JAK2-V617F and interferon-α induce megakaryocyte-biased stem cells characterized by decreased long-term functionality

Loss of Dnmt3a increases self-renewal and resistance to pegIFN-α in JAK2-V617F-positive myeloproliferative neoplasms

ABSTRACT

Pegylated interferon alfa (pegIFN-α) can induce molecular remissions in patients with JAK2-V617F-positive myeloproliferative neoplasms (MPNs) by targeting long-term hematopoietic stem cells (LT-HSCs). Additional somatic mutations in genes regulating LT-HSC self-renewal, such as DNMT3A, have been reported to have poorer responses to pegIFN-α. We investigated whether DNMT3A loss leads to alterations in JAK2-V617F LT-HSC functions conferring resistance to pegIFN-α treatment in a mouse model of MPN and in hematopoietic progenitors from patients with MPN. Long-term treatment with pegIFN-α normalized blood parameters and reduced splenomegaly and JAK2-V617F chimerism in single-mutant JAK2-V617F (VF) mice. However, pegIFN-α in VF;Dnmt3aΔ/Δ (VF;DmΔ/Δ) mice worsened splenomegaly and failed to reduce JAK2-V617F chimerism. Furthermore, LT-HSCs from VF;DmΔ/Δ mice compared with VF were less prone to accumulate DNA damage and exit dormancy upon pegIFN-α treatment. RNA sequencing showed that IFN-α induced stronger upregulation of inflammatory pathways in LT-HSCs from VF;DmΔ/Δ than from VF mice, indicating that the resistance of VF;DmΔ/Δ LT-HSC was not due to failure in IFN-α signaling. Transplantations of bone marrow from pegIFN-α-treated VF;DmΔ/Δ mice gave rise to more aggressive disease in secondary and tertiary recipients. Liquid cultures of hematopoietic progenitors from patients with MPN with JAK2-V617F and DNMT3A mutation showed increased percentages of JAK2-V617F-positive colonies upon IFN-α exposure, whereas in patients with JAK2-V617F alone, the percentages of JAK2-V617F-positive colonies decreased or remained unchanged. PegIFN-α combined with 5-azacytidine only partially overcame resistance in VF;DmΔ/Δ mice. However, this combination strongly decreased the JAK2-mutant allele burden in mice carrying VF mutation only, showing potential to inflict substantial damage preferentially to the JAK2-mutant clone.

The role of leukocytes in myeloproliferative neoplasm thromboinflammation

Classic myeloproliferative neoplasms lacking the Philadelphia chromosome are stem cell disorders characterized by the proliferation of myeloid cells in the bone marrow and increased counts of peripheral blood cells. The occurrence of thrombotic events is a common complication in myeloproliferative neoplasms. The heightened levels of cytokines play a substantial role in the morbidity and mortality of these patients, establishing a persistent proinflammatory condition that culminates in thrombosis. The etiology of thrombosis remains intricate and multifaceted, involving blood cells and endothelial dysfunction, the inflammatory state, and the coagulation cascade, leading to hypercoagulability. Leukocytes play a pivotal role in the thromboinflammatory process of myeloproliferative neoplasms by releasing various proinflammatory and prothrombotic factors as well as interacting with other cells, which contributes to the amplification of the clotting cascade and subsequent thrombosis. The correlation between increased leukocyte counts and thrombotic risk has been established. However, there is a need for an accurate biomarker to assess leukocyte activation. Lastly, tailored treatments to address the thrombotic risk in myeloproliferative neoplasms are needed. Therefore, this review aims to summarize the potential mechanisms of leukocyte involvement in myeloproliferative neoplasm thromboinflammation, propose potential biomarkers for leukocyte activation, and discuss promising treatment options for controlling myeloproliferative neoplasm thromboinflammation.

Deficiency of thioredoxin-interacting protein results in age-related thrombocytopenia due to megakaryocyte oxidative stress

BACKGROUND

Platelets are generated from megakaryocytes (MKs), mainly located in the bone marrow (BM). Megakaryopoiesis can be affected by genetic disorders, metabolic diseases, and aging. The molecular mechanisms underlying platelet count regulation have not been fully elucidated.

OBJECTIVES

In the present study, we investigated the role of thioredoxin-interacting protein (TXNIP), a protein that regulates cellular metabolism in megakaryopoiesis, using a Txnip-/- mouse model.

METHODS

Wild-type (WT) and Txnip-/- mice (2-27-month-old) were studied. BM-derived MKs were analyzed to investigate the role of TXNIP in megakaryopoiesis with age. The global transcriptome of BM-derived CD41+ megakaryocyte precursors (MkPs) of WT and Txnip-/- mice were compared. The CD34+ hematopoietic stem cells isolated from human cord blood were differentiated into MKs.

