, E1-ubiquitin-activating enzyme, X-linked, autoinflammatory, somatic (VEXAS) syndrome, caused by an acquired mutation in the ubiquitin-activating enzyme ubiquitin-like modifier activating enzyme 1 (UBA1), was discovered in 2020. Since then, many cases have been reported worldwide. Recently, we performed UBA1 genetic testing in suspected cases of VEXAS throughout Japan and investigated the clinical features of these cases. Most cases were elderly patients in their 70s with clinical features consistent with VEXAS syndrome, such as myelodysplastic syndrome, high-grade fever, skin rash, chondritis, and pulmonary infiltration. However, approximately half of the analyzed patients were negative for the UBA1 variant. As the concept of "acquired autoinflammatory diseases," including VEXAS syndrome, has gained popularity, the number of suspected cases is expected to increase. Currently, there are no established diagnostic or treatment guidelines for these conditions, and they need to be urgently developed. This review summarizes the clinical problems faced by patients with acquired autoinflammatory diseases, including VEXAS.

Role of RANKL Signaling in Bone Homeostasis

RANKL and its cognate receptor RANK are crucial regulators of bone metabolism in physiological as well as in pathological conditions. Here we go through the works that unveiled the paramount role of this signaling pathway. We focus on the RANKL cytokine, whose alterations are responsible for rare and common bone diseases. We describe recent insights on the regulation of RANKL expression, which provide new hints for the pharmacological regulation of this molecule. Based on the multiple functions exerted by RANKL (within and outside the bone tissue), we advise caution regarding the potential unintended consequences of its inhibition.

Tet2-mediated clonal hematopoiesis modestly improves neurological deficits and is associated with inflammation resolution in the subacute phase of experimental stroke

Introduction

Recent work has revealed that clonal hematopoiesis (CH) is associated with a higher risk of numerous age-related diseases, including ischemic stroke, however little is known about whether it influences stroke outcome independent of its widespread effects on cardiovascular disease. Studies suggest that leukocytes carrying CH driver mutations have an enhanced inflammatory profile, which could conceivably exacerbate brain injury after a stroke.

Methods

Using a competitive bone marrow transplant model of Tet2-mediated CH, we tested the hypothesis that CH would lead to a poorer outcome after ischemic stroke by augmenting brain inflammation. Stroke was induced in mice by middle cerebral artery occlusion and neurological outcome was assessed at acute (24 h) and subacute (14 d) timepoints. Brains were collected at both time points for histological, immunofluorescence and gene expression assays.

Results

Unexpectedly, Tet2-mediated CH had no effect on acute stroke outcome but led to a reduction in neurological deficits during the subacute phase. This improved neurological outcome was associated with lower levels of brain inflammation as evidenced by lower transcript levels of various inflammatory molecules alongside reduced astrogliosis.

Discussion

These findings suggest that Tet2-mediated CH may have beneficial effects on outcome after stroke, contrasting with the conventional understanding of CH whereby leukocytes with driver mutations promote disease by exacerbating inflammation.

Clonal hematopoiesis of indeterminate potential (CHIP): A potential contributor to lymphoma

Clonal hematopoiesis (CH) typically refers to the clonal expansion of hematopoietic stem cells (HSCs) due to genetic mutations, serving as the pathogenic basis for various diseases. Clonal hematopoiesis of indeterminate potential (CHIP) is a subtype of CH, emerging as a significant risk factor for myeloid malignancies and cardiovascular diseases, which has attracted increasing attention. However, recent research has unveiled previously overlooked links between CHIP and lymphoma. This paper reviews the relationship between CHIP and lymphoma, focusing on the role and mechanism of TET2 and DNMT3A-mediated CHIP in lymphoma from the perspective of laboratory research and clinical observation. Additionally, we explore the therapeutic implications of targeting CHIP genes and inflammatory pathways in lymphoma. Our findings underscore the multifaceted influence of CHIP on lymphoma development and provide a promising avenue for therapeutic interventions in CHIP mediated lymphoma.

Inflammatory Mesenchymal Stromal Cells and IFN-responsive T cells are key mediators of human bone marrow niche remodeling in CHIP and MDS

Somatic mutations in hematopoietic stem/progenitor cells (HSPCs) can lead to clonal hematopoiesis of indeterminate potential (CHIP), potentially progressing to myelodysplastic syndromes (MDS). Here, we investigated how CHIP and MDS remodel the human bone marrow (BM) niche relative to healthy elderly donors, using single cell and anatomical analyses in a large BM cohort. We found distinct inflammatory remodeling of the BM in CHIP and MDS. Furthermore, the stromal compartment progressively lost its HSPC-supportive adipogenic CXCL12-abundant reticular cells while an inflammatory mesenchymal stroma cell (iMSCs) population emerged in CHIP, which expanded in MDS. iMSCs exhibited distinct functional signatures in CHIP and MDS, retaining residual HSPC-support and angiogenic activity in MDS, corresponding with an increase in microvasculature in the MDS niche. Additionally, an IFN-responsive T cell population was linked to fueling inflammation in the stroma. Overall, these findings open new avenues for early intervention in hematological malignancies.

Human Plasma Proteomic Profile of Clonal Hematopoiesis

Plasma proteomic profiles associated with subclinical somatic mutations in blood cells may offer novel insights into downstream clinical consequences. Here, we explore such patterns in clonal hematopoiesis of indeterminate potential (CHIP), which is linked to several cancer and non-cancer outcomes, including coronary artery disease (CAD). Among 61,833 ancestrally diverse participants (3,881 with CHIP) from NHLBI TOPMed and UK Biobank with blood-based DNA sequencing and proteomic measurements (1,148 proteins by SomaScan in TOPMed and 2,917 proteins by Olink in UK Biobank), we identified 32 and 345 unique proteins from TOPMed and UK Biobank, respectively, associated with the most prevalent driver genes ( DNMT3A , TET2 , and ASXL1 ). These associations showed substantial heterogeneity by driver genes, sex, and race, and were enriched for immune response and inflammation pathways. Mendelian randomization in humans, coupled with ELISA in hematopoietic Tet2 -/- vs wild-type mice validation, disentangled causal proteomic perturbations from TET2 CHIP. Lastly, we identified plasma proteins shared between CHIP and CAD.

