Subcellular mislocalization of the transcription factor NF-E2 in erythroid cells discriminates prefibrotic primary myelofibrosis from essential thrombocythemia

Nrf2 Plays a Key Role in Erythropoiesis during Aging

Aging is characterized by increased oxidation and reduced efficiency of cytoprotective mechanisms. Nuclear factor erythroid-2-related factor (Nrf2) is a key transcription factor, controlling the expression of multiple antioxidant proteins. Here, we show that Nrf2-/- mice displayed an age-dependent anemia, due to the combined contributions of reduced red cell lifespan and ineffective erythropoiesis, suggesting a role of Nrf2 in erythroid biology during aging. Mechanistically, we found that the expression of antioxidants during aging is mediated by activation of Nrf2 function by peroxiredoxin-2. The absence of Nrf2 resulted in persistent oxidation and overactivation of adaptive systems such as the unfolded protein response (UPR) system and autophagy in Nrf2-/- mouse erythroblasts. As Nrf2 is involved in the expression of autophagy-related proteins such as autophagy-related protein (Atg) 4-5 and p62, we found impairment of late phase of autophagy in Nrf2-/- mouse erythroblasts. The overactivation of the UPR system and impaired autophagy drove apoptosis of Nrf2-/- mouse erythroblasts via caspase-3 activation. As a proof of concept for the role of oxidation, we treated Nrf2-/- mice with astaxanthin, an antioxidant, in the form of poly (lactic-co-glycolic acid) (PLGA)-loaded nanoparticles (ATS-NPs) to improve its bioavailability. ATS-NPs ameliorated the age-dependent anemia and decreased ineffective erythropoiesis in Nrf2-/- mice. In summary, we propose that Nrf2 plays a key role in limiting age-related oxidation, ensuring erythroid maturation and growth during aging.

Prevalence and characteristics of myeloproliferative neoplasms with concomitant monoclonal gammopathy

Of BCR-ABL negative myeloproliferative neoplasm (MPN) patients, 3-14 % display a concomitant monoclonal gammopathy (MGUS). Nonetheless, literature on co-occurring MPN and MGUS is scarce, the molecular underpinnings are unknown and it is unclear whether patients require a specific management. Here, we compared the clinical and genetic features of MPN patients with and without concomitant MGUS. Of 114 MPN patients prospectively studied by serum immunofixation (median age, 67 years; 36.0 % essential thrombocythemia [ET], 24.6 % polycythemia vera [PV], 11.4 % secondary myelofibrosis [sMF], 28.1 % primary myelofibrois [PMF]; 73.7 % JAK2 V617F positive), 10 (9 %) harbored an M-protein. No relevant clinical differences existed between MPN patients with or without M-protein. Seven additional MPN/MGUS patients were retrospectively identified in our MPN registry, yielding a total of 17 patients (7 ET, 3 PV, 3 sMF, 4 PMF). One patient developed multiple myeloma (MM) and one smoldering MM. Seven of 12 patients analyzed carried mutations (e.g. in ASXL1 or TET2) in addition to those in JAK2 or CALR, and 4 of 10 patients showed aberrant cytogenetics. M-protein was mainly IgG (12/17), followed by IgM (4/17). In the two patients that underwent allogeneic stem cell transplantation mutant JAK2 and M-protein were no longer detectable post-transplant. In conclusion, MGUS prevalence in our cohort was in the range of previous reports and at most slightly higher than expected in the general population. MGUS presence did not correlate with a specific MPN entity, clinical features or genetic alterations. Our observations suggest that there is no strong clinical or biological relationship between the occurrence of MGUS and MPN.

[Protein-dysregulation in human and murine myeloproliferative neoplasms]

In this work different types of dysregulation of signaling proteins in the context of myeloproliferative neoplasms are examined. In this heterogeneous disease group, uncontrolled cell proliferation plays a crucial role for the initiation of tumorigenesis, which Robert Weinberg described as a "hallmark" for the development of cancer. Protein dysregulation in form of overexpression of GAB2, a protein involved in formation of the CML-pathognomonic BCR/ABL-translocation complex, results in an enhanced disease phenotype in a Bcr/Abl-positive mouse model and disease acceleration is associated with a change of the subcellular localization of GAB2 in human blasts in CML-bone marrow biopsies. Furthermore, analyses of a mouse model show that a protein dysregulation caused by a distinct translocation (Tel-Syk) leads to the formation of a specific and morphologically very characteristic phenotype in the bone marrow of diseased mice. Moreover, results were presented which show that in certain subgroups of Myeloproliferative Neoplasms the protein NFE2, which is initially known only as a translocating factor, is apparently regulated by altering its subcellular localization. The difference in the subcellular localization of NFE2 in erythroid bone marrow cells is so clear between Essential Thrombocythemia and Primary Myelofibrosis that quantitative NFE2 immunohistochemistry can be used as an ancillary tool to diagnostically discriminate these two entities in an early stage.

