Ten-Eleven-Translocation 2 (TET2) negatively regulates homeostasis and differentiation of hematopoietic stem cells in mice

Epigenetic biomarkers in aging and longevity: Current and future application

The aging process has been one of the most necessary research fields in the current century, and knowing different theories of aging and the role of different genetic, epigenetic, molecular, and environmental modulating factors in increasing the knowledge of aging mechanisms and developing appropriate diagnostic, therapeutic, and preventive ways would be helpful. One of the most conserved signs of aging is epigenetic changes, including DNA methylation, histone modifications, chromatin remodeling, noncoding RNAs, and extracellular RNAs. Numerous biological processes and hallmarks are vital in aging development, but epigenomic alterations are especially notable because of their importance in gene regulation and cellular identity. The mounting evidence points to a possible interaction between age-related epigenomic alterations and other aging hallmarks, like genome instability. To extend a healthy lifespan and possibly reverse some facets of aging and aging-related diseases, it will be crucial to comprehend global and locus-specific epigenomic modifications and recognize corresponding regulators of health and longevity. In the current study, we will aim to discuss the role of epigenomic mechanisms in aging and the most recent developments in epigenetic diagnostic biomarkers, which have the potential to focus efforts on reversing the destructive signs of aging and extending the lifespan.

Chronic TNF in the aging microenvironment exacerbates Tet2 loss-of-function myeloid expansion

ABSTRACT

Somatic mutations in the TET2 gene occur more frequently with age, imparting an intrinsic hematopoietic stem cells (HSCs) advantage and contributing to a phenomenon termed clonal hematopoiesis of indeterminate potential (CHIP). Individuals with TET2-mutant CHIP have a higher risk of developing myeloid neoplasms and other aging-related conditions. Despite its role in unhealthy aging, the extrinsic mechanisms driving TET2-mutant CHIP clonal expansion remain unclear. We previously showed an environment containing tumor necrosis factor (TNF) favors TET2-mutant HSC expansion in vitro. We therefore postulated that age-related increases in TNF also provide an advantage to HSCs with TET2 mutations in vivo. To test this hypothesis, we generated mixed bone marrow chimeric mice of old wild-type (WT) and TNF-/- genotypes reconstituted with WT CD45.1+ and Tet2-/- CD45.2+ HSCs. We show that age-associated increases in TNF dramatically increased the expansion of Tet2-/- cells in old WT recipient mice, with strong skewing toward the myeloid lineage. This aberrant myelomonocytic advantage was mitigated in old TNF-/- recipient mice, suggesting that TNF signaling is essential for the expansion Tet2-mutant myeloid clones. Examination of human patients with rheumatoid arthritis with clonal hematopoiesis revealed that hematopoietic cells carrying certain mutations, including in TET2, may be sensitive to reduced TNF bioactivity following blockade with adalimumab. This suggests that targeting TNF may reduce the burden of some forms of CHIP. To our knowledge, this is the first evidence to demonstrate that TNF has a causal role in driving TET2-mutant CHIP in vivo. These findings highlight TNF as a candidate therapeutic target to control TET2-mutant CHIP.

SDHAF1 confers metabolic resilience to aging hematopoietic stem cells by promoting mitochondrial ATP production

Aging generally predisposes stem cells to functional decline, impairing tissue homeostasis. Here, we report that hematopoietic stem cells (HSCs) acquire metabolic resilience that promotes cell survival. High-resolution real-time ATP analysis with glucose tracing and metabolic flux analysis revealed that old HSCs reprogram their metabolism to activate the pentose phosphate pathway (PPP), becoming more resistant to oxidative stress and less dependent on glycolytic ATP production at steady state. As a result, old HSCs can survive without glycolysis, adapting to the physiological cytokine environment in bone marrow. Mechanistically, old HSCs enhance mitochondrial complex II metabolism during stress to promote ATP production. Furthermore, increased succinate dehydrogenase assembly factor 1 (SDHAF1) in old HSCs, induced by physiological low-concentration thrombopoietin (TPO) exposure, enables rapid mitochondrial ATP production upon metabolic stress, thereby improving survival. This study provides insight into the acquisition of resilience through metabolic reprogramming in old HSCs and its molecular basis to ameliorate age-related hematopoietic abnormalities.

Selective advantage of mutant stem cells in human clonal hematopoiesis is associated with attenuated response to inflammation and aging

Clonal hematopoiesis (CH) arises when hematopoietic stem cells (HSCs) acquire mutations, most frequently in the DNMT3A and TET2 genes, conferring a competitive advantage through mechanisms that remain unclear. To gain insight into how CH mutations enable gradual clonal expansion, we used single-cell multi-omics with high-fidelity genotyping on human CH bone marrow (BM) samples. Most of the selective advantage of mutant cells occurs within HSCs. DNMT3A- and TET2-mutant clones expand further in early progenitors, while TET2 mutations accelerate myeloid maturation in a dose-dependent manner. Unexpectedly, both mutant and non-mutant HSCs from CH samples are enriched for inflammatory and aging transcriptomic signatures, compared with HSCs from non-CH samples, revealing a non-cell-autonomous effect. However, DNMT3A- and TET2-mutant HSCs have an attenuated inflammatory response relative to wild-type HSCs within the same sample. Our data support a model whereby CH clones are gradually selected because they are resistant to the deleterious impact of inflammation and aging.

IL-1 in aging and pathologies of hematopoietic stem cells

ABSTRACT

Defense-oriented inflammatory reactivity supports survival at younger age but might contribute to health impairments in modern, aging societies. The interleukin-1 (IL-1) cytokines are highly conserved and regulated, pleiotropic mediators of inflammation, essential to respond adequately to infection and tissue damage but also with potential host damaging effects when left unresolved. In this review, we discuss how continuous low-level IL-1 signaling contributes to aging-associated hematopoietic stem and progenitor cell (HSPC) functional impairments and how this inflammatory selective pressure acts as a driver of more profound hematological alterations, such as clonal hematopoiesis of indeterminate potential, and to overt HSPC diseases, like myeloproliferative and myelodysplastic neoplasia as well as acute myeloid leukemia. Based on this, we outline how IL-1 pathway inhibition might be used to prevent or treat inflammaging-associated HSPC pathologies.

Increased CXCL10 (IP-10) is associated with advanced myeloproliferative neoplasms and its loss dampens erythrocytosis in mouse models

Key studies in pre-leukemic disorders have linked increases in pro-inflammatory cytokines with accelerated phases of the disease, but the precise role of the cellular microenvironment in disease initiation and evolution remains poorly understood. In myeloproliferative neoplasms (MPNs), higher levels of specific cytokines have been previously correlated with increased disease severity (tumor necrosis factor-alpha [TNF-α], interferon gamma-induced protein-10 [IP-10 or CXCL10]) and decreased survival (interleukin 8 [IL-8]). Whereas TNF-α and IL-8 have been studied by numerous groups, there is a relative paucity of studies on IP-10 (CXCL10). Here we explore the relationship of IP-10 levels with detailed genomic and clinical data and undertake a complementary cytokine screen alongside functional assays in a wide range of MPN mouse models. Similar to patients, levels of IP-10 were increased in mice with more severe disease phenotypes (e.g., JAK2V617F/V617F TET2-/- double-mutant mice) compared with those with less severe phenotypes (e.g., CALRdel52 or JAK2+/V617F mice) and wild-type (WT) littermate controls. Although exposure to IP-10 did not directly alter proliferation or survival in single hematopoietic stem cells (HSCs) in vitro, IP-10-/- mice transplanted with disease-initiating HSCs developed an MPN phenotype more slowly, suggesting that the effect of IP-10 loss was noncell-autonomous. To explore the broader effects of IP-10 loss, we crossed IP-10-/- mice into a series of MPN mouse models and showed that its loss reduces the erythrocytosis observed in mice with the most severe phenotype. Together, these data point to a potential role for blocking IP-10 activity in the management of MPNs.