Hematopoietic aging promotes cancer by fueling IL-1⍺-driven emergency myelopoiesis

Age is a major risk factor for cancer, but how aging impacts tumor control remains unclear. In this study, we establish that aging of the immune system, regardless of the age of the stroma and tumor, drives lung cancer progression. Hematopoietic aging enhances emergency myelopoiesis, resulting in the local accumulation of myeloid progenitor-like cells in lung tumors. These cells are a major source of interleukin (IL)-1⍺, which drives the enhanced myeloid response. The age-associated decline of DNA methyltransferase 3A enhances IL-1⍺ production, and disrupting IL-1 receptor 1 signaling early during tumor development normalized myelopoiesis and slowed the growth of lung, colonic, and pancreatic tumors. In human tumors, we identified an enrichment for IL-1⍺-expressing monocyte-derived macrophages linked to age, poorer survival, and recurrence, unraveling how aging promotes cancer and offering actionable therapeutic strategies.

The emerging role of clonal haematopoiesis in the pathogenesis of dilated cardiomyopathy

The increased sensitivity of novel DNA sequencing techniques has made it possible to identify somatic mutations in small circulating clones of haematopoietic stem cells. When the mutation affects a 'driver' gene, the mutant clone gains a competitive advantage and has the potential to expand over time, a phenomenon referred to as clonal haematopoiesis (CH), which is emerging as a new risk factor for various non-haematological conditions, most notably cardiovascular disease (e.g. heart failure). Dilated cardiomyopathy (DCM) is a form of non-ischaemic heart failure that is characterized by a heterogeneous aetiology. The first evidence is arising that CH plays an important role in the disease course in patients with DCM, and a strong association of CH with multiple aetiologies of DCM has been described (e.g. inflammation, chemotherapy, and atrial fibrillation). The myocardial inflammation induced by CH may be an important trigger for DCM development for an already susceptible heart, e.g. in the presence of genetic variants, environmental triggers, and comorbidities. Studies investigating the role of CH in the pathogenesis of DCM are expected to increase rapidly. To move the field forward, it will be important to report the methodology and results in a standardized manner, so results can be combined and compared. The accurate measurement of CH in patients with DCM can provide guidance of specific (anti-inflammatory) therapies, as mutations in the CH driver genes prime the inflammasome pathway.

Targetable treatment resistance in thyroid cancer with clonal hematopoiesis

Anaplastic thyroid cancer (ATC) is a clinically aggressive malignancy with a dismal prognosis. Combined BRAF/MEK inhibition offers significant therapeutic benefit in patients with BRAF V600E -mutant ATCs. However, relapses are common and overall survival remains poor. Compared with differentiated thyroid cancer, a hallmark of ATCs is significant infiltration with myeloid cells, particularly macrophages. ATCs are most common in the aging population, which also has an increased incidence of TET2 -mutant clonal hematopoiesis (CH). CH-mutant macrophages have been shown to accelerate CH-associated pathophysiology including atherosclerosis. However, the clinical and mechanistic contribution of CH-mutant clones to solid tumour biology, prognosis and therapeutic response has not been elucidated. Here we show that TET2 -mutant CH is enriched in the tumour microenvironment of patients with solid tumours and associated with adverse prognosis in ATC patients. We find that Tet2 -mutant macrophages selectively infiltrate mouse Braf V600E -mutant ATC and that their overexpression of Tgfβ-family ligands mediates resistance to BRAF/MEK inhibition. Importantly, inhibition of Tgfβ signaling restores sensitivity to MAPK pathway inhibition, opening a path for synergistic strategies to improve outcomes of patients with ATCs and concurrent CH.

Distinct landscape and clinical implications of therapy-related clonal hematopoiesis

Therapy-related clonal hematopoiesis (t-CH) is defined as clonal hematopoiesis detected in individuals previously treated with chemotherapy and/or radiation therapy. With the increased use of genetic analysis in oncological care, the detection of t-CH among cancer patients is becoming increasingly common. t-CH arises through the selective bottleneck imposed by chemotherapies and potentially through direct mutagenesis from chemotherapies, resulting in a distinct mutational landscape enriched with mutations in DNA damage-response pathway genes such as TP53, PPM1D, and CHEK2. Emerging evidence sheds light on the mechanisms of t-CH development and potential strategies to mitigate its emergence. Due to its unique characteristics that predominantly affect cancer patients, t-CH has clinical implications distinct from those of CH in the general population. This Review discusses the potential mechanisms of t-CH development, its mutational landscape, mutant-drug relationships, and its clinical significance. We highlight the distinct nature of t-CH and call for intensified research in this field.

Unidirectional association of clonal hematopoiesis with atherosclerosis development

Clonal hematopoiesis, a condition in which acquired somatic mutations in hematopoietic stem cells lead to the outgrowth of a mutant hematopoietic clone, is associated with a higher risk of hematological cancer and a growing list of nonhematological disorders, most notably atherosclerosis and associated cardiovascular disease. However, whether accelerated atherosclerosis is a cause or a consequence of clonal hematopoiesis remains a matter of debate. Some studies support a direct contribution of certain clonal hematopoiesis-related mutations to atherosclerosis via exacerbation of inflammatory responses, whereas others suggest that clonal hematopoiesis is a symptom rather than a cause of atherosclerosis, as atherosclerosis or related traits may accelerate the expansion of mutant hematopoietic clones. Here we combine high-sensitivity DNA sequencing in blood and noninvasive vascular imaging to investigate the interplay between clonal hematopoiesis and atherosclerosis in a longitudinal cohort of healthy middle-aged individuals. We found that the presence of a clonal hematopoiesis-related mutation confers an increased risk of developing de novo femoral atherosclerosis over a 6-year period, whereas neither the presence nor the extent of atherosclerosis affects mutant cell expansion during this timeframe. These findings indicate that clonal hematopoiesis unidirectionally promotes atherosclerosis, which should help translate the growing understanding of this condition into strategies for the prevention of atherosclerotic cardiovascular disease in individuals exhibiting clonal hematopoiesis.

Genetic and epigenetic regulation of inflammasomes: Role in atherosclerosis

The cardiovascular complications of atherosclerosis are thought to arise from an inflammatory response to the accumulation of cholesterol-rich lipoproteins in the arterial wall. The positive outcome of CANTOS (Canakinumab Anti-inflammatory Thrombosis Outcome Study) provided key evidence to support this concept and suggested that inflammasomes and IL-1β are important inflammatory mediators in human atherosclerotic cardiovascular diseases (ACVD). In specific settings NLRP3 or AIM2 inflammasomes can induce inflammatory responses in the arterial wall and promote the formation of unstable atherosclerotic plaques. Clonal hematopoiesis (CH) has recently emerged as a major independent risk factor for ACVD. CH mutations arise during ageing and commonly involves variants in genes mediating epigenetic modifications (TET2, DNMT3A, ASXL1) or cytokine signaling (JAK2). Accumulating evidence points to the role of inflammasomes in the progression of CH-induced ACVD events and has shed light on the regulatory pathways and possible therapeutic approaches that specifically target inflammasomes in atherosclerosis. Epigenetic dynamics play a vital role in regulating the generation and activation of inflammasome components by causing changes in DNA methylation patterns and chromatin assembly. This review examines the genetic and epigenetic regulation of inflammasomes, the intersection of macrophage cholesterol accumulation with inflammasome activation and their roles in atherosclerosis. Understanding the involvement of inflammasomes in atherosclerosis pathogenesis may lead to customized treatments that reduce the burden of ACVD.