RESULTS

Txnip-/- mice developed thrombocytopenia at 4 to 5 months that worsened with age. During ex vivo megakaryopoiesis, Txnip-/- MkPs remained small, with decreased levels of MK-specific markers. Critically, Txnip-/- MkPs exhibited reduced mitochondrial reactive oxygen species, which was related to AKT activity. Txnip-/- MkPs also showed elevated glycolysis alongside increased glucose uptake for ATP production. Total RNA sequencing revealed enrichment for oxidative stress- and apoptosis-related genes in differentially expressed genes between Txnip-/- and WT MkPs. The effects of TXNIP on MKs were recapitulated during the differentiation of human cord blood-derived CD34+ hematopoietic stem cells.

CONCLUSION

We provide evidence that the megakaryopoiesis pathway becomes exhausted with age in Txnip-/- mice with a decrease in terminal, mature MKs that response to thrombocytopenic challenge. Overall, this study demonstrates the role of TXNIP in megakaryopoiesis, regulating mitochondrial metabolism.

Interferons in the treatment of myeloproliferative neoplasms

Interferons are cytokines with immunomodulatory properties and disease-modifying effects that have been used to treat myeloproliferative neoplasms (MPNs) for more than 35 years. The initial use of interferons was limited due to difficulties with administration and a significant toxicity profile. Many of these shortcomings were addressed by covalently binding polyethylene glycol to the interferon structure, which increases the stability, prolongs activity, and reduces immunogenicity of the molecule. In the current therapeutic landscape, pegylated interferons are recommended for use in the treatment of polycythemia vera, essential thrombocythemia, and primary myelofibrosis. We review recent efficacy, molecular response, and safety data for the two available pegylated interferons, peginterferon alfa-2a (Pegasys) and ropeginterferon alfa-2b-njft (BESREMi). The practical management of interferon-based therapies is discussed, along with our opinions on whether to and how to switch from hydroxyurea to one of these therapies. Key topics and questions related to use of interferons, such as their safety and tolerability, the significance of variant allele frequency, advantages of early treatment, and what the future of interferon therapy may look like, will be examined. Pegylated interferons represent an important therapeutic option for patients with MPNs; however, more research is still required to further refine interferon therapy.

Molecular Genetic Profile of Myelofibrosis: Implications in the Diagnosis, Prognosis, and Treatment Advancements

Myelofibrosis (MF) is an essential element of primary myelofibrosis, whereas secondary MF may develop in the advanced stages of other myeloid neoplasms, especially polycythemia vera and essential thrombocythemia. Over the last two decades, advances in molecular diagnostic techniques, particularly the integration of next-generation sequencing in clinical laboratories, have revolutionized the diagnosis, classification, and clinical decision making of myelofibrosis. Driver mutations involving JAK2, CALR, and MPL induce hyperactivity in the JAK-STAT signaling pathway, which plays a central role in cell survival and proliferation. Approximately 80% of myelofibrosis cases harbor additional mutations, frequently in the genes responsible for epigenetic regulation and RNA splicing. Detecting these mutations is crucial for diagnosing myeloproliferative neoplasms (MPNs), especially in cases where no mutations are present in the three driver genes (triple-negative MPNs). While fibrosis in the bone marrow results from the disturbance of inflammatory cytokines, it is fundamentally associated with mutation-driven hematopoiesis. The mutation profile and order of acquiring diverse mutations influence the MPN phenotype. Mutation profiling reveals clonal diversity in MF, offering insights into the clonal evolution of neoplastic progression. Prognostic prediction plays a pivotal role in guiding the treatment of myelofibrosis. Mutation profiles and cytogenetic abnormalities have been integrated into advanced prognostic scoring systems and personalized risk stratification for MF. Presently, JAK inhibitors are part of the standard of care for MF, with newer generations developed for enhanced efficacy and reduced adverse effects. However, only a minority of patients have achieved a significant molecular-level response. Clinical trials exploring innovative approaches, such as combining hypomethylation agents that target epigenetic regulators, drugs proven effective in myelodysplastic syndrome, or immune and inflammatory modulators with JAK inhibitors, have demonstrated promising results. These combinations may be more effective in patients with high-risk mutations and complex mutation profiles. Expanding mutation profiling studies with more sensitive and specific molecular methods, as well as sequencing a broader spectrum of genes in clinical patients, may reveal molecular mechanisms in cases currently lacking detectable driver mutations, provide a better understanding of the association between genetic alterations and clinical phenotypes, and offer valuable information to advance personalized treatment protocols to improve long-term survival and eradicate mutant clones with the hope of curing MF.