Emerging DNA Methylome Targets in FLT3-ITD-Positive Acute Myeloid Leukemia: Combination Therapy with Clinically Approved FLT3 Inhibitors

OPINION STATEMENT

The internal tandem duplication (ITD) mutation of the FMS-like receptor tyrosine kinase 3 (FLT3-ITD) is the most common mutation observed in approximately 30% of acute myeloid leukemia (AML) patients. It represents poor prognosis due to continuous activation of downstream growth-promoting signaling pathways such as STAT5 and PI3K/AKT. Hence, FLT3 is considered an attractive druggable target; selective small FLT3 inhibitors (FLT3Is), such as midostaurin and quizartinib, have been clinically approved. However, patients possess generally poor remission rates and acquired resistance when FLT3I used alone. Various factors in patients could cause these adverse effects including altered epigenetic regulation, causing mainly abnormal gene expression patterns. Epigenetic modifications are required for hematopoietic stem cell (HSC) self-renewal and differentiation; however, critical driver mutations have been identified in genes controlling DNA methylation (such as DNMT3A, TET2, IDH1/2). These regulators cause leukemia pathogenesis and affect disease diagnosis and prognosis when they co-occur with FLT3-ITD mutation. Therefore, understanding the role of different epigenetic alterations in FLT3-ITD AML pathogenesis and how they modulate FLT3I's activity is important to rationalize combinational treatment approaches including FLT3Is and modulators of methylation regulators or pathways. Data from ongoing pre-clinical and clinical studies will further precisely define the potential use of epigenetic therapy together with FLT3Is especially after characterized patients' mutational status in terms of FLT3 and DNA methlome regulators.

Targeted mutational profiling of Epstein Barr virus-positive mucocutaneous ulcer: Implications for differential diagnosis with EBV-positive diffuse large B-cell lymphoma

Epstein Barr Virus-positive mucocutaneous ulcer (EBVMCU) can be difficult to distinguish from EBV-positive diffuse large B cell lymphoma (DLBCL). We used targeted next-generation sequencing (NGS) to explore genetic alterations in EBVMCU to aid in this diagnostic challenge. Ten cases of EBVMCU were evaluated by a targeted NGS panel of 164 genes. Targeted NGS identified 18 variants in 15 genes in eight cases of EBVMCU. Loss of function TET2 variants were most frequently identified (3 of 10 cases, 30 %). One TET2 variant occurred at low variant allele frequency (VAF) of 3 %, which may be suggestive of clonal hematopoiesis of indeterminate potential. One case harbored a loss of function DNMT3A variant at low VAF. Two cases demonstrated missense variants in the IRF8 gene. Both variants occurred at a VAF close to 50 % and with an estimated high burden of disease (75 %). Two cases of mucosal gastrointestinal involvement had no reportable variants. Mutational profiling of EBVMCU identified TET2 loss of function variants at an elevated frequency in our cohort; however, the findings are not specific and its clinical significance cannot be completely elucidated. Further studies are needed to confirm the findings in an independent and larger cohort of EBVMCU, to determine the cell of origin of the variants, and to further assess their significance in the pathogenesis of this disorder.

Unveiling aging dynamics in the hematopoietic system insights from single-cell technologies

As the demographic structure shifts towards an aging society, strategies aimed at slowing down or reversing the aging process become increasingly essential. Aging is a major predisposing factor for many chronic diseases in humans. The hematopoietic system, comprising blood cells and their associated bone marrow microenvironment, intricately participates in hematopoiesis, coagulation, immune regulation and other physiological phenomena. The aging process triggers various alterations within the hematopoietic system, serving as a spectrum of risk factors for hematopoietic disorders, including clonal hematopoiesis, immune senescence, myeloproliferative neoplasms and leukemia. The emerging single-cell technologies provide novel insights into age-related changes in the hematopoietic system. In this review, we summarize recent studies dissecting hematopoietic system aging using single-cell technologies. We discuss cellular changes occurring during aging in the hematopoietic system at the levels of the genomics, transcriptomics, epigenomics, proteomics, metabolomics and spatial multi-omics. Finally, we contemplate the future prospects of single-cell technologies, emphasizing the impact they may bring to the field of hematopoietic system aging research.

Iterative oxidation by TET1 is required for reprogramming of imprinting control regions and patterning of mouse sperm hypomethylated regions

Ten-eleven translocation (TET) enzymes iteratively oxidize 5-methylcytosine (5mC) to generate 5-hydroxymethylcytosine (5hmC), 5-formylcytosine, and 5-carboxylcytosine to facilitate active genome demethylation. Whether these bases are required to promote replication-coupled dilution or activate base excision repair during mammalian germline reprogramming remains unresolved due to the inability to decouple TET activities. Here, we generated two mouse lines expressing catalytically inactive TET1 (Tet1-HxD) and TET1 that stalls oxidation at 5hmC (Tet1-V). Tet1 knockout and catalytic mutant primordial germ cells (PGCs) fail to erase methylation at select imprinting control regions and promoters of meiosis-associated genes, validating the requirement for the iterative oxidation of 5mC for complete germline reprogramming. TET1V and TET1HxD rescue most hypermethylation of Tet1-/- sperm, suggesting the role of TET1 beyond its oxidative capability. We additionally identify a broader class of hypermethylated regions in Tet1 mutant mouse sperm that depend on TET oxidation for reprogramming. Our study demonstrates the link between TET1-mediated germline reprogramming and sperm methylome patterning.

Inhibition of cytosine 5-hydroxymethylation during progression of cancer precursor lesions in the uterine cervix

Methylation and hydroxymethylation of cytosine moieties in CpG islands of specific genes are epigenetic processes shown to be involved in the development of cervical (pre)neoplastic lesions. We studied global (hydroxy)methylation during the subsequent steps in the carcinogenic process of the uterine cervix by using immunohistochemical protocols for the detection of 5-methylcytosine (5-mC) and 5-hydroxymethylcytosine (5-hmC) in paraffin-embedded tissues of the normal epithelia and (pre)malignant lesions. This approach allowed obtaining spatially resolved information of (epi)genetic alterations for individual cell populations in morphologically heterogeneous tissue samples. The normal ectocervical squamous epithelium showed a high degree of heterogeneity for both modifications, with a major positivity for 5-mC in the basal and parabasal layers in the ectocervical region, while 5-hmC immunostaining was even more restricted to the cells in the basal layer. Immature squamous metaplasia, characterized by expression of SOX17, surprisingly showed a decrease of 5-hmC in the basal compartments and an increase in the more superficial layers of the epithelium. The normal endocervical glandular epithelium showed a strong immunostaining reactivity for both modifications. At the squamocolumnar junctions, a specific 5-hmC pattern was observed in the squamous epithelium, resembling that of metaplasia, with the typical weak to negative reaction for 5-hmC in the basal cell compartment. The reserve cells underlying the glandular epithelium were also largely negative for 5-hmC but showed immunostaining for 5-mC. While the overall methylation status remained relatively constant, about 20% of the high-grade squamous lesions showed a very low immunostaining reactivity for 5-hmC. The (pre)malignant glandular lesions, including adenocarcinoma in situ (AIS) and adenocarcinoma showed a progressive decrease of hydroxymethylation with advancement of the lesion, resulting in cases with regions that were negative for 5-hmC immunostaining. These data indicate that inhibition of demethylation, which normally follows cytosine hydroxymethylation, is an important epigenetic switch in the development of cervical cancer.