Osteoclast-derived exosomes influence osteoblast differentiation in osteoporosis progression via the lncRNA AW011738/ miR-24-2-5p/ TREM1 axis

AIMS

To investigate the molecular mechanism of osteoclast-derived exosomes in osteoporosis.

MAIN METHODS

RANKL induced osteoclast model was screened for significantly differentially expressed lncRNAs and mRNAs by whole RNA sequencing. Exosomes were characterized using electron microscopy, western blotting and nanosight. Overexpression or knockdown of AW011738 was performed to explore its function. The degree of osteoporosis in an osteoporosis model was assessed by mirco-CT. The osteoclast model, osteoblast differentiation ability and the molecular mechanism of lncRNA AW011738/miR-24-2-5p/TREM1 axis in osteoporosis were assessed by dual luciferase reporter gene assay, Western blotting (WB), immunofluorescence and ALP staining. Bioinformatics was used to predict interactions of key osteoporosis-related genes with miRNAs, transcription factors, and potential drugs after upregulation of AW011738. To predict the protein-protein interaction (PPI) network associated with key genes, GO and KEGG analyses were performed on the key genes. The ssGSVA was used to predict changes in the immune microenvironment.

KEY FINDINGS

Osteoclast-derived exosomes containing lncRNA AW011738 decreased the osteogenesis-related markers and accelerated bone loss in OVX mice. Osteoclast (si-AW011738)-derived exosomes showed a significant increase in biomarkers of osteoblast differentiation in vitro compared to the si-NC group. As analyzed by mirco-CT, tail vein injected si-AW011738 OVX mice were less osteoporotic than the control group. AW011738 inhibited osteoblast differentiation by regulating TREM1 expression through microRNA. Meanwhile, overexpression of miR-24-2-5p inhibited TREM1 expression to promote osteoblast differentiation.

SIGNIFICANCE

Osteoclast-derived exosomes containing lncRNA AW011738 inhibit osteogenesis in MC3T3-E1 cells through the lncRNA AW011738/miR-24-2-5p/TREM1 axis and exacerbate osteoporosis in OVX mice.

Clinical and Therapeutic Implications of Clonal Hematopoiesis

Clonal hematopoiesis (CH) is an age-related process whereby hematopoietic stem and progenitor cells (HSPCs) acquire mutations that lead to a proliferative advantage and clonal expansion. The most commonly mutated genes are epigenetic regulators, DNA damage response genes, and splicing factors, which are essential to maintain functional HSPCs and are frequently involved in the development of hematologic malignancies. Established risk factors for CH, including age, prior cytotoxic therapy, and smoking, increase the risk of acquiring CH and/or may increase CH fitness. CH has emerged as a novel risk factor in many age-related diseases, such as hematologic malignancies, cardiovascular disease, diabetes, and autoimmune disorders, among others. Future characterization of the mechanisms driving CH evolution will be critical to develop preventative and therapeutic approaches.

Clonal hematopoiesis of indeterminate potential as a prognostic factor: a systematic review and meta-analysis

ABSTRACT

With advances in sequencing, individuals with clonal hematopoiesis of indeterminate potential (CHIP) are increasingly being identified, making it essential to understand its prognostic implications. We conducted a systematic review of studies comparing the risk of clinical outcomes in individuals with and without CHIP. We searched MEDLINE and EMBASE and included original research reporting an outcome risk measure in individuals with CHIP, adjusted for the effect of age. From the 3305 studies screened, we included 88 studies with 45 to 470 960 participants. Most studies had a low-to-moderate risk of bias in all domains of the Quality in Prognostic Factor Studies tool. Random-effects meta-analyses were performed for outcomes reported in at least 3 studies. CHIP conferred an increased risk of all-cause mortality (hazard ratio [HR], 1.34; 95% confidence interval, 1.19-1.50), cancer mortality (HR, 1.46; 1.13-1.88), composite cardiovascular events (HR, 1.40; 1.19-1.65), coronary heart disease (HR, 1.76; 1.27-2.44), stroke (HR, 1.16; 1.05-1.28), heart failure (HR, 1.27; 1.15-1.41), hematologic malignancy (HR, 4.28; 2.29-7.98), lung cancer (HR, 1.40; 1.27-1.54), renal impairment (HR, 1.25; 1.18-1.33) and severe COVID-19 (odds ratio [OR], 1.46; 1.18-1.80). CHIP was not associated with cardiovascular mortality (HR, 1.09; 0.97-1.22), except in the subgroup analysis restricted to larger clones (HR, 1.31; 1.12-1.54). Isolated DNMT3A mutations did not increase the risk of myeloid malignancy, all-cause mortality, or renal impairment. The reasons for heterogeneity between studies included differences in definitions and measurements of CHIP and the outcomes, and populations studied. In summary, CHIP is associated with diverse clinical outcomes, with clone size, specific gene, and inherent patient characteristics important mediators of risk.

Multiomic profiling of human clonal hematopoiesis reveals genotype and cell-specific inflammatory pathway activation

ABSTRACT

Clonal hematopoiesis (CH) is an age-associated phenomenon that increases the risk of hematologic malignancy and cardiovascular disease. CH is thought to enhance disease risk through inflammation in the peripheral blood.1 Here, we profile peripheral blood gene expression in 66 968 single cells from a cohort of 17 patients with CH and 7 controls. Using a novel mitochondrial DNA barcoding approach, we were able to identify and separately compare mutant Tet methylcytosine dioxygenase 2 (TET2) and DNA methyltransferase 3A (DNMT3A) cells with nonmutant counterparts. We discovered the vast majority of mutated cells were in the myeloid compartment. Additionally, patients harboring DNMT3A and TET2 CH mutations possessed a proinflammatory profile in CD14+ monocytes through previously unrecognized pathways such as galectin and macrophage inhibitory factor. We also found that T cells from patients with CH, although mostly unmutated, had decreased expression of GTPase of the immunity associated protein genes, which are critical to T-cell development, suggesting that CH impairs T-cell function.