Complementary and countervailing actions of Jak2 and Ikk2 in hematopoiesis in mice

Hyperactivation of JAK2 kinase is a unifying feature of human Ph- myeloproliferative neoplasms (MPNs), most commonly due to the JAK2 V617F mutation. Mice harboring a homologous mutation in the Jak2 locus exhibit a phenotype resembling polycythemia vera. NFκB pathway hyperactivation is present in myeloid neoplasms, including MPNs, despite scarcity of mutations in NFκB pathway genes. To determine the impact of NFκB pathway hyperactivation in conjunction with Jak2 V617F, we utilized Ikk2 (Ikk2-CA) mice. Pan-hematopoietic Ikk2-CA alone produced depletion of hematopoietic stem cells and B cells. When combined with the Jak2 V617F mutation, Ikk2-CA rescued the polycythemia vera phenotype of Jak2 V617F. Likewise, Jak2 V617F ameliorated defects in hematopoiesis produced by Ikk2-CA. Single-cell RNA sequencing of hematopoietic stem and progenitor cells revealed multiple genes antagonistically regulated by Jak2 and Ikk2, including subsets whose expression was altered by Jak2 V617F and/or Ikk2-CA but partly or fully rectified in the double mutant. We hypothesize that Jak2 promotes hematopoietic stem cell population self-renewal, whereas Ikk2 promotes myeloid lineage differentiation, and biases cell fates at several branch points in hematopoiesis. Jak2 and Ikk2 both regulate multiple genes affecting myeloid maturation and cell death. Therefore, the presence of dual Jak2 and NFκB hyperactivation may present neomorphic therapeutic vulnerabilities in myeloid neoplasms.

Recent advances in therapies for primary myelofibrosis

Primary myelofibrosis (PMF), polycythemia vera (PV) and essential thrombocythemia (ET) form the classical BCR-ABL1-negative myeloproliferative neoplasms (MPNs) that are driven by a constitutive activation of JAK2 signaling. PMF as well as secondary MF (post-ET and post-PV MF) are the most aggressive MPNs. Presently, there is no curative treatment, except allogenic hematopoietic stem cell transplantation. JAK inhibitors, essentially ruxolitinib, are the therapy of reference for intermediate and high-risk MF. However, presently the current JAK inhibitors behave mainly as anti-inflammatory drugs, improving general symptoms and spleen size without major impact on disease progression. A better understanding of the genetics of MF, the biology of its leukemic stem cells (LSCs), the mechanisms of fibrosis and of cytopenia and the role of inflammatory cytokines has led to new approaches with the development of numerous therapeutic agents that target epigenetic regulation, telomerase, apoptosis, cell cycle, cytokines and signaling. Furthermore, the use of a new less toxic form of interferon-α has been revived, as it is presently one of the only molecules that targets the mutated clone. These new approaches have different aims: (a) to provide alternative therapy to JAK inhibition; (b) to correct cytopenia; and (c) to inhibit fibrosis development. However, the main important goal is to find new disease modifier treatments, which will profoundly modify the progression of the disease without major toxicity. Presently the most promising approaches consist of the inhibition of telomerase and the combination of JAK2 inhibitors (ruxolitinib) with either a BCL2/BCL-xL or BET inhibitor. Yet, the most straightforward future approaches can be considered to be the development of and/or selective inhibition of JAK2V617F and the targeting MPL and calreticulin mutants by immunotherapy. It can be expected that the therapy of MF will be significantly improved in the coming years.

Molecular Studies for the Early Detection of Philadelphia-Negative Myeloproliferative Neoplasms

JAK2 V617F is the predominant driver mutation in patients with Philadelphia-negative myeloproliferative neoplasms (MPN). JAK2 mutations are also frequent in clonal hematopoiesis of indeterminate potential (CHIP) in otherwise "healthy" individuals. However, the period between mutation acquisition and MPN diagnosis (known as latency) varies widely between individuals, with JAK2 mutations detectable several decades before diagnosis and even from birth in some individuals. Here, we will review the current evidence on the biological factors, such as additional mutations and chronic inflammation, which influence clonal expansion and may determine why some JAK2-mutated individuals will progress to an overt neoplasm during their lifetime while others will not. We will also introduce several germline variants that predispose individuals to CHIP (as well as MPN) identified from genome-wide association studies. Finally, we will explore possible mutation screening or interventions that could help to minimize MPN-associated cardiovascular complications or even delay malignant progression.

SRSF2-P95H decreases JAK/STAT signaling in hematopoietic cells and delays myelofibrosis development in mice