Neutrophil-mediated innate immune resistance to bacterial pneumonia is dependent on Tet2 function

Individuals with clonal hematopoiesis of indeterminate potential (CHIP) are at increased risk of aging related health conditions and all-cause mortality, but whether CHIP affects risk of infection is much less clear. Using UK Biobank data, we revealed a positive association between CHIP and incident pneumonia in 438,421 individuals. We show that inflammation enhanced pneumonia risk, as CHIP carriers with a hypomorphic IL6 receptor polymorphism were protected. To better characterize the pathways of susceptibility, we challenged hematopoietic Tet Methylcytosine Dioxygenase 2-knockout (Tet2-/-) and floxed control mice (Tet2fl/fl) with Streptococcus pneumoniae. As with human CHIP carriers, Tet2-/- mice had hematopoietic abnormalities resulting in the expansion of inflammatory monocytes and neutrophils in peripheral blood. Yet, these cells were insufficient in defending against S. pneumoniae and resulted in increased pathology, impaired bacterial clearance, and higher mortality in Tet2-/- mice. We delineated the transcriptional landscape of Tet2-/- neutrophils and found that, while inflammation-related pathways were upregulated in Tet2-/- neutrophils, migration and motility pathways were compromised. Using live-imaging techniques, we demonstrated impairments in motility, pathogen uptake, and neutrophil extracellular trap (NET) formation by Tet2-/- neutrophils. Collectively, we show that CHIP is a risk factor for bacterial pneumonia related to innate immune impairments.

Targeting the chromatin structural changes of antitumor immunity

Epigenomic imbalance drives abnormal transcriptional processes, promoting the onset and progression of cancer. Although defective gene regulation generally affects carcinogenesis and tumor suppression networks, tumor immunogenicity and immune cells involved in antitumor responses may also be affected by epigenomic changes, which may have significant implications for the development and application of epigenetic therapy, cancer immunotherapy, and their combinations. Herein, we focus on the impact of epigenetic regulation on tumor immune cell function and the role of key abnormal epigenetic processes, DNA methylation, histone post-translational modification, and chromatin structure in tumor immunogenicity, and introduce these epigenetic research methods. We emphasize the value of small-molecule inhibitors of epigenetic modulators in enhancing antitumor immune responses and discuss the challenges of developing treatment plans that combine epigenetic therapy and immunotherapy through the complex interaction between cancer epigenetics and cancer immunology.

Epigenetic regulation of innate immune dynamics during inflammation

Innate immune cells play essential roles in modulating both immune defense and inflammation by expressing a diverse array of cytokines and inflammatory mediators, phagocytizing pathogens to promote immune clearance, and assisting with the adaptive immune processes through antigen presentation. Rudimentary innate immune "memory" states such as training, tolerance, and exhaustion develop based on the nature, strength, and duration of immune challenge, thereby enabling dynamic transcriptional reprogramming to alter present and future cell behavior. Underlying transcriptional reprogramming are broad changes to the epigenome, or chromatin alterations above the level of DNA sequence. These changes include direct modification of DNA through cytosine methylation as well as indirect modifications through alterations to histones that comprise the protein core of nucleosomes. In this review, we will discuss recent advances in our understanding of how these epigenetic changes influence the dynamic behavior of the innate immune system during both acute and chronic inflammation, as well as how stable changes to the epigenome result in long-term alterations of innate cell behavior related to pathophysiology.

Loss of TET2 increases B-1 cell number and IgM production while limiting CDR3 diversity

Recent studies have demonstrated a role for Ten-Eleven Translocation-2 (TET2), an epigenetic modulator, in regulating germinal center formation and plasma cell differentiation in B-2 cells, yet the role of TET2 in regulating B-1 cells is largely unknown. Here, B-1 cell subset numbers, IgM production, and gene expression were analyzed in mice with global knockout of TET2 compared to wildtype (WT) controls. Results revealed that TET2-KO mice had elevated numbers of B-1a and B-1b cells in their primary niche, the peritoneal cavity, as well as in the bone marrow (B-1a) and spleen (B-1b). Consistent with this finding, circulating IgM, but not IgG, was elevated in TET2-KO mice compared to WT. Analysis of bulk RNASeq of sort purified peritoneal B-1a and B-1b cells revealed reduced expression of heavy and light chain immunoglobulin genes, predominantly in B-1a cells from TET2-KO mice compared to WT controls. As expected, the expression of IgM transcripts was the most abundant isotype in B-1 cells. Yet, only in B-1a cells there was a significant increase in the proportion of IgM transcripts in TET2-KO mice compared to WT. Analysis of the CDR3 of the BCR revealed an increased abundance of replicated CDR3 sequences in B-1 cells from TET2-KO mice, which was more clearly pronounced in B-1a compared to B-1b cells. V-D-J usage and circos plot analysis of V-J combinations showed enhanced usage of VH11 and VH12 pairings. Taken together, our study is the first to demonstrate that global loss of TET2 increases B-1 cell number and IgM production and reduces CDR3 diversity, which could impact many biological processes and disease states that are regulated by IgM.

Exploring Epigenetic and Genetic Modulation in Animal Responses to Thermal Stress

There is increasing evidence indicating that global temperatures are rising significantly, a phenomenon commonly referred to as 'global warming', which in turn is believed to be causing drastic changes to the global climate. Global warming (GW) directly impacts animal health, reproduction, production, and welfare, presenting several challenges to livestock enterprises. Thermal stress (TS) is one of the key consequences of GW, and all animal species, including livestock, have diverse physiological, epigenetic and genetic mechanisms to respond to TS. As a result, TS can significantly affect an animals' health, immune responsiveness, metabolic pathways etc. which can also influence the productivity, performance, and welfare of animals. Moreover, prolonged exposure to TS can lead to transgenerational and intergenerational changes that are mediated by epigenetic changes. For example, in several animal species, the effects of TS are encoded epigenetically during the animals' growth or productive stage, and these epigenetic changes can be transmitted intergenerationally. Such epigenetic changes can affect animal productivity by changing the phenotype so that it aligns with its ancestors' environment, irrespective of its immediate environment. Furthermore, epigenetic and genetic changes can also help protect cells from the adverse effects of TS by modulating the transcriptional status of heat-responsive genes in animals. This review focuses on the genetic and epigenetic modulation and regulation that occurs in TS conditions via HSPs, histone alterations and DNA methylation.