Clonal hematopoiesis driven by mutated DNMT3A promotes inflammatory bone loss

Clonal hematopoiesis of indeterminate potential (CHIP) arises from aging-associated acquired mutations in hematopoietic progenitors, which display clonal expansion and produce phenotypically altered leukocytes. We associated CHIP-DNMT3A mutations with a higher prevalence of periodontitis and gingival inflammation among 4,946 community-dwelling adults. To model DNMT3A-driven CHIP, we used mice with the heterozygous loss-of-function mutation R878H, equivalent to the human hotspot mutation R882H. Partial transplantation with Dnmt3aR878H/+ bone marrow (BM) cells resulted in clonal expansion of mutant cells into both myeloid and lymphoid lineages and an elevated abundance of osteoclast precursors in the BM and osteoclastogenic macrophages in the periphery. DNMT3A-driven clonal hematopoiesis in recipient mice promoted naturally occurring periodontitis and aggravated experimentally induced periodontitis and arthritis, associated with enhanced osteoclastogenesis, IL-17-dependent inflammation and neutrophil responses, and impaired regulatory T cell immunosuppressive activity. DNMT3A-driven clonal hematopoiesis and, subsequently, periodontitis were suppressed by rapamycin treatment. DNMT3A-driven CHIP represents a treatable state of maladaptive hematopoiesis promoting inflammatory bone loss.

DNMT3A dysfunction promotes neuroinflammation and exacerbates acute ischemic stroke

Somatic mutations related to clonal hematopoiesis of indeterminate potential (CHIP) are risk factors for stroke. The impact of DNMT3A, the most mutated gene in CHIP, on clinical functional outcomes of acute ischemic stroke (AIS) remains unclear. In a well-characterized cohort of 8524 ischemic stroke patients, we demonstrated that DNMT3A-driven CHIP was significantly associated with neurological disability in these patients. With a stroke mouse model of transient middle cerebral artery occlusion (tMCAO), we demonstrated that DNMT3A protein levels in the brain penumbra increased. The DNMT3A inhibitor RG108 administration amplified neutrophil proliferation in the blood, promoted neutrophil infiltration into the brain penumbra, and exaggerated proinflammatory activation in tMCAO male mice. DNMT3A inhibition also significantly increased infarct volume and worsened neurobehavioral function in tMCAO male mice. In conclusion, DNMT3A somatic mutations are associated with worsened neurological disability in some patients with AIS, potentially through increased neutrophil proliferation and infiltration in the ischemic brain region. These findings suggest a possible mechanism for proinflammatory activation and tissue damage in the affected brain tissue, highlighting the need for further research in this area.

Clonal expansion in normal tissues

Cancer originates from a single ancestral cell that acquires a driver mutation, which confers a growth or survival advantage, followed by the acquisition of additional driver mutations by descendant cells. Recently, it has become evident that somatic cell mutations accumulate in normal tissues with aging and exposure to environmental factors, such as alcohol, smoking, and UV rays, increases the mutation rate. Clones harboring driver mutations expand with age, leading to tissue remodeling. Lineage analysis of myeloproliferative neoplasms and der(1;16)-positive breast cancer revealed that driver mutations were acquired early in our lives and that the development of cancer takes decades, unveiling the previously unknown early process of cancer development. Evidence that clonal hematopoiesis affects various diseases, including nonneoplastic diseases, highlights the potential role of the identification and functional analysis of mutated clones in unraveling unknown pathologies. In this review, we summarize the recent updates on clonal expansion in normal tissues and the natural history of cancer revealed through lineage analysis of noncancerous and cancerous tissues.

Cost-Effective and Scalable Clonal Hematopoiesis Assay Provides Insight into Clonal Dynamics

Clonal hematopoiesis of indeterminate potential (CHIP) is a common age-related phenomenon in which hematopoietic stem cells acquire mutations in a select set of genes commonly mutated in myeloid neoplasia which then expand clonally. Current sequencing assays to detect CHIP mutations are not optimized for the detection of these variants and can be cost-prohibitive when applied to large cohorts or to serial sequencing. In this study, an affordable (approximately US $8 per sample), accurate, and scalable sequencing assay for CHIP is introduced and validated. The efficacy of the assay was demonstrated by identifying CHIP mutations in a cohort of 456 individuals with DNA collected at multiple time points in Vanderbilt University's biobank and quantifying clonal expansion rates over time. A total of 101 individuals with CHIP/clonal cytopenia of undetermined significance were identified, and individual-level clonal expansion rate was calculated using the variant allele fraction at both time points. Differences in clonal expansion rate by driver gene were observed, but there was also significant individual-level heterogeneity, emphasizing the multifactorial nature of clonal expansion. Additionally, mutation co-occurrence and clonal competition between multiple driver mutations were explored.

Clonal hematopoiesis of indeterminate potential contributes to accelerated chronic kidney disease progression

Background

Clonal hematopoiesis of indeterminate potential (CHIP) is a common inflammatory condition of aging that causes myriad end-organ damage. We have recently shown associations for CHIP with acute kidney injury and with kidney function decline in the general population, with stronger associations for CHIP driven by mutations in genes other than DNMT3A (non- DNMT3A CHIP). Longitudinal kidney function endpoints in individuals with pre-existing chronic kidney disease (CKD) and CHIP have been examined in two previous studies, which reported conflicting findings and were limited by small sample sizes.

Methods

In this study, we examined the prospective associations between CHIP and CKD progression events in four cohorts of CKD patients (total N = 5,772). The primary outcome was a composite of 50% kidney function decline or kidney failure. The slope of eGFR decline was examined as a secondary outcome. Mendelian randomization techniques were then used to investigate potential causal effects of CHIP on eGFR decline. Finally, kidney function was assessed in adenine-fed CKD model mice having received a bone marrow transplant recapitulating Tet2 -CHIP compared to controls transplanted wild-type bone marrow.

Results

Across all cohorts, the average age was 66.4 years, the average baseline eGFR was 42.6 ml/min/1.73m 2 , and 24% had CHIP. Upon meta-analysis, non- DNMT3A CHIP was associated with a 59% higher relative risk of incident CKD progression (HR 1.59, 95% CI: 1.02-2.47). This association was more pronounced among individuals with diabetes (HR 1.29, 95% CI: 1.03-1.62) and with baseline eGFR ≥ 30 ml/min/1.73m (HR 1.80, 95% CI: 1.11-2.90). Additionally, the annualized slope of eGFR decline was steeper among non- DNMT3A CHIP carriers, relative to non-carriers (β -0.61 ± 0.31 ml/min/1.73m 2 , p = 0.04). Mendelian randomization analyses suggested a causal role for CHIP in eGFR decline among individuals with diabetes. In a dietary adenine mouse model of CKD, Tet2 -CHIP was associated with lower GFR as well as greater kidney inflammation, tubular injury, and tubulointerstitial fibrosis.