Heterozygous mutation targeting proline 95 in Serine/Arginine-rich Splicing Factor 2 (SRSF2) is associated with V617F mutation in Janus Activated Kinase 2 (JAK2) in some myeloproliferative neoplasms (MPNs), most commonly primary myelofibrosis. To explore the interaction of Srsf2^P95H with Jak2^V617F, we generated Cre-inducible knock-in mice expressing these mutants under control of the stem cell leukemia (Scl) gene promoter. In transplantation experiments, Srsf2^P95H unexpectedly delayed myelofibrosis induced by Jak2^V617F and decreased TGFβ1 serum level. Srsf2^P95H reduced the competitiveness of transplanted Jak2^V617F hematopoietic stem cells while preventing their exhaustion. RNA sequencing of sorted megakaryocytes identified an increased number of splicing events when the two mutations were combined. Focusing on JAK/STAT pathway, Jak2 exon 14 skipping was promoted by Srsf2^P95H, an event detected in patients with JAK2^V617F and SRSF2^P95 co-mutation. The skipping event generates a truncated inactive JAK2 protein. Accordingly, Srsf2^P95H delays myelofibrosis induced by the thrombopoietin receptor agonist Romiplostim in Jak2 wild-type animals. These results unveil JAK2 exon 14 skipping promotion as a strategy to reduce JAK/STAT signaling in pathological conditions.

Genetic basis and molecular profiling in myeloproliferative neoplasms

BCR::ABL1-negative myeloproliferative neoplasms (MPNs) are clonal diseases originating from a single hematopoietic stem cell that cause excessive production of mature blood cells. The 3 subtypes, that is, polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF), are diagnosed according to the World Health Organization (WHO) and international consensus classification (ICC) criteria. Acquired gain-of-function mutations in 1 of 3 disease driver genes (JAK2, CALR, and MPL) are the causative events that can alone initiate and promote MPN disease without requiring additional cooperating mutations. JAK2-p.V617F is present in >95% of PV patients, and also in about half of the patients with ET or PMF. ET and PMF are also caused by mutations in CALR or MPL. In ∼10% of MPN patients, those referred to as being "triple negative," none of the known driver gene mutations can be detected. The common theme between the 3 driver gene mutations and triple-negative MPN is that the Janus kinase-signal transducer and activator of transcription (JAK/STAT) signaling pathway is constitutively activated. We review the recent advances in our understanding of the early events after the acquisition of a driver gene mutation. The limiting factor that determines the frequency at which MPN disease develops with a long latency is not the acquisition of driver gene mutations, but rather the expansion of the clone. Factors that control the conversion from clonal hematopoiesis to MPN disease include inherited predisposition, presence of additional mutations, and inflammation. The full extent of knowledge of the mutational landscape in individual MPN patients is now increasingly being used to predict outcome and chose the optimal therapy.

Biology and therapeutic targeting of molecular mechanisms in MPNs

Myeloproliferative neoplasms (MPNs) are clonal hematopoietic stem cell disorders characterized by activated Janus kinase (JAK)-signal transducer and activator of transcription signaling. As a result, JAK inhibitors have been the standard therapy for treatment of patients with myelofibrosis (MF). Although currently approved JAK inhibitors successfully ameliorate MPN-related symptoms, they are not known to substantially alter the MF disease course. Similarly, in essential thrombocythemia and polycythemia vera, treatments are primarily aimed at reducing the risk of cardiovascular and thromboembolic complications, with a watchful waiting approach often used in patients who are considered to be at a lower risk for thrombosis. However, better understanding of MPN biology has led to the development of rationally designed therapies, with the goal of not only addressing disease complications but also potentially modifying disease course. We review the most recent data elucidating mechanisms of disease pathogenesis and highlight emerging therapies that target MPN on several biologic levels, including JAK2-mutant MPN stem cells, JAK and non-JAK signaling pathways, mutant calreticulin, and the inflammatory bone marrow microenvironment.

Establishment of isogenic induced pluripotent stem cells with or without pathogenic mutation for understanding the pathogenesis of myeloproliferative neoplasms

Identification and functional characterization of disease-associated genetic traits are crucial for understanding the pathogenesis of hematologic malignancies. Various in vitro and in vivo models, including cell lines, primary cells, and animal models, have been established to examine these genetic alterations. However, their nonphysiologic conditions, diverse genetic backgrounds, and species-specific differences often limit data interpretation. To evaluate somatic mutations in myeloproliferative neoplasms (MPNs), we used CRISPR/Cas9 combined with the piggyBac transposon system to establish isogenic induced pluripotent stem (iPS) cell lines with or without JAK2V617F mutation, a driver mutation of MPNs. We induced hematopoietic stem/progenitor cells (HSPCs) from these iPS cells and observed phenotypic differences during hematopoiesis using fluorescence-activated cell sorting analysis. HSPCs with pathogenic mutations exhibited cell-autonomous erythropoiesis and megakaryopoiesis, which are hallmarks in the bone marrow of patients with MPNs. Furthermore, we used these HSPCs as a model to validate therapeutic compounds and showed that interferon alpha selectively inhibited erythropoiesis and megakaryopoiesis in mutant HSPCs. These results demonstrate that genome editing is feasible for establishing isogenic iPS cells, studying genetic elements to understand the pathogenesis of MPNs, and evaluating therapeutic compounds against MPNs.