5-Hydroxymethylcytosine: the many faces of the sixth base of mammalian DNA

Epigenetic phenomena play a central role in cell regulatory processes and are important factors for understanding complex human disease. One of the best understood epigenetic mechanisms is DNA methylation. In the mammalian genome, cytosines (C) in CpG dinucleotides were long known to undergo methylation at the 5-position of the pyrimidine ring (mC). Later it was found that mC can be oxidized to 5-hydroxymethylcytosine (hmC) or even further to 5-formylcytosine (fC) and to 5-carboxylcytosine (caC) by the action of 2-oxoglutarate-dependent dioxygenases of the TET family. These findings unveiled a long elusive mechanism of active DNA demethylation and bolstered a wave of studies in the area of epigenetic regulation in mammals. This review is dedicated to critical assessment of recent data on biochemical and chemical aspects of the formation and conversion of hmC in DNA, analytical techniques used for detection and mapping of this nucleobase in mammalian genomes as well as epigenetic roles of hmC in DNA replication, transcription, cell differentiation and human disease.

Ten-eleven translocation (Tet) methylcytosine dioxygenase-dependent viral DNA demethylation mediates in vivo hepatitis B virus (HBV) biosynthesis

Liver-specific ten-eleven translocation (Tet) methylcytosine dioxygenases 2 and 3 (Tet2 plus Tet3)-deficient hepatitis B virus (HBV) transgenic mice fail to support viral biosynthesis. The levels of viral transcription and replication intermediates are dramatically reduced. Hepatitis B core antigen is only observed in a very limited number of pericentral hepatocytes in a pattern that is similar to glutamate-ammonia ligase (Glul), a β-catenin target gene. HBV transcript abundance in adult Tet-deficient mice resembles that observed in wild-type neonatal mice. Furthermore, the RNA levels of several β-catenin target genes including Glul, Lhpp, Notun, Oat, Slc1a2, and Tbx3 in Tet-deficient mice were also similar to that observed in wild-type neonatal mice. As HBV transcription is regulated by β-catenin, these findings support the suggestion that neonatal Tet deficiency might limit β-catenin target gene expression, limiting viral biosynthesis. Additionally, HBV transgene DNA displays increased 5-methylcytosine (5mC) frequency at CpG sequences consistent with neonatal Tet deficiency being responsible for decreased developmental viral DNA demethylation mediated by 5mC oxidation to 5-hydroxymethylcytosine, a process that might be responsible for the reduction in cellular β-catenin target gene expression and viral transcription and replication.IMPORTANCEChronic hepatitis B virus (HBV) infection causes significant worldwide morbidity and mortality. There are no curative therapies available to resolve chronic HBV infections, and the small viral genome limits molecular targets for drug development. An alternative approach to drug development is to target cellular genes essential for HBV biosynthesis. In the liver, ten-eleven translocation (Tet) genes encode cellular enzymes that are not essential for postnatal mouse development but represent essential activities for viral DNA demethylation and transcription. Consequently, Tet inhibitors may potentially be developed into therapeutic agents capable of inducing and/or maintaining HBV covalently closed circular DNA methylation, resulting in transcriptional silencing and the resolution of chronic viral infection.

TET2 mutation as prototypic clonal hematopoiesis lesion

Loss of function TET2 mutation (TET2MT) is one of the most frequently observed lesions in clonal hematopoiesis (CH). TET2 a member TET-dioxygenase family of enzymes that along with TET1 and TET3, progressively oxidize 5-methyl cytosine (mC) resulting in regulated demethylation of promoter, enhancer and silencer elements of the genome. This process is critical for efficient transcription that determine cell lineage fate, proliferation and survival and the maintenance of the genomic fidelity with aging of the organism. Partial or complete loss-of-function TET2 mutations create regional and contextual DNA hypermethylation leading to gene silencing or activation that result in skewed myeloid differentiation and clonal expansion. In addition to myeloid skewing, loss of TET2 creates differentiation block and provides proliferative advantage to hematopoietic stem and progenitor cells (HSPCs). TET2MT is a prototypical lesion in CH, since the mutant clones dominate during stress hematopoiesis and often associates with evolution of myeloid malignancies. TET2MT clones has unique privilege to create and persist in pro-inflammatory milieu. Despite extensive knowledge regarding biochemical mechanisms underlying distorted myeloid differentiation, and enhanced self-replication of TET2MT HSPC, the mechanistic link of various pathogenesis associated with TET2 loss in CHIP is less understood. Here we review the recent development in TET2 biology and its probable mechanistic link in CH with aging and inflammation. We also explored the therapeutic strategies of targeting TET2MT associated CHIP and the utility of targeting TET2 in normal hematopoiesis and somatic cell reprograming. We explore the biochemical mechanisms and candidate therapies that emerged in last decade of research.

TET1 Regulates Skeletal Stem-Cell Mediated Cartilage Regeneration

OBJECTIVE

Adult skeletal stem cells (SSCs) that give rise to chondrocytes, osteocytes, and stromal cells as progeny have been shown to contribute to cartilage regeneration in osteoarthritis (OA). Understanding extrinsic and intrinsic regulators of SSC fate and function can therefore identify putative candidate factors to enhance cartilage regeneration. This study explores how the DNA hydroxymethylase Tet1 regulates SSC function in OA.

METHODS

We investigated the differences in the SSC lineage tree and differentiation potential in neonatal and adult Tet1+/+ and Tet1-/- mice with and without injury and upon OA induction and progression. Using RNA sequencing, the transcriptomic differences between SSCs and bone cartilage stroma progenitor cells (BCSPs) were identified in Tet1+/+ mice and Tet1-/- mice.

RESULTS

Loss of Tet1 skewed the SSC lineage tree by expanding the SSC pool and enhanced the chondrogenic potential of SSCs and BCSPs. Tet1 inhibition led to enhanced chondrogenesis in human SSCs and chondroprogenitors isolated from human cartilage. Importantly, TET1 inhibition in vivo in late stages of a mouse model of OA led to increased cartilage regeneration. Transcriptomic analyses of SSCs and BCSPs lacking Tet1 revealed pathway alterations in transforming growth factor β signaling, melatonin degradation, and cartilage development-associated genes. Lastly, we report that use of the hormone melatonin can dampen inflammation and improve cartilage health.

CONCLUSION

Although Tet1 is a broad epigenetic regulator, melatonin can mimic the inhibition ability of TET1 to enhance the chondrogenic ability of SSCs. Melatonin administration has the potential to be an attractive stem cell-based therapy for cartilage regeneration.

Cellular carcinogenesis in preleukemic conditions:drivers and defenses

Acute myeloid leukemia (AML) arises from preleukemic conditions. We have investigated the pathogenesis of typical preleukemia, myeloproliferative neoplasms, and clonal hematopoiesis. Hematopoietic stem cells in both preleukemic conditions harbor recurrent driver mutations; additional mutation provokes further malignant transformation, leading to AML onset. Although genetic alterations are defined as the main cause of malignant transformation, non-genetic factors are also involved in disease progression. In this review, we focus on a non-histone chromatin protein, high mobility group AT-hook2 (HMGA2), and a physiological p53 inhibitor, murine double minute X (MDMX). HMGA2 is mainly overexpressed by dysregulation of microRNAs or mutations in polycomb components, and provokes expansion of preleukemic clones through stem cell signature disruption. MDMX is overexpressed by altered splicing balance in myeloid malignancies. MDMX induces leukemic transformation from preleukemia via suppression of p53 and p53-independent activation of WNT/β-catenin signaling. We also discuss how these non-genetic factors can be targeted for leukemia prevention therapy.