Conclusion

Non- DNMT3A CHIP is a potentially targetable novel risk factor for CKD progression.

Dynamics of clonal hematopoiesis under DNA-damaging treatment in patients with ovarian cancer

Clonal hematopoiesis (CH) driven by mutations in the DNA damage response (DDR) pathway is frequent in patients with cancer and is associated with a higher risk of therapy-related myeloid neoplasms (t-MNs). Here, we analyzed 423 serial whole blood and plasma samples from 103 patients with relapsed high-grade ovarian cancer receiving carboplatin, poly(ADP-ribose) polymerase inhibitor (PARPi) and heat shock protein 90 inhibitor (HSP90i) treatment within the phase II EUDARIO trial using error-corrected sequencing of 72 genes. DDR-driven CH was detected in 35% of patients and was associated with longer duration of prior PARPi treatment. TP53- and PPM1D-mutated clones exhibited substantially higher clonal expansion rates than DNMT3A- or TET2-mutated clones during treatment. Expansion of DDR clones correlated with HSP90i exposure across the three study arms and was partially abrogated by the presence of germline mutations related to homologous recombination deficiency. Single-cell DNA sequencing of selected samples revealed clonal exclusivity of DDR mutations, and identified DDR-mutated clones as the origin of t-MN in two investigated cases. Together, these results provide unique insights into the architecture and the preferential selection of DDR-mutated hematopoietic clones under intense DNA-damaging treatment. Specifically, PARPi and HSP90i therapies pose an independent risk for the expansion of DDR-CH in a dose-dependent manner.

Clonal hematopoiesis and its impact on the aging osteo-hematopoietic niche

Clonal hematopoiesis (CH) defines a premalignant state predominantly found in older persons that increases the risk of developing hematologic malignancies and age-related inflammatory diseases. However, the risk for malignant transformation or non-malignant disorders is variable and difficult to predict, and defining the clinical relevance of specific candidate driver mutations in individual carriers has proved to be challenging. In addition to the cell-intrinsic mechanisms, mutant cells rely on and alter cell-extrinsic factors from the bone marrow (BM) niche, which complicates the prediction of a mutant cell's fate in a shifting pre-malignant microenvironment. Therefore, identifying the insidious and potentially broad impact of driver mutations on supportive niches and immune function in CH aims to understand the subtle differences that enable driver mutations to yield different clinical outcomes. Here, we review the changes in the aging BM niche and the emerging evidence supporting the concept that CH can progressively alter components of the local BM microenvironment. These alterations may have profound implications for the functionality of the osteo-hematopoietic niche and overall bone health, consequently fostering a conducive environment for the continued development and progression of CH. We also provide an overview of the latest technology developments to study the spatiotemporal dependencies in the CH BM niche, ideally in the context of longitudinal studies following CH over time. Finally, we discuss aspects of CH carrier management in clinical practice, based on work from our group and others.

Tissue mosaicism following stem cell aging: blood as an exemplar

Loss of stem cell regenerative potential underlies aging of all tissues. Somatic mosaicism, the emergence of cellular patchworks within tissues, increases with age and has been observed in every organ yet examined. In the hematopoietic system, as in most tissues, stem cell aging through a variety of mechanisms occurs in lockstep with the emergence of somatic mosaicism. Here, we draw on insights from aging hematopoiesis to illustrate fundamental principles of stem cell aging and somatic mosaicism. We describe the generalizable changes intrinsic to aged stem cells and their milieu that provide the backdrop for somatic mosaicism to emerge. We discuss genetic and nongenetic mechanisms that can result in tissue somatic mosaicism and existing methodologies to detect such clonal outgrowths. Finally, we propose potential avenues to modify mosaicism during aging, with the ultimate aim of increasing tissue resiliency.

Ferroptosis in Osteocytes as a Target for Protection Against Postmenopausal Osteoporosis

Ferroptosis is a necrotic form of iron-dependent regulatory cell death. Estrogen withdrawal can interfere with iron metabolism, which is responsible for the pathogenesis of postmenopausal osteoporosis (PMOP). Here, it is demonstrated that estrogen withdrawal induces iron accumulation in the skeleton and the ferroptosis of osteocytes, leading to reduced bone mineral density. Furthermore, the facilitatory effect of ferroptosis of osteocytes is verified in the occurrence and development of postmenopausal osteoporosis is associated with over activated osteoclastogenesis using a direct osteocyte/osteoclast coculture system and glutathione peroxidase 4 (GPX4) knockout ovariectomized mice. In addition, the nuclear factor erythroid derived 2-related factor-2 (Nrf2) signaling pathway is confirmed to be a crucial factor in the ferroptosis of osteocytic cells. Nrf2 regulates the expression of nuclear factor kappa-B ligand (RANKL) by regulating the DNA methylation level of the RANKL promoter mediated by DNA methyltransferase 3a (Dnmt3a), which is as an important mechanism in osteocytic ferroptosis-mediated osteoclastogenesis. Taken together, this data suggests that osteocytic ferroptosis is involved in PMOP and can be targeted to tune bone homeostasis.

Clonal haematopoiesis, ageing and kidney disease

Clonal haematopoiesis of indeterminate potential (CHIP) is a preclinical condition wherein a sizeable proportion of an individual's circulating blood cells are derived from a single mutated haematopoietic stem cell. CHIP occurs frequently with ageing - more than 10% of individuals over 65 years of age are affected - and is associated with an increased risk of disease across several organ systems and premature death. Emerging evidence suggests that CHIP has a role in kidney health, including associations with predisposition to acute kidney injury, impaired recovery from acute kidney injury and kidney function decline, both in the general population and among those with chronic kidney disease. Beyond its direct effect on the kidney, CHIP elevates the susceptibility of individuals to various conditions that can detrimentally affect the kidneys, including cardiovascular disease, obesity and insulin resistance, liver disease, gout, osteoporosis and certain autoimmune diseases. Aberrant pro-inflammatory signalling, telomere attrition and epigenetic ageing are potential causal pathophysiological pathways and mediators that underlie CHIP-related disease risk. Experimental animal models have shown that inhibition of inflammatory cytokine signalling can ameliorate many of the pathological effects of CHIP, and assessment of the efficacy and safety of this class of medications for human CHIP-associated pathology is ongoing.