Single-cell methods in myeloproliferative neoplasms: old questions, new technologies

Myeloproliferative neoplasms (MPN) are a group of clonal stem cell-derived hematopoietic malignancies driven by aberrant Janus kinase-signal transducer and activator of transcription proteins (JAK/STAT) signaling. Although these are genetically simple diseases, MPNs are phenotypically heterogeneous, reflecting underlying intratumoral heterogeneity driven by the interplay of genetic and nongenetic factors. Their evolution is determined by factors that enable certain cellular subsets to outcompete others. Therefore, techniques that resolve cellular heterogeneity at the single-cell level are ideally placed to provide new insights into MPN biology. With these insights comes the potential to uncover new approaches to predict the clinical course and treat these cancers, ultimately improving outcomes for patients. MPNs present a particularly tractable model of cancer evolution, because most patients present in an early disease phase and only a small proportion progress to aggressive disease. Therefore, it is not surprising that many groundbreaking technological advances in single-cell omics have been pioneered by their application in MPNs. In this review article, we explore how single-cell approaches have provided transformative insights into MPN disease biology, which are broadly applicable across human cancers, and discuss how these studies might be swiftly translated into clinical pathways and may eventually underpin precision medicine.

P16INK4a Regulates ROS-Related Autophagy and CDK4/6-Mediated Proliferation: A New Target of Myocardial Regeneration Therapy

Neonatal mice achieve complete cardiac repair through endogenous myocardial regeneration after apical resection (AR), but this capacity is rapidly lost 7 days after birth. As an upstream inhibitor of cyclin-dependent kinase 4/6- (CDK4/6-) mediated cell cycle activity, p16^INK4a is widely involved in regulating tumor and senescence. Given that p16^INK4a had a significant negative regulation on cell proliferation, targeting cardiomyocytes (CMs) to inhibit p16^INK4a seems to be a promising attempt at myocardial regeneration therapy. The p16^INK4a expression was upregulated during perimyocardial regeneration time. Knockdown of p16^INK4a stimulated CM proliferation, while p16^INK4a overexpression had the opposite effect. In addition, p16^INK4a knockdown prolonged the proliferation time window of newborn myocardium. And p16^INK4a overexpression inhibited cell cycle activity and deteriorated myocardial regeneration after AR. The quantitative proteomic analysis showed that p16^INK4a knockdown mediated the cell cycle progression and intervened in energy metabolism homeostasis. Mechanistically, overexpression of p16^INK4a causes abnormal accumulation of reactive oxygen species (ROS) to induce autophagy, while scavenging ROS with N-acetylcysteine can alleviate autophagy and regulate p16^INK4a, CDK4/6, and CyclinD1 in a covering manner. And the effect of inhibiting the proliferation of p16^INK4a-activated CMs was significantly blocked by the CDK4/6 inhibitor Palbociclib. In summary, p16^INK4a regulated CM proliferation progression through CDK4/6 and ROS-related autophagy to jointly affect myocardial regeneration repair. Our study revealed that p16^INK4a might be a potential therapeutic target for myocardial regeneration after injury.

Inhibition of interleukin-1β reduces myelofibrosis and osteosclerosis in mice with JAK2-V617F driven myeloproliferative neoplasm

Interleukin-1β (IL-1β) is a master regulator of inflammation. Increased activity of IL-1β has been implicated in various pathological conditions including myeloproliferative neoplasms (MPNs). Here we show that IL-1β serum levels and expression of IL-1 receptors on hematopoietic progenitors and stem cells correlate with JAK2-V617F mutant allele fraction in peripheral blood of patients with MPN. We show that the source of IL-1β overproduction in a mouse model of MPN are JAK2-V617F expressing hematopoietic cells. Knockout of IL-1β in hematopoietic cells of JAK2-V617F mice reduces inflammatory cytokines, prevents damage to nestin-positive niche cells and reduces megakaryopoiesis, resulting in decrease of myelofibrosis and osteosclerosis. Inhibition of IL-1β in JAK2-V617F mutant mice by anti-IL-1β antibody also reduces myelofibrosis and osteosclerosis and shows additive effects with ruxolitinib. These results suggest that inhibition of IL-1β with anti-IL-1β antibody alone or in combination with ruxolitinib could have beneficial effects on the clinical course in patients with myelofibrosis.

Developmental cues license megakaryocyte priming in murine hematopoietic stem cells

The fetal-to-adult switch in hematopoietic stem cell (HSC) behavior is characterized by alterations in lineage output and entry into deep quiescence. Here we identify the emergence of megakaryocyte (Mk)-biased HSCs as an event coinciding with this developmental switch. Single-cell chromatin accessibility analysis reveals a ubiquitous acquisition of Mk lineage priming signatures in HSCs during the fetal-to-adult transition. These molecular changes functionally coincide with increased amplitude of early Mk differentiation events after acute inflammatory insult. Importantly, we identify LIN28B, known for its role in promoting fetal-like self-renewal, as an insulator against the establishment of an Mk-biased HSC pool. LIN28B protein is developmentally silenced in the third week of life, and its prolonged expression delays emergency platelet output in young adult mice. We propose that developmental regulation of Mk priming may represent a switch for HSCs to toggle between prioritizing self-renewal in the fetus and increased host protection in postnatal life.