Clonal Hematopoiesis, Inflammation, and Hematologic Malignancy

Somatic or acquired mutations are postzygotic genetic variations that can occur within any tissue. These mutations accumulate during aging and have classically been linked to malignant processes. Tremendous advancements over the past years have led to a deeper understanding of the role of somatic mutations in benign and malignant age-related diseases. Here, we review the somatic mutations that accumulate in the blood and their connection to disease states, with a particular focus on inflammatory diseases and myelodysplastic syndrome. We include a definition of clonal hematopoiesis (CH) and an overview of the origins and implications of these mutations. In addition, we emphasize somatic disorders with overlapping inflammation and hematologic disease beyond CH, including paroxysmal nocturnal hemoglobinuria and aplastic anemia, focusing on VEXAS (vacuoles, E1 enzyme, X-linked, autoinflammatory, somatic) syndrome. Finally, we provide a practical view of the implications of somatic mutations in clinical hematology, pathology, and beyond.

Regulation of lymphoid-myeloid lineage bias through regnase-1/3-mediated control of Nfkbiz

ABSTRACT

Regulation of lineage biases in hematopoietic stem and progenitor cells (HSPCs) is pivotal for balanced hematopoietic output. However, little is known about the mechanism behind lineage choice in HSPCs. Here, we show that messenger RNA (mRNA) decay factors regnase-1 (Reg1; Zc3h12a) and regnase-3 (Reg3; Zc3h12c) are essential for determining lymphoid fate and restricting myeloid differentiation in HSPCs. Loss of Reg1 and Reg3 resulted in severe impairment of lymphopoiesis and a mild increase in myelopoiesis in the bone marrow. Single-cell RNA sequencing analysis revealed that Reg1 and Reg3 regulate lineage directions in HSPCs via the control of a set of myeloid-related genes. Reg1- and Reg3-mediated control of mRNA encoding Nfkbiz, a transcriptional and epigenetic regulator, was essential for balancing lymphoid/myeloid lineage output in HSPCs in vivo. Furthermore, single-cell assay for transposase-accessible chromatin sequencing analysis revealed that Reg1 and Reg3 control the epigenetic landscape on myeloid-related gene loci in early stage HSPCs via Nfkbiz. Consistently, an antisense oligonucleotide designed to inhibit Reg1- and Reg3-mediated Nfkbiz mRNA degradation primed hematopoietic stem cells toward myeloid lineages by enhancing Nfkbiz expression. Collectively, the collaboration between posttranscriptional control and chromatin remodeling by the Reg1/Reg3-Nfkbiz axis governs HSPC lineage biases, ultimately dictating the fate of lymphoid vs myeloid differentiation.

Increased iron uptake by splenic hematopoietic stem cells promotes TET2-dependent erythroid regeneration

Hematopoietic stem cells (HSCs) are capable of regenerating the blood system, but the instructive cues that direct HSCs to regenerate particular lineages lost to the injury remain elusive. Here, we show that iron is increasingly taken up by HSCs during anemia and induces erythroid gene expression and regeneration in a Tet2-dependent manner. Lineage tracing of HSCs reveals that HSCs respond to hemolytic anemia by increasing erythroid output. The number of HSCs in the spleen, but not bone marrow, increases upon anemia and these HSCs exhibit enhanced proliferation, erythroid differentiation, iron uptake, and TET2 protein expression. Increased iron in HSCs promotes DNA demethylation and expression of erythroid genes. Suppressing iron uptake or TET2 expression impairs erythroid genes expression and erythroid differentiation of HSCs; iron supplementation, however, augments these processes. These results establish that the physiological level of iron taken up by HSCs has an instructive role in promoting erythroid-biased differentiation of HSCs.

Recurrent Aortic Thromboembolism Associated With TET2 Mutation in Chronic Myelomonocytic Leukemia

Ten-eleven translocation 2 (TET2) plays a pivotal role in epigenetic regulation, cell differentiation, and the inflammatory response. It also mediates the transcriptional regulation for inflammatory cytokines, particularly interleukin-6. While loss-of-function mutation in TET2 has been associated with hematological malignancies, it has been increasingly recognized to cause atherosclerotic disease. The increased atherogenicity is thought to be the result of increased production of pro-inflammatory interleukin-1β cytokines following activation of NLRP3 inflammasomes. We present a unique case of recurrent atherothrombosis in an elderly man who was diagnosed with chronic myelomonocytic leukemia in the setting of TET2 mutation.

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.

Bidirectional interplay between metabolism and epigenetics in hematopoietic stem cells and leukemia

During the last decades, remarkable progress has been made in further understanding the complex molecular regulatory networks that maintain hematopoietic stem cell (HSC) function. Cellular and organismal metabolisms have been shown to directly instruct epigenetic alterations, and thereby dictate stem cell fate, in the bone marrow. Epigenetic regulatory enzymes are dependent on the availability of metabolites to facilitate DNA- and histone-modifying reactions. The metabolic and epigenetic features of HSCs and their downstream progenitors can be significantly altered by environmental perturbations, dietary habits, and hematological diseases. Therefore, understanding metabolic and epigenetic mechanisms that regulate healthy HSCs can contribute to the discovery of novel metabolic therapeutic targets that specifically eliminate leukemia stem cells while sparing healthy HSCs. Here, we provide an in-depth review of the metabolic and epigenetic interplay regulating hematopoietic stem cell fate. We discuss the influence of metabolic stress stimuli, as well as alterations occurring during leukemic development. Additionally, we highlight recent therapeutic advancements toward eradicating acute myeloid leukemia cells by intervening in metabolic and epigenetic pathways.

STING activation in TET2-mutated hematopoietic stem/progenitor cells contributes to the increased self-renewal and neoplastic transformation

Somatic loss-of-function mutations of the dioxygenase Ten-eleven translocation-2 (TET2) occur frequently in individuals with clonal hematopoiesis (CH) and acute myeloid leukemia (AML). These common hematopoietic disorders can be recapitulated in mouse models. However, the underlying mechanisms by which the deficiency in TET2 promotes these disorders remain unclear. Here we show that the cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS)-stimulator of interferon genes (STING) pathway is activated to mediate the effect of TET2 deficiency in dysregulated hematopoiesis in mouse models. DNA damage arising in Tet2-deficient hematopoietic stem/progenitor cells (HSPCs) leads to activation of the cGAS-STING pathway which in turn promotes the enhanced self-renewal and development of CH. Notably, both pharmacological inhibition and genetic deletion of STING suppresses Tet2 mutation-induced aberrant hematopoiesis. In patient-derived xenograft (PDX) models, STING inhibition specifically attenuates the proliferation of leukemia cells from TET2-mutated individuals. These observations suggest that the development of CH associated with TET2 mutations is powered through chronic inflammation dependent on the activated cGAS-STING pathway and that STING may represent a potential target for intervention of relevant hematopoietic diseases.