Clonal Hematopoiesis of Indeterminate Potential in Chronic Thromboembolic Pulmonary Hypertension: A Multicenter Study

BACKGROUND

The pathogenesis of chronic thromboembolic pulmonary hypertension (CTEPH) is multifactorial and growing evidence has indicated that hematological disorders are involved. Clonal hematopoiesis of indeterminate potential (CHIP) has recently been associated with an increased risk of both hematological malignancies and cardiovascular diseases. However, the prevalence and clinical relevance of CHIP in patients with CTEPH remains unclear.

METHODS

Using stepwise calling on next-generation sequencing data from 499 patients with CTEPH referred to 3 centers between October 2006 and December 2021, CHIP mutations were identified. We associated CHIP with all-cause mortality in patients with CTEPH. To provide insights into potential mechanisms, the associations between CHIP and inflammatory markers were also determined.

RESULTS

In total, 47 (9.4%) patients with CTEPH carried at least 1 CHIP mutation at a variant allele frequency of ≥2%. The most common mutations were in DNMT3A, TET2, RUNX1, and ASXL1. During follow-up (mean, 55 months), deaths occurred in 22 (46.8%) and 104 (23.0%) patients in the CHIP and non-CHIP groups, respectively (P<0.001, log-rank test). The association of CHIP with mortality remained robust in the fully adjusted model (hazard ratio, 2.190 [95% CI, 1.257-3.816]; P=0.006). Moreover, patients with CHIP mutations showed higher circulating interleukin-1β and interleukin-6 and lower interleukin-4 and IgG galactosylation levels.

CONCLUSIONS

This is the first study to show that CHIP mutations occurred in 9.4% of patients with CTEPH are associated with a severe inflammatory state and confer a poorer prognosis in long-term follow-up.

Association of clonal haematopoiesis with severe postoperative complications in patients undergoing radical oesophagectomy

BACKGROUND

Clonal haematopoiesis (CH) is an age-associated clonal expansion of blood cells driven by leukaemia-associated somatic mutations. Although CH has been reported to be a risk factor for leukaemia and a number of non-haematopoietic diseases, its role in perioperative medicine remains unexplored.

METHODS

This was a single-centre, prospective, observational study. Patients undergoing radical oesophagectomy were enrolled, and peripheral blood samples were collected for DNA sequencing. Patients with haematopoietic somatic mutations (variant allele frequencies ≥1%) in the DNMT3A gene, TET2 gene, or both were defined as CH carriers. The primary outcome was the incidence of severe postoperative complications (Clavien-Dindo classification ≥3). The secondary outcomes included the major types of postoperative complications, mortality, and other common perioperative variables.

RESULTS

Clonal haematopoiesis was found in 21.2% (33/156) of the patients (mean age: 66 yr [range: 26-79 yr]; 83% males). Some 14/33 (42.4%) patients with CH had severe postoperative complications, compared with patients without CH carriers (28/123 [22.8%]; P=0.024). Multivariable logistic regression analysis showed that CH was associated with an increased risk of developing severe postoperative complications (odds ratio, 3.63; 95% confidence interval, 1.37-9.66; P=0.010). Among the major postoperative complications, the incidence of pulmonary complications was significantly higher in the patients with CH than in those without CH (15 in 33 [45.5%] vs 30 in 123 [24.4%], P=0.018).

CONCLUSIONS

Clonal haematopoiesis was associated with a higher incidence of severe postoperative complications in patients undergoing radical oesophagectomy, suggesting that clonal haematopoiesis can play an important role in perioperative medicine.

CLINICAL TRIAL REGISTRATION

ChiCTR2100044175 (Chinese Clinical Trial Registry, http://www.chictr.org.cn/showproj.aspx?proj=123193).

Identification of mitophagy-related biomarkers in human osteoporosis based on a machine learning model

Background: Osteoporosis (OP) is a chronic bone metabolic disease and a serious global public health problem. Several studies have shown that mitophagy plays an important role in bone metabolism disorders; however, its role in osteoporosis remains unclear. Methods: The Gene Expression Omnibus (GEO) database was used to download GSE56815, a dataset containing low and high BMD, and differentially expressed genes (DEGs) were analyzed. Mitochondrial autophagy-related genes (MRG) were downloaded from the existing literature, and highly correlated MRG were screened by bioinformatics methods. The results from both were taken as differentially expressed (DE)-MRG, and Gene Ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis were performed. Protein-protein interaction network (PPI) analysis, support vector machine recursive feature elimination (SVM-RFE), and Boruta method were used to identify DE-MRG. A receiver operating characteristic curve (ROC) was drawn, a nomogram model was constructed to determine its diagnostic value, and a variety of bioinformatics methods were used to verify the relationship between these related genes and OP, including GO and KEGG analysis, IP pathway analysis, and single-sample Gene Set Enrichment Analysis (ssGSEA). In addition, a hub gene-related network was constructed and potential drugs for the treatment of OP were predicted. Finally, the specific genes were verified by real-time quantitative polymerase chain reaction (RT-qPCR). Results: In total, 548 DEGs were identified in the GSE56815 dataset. The weighted gene co-expression network analysis(WGCNA) identified 2291 key module genes, and 91 DE-MRG were obtained by combining the two. The PPI network revealed that the target gene for AKT1 interacted with most proteins. Three MRG (NELFB, SFSWAP, and MAP3K3) were identified as hub genes, with areas under the curve (AUC) 0.75, 0.71, and 0.70, respectively. The nomogram model has high diagnostic value. GO and KEGG analysis showed that ribosome pathway and cellular ribosome pathway may be the pathways regulating the progression of OP. IPA showed that MAP3K3 was associated with six pathways, including GNRH Signaling. The ssGSEA indicated that NELFB was highly correlated with iDCs (cor = -0.390, p < 0.001). The regulatory network showed a complex relationship between miRNA, transcription factor(TF) and hub genes. In addition, 4 drugs such as vinclozolin were predicted to be potential therapeutic drugs for OP. In RT-qPCR verification, the hub gene NELFB was consistent with the results of bioinformatics analysis. Conclusion: Mitophagy plays an important role in the development of osteoporosis. The identification of three mitophagy-related genes may contribute to the early diagnosis, mechanism research and treatment of OP.

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.