JAK2V617F Mutant Megakaryocytes Contribute to Hematopoietic Aging in a Murine Model of Myeloproliferative Neoplasm

Megakaryocytes (MKs) is an important component of the hematopoietic niche. Abnormal MK hyperplasia is a hallmark feature of myeloproliferative neoplasms (MPNs). The JAK2V617F mutation is present in hematopoietic cells in a majority of patients with MPNs. Using a murine model of MPN in which the human JAK2V617F gene is expressed in the MK lineage, we show that the JAK2V617F-bearing MKs promote hematopoietic stem cell (HSC) aging, manifesting as myeloid-skewed hematopoiesis with an expansion of CD41+ HSCs, a reduced engraftment and self-renewal capacity, and a reduced differentiation capacity. HSCs from 2-year-old mice with JAK2V617F-bearing MKs were more proliferative and less quiescent than HSCs from age-matched control mice. Examination of the marrow hematopoietic niche reveals that the JAK2V617F-bearing MKs not only have decreased direct interactions with hematopoietic stem/progenitor cells during aging but also suppress the vascular niche function during aging. Unbiased RNA expression profiling reveals that HSC aging has a profound effect on MK transcriptomic profiles, while targeted cytokine array shows that the JAK2V617F-bearing MKs can alter the hematopoietic niche through increased levels of pro-inflammatory and anti-angiogenic factors. Therefore, as a hematopoietic niche cell, MKs represent an important connection between the extrinsic and intrinsic mechanisms for HSC aging.

[What's new in myeloproliferative neoplasia?]

Treatment of myeloproliferative neoplasia (MPN) is based on patients' individual risk-stratification and includes cytoreductive agents for high-risk essential thrombocythemia (ET), polycythemia vera (PV) and Myelofibrosis (MF). Classical cytoreductive drugs largely fail to modify the basic clonal composition of the disease. In contrast, in PV for example treatment with Ropeg-Interferon not only results in higher hematological response rates compared to hydroxyurea but in addition significantly reduces JAK2 allele-burden in high-risk PV patients as well as it depletes concurrent cytogenetic and molecular abnormalities. Treatment with Ropeg-Interferon so far is only approved for high-risk PV. A very recent trial however also demonstrated this disease-modifying effect also in low-risk PV patients in addition to an increased rate of transfusion independence. Thus, Ropeg-Interferon is the current standard for first line treatment of high-risk PV and we assume that the data in low-risk PV will lead also to a broader clinical use of Ropeg-Interferon this particular patient group, as it may decrease transformation to MF or even MPN-blast crisis.Myelofibrosis management has been extended by novel JAKi. Fedratinib is the first second generation JAK-inhibitor approved for Ruxolitinib-intolerant or refractory patients. Fedratinib reduces both spleen volume as well as symptom burden. Two other second generation JAK-inhibitors are in clinical development for MPN treatment. Pacritinib has demonstrated efficacy in reducing both spleen volume and symptom score in MF including a cohort of Ruxolitinib-pretreated patients and Momelotinib is the only JAK-inhibitor which has been shown to alleviate anemia in addition to its effect on improving spleen volume and symptom. So far, neither Pacritinib nor Momelotinib are currently EMA-approved for MPN treatment.Finally, it has recently been acknowledged that inflammation is a key driver of MPN pathogenesis. Both, mutated as well as non-clonal inflammatory and other stromal cells produce significant amounts of local cytokines. Also the initiation of the neoplastic process itself seems to depend on inflammatory cytokines. Recent scRNASeq data revealed components of the alarmin complex (S100A8 und S100A9) drive this local sterile inflammation process, which also represents a potential therapeutic target, as the S100A8 and A9 inhibitor Tasquinimod reduced fibrosis in a pre-clinical animal model.