Transient TKI-resistant CD44+pBAD+ blasts undergo intrinsic homeostatic adaptation to promote the survival of acute myeloid leukemia in vitro

Acute myeloid leukemia (AML) patients have frequent mutations in FMS-like receptor tyrosine kinase 3 (FLT3-mut AML), who respond poorly to salvage chemotherapies and targeted therapies such as tyrosine kinase inhibitors (TKIs). Disease relapse is a common reason of treatment failures in FLT3-mut AML patients, but its intracellular refractory mechanism remains to be discovered. In this study, we designed serial in vitro time-course studies to investigate the biomarkers of TKI-resistant blasts and their survival mechanism. First, we found that a group of transient TKI-resistant blasts were CD44+Phosphorylated-BAD (pBAD)+ and that they could initiate the regrowth of blast clusters in vitro. Notably, TKI-treatments upregulated the compensation pathways to promote PIM2/3-mediated phosphorylation of BAD to initiate the blast survival. Next, we discovered a novel process of intracellular adaptive responses in these transient TKI-resistant blasts, including upregulated JAK/STAT signaling pathways for PIM2/3 expressions and activated SOCS1/SOCS3/PIAS2 inhibitory pathways to down-regulate redundant signal transduction and kinase phosphorylation to regain intracellular homeostasis. Finally, we found that the combination of TKIs with TYK2/STAT4 pathways-driven inhibitors could effectively treat FLT3-mut AML in vitro. In summary, our findings reveal that TKI-treatment can activate a JAK/STAT-PIM2/3 axis-mediated signaling pathways to promote the survival of CD44+pBAD+blasts in vitro. Disrupting these TKIs-activated redundant pathways and blast homeostasis could be a novel therapeutic strategy to treat FLT3-mut AML and prevent disease relapse in vivo.

TET2 modulates spatial relocalization of heterochromatin in aged hematopoietic stem and progenitor cells

DNA methylation deregulation at partially methylated domains (PMDs) represents an epigenetic signature of aging and cancer, yet the underlying molecular basis and resulting biological consequences remain unresolved. We report herein a mechanistic link between disrupted DNA methylation at PMDs and the spatial relocalization of H3K9me3-marked heterochromatin in aged hematopoietic stem and progenitor cells (HSPCs) or those with impaired DNA methylation. We uncover that TET2 modulates the spatial redistribution of H3K9me3-marked heterochromatin to mediate the upregulation of endogenous retroviruses (ERVs) and interferon-stimulated genes (ISGs), hence contributing to functional decline of aged HSPCs. TET2-deficient HSPCs retain perinuclear distribution of heterochromatin and exhibit age-related clonal expansion. Reverse transcriptase inhibitors suppress ERVs and ISGs expression, thereby restoring age-related defects in aged HSPCs. Collectively, our findings deepen the understanding of the functional interplay between DNA methylation and histone modifications, which is vital for maintaining heterochromatin function and safeguarding genome stability in stem cells.

[Effect of clonal hematopoiesis in remission on hematopoiesis recovery in patients with NPM1 mutated acute myeloid leukemia after chemotherapy]

Objective: To investigate the effect of clonal hematopoiesis (CH) in remission on hematopoiesis recovery in patients with NPM1 mutated acute myeloid leukemia (AML) after chemotherapy. Methods: Retrospective analysis was performed on 86 patients with NPM1(mut) AML newly diagnosed and treated in the First Affiliated Hospital of Soochow University between July 2016 and June 2019. Their clinical data and NGS test results at diagnosis were analyzed. Moreover, bone marrow samples in remission were tested using Sanger sequencing. The log-rank test was used to analyze the difference in hematopoietic recovery, and Cox proportional hazard models were used to analyze the prognostic factors affecting hematopoietic recovery. Results: The median age of the 86 NPM1(mut) AML patients was 50 years (15-69 years). There were 39 males and 47 females. Forty-one patients were induced with intensity chemotherapy ("7 + 3"), whereas 45 patients were treated with low-dose cytarabine-based induction chemotherapy. At diagnosis, The most common mutations in the patients were FLT3, DNMT3A, TET2, and IDH1/IDH2 mutations. CH-associated mutations persisted in 21 patients during remission, and the mutations were DNMT3A, TET2, ASXL1, and IDH1/IDH2. The recovery time of neutrophils in patients with CH-associated mutations in remission was consistent with that in patients without CH in remission (P=0.282) but the recovery time of platelets in patients with CH in remission was significantly longer[26 (95% CI 21-32) days vs 25 (95% CI 23-26) days, P=0.032]. Furthermore, univariate analysis indicated that age, induced chemotherapy program, and CH in remission were risk factors for platelet recovery, whereas multivariate analysis indicated that induced chemotherapy program and CH in remission were independent risk factors for platelet recovery (HR=0.454, P=0.001 and HR=0.520, P=0.027, respectively) . Conclusion: CH in remission delays the hematopoietic recovery of patients with NPM1(mut) AML after chemotherapy.

HDAC6 deacetylates IDH1 to promote the homeostasis of hematopoietic stem and progenitor cells

Hematopoietic stem and progenitor cells (HSPCs) are cells mainly present in the bone marrow and capable of forming mature blood cells. However, the epigenetic mechanisms governing the homeostasis of HSPCs remain elusive. Here, we demonstrate an important role for histone deacetylase 6 (HDAC6) in regulating this process. Our data show that the percentage of HSPCs in Hdac6 knockout mice is lower than in wild-type mice due to decreased HSPC proliferation. HDAC6 interacts with isocitrate dehydrogenase 1 (IDH1) and deacetylates IDH1 at lysine 233. The deacetylation of IDH1 inhibits its catalytic activity and thereby decreases the 5-hydroxymethylcytosine level of ten-eleven translocation 2 (TET2) target genes, changing gene expression patterns to promote the proliferation of HSPCs. These findings uncover a role for HDAC6 and IDH1 in regulating the homeostasis of HSPCs and may have implications for the treatment of hematological diseases.

Biological insights into the role of TET2 in T cell lymphomas

Peripheral T cell lymphomas (PTCL) are a heterogenous group of mature T cell lymphomas with an overall poor prognosis. Understanding the molecular heterogeneity in PTCL subtypes may lead to improved understanding of the underlying biological mechanisms driving these diseases. Mutations in the epigenetic regulator TET2 are among the most frequent mutations identified in PTCL, with the highest frequency in angioimmunoblastic T cell lymphomas and other nodal T follicular helper (TFH) lymphomas. This review dissects the role of TET2 in nodal TFH cell lymphomas with a focus on emerging biological insights into the molecular mechanism promoting lymphomagenesis and the potential for epigenetic therapies to improve clinical outcomes.

Tet2 deletion in CD4+ T cells disrupts Th1 lineage commitment in memory cells and enhances T follicular helper cell recall responses to viral rechallenge

Following viral clearance, antigen-specific CD4+ T cells contract and form a pool of distinct Th1 and Tfh memory cells that possess unique epigenetic programs, allowing them to rapidly recall their specific effector functions upon rechallenge. DNA methylation programing mediated by the methylcytosine dioxygenase Tet2 contributes to balancing Th1 and Tfh cell differentiation during acute viral infection; however, the role of Tet2 in CD4+ T cell memory formation and recall is unclear. Using adoptive transfer models of antigen-specific wild type and Tet2 knockout CD4+ T cells, we find that Tet2 is required for full commitment of CD4+ T cells to the Th1 lineage and that in the absence of Tet2, memory cells preferentially recall a Tfh like phenotype with enhanced expansion upon secondary challenge. These findings demonstrate an important role for Tet2 in enforcing lineage commitment and programing proliferation potential, and highlight the potential of targeting epigenetic programing to enhance adaptive immune responses.