Causes and consequences of clonal hematopoiesis

ABSTRACT

Clonal hematopoiesis (CH) is described as the outsized contribution of expanded clones of hematopoietic stem and progenitor cells (HSPCs) to blood cell production. The prevalence of CH increases dramatically with age. CH can be caused by somatic mutations in individual genes or by gains and/or losses of larger chromosomal segments. CH is a premalignant state; the somatic mutations detected in CH are the initiating mutations for hematologic malignancies, and CH is a strong predictor of the development of blood cancers. Moreover, CH is associated with nonmalignant disorders and increased overall mortality. The somatic mutations that drive clonal expansion of HSPCs can alter the function of terminally differentiated blood cells, including the release of elevated levels of inflammatory cytokines. These cytokines may then contribute to a broad range of inflammatory disorders that increase in prevalence with age. Specific somatic mutations in the peripheral blood in coordination with blood count parameters can powerfully predict the development of hematologic malignancies and overall mortality in CH. In this review, we summarize the current understanding of CH nosology and origins. We provide an overview of available tools for risk stratification and discuss management strategies for patients with CH presenting to hematology clinics.

Molecular and clinical aspects relevant for counseling individuals with clonal hematopoiesis of indeterminate potential

Clonal hematopoiesis of indeterminate potential (CHIP) has fascinated the medical community for some time. Discovered about a decade ago, this phenomenon links age-related alterations in hematopoiesis not only to the later development of hematological malignancies but also to an increased risk of early-onset cardiovascular disease and some other disorders. CHIP is detected in the blood and is characterized by clonally expanded somatic mutations in cancer-associated genes, predisposing to the development of hematologic neoplasms such as MDS and AML. CHIP-associated mutations often involve DNA damage repair genes and are frequently observed following prior cytotoxic cancer therapy. Genetic predisposition seems to be a contributing factor. It came as a surprise that CHIP significantly elevates the risk of myocardial infarction and stroke, and also contributes to heart failure and pulmonary hypertension. Meanwhile, evidence of mutant clonal macrophages in vessel walls and organ parenchyma helps to explain the pathophysiology. Besides aging, there are some risk factors promoting the appearance of CHIP, such as smoking, chronic inflammation, chronic sleep deprivation, and high birth weight. This article describes fundamental aspects of CHIP and explains its association with hematologic malignancies, cardiovascular disorders, and other medical conditions, while also exploring potential progress in the clinical management of affected individuals. While it is important to diagnose conditions that can lead to adverse, but potentially preventable, effects, it is equally important not to stress patients by confronting them with disconcerting findings that cannot be remedied. Individuals with diagnosed or suspected CHIP should receive counseling in a specialized outpatient clinic, where professionals from relevant medical specialties may help them to avoid the development of CHIP-related health problems. Unfortunately, useful treatments and clinical guidelines for managing CHIP are still largely lacking. However, there are some promising approaches regarding the management of cardiovascular disease risk. In the future, strategies aimed at restoration of gene function or inhibition of inflammatory mediators may become an option.

How low can you go?: Methodologic considerations in clonal hematopoiesis variant calling

Clonal hematopoiesis (CH) is defined by the presence of an expanded clonal hematopoietic cell population due to an acquired mutation conferring a selective growth advantage and is known to predispose to hematologic malignancy. In this review, we discuss sequencing methods for CH detection in bulk sequencing data and corresponding bioinformatic approaches for variant calling, filtering, and curation. We detail practical recommendations for CH calling. Finally, we discuss how improvements in CH sequencing and bioinformatic approaches will enable the characterization of CH trajectories, its impact on human health, and therapeutic approaches to mitigate its adverse effects.

Cost-effective and scalable clonal hematopoiesis assay provides insight into clonal dynamics

Clonal hematopoiesis of indeterminate potential (CHIP) is a common age-related phenomenon that occurs when hematopoietic stem cells acquire mutations in a select set of genes commonly mutated in myeloid neoplasia which then expand clonally. Current sequencing assays to detect CHIP are not optimized for the detection of these variants and can be cost-prohibitive when applied to large cohorts or serial sequencing. Here, we present and validate a CHIP targeted sequencing assay that is affordable (∼$8/sample), accurate and highly scalable. To demonstrate the utility of this assay, we detected CHIP in a cohort of 456 individuals with DNA collected at multiple timepoints in the Vanderbilt BioVU biobank and quantified clonal expansion rates over time. A total of 101 individuals with CHIP were identified, and individual-level clonal expansion rate was calculated using the variant allele fraction (VAF) at both timepoints. Differences in clonal expansion rate by driver gene were observed, but there was also significant individual-level heterogeneity, emphasizing the multifactorial nature of clonal expansion. We further describe the mutation co-occurrence and clonal competition between multiple driver mutations.

Hematopoietic-specific heterozygous loss of Dnmt3a exacerbates colitis-associated colon cancer

Clonal hematopoiesis (CH) is defined as clonal expansion of mutant hematopoietic stem cells absent diagnosis of a hematologic malignancy. Presence of CH in solid tumor patients, including colon cancer, correlates with shorter survival. We hypothesized that bone marrow-derived cells with heterozygous loss-of-function mutations of DNMT3A, the most common genetic alteration in CH, contribute to the pathogenesis of colon cancer. In a mouse model that combines colitis-associated colon cancer (CAC) with experimental CH driven by Dnmt3a+/Δ, we found higher tumor penetrance and increased tumor burden compared with controls. Histopathological analysis revealed accentuated colonic epithelium injury, dysplasia, and adenocarcinoma formation. Transcriptome profiling of colon tumors identified enrichment of gene signatures associated with carcinogenesis, including angiogenesis. Treatment with the angiogenesis inhibitor axitinib eliminated the colon tumor-promoting effect of experimental CH driven by Dnmt3a haploinsufficiency and rebalanced hematopoiesis. This study provides conceptually novel insights into non-tumor-cell-autonomous effects of hematopoietic alterations on colon carcinogenesis and identifies potential therapeutic strategies.

Defects in Bone and Bone Marrow in Inherited Anemias: the Chicken or the Egg

PURPOSE OF REVIEW

Recently, there has been an increasing number of studies on the crosstalk between the bone and the bone marrow and how it pertains to anemia. Here, we discuss four heritable clinical syndromes contrasting those in which anemia affects bone growth and development, with those in which abnormal bone development results in anemia, highlighting the multifaceted interactions between skeletal development and hematopoiesis.

RECENT FINDINGS

Anemia results from both inherited and acquired disorders caused by either impaired production or premature destruction of red blood cells or blood loss. The downstream effects on bone development and growth in patients with anemia often constitute an important part of their clinical condition. We will discuss the interdependence of abnormal bone development and growth and hematopoietic abnormalities, with a focus on the erythroid lineage. To illustrate those points, we selected four heritable anemias that arise from either defective hematopoiesis impacting the skeletal system (the hemoglobinopathies β-thalassemia and sickle cell disease) versus defective osteogenesis resulting in impaired hematopoiesis (osteopetrosis). Finally, we will discuss recent findings in Diamond Blackfan anemia, an intrinsic disorder of both the erythron and the bone. By focusing on four representative hereditary hematopoietic disorders, this complex relationship between bone and blood should lead to new areas of research in the field.