Investigating Various Thresholds as Immunohistochemistry Cutoffs for Observer Agreement

BACKGROUND

Clinical translation of immunohistochemistry (IHC) biomarkers requires reliable and reproducible cutoffs or thresholds for interpretation of immunostaining. Most IHC biomarker research focuses on the clinical relevance (diagnostic, prognostic, or predictive utility) of cutoffs, with less emphasis on observer agreement using these cutoffs. From the literature, we identified 3 commonly used cutoffs of 10% positive epithelial cells, 20% positive epithelial cells, and moderate to strong staining intensity (+2/+3 hereafter) to use for investigating observer agreement.

MATERIALS AND METHODS

A series of 36 images of microarray cores stained for 4 different IHC biomarkers, with variable staining intensity and percentage of positive cells, was used for investigating interobserver and intraobserver agreement. Seven pathologists scored the immunostaining in each image using the 3 cutoffs for positive and negative staining. Kappa (κ) statistic was used to assess the strength of agreement for each cutoff.

RESULTS

The interobserver agreement between all 7 pathologists using the 3 cutoffs was reasonably good, with mean κ scores of 0.64, 0.59, and 0.62, respectively, for 10%, 20%, and +2/+3 cutoffs. A good agreement was observed for experienced pathologists using the 10% cutoff, and their agreement was statistically higher than for junior pathologists (P=0.02). In addition, the mean intraobserver agreement for all 7 pathologists using the 3 cutoffs was reasonably good, with mean κ scores of 0.71, 0.60, and 0.73, respectively, for 10%, 20%, and +2/+3 cutoffs. For all 3 cutoffs, a positive correlation was observed with perceived ease of interpretation (P<0.003). Finally, cytoplasmic-only staining achieved higher agreement using all 3 cutoffs than mixed staining patterns.

CONCLUSIONS

All 3 cutoffs investigated achieve reasonable strength of agreement, modestly decreasing interobserver and intraobserver variability in IHC interpretation. These cutoffs have previously been used in cancer pathology, and this study provides evidence that these cutoffs can be reproducible between practicing pathologists.

Mutations in myeloproliferative neoplasms - their significance and clinical use

INTRODUCTION

Clonal hematologic diseases of the blood such as polycythemia vera, essential thrombocythemia and primary myelofibrosis belong to the BCR-ABL negative Myeloproliferative Neoplasms (MPN). These diseases are characterized by clonal expansion of hematopoietic precursor cells followed by increased production of differentiated cells of the myeloid lineage. Initiation of clonal hematopoiesis, formation of a clinical phenotype as well as disease progression form part of MPN disease evolution. The disease is driven by acquired somatic mutations in critical pathways such as cytokine signaling, epigenetic regulation, RNA splicing, and transcription factor signaling. Areas covered: The following review aims to provide an overview of the mutational landscape of MPN, the impact of these mutations in MPN pathogenesis as well as their prognostic value. Finally, a summary of how these mutations are being used or could potentially be used for the treatment of MPN patients is presented. Expert commentary: The genetic landscape of MPN patients has been successfully dissected within the past years with the advent of new sequencing technologies. Integrating the genetic information within a clinical setting is already benefitting patients in terms of disease monitoring and prognostic information of disease progression but will be further intensified within the next years.

A 7-Gene Signature Depicts the Biochemical Profile of Early Prefibrotic Myelofibrosis