Genetic Polymorphism Study of IDH 1/2 and TET2 Genes in Acute Myeloid leukemia Patients

BACKGROUND AND OBJECTIVE

Isocitrate dehydrogenase genes (IDH1 and IDH2) encode important enzymes that play pivotal role in cellular metabolism. Mutations in TET2 have been demonstrated to contribute to DNA hypermethylation, either expression of mutant IDH1/2 or TET2 resulted in poor cell differentiation and epigenetic alterations in hematopoietic cells, suggesting a sharing of the oncogenetic impact. In this study, we investigated the frequency of genetic alterations in IDH1/2 and TET2 genes in Egyptian cohort of adult patients with de novo AML, and the association of IDH1/2 and TET2 genetic Polymorphism with AML prognostic criteria and explore prognostic molecular markers with clinical outcome.

METHODS

The SNP assay for IDH1, IDH2 and TET2 genes polymorphism tested with RT-PCR included three polymorphisms that are rs121913500, rs121913503, and rs2454206 respectively, were tested on 141 adult Egyptian patients fulfilling the AML diagnostic criteria.

RESULT

The incidence of IDH mutations is 11/141 (7.8%); 5/141 (3.5%) IDH1 mutant and 6/141 (4.3%) IDH2 mutant. And the incidence of TET2 mutations is 72/141 (51.1%); 15/141 (10.7%) homozygous mutation and 57/141 (40.4%) heterozygous mutations. IDH1, IDH2 and TET2 genes mutations with DFS and OS in AML patients were not significantly correlated.

CONCLUSIONS

TET2 SNP is common in Egyptian AML patients. Further research on IDH, TET2 and their relationships to other hematological malignancies and leukemogenesis transformation is advised and a study of a larger number of cases is needed for potential statistical significance.

TET (Ten-eleven translocation) family proteins: structure, biological functions and applications

Ten-eleven translocation (TET) family proteins (TETs), specifically, TET1, TET2 and TET3, can modify DNA by oxidizing 5-methylcytosine (5mC) iteratively to yield 5-hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC), and 5-carboxycytosine (5caC), and then two of these intermediates (5fC and 5caC) can be excised and return to unmethylated cytosines by thymine-DNA glycosylase (TDG)-mediated base excision repair. Because DNA methylation and demethylation play an important role in numerous biological processes, including zygote formation, embryogenesis, spatial learning and immune homeostasis, the regulation of TETs functions is complicated, and dysregulation of their functions is implicated in many diseases such as myeloid malignancies. In addition, recent studies have demonstrated that TET2 is able to catalyze the hydroxymethylation of RNA to perform post-transcriptional regulation. Notably, catalytic-independent functions of TETs in certain biological contexts have been identified, further highlighting their multifunctional roles. Interestingly, by reactivating the expression of selected target genes, accumulated evidences support the potential therapeutic use of TETs-based DNA methylation editing tools in disorders associated with epigenetic silencing. In this review, we summarize recent key findings in TETs functions, activity regulators at various levels, technological advances in the detection of 5hmC, the main TETs oxidative product, and TETs emerging applications in epigenetic editing. Furthermore, we discuss existing challenges and future directions in this field.

TET2 is required to suppress mTORC1 signaling through urea cycle with therapeutic potential

Tumor development, involving both cell growth (mass accumulation) and cell proliferation, is a complex process governed by the interplay of multiple signaling pathways. TET2 mainly functions as a DNA dioxygenase, which modulates gene expression and biological functions via oxidation of 5mC in DNA, yet whether it plays a role in regulating cell growth remains unknown. Here we show that TET2 suppresses mTORC1 signaling, a major growth controller, to inhibit cell growth and promote autophagy. Mechanistically, TET2 functions as a 5mC "eraser" by mRNA oxidation, abolishes YBX1-HuR binding and promotes decay of urea cycle enzyme mRNAs, thus negatively regulating urea cycle and arginine production, which suppresses mTORC1 signaling. Therefore, TET2-deficient tumor cells are more sensitive to mTORC1 inhibition. Our results uncover a novel function for TET2 in suppressing mTORC1 signaling and inhibiting cell growth, linking TET2-mediated mRNA oxidation to cell metabolism and cell growth control. These findings demonstrate the potential of mTORC1 inhibition as a possible treatment for TET2-deficient tumors.

TET2-mediated mRNA demethylation regulates leukemia stem cell homing and self-renewal

TET2 is recurrently mutated in acute myeloid leukemia (AML) and its deficiency promotes leukemogenesis (driven by aggressive oncogenic mutations) and enhances leukemia stem cell (LSC) self-renewal. However, the underlying cellular/molecular mechanisms have yet to be fully understood. Here, we show that Tet2 deficiency significantly facilitates leukemogenesis in various AML models (mediated by aggressive or less aggressive mutations) through promoting homing of LSCs into bone marrow (BM) niche to increase their self-renewal/proliferation. TET2 deficiency in AML blast cells increases expression of Tetraspanin 13 (TSPAN13) and thereby activates the CXCR4/CXCL12 signaling, leading to increased homing/migration of LSCs into BM niche. Mechanistically, TET2 deficiency results in the accumulation of methyl-5-cytosine (m5C) modification in TSPAN13 mRNA; YBX1 specifically recognizes the m5C modification and increases the stability and expression of TSPAN13 transcripts. Collectively, our studies reveal the functional importance of TET2 in leukemogenesis, leukemic blast cell migration/homing, and LSC self-renewal as an mRNA m5C demethylase.

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.

RNA splicing factor Rbm25 underlies heterogeneous preleukemic clonal expansion in mice

Clonal expansion sets the stage for cancer genesis by allowing for the accumulation of molecular alterations. Although genetic mutations such as Tet2 that induce clonal expansion and malignancy have been identified, these mutations are also frequently found in healthy individuals. Here, we tracked preleukemic clonal expansion using genetic barcoding in an inducible Tet2 knockout mouse model and found that only a small fraction of hematopoietic stem cells (HSCs) expanded excessively upon Tet2 knockout. These overexpanded HSCs expressed significantly lower levels of genes associated with leukemia and RNA splicing than nonoverexpanded Tet2 knockout HSCs. Knocking down Rbm25, an identified RNA splicing factor, accelerated the expansion of Tet2-knockout hematopoietic cells in vitro and in vivo. Our data suggest that mutations of an epigenetic factor Tet2 induce variability in the expression of an RNA splicing factor Rbm25, which subsequently drives heterogeneous preleukemic clonal expansion. This heterogeneous clonal expansion could contribute to the variable disease risks across individuals.

Loss of TET2 in human hematopoietic stem cells alters the development and function of neutrophils

Somatic mutations commonly occur in hematopoietic stem cells (HSCs). Some mutant clones outgrow through clonal hematopoiesis (CH) and produce mutated immune progenies shaping host immunity. Individuals with CH are asymptomatic but have an increased risk of developing leukemia, cardiovascular and pulmonary inflammatory diseases, and severe infections. Using genetic engineering of human HSCs (hHSCs) and transplantation in immunodeficient mice, we describe how a commonly mutated gene in CH, TET2, affects human neutrophil development and function. TET2 loss in hHSCs produce a distinct neutrophil heterogeneity in bone marrow and peripheral tissues by increasing the repopulating capacity of neutrophil progenitors and giving rise to low-granule neutrophils. Human neutrophils that inherited TET2 mutations mount exacerbated inflammatory responses and have more condensed chromatin, which correlates with compact neutrophil extracellular trap (NET) production. We expose here physiological abnormalities that may inform future strategies to detect TET2-CH and prevent NET-mediated pathologies associated with CH.