Treatment and Clinical Endpoints in Polycythemia Vera: Seeking the Best Obtainable Version of the Truth

Polycythemia vera (PV) is a Philadelphia chromosome-negative myeloproliferative neoplasm driven by the JAK2 V617F (or rarely exon 12) mutation. Its natural history can extend over a few decades, and therefore treatment planning is predicated on continual re-assessment of traditional risk features (age, prior thrombosis) to evaluate the need for cytoreduction besides foundational therapy with low-dose aspirin and stringent phlebotomy. Shorter- and longer-term patient goals should be considered in light of several variables such as co-morbid conditions (especially cardiovascular risk factors), disease symptoms, and the risk-benefit profile of available drugs. While hydroxyurea has been the pro forma choice of cytoreduction for many practitioners over the last half-century, the more recent regulatory approvals of ruxolitinib and ropeginterferon-alfa-2b, based on phase 3 randomized trials, highlight an expanding portfolio of active drugs. Obtaining high-level evidence for short-term clinical trial endpoints such as hematocrit control, symptom burden/quality of life, splenomegaly, and JAK2 V617F allele burden lies within the timeline of most studies. However, in many cases, it may not be possible to adequately power trials to capture significant differences in the typically low event rates of thrombosis, as well as longer-horizon endpoints such as evolution to myelofibrosis and acute myeloid leukemia, and survival. This Perspective highlights the challenges of addressing these data gaps and outstanding questions in the emerging treatment landscape of PV.

ATP citrate lyase controls hematopoietic stem cell fate and supports bone marrow regeneration

In order to support bone marrow regeneration after myeloablation, hematopoietic stem cells (HSCs) actively divide to provide both stem and progenitor cells. However, the mechanisms regulating HSC function and cell fate choice during hematopoietic recovery remain unclear. We herein provide novel insights into HSC regulation during regeneration by focusing on mitochondrial metabolism and ATP citrate lyase (ACLY). After 5-fluorouracil-induced myeloablation, HSCs highly expressing endothelial protein C receptor (EPCR^high ) were enriched within the stem cell fraction at the expense of more proliferative EPCR^Low HSCs. These EPCR^High HSCs were initially more primitive than EPCR^Low HSCs and enabled stem cell expansion by enhancing histone acetylation, due to increased activity of ACLY in the early phase of hematopoietic regeneration. In the late phase of recovery, HSCs enhanced differentiation potential by increasing the accessibility of cis-regulatory elements in progenitor cell-related genes, such as CD48. In conditions of reduced mitochondrial metabolism and ACLY activity, these HSCs maintained stem cell phenotypes, while ACLY-dependent histone acetylation promoted differentiation into CD48⁺ progenitor cells. Collectively, these results indicate that the dynamic control of ACLY-dependent metabolism and epigenetic alterations is essential for HSC regulation during hematopoietic regeneration.

The immune landscape in BCR-ABL negative myeloproliferative neoplasms: inflammation, infections and opportunities for immunotherapy

Breakpoint cluster region-Abelson (BCR-ABL) negative myeloproliferative neoplasms (MPNs) are chronic myeloid neoplasms initiated by the acquisition of gene mutation(s) in a haematopoietic stem cell, leading to clonal expansion and over-production of blood cells and their progenitors. MPNs encompass a spectrum of disorders with overlapping but distinct molecular, laboratory and clinical features. This includes polycythaemia vera, essential thrombocythaemia and myelofibrosis. Dysregulation of the immune system is key to the pathology of MPNs, supporting clonal evolution, mediating symptoms and resulting in varying degrees of immunocompromise. Targeting immune dysfunction is an important treatment strategy. In the present review, we focus on the immune landscape in patients with MPNs - the role of inflammation in disease pathogenesis, susceptibility to infection and emerging strategies for therapeutic immune modulation. Further detailed work is required to delineate immune perturbation more precisely in MPNs to determine how and why vulnerability to infection differs between clinical subtypes and to better understand how inflammation results in a competitive advantage for the MPN clone. These studies may help shed light on new designs for disease-modifying therapies.

Inferring the dynamic of mutated hematopoietic stem and progenitor cells induced by IFNα in myeloproliferative neoplasms

Classical BCR-ABL-negative myeloproliferative neoplasms (MPN) are clonal disorders of hematopoietic stem cells (HSC) caused mainly by recurrent mutations in genes encoding JAK2 (JAK2), calreticulin (CALR), or the thrombopoietin receptor (MPL). Interferon alpha (IFNα) has demonstrated some efficacy in inducing molecular remission in MPN. In order to determine factors that influence molecular response rate, we evaluated the long-term molecular efficacy of IFNα in MPN patients by monitoring the fate of cells carrying driver mutations in a prospective observational and longitudinal study of 48 patients over more than 5 years. We measured several times per year the clonal architecture of early and late hematopoietic progenitors (84,845 measurements) and the global variant allele frequency in mature cells (409 measurements). Using mathematical modeling and hierarchical Bayesian inference, we further inferred the dynamics of IFNα-targeted mutated HSC. Our data support the hypothesis that IFNα targets JAK2V617F HSC by inducing their exit from quiescence and differentiation into progenitors. Our observations indicate that treatment efficacy is higher in homozygous than heterozygous JAK2V617F HSC and increases with high IFNα dosage in heterozygous JAK2V617F HSC. Besides, we found that the molecular responses of CALRm HSC to IFNα were heterogeneous, varying between type 1 and type 2 CALRm, and high dosage of IFNα correlates with worse outcomes. Together, our work indicates that the long-term molecular efficacy of IFNα implies an HSC exhaustion mechanism and depends on both the driver mutation type and IFNα dosage.