Loss-of-function mutations in Dnmt3a and Tet2 lead to accelerated atherosclerosis and concordant macrophage phenotypes

Clonal hematopoiesis of indeterminate potential (CHIP) is defined by the presence of a cancer-associated somatic mutation in white blood cells in the absence of overt hematological malignancy. It arises most commonly from loss-of-function mutations in the epigenetic regulators DNMT3A and TET2. CHIP predisposes to both hematological malignancies and atherosclerotic cardiovascular disease in humans. Here we demonstrate that loss of Dnmt3a in myeloid cells increased murine atherosclerosis to a similar degree as previously seen with loss of Tet2. Loss of Dnmt3a enhanced inflammation in macrophages in vitro and generated a distinct adventitial macrophage population in vivo which merges a resident macrophage profile with an inflammatory cytokine signature. These changes surprisingly phenocopy the effect of loss of Tet2. Our results identify a common pathway promoting heightened innate immune cell activation with loss of either gene, providing a biological basis for the excess atherosclerotic disease burden in carriers of these two most prevalent CHIP mutations.

Clonal haematopoiesis and dysregulation of the immune system

Age-related diseases are frequently linked to pathological immune dysfunction, including excessive inflammation, autoreactivity and immunodeficiency. Recent analyses of human genetic data have revealed that somatic mutations and mosaic chromosomal alterations in blood cells - a condition known as clonal haematopoiesis (CH) - are associated with ageing and pathological immune dysfunction. Indeed, large-scale epidemiological studies and experimental mouse models have demonstrated that CH can promote cardiovascular disease, chronic obstructive pulmonary disease, chronic liver disease, osteoporosis and gout. The genes most frequently mutated in CH, the epigenetic regulators TET2 and DNMT3A, implicate increased chemokine expression and inflammasome hyperactivation in myeloid cells as a possible mechanistic connection between CH and age-related diseases. In addition, TET2 and DNMT3A mutations in lymphoid cells have been shown to drive methylation-dependent alterations in differentiation and function. Here we review the observational and mechanistic studies describing the connection between CH and pathological immune dysfunction, the effects of CH-associated genetic alterations on the function of myeloid and lymphoid cells, and the clinical and therapeutic implications of CH as a target for immunomodulation.

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.

Hematopoietic stem cell aging and leukemia transformation

With aging, hematopoietic stem cells (HSCs) have an impaired ability to regenerate, differentiate, and produce an entire repertoire of mature blood and immune cells. Owing to dysfunctional hematopoiesis, the incidence of hematologic malignancies increases among elderly individuals. Here, we provide an update on HSC-intrinsic and -extrinsic factors and processes that were recently discovered to contribute to the functional decline of HSCs during aging. In addition, we discuss the targets and timing of intervention approaches to maintain HSC function during aging and the extent to which these same targets may prevent or delay transformation to hematologic malignancies.

Haplodeficiency of the 9p21 tumor suppressor locus causes myeloid disorders driven by the bone marrow microenvironment

The chromosome 9p21 locus comprises several tumor suppressor genes including MTAP, CDKN2A, and CDKN2B, and its homo- or heterozygous deletion is associated with reduced survival in multiple cancer types. We report that mice with germ line monoallelic deletion or induced biallelic deletion of the 9p21-syntenic locus (9p21s) developed a fatal myelodysplastic syndrome/myeloproliferative neoplasm (MDS/MPN)-like disease associated with aberrant trabecular bone formation and/or fibrosis in the bone marrow (BM). Reciprocal BM transfers and conditional targeting of 9p21s suggested that the disease originates in the BM stroma. Single-cell analysis of 9p21s-deficient BM stroma revealed the expansion of chondrocyte and osteogenic precursors, reflected in increased osteogenic differentiation in vitro. It also showed reduced expression of factors maintaining hematopoietic stem/progenitor cells, including Cxcl12. Accordingly, 9p21s-deficient mice showed reduced levels of circulating Cxcl12 and concomitant upregulation of the profibrotic chemokine Cxcl13 and the osteogenesis- and fibrosis-related multifunctional glycoprotein osteopontin/Spp1. Our study highlights the potential of mutations in the BM microenvironment to drive MDS/MPN-like disease.

Clonal hematopoiesis and inflammation - the perpetual cycle

Acquired genetic or cytogenetic alterations in a blood stem cell that confer clonal fitness promote its relative expansion leading to clonal hematopoiesis (CH). Despite a largely intact hematopoietic output, CH is associated with a heightened risk of progression to hematologic malignancies and with non-hematologic health manifestations, including cardiovascular disease and overall mortality. We focus on the evidence for the role of inflammation in establishing, maintaining and reciprocally being affected by CH. We describe the known pro-inflammatory signals associated with CH and preclinical studies that elucidated the cellular mechanisms involved. We review the evolving literature on early-onset CH in germline predisposition conditions and the possible role of immune dysregulation in this context.

Clonal Hematopoiesis in Young Women Treated for Breast Cancer

PURPOSE

Young women treated for breast cancer with cytotoxic therapies are at risk for clonal hematopoiesis of indeterminate potential (CHIP), a condition in which blood cells carrying a somatic mutation associated with hematologic malignancy comprise at least 4% of the total blood system. CHIP has primarily been studied in older patient cohorts with limited clinical phenotyping.

EXPERIMENTAL DESIGN

We performed targeted sequencing on longitudinal blood samples to characterize the clonal hematopoietic landscape of 878 women treated for breast cancer enrolled in the prospective Young Women's Breast Cancer Study.

RESULTS

We identified somatic driver mutations in 252 study subjects (28.7%), but only 24 (2.7%) had clones large enough to meet criteria for CHIP. The most commonly mutated genes were DNMT3A and TET2, similar to mutations observed in noncancer cohorts. At 9-year median follow-up, we found no association between the presence of a somatic blood mutation (regardless of clone size) and adverse breast cancer (distant relapse-free survival) or non-breast cancer-related outcomes in this cohort. A subset of paired blood samples obtained over 4 years showed no evidence of mutant clonal expansion, regardless of genotype. Finally, we identified a subset of patients with likely germline mutations in genes known to contribute to inherited cancer risk, such as TP53 and ATM.

CONCLUSIONS

Our data show that for young women with early-stage breast cancer, CHIP is uncommon after cytotoxic exposure, is unlikely to contribute to adverse outcomes over the decade-long follow-up and may not require additional monitoring if discovered incidentally.

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

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

SIGNIFICANCE

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