Obesity-induced inflammation exacerbates clonal hematopoiesis

Characterized by the accumulation of somatic mutations in blood cell lineages, clonal hematopoiesis of indeterminate potential (CHIP) is frequent in aging and involves the expansion of mutated hematopoietic stem and progenitor cells (HSC/Ps) that leads to an increased risk of hematologic malignancy. However, the risk factors that contribute to CHIP-associated clonal hematopoiesis (CH) are poorly understood. Obesity induces a proinflammatory state and fatty bone marrow (FBM), which may influence CHIP-associated pathologies. We analyzed exome sequencing and clinical data for 47,466 individuals with validated CHIP in the UK Biobank. CHIP was present in 5.8% of the study population and was associated with a significant increase in the waist-to-hip ratio (WHR). Mouse models of obesity and CHIP driven by heterozygosity of Tet2, Dnmt3a, Asxl1, and Jak2 resulted in exacerbated expansion of mutant HSC/Ps due in part to excessive inflammation. Our results show that obesity is highly associated with CHIP and that a proinflammatory state could potentiate the progression of CHIP to more significant hematologic neoplasia. The calcium channel blockers nifedipine and SKF-96365, either alone or in combination with metformin, MCC950, or anakinra (IL-1 receptor antagonist), suppressed the growth of mutant CHIP cells and partially restored normal hematopoiesis. Targeting CHIP-mutant cells with these drugs could be a potential therapeutic approach to treat CH and its associated abnormalities in individuals with obesity.

The impact of epigenetic modifications on allogeneic hematopoietic stem cell transplantation

The field of epigenetics studies the complex processes that regulate gene expression without altering the DNA sequence itself. It is well established that epigenetic modifications are crucial to cellular homeostasis and differentiation and play a vital role in hematopoiesis and immunity. Epigenetic marks can be mitotically and/or meiotically heritable upon cell division, forming the basis of cellular memory, and have the potential to be reversed between cellular fate transitions. Hence, over the past decade, there has been increasing interest in the role that epigenetic modifications may have on the outcomes of allogeneic hematopoietic transplantation and growing enthusiasm in the therapeutic potential these pathways may hold. In this brief review, we provide a basic overview of the types of epigenetic modifications and their biological functions, summarizing the current literature with a focus on hematopoiesis and immunity specifically in the context of allogeneic hematopoietic stem cell transplantation.

Review: MDMX plays a central role in leukemic transformation and may be a promising target for leukemia prevention strategies

Acute myeloid leukemia (AML) is a fatal disease resulting from preleukemic hematopoietic conditions including asymptomatic clonal hematopoiesis. The accumulation of genetic changes is one of the causes of leukemic transformation. However, nongenetic factors including the overexpression of specific genes also contribute to preleukemic to leukemic transition. Among them, the p53 inhibitor Murine Double Minute X (MDMX) plays crucial roles especially in leukemia initiation. MDMX is broadly overexpressed in vast majority of AML cases, including in hematopoietic stem/progenitor cell (HSPC) level. Recently, high expression of MDMX in HSPC has been shown to be associated with leukemic transformation in patients with myelodysplastic syndromes, and preclinical studies demonstrated that MDMX overexpression accelerates the transformation of preleukemic murine models, including models of clonal hematopoiesis. MDMX inhibition, through activation of cell-intrinsic p53 activity, shows antileukemic effects. However, the molecular mechanisms of MDMX in provoking leukemic transformation are complicated. Both p53-dependent and independent mechanisms are involved in the progression of the disease. This review discusses the canonical and noncanonical functions of MDMX and how these functions are involved in the maintenance, expansion, and progression to malignancy of preleukemic stem cells. Moreover, strategies on how leukemic transformation could possibly be prevented by targeting MDMX in preleukemic stem cells are discussed.

CHIP Happens: Clonal Hematopoiesis of Indeterminate Potential and Its Relationship to Solid Tumors

Clonal hematopoiesis of indeterminate potential (CHIP) is characterized by the expansion of hematopoietic cells harboring leukemia-associated somatic mutations in otherwise healthy people and occurs in at least 10% of adults over 70. It is well established that people with CHIP have increased rates of hematologic malignancy, increased risk of cardiovascular disease, and worse all-cause mortality compared with those without CHIP. Despite recent advancements in understanding CHIP as it relates to these known outcomes, much remains to be learned about the development and role of CHIP in other disease states. Emerging research has identified high rates of CHIP in patients with solid tumors, driven in part by oncologic therapy, and revealed associations between CHIP and differential outcomes in both solid tumors and other diseases. Recent studies have demonstrated that CHIP can contribute to dysregulated inflammatory signaling in multiple contexts, underscoring the importance of interrogating how CHIP might alter tumor immunology. Here, we review the role of CHIP mutations in clonal expansion of hematopoietic cells, explore the relationship between CHIP and solid tumors, and discuss the potential roles of CHIP in inflammation and solid tumor biology.

Clonal Hematopoiesis and the Heart: a Toxic Relationship

PURPOSE OF REVIEW

Clonal hematopoiesis (CH) refers to the expansion of hematopoietic stem cell clones and their cellular progeny due to somatic mutations, mosaic chromosomal alterations (mCAs), or copy number variants which naturally accumulate with age. CH has been linked to increased risk of blood cancers, but CH has also been linked to adverse cardiovascular outcomes.

RECENT FINDINGS

A combination of clinical outcome studies and mouse models have offered strong evidence that CH mutations either correlate with or cause atherosclerosis, diabetes mellitus, chronic kidney disease, heart failure, pulmonary hypertension, aortic aneurysm, myocardial infarction, stroke, aortic stenosis, poor outcomes following transcatheter aortic valve replacement (TAVR) or orthotopic heart transplant, death or need of renal replacement therapy secondary to cardiogenic shock, death from cardiovascular causes at large, and enhance anthracycline cardiac toxicity. Mechanistically, some adverse outcomes are caused by macrophage secretion of IL-1β and IL-6, neutrophil invasion of injured myocardium, and T-cell skewing towards inflammatory phenotypes. CH mutations lead to harmful inflammation and arterial wall invasion by bone marrow-derived cells resulting in poor cardiovascular health and outcomes. Blockade of IL-1β or JAK2 signaling are potential avenues for preventing CH-caused cardiovascular morbidity and mortality.

Emerging Role of Acquired Mutations and Clonal Hematopoiesis in Atherosclerosis - Beyond Conventional Cardiovascular Risk Factors

Accumulating evidence suggests that conventional cardiovascular risk factors are incompletely predictive of cardiovascular disease, as a substantial risk remains even when these factors are apparently managed well. In this context, clonal hematopoiesis has emerged as a new and potent risk factor for atherosclerotic cardiovascular disease and other cardiometabolic conditions. Clonal hematopoiesis typically arises from somatic mutations that confer a competitive advantage to a mutant hematopoietic stem cell, leading to its clonal expansion in the stem cell population and its progeny of blood leukocytes. Human sequencing studies and experiments in mice suggest that clonal hematopoiesis, at least when driven by certain mutations, contributes to accelerated atherosclerosis development. However, the epidemiology, biology and clinical implications of this phenomenon remain incompletely understood. Here, we review the current understanding of the connection between clonal hematopoiesis and atherosclerosis, and highlight knowledge gaps in this area of research.

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

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