Molecular pathogenesis of the myeloproliferative neoplasms

The Philadelphia negative myeloproliferative neoplasms (MPN) compromise a heterogeneous group of clonal myeloid stem cell disorders comprising polycythaemia vera, essential thrombocythaemia and primary myelofibrosis. Despite distinct clinical entities, these disorders are linked by morphological similarities and propensity to thrombotic complications and leukaemic transformation. Current therapeutic options are limited in disease-modifying activity with a focus on the prevention of thrombus formation. Constitutive activation of the JAK/STAT signalling pathway is a hallmark of pathogenesis across the disease spectrum with driving mutations in JAK2, CALR and MPL identified in the majority of patients. Co-occurring somatic mutations in genes associated with epigenetic regulation, transcriptional control and splicing of RNA are variably but recurrently identified across the MPN disease spectrum, whilst epigenetic contributors to disease are increasingly recognised. The prognostic implications of one MPN diagnosis may significantly limit life expectancy, whilst another may have limited impact depending on the disease phenotype, genotype and other external factors. The genetic and clinical similarities and differences in these disorders have provided a unique opportunity to understand the relative contributions to MPN, myeloid and cancer biology generally from specific genetic and epigenetic changes. This review provides a comprehensive overview of the molecular pathophysiology of MPN exploring the role of driver mutations, co-occurring mutations, dysregulation of intrinsic cell signalling, epigenetic regulation and genetic predisposing factors highlighting important areas for future consideration.

Inflammation as a regulator of hematopoietic stem cell function in disease, aging, and clonal selection

Inflammation is an evolutionarily selected defense response to infection or tissue damage that involves activation and consumption of immune cells in order to reestablish and maintain organismal integrity. In this process, hematopoietic stem cells (HSCs) are themselves exposed to inflammatory cues and via proliferation and differentiation, replace mature immune cells in a demand-adapted fashion. Here, we review how major sources of systemic inflammation act on and subsequently shape HSC fate and function. We highlight how lifelong inflammatory exposure contributes to HSC inflamm-aging and selection of premalignant HSC clones. Finally, we explore emerging areas of interest and open questions remaining in the field.

MAPK14 over-expression is a transcriptomic feature of polycythemia vera and correlates with adverse clinical outcomes

Background

The transcriptomic signature has not been fully elucidated in PV, as well as mRNA markers for clinical variables (thrombosis, leukemic transformation, survival, etc.). We attempted to reveal and validate crucial co-expression modules and marker mRNAs correlating with polycythemia vera (PV) by weighted gene co-expression network analysis (WGCNA).

Material and methods

The GSE57793/26014/61629 datasets were downloaded from Gene Expression Omnibus (GEO) database and integrated into one fused dataset. By R software and ‘WGCNA’ package, the PV-specific co-expression module was identified, the pathway enrichment profile of which was obtained by over-representation analysis (ORA). Protein–protein interaction (PPI) network and hub gene analysis identified MAPK14 as our target gene. Then the distribution of MAPK14 expression in different disease/mutation types, were depicted based on external independent datasets. Genome-scale correlation analysis revealed the association of MAPK14 and JAK/STAT family genes. Then gene set enrichment analysis (GSEA) was performed to detect the activated and suppressed pathways associating with MAPK14 expression. Moreover, GSE47018 dataset was utilized to compare clinical variables (thrombosis, leukemic transformation, survival, etc.) between MAPK14-high and MAPK14-low groups.

Results

An integrated dataset including 177 samples (83 PV, 35 ET, 17 PMF and 42 normal donors) were inputted into WGCNA. The ‘tan’ module was identified as the PV-specific module (R² = 0.56, p = 8e−16), the genes of which were dominantly enriched in pro-inflammatory pathways (Toll-like receptor (TLR)/TNF signaling, etc.). MAPK14 is identified as the top hub gene in PV-related PPI network with the highest betweenness. External datasets validated that the MAPK14 expression was significantly higher in PV than that of essential thrombocytosis (ET)/primary myelofibrosis (PMF) patients and normal donors. JAK2 homozygous mutation carriers have higher level of MAPK14 than that of other mutation types. The expression of JAK/STAT family genes significantly correlated with MAPK14, which also contributed to the activation of oxidated phosphorylation, interferon-alpha (IFNα) response and PI3K-Akt-mTOR signaling, etc. Moreover, MAPK14-high group have more adverse clinical outcomes (splenectomy, thrombosis, disease aggressiveness) and inferior survival than MAPK14-low group.

Conclusion

MAPK14 over-expression was identified as a transcriptomic feature of PV, which was also related to inferior clinical outcomes. The results provided novel insights for biomarkers and therapeutic targets for PV.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-021-02913-3.