Recent studies have shown that a large proportion of patients classified as essential thrombocythemia (ET) actually have early primary prefibrotic myelofibrosis (prePMF), which implies an inferior prognosis as compared to patients being diagnosed with so-called genuine or true ET. According to the World Health Organization (WHO) 2008 classification, bone marrow histology is a major component in the distinction between these disease entities. However, the differential diagnosis between them may be challenging and several studies have not been able to distinguish between them. Most lately, it has been argued that simple blood tests, including the leukocyte count and plasma lactate dehydrogenase (LDH) may be useful tools to separate genuine ET from prePMF, the latter disease entity more often being featured by anemia, leukocytosis and elevated LDH. Whole blood gene expression profiling was performed in 17 and 9 patients diagnosed with ET and PMF, respectively. Using elevated LDH obtained at the time of diagnosis as a marker of prePMF, a 7-gene signature was identified which correctly predicted the prePMF group with a sensitivity of 100% and a specificity of 89%. The 7 genes included MPO, CEACAM8, CRISP3, MS4A3, CEACAM6, HEMGN, and MMP8, which are genes known to be involved in inflammation, cell adhesion, differentiation and proliferation. Evaluation of bone marrow biopsies and the 7-gene signature showed a concordance rate of 71%, 79%, 62%, and 38%. Our 7-gene signature may be a useful tool to differentiate between genuine ET and prePMF but needs to be validated in a larger cohort of "ET" patients.

A novel role for nuclear factor-erythroid 2 in erythroid maturation by modulation of mitochondrial autophagy

We have recently demonstrated that the transcription factor nuclear factor-erythroid 2, which is critical for erythroid maturation and globin gene expression, plays an important role in the pathophysiology of myeloproliferative neoplasms. Myeloproliferative neoplasm patients display elevated levels of nuclear factor-erythroid 2 and transgenic mice overexpressing the transcription factor develop myeloproliferative neoplasm, albeit, surprisingly without erythrocytosis. Nuclear factor-erythroid 2 transgenic mice show both a reticulocytosis and a concomitant increase in iron deposits in the spleen, suggesting both enhanced erythrocyte production and increased red blood cell destruction. We therefore hypothesized that elevated nuclear factor-erythroid 2 levels may lead to increased erythrocyte destruction by interfering with organelle clearance during erythroid maturation. We have previously shown that nuclear factor-erythroid 2 overexpression delays erythroid maturation of human hematopoietic stem cells. Here we report that increased nuclear factor-erythroid 2 levels also impede murine maturation by retarding mitochondrial depolarization and delaying mitochondrial elimination. In addition, ribosome autophagy is delayed in transgenics. We demonstrate that the autophagy genes NIX and ULK1 are direct novel nuclear factor-erythroid 2 target genes, as these loci are bound by nuclear factor-erythroid 2 in chromatin immunoprecipitation assays. Moreover, Nix and Ulk1 expression is increased in transgenic mice and in granulocytes from polycythemia vera patients. This is the first report implying a role for nuclear factor-erythroid 2 in erythroid maturation by affecting autophagy.

The Role of Reactive Oxygen Species in Myelofibrosis and Related Neoplasms

Reactive oxygen species (ROS) have been implicated in a wide variety of disorders ranging between traumatic, infectious, inflammatory, and malignant diseases. ROS are involved in inflammation-induced oxidative damage to cellular components including regulatory proteins and DNA. Furthermore, ROS have a major role in carcinogenesis and disease progression in the myeloproliferative neoplasms (MPNs), where the malignant clone itself produces excess of ROS thereby creating a vicious self-perpetuating circle in which ROS activate proinflammatory pathways (NF-κB) which in turn create more ROS. Targeting ROS may be a therapeutic option, which could possibly prevent genomic instability and ultimately myelofibrotic and leukemic transformation. In regard to the potent efficacy of the ROS-scavenger N-acetyl-cysteine (NAC) in decreasing ROS levels, it is intriguing to consider if NAC treatment might benefit patients with MPN. The encouraging results from studies in cystic fibrosis, systemic lupus erythematosus, and chronic obstructive pulmonary disease warrant such studies. In addition, the antioxidative potential of the widely used agents, interferon-alpha2, statins, and JAK inhibitors, should be investigated as well. A combinatorial approach using old agents with anticancer properties together with novel JAK1/2 inhibitors may open a new era for patients with MPNs, the outlook not only being “minimal residual disease” and potential cure but also a marked improvement in inflammation-mediated comorbidities.

Regulation and function of the NFE2 transcription factor in hematopoietic and non-hematopoietic cells

The NFE2 transcription factor was identified over 25 years ago. The NFE2 protein forms heterodimers with small MAF proteins, and the resulting complex binds to regulatory elements in a large number of target genes. In contrast to other CNC transcription family members including NFE2L1 (NRF1), NFE2L2 (NRF2) and NFE2L3 (NRF3), which are widely expressed, earlier studies had suggested that the major sites of NFE2 expression are hematopoietic cells. Based on cell culture studies it was proposed that this protein acts as a critical regulator of globin gene expression. However, the knockout mouse model displayed only mild erythroid abnormalities, while the major phenotype was a defect in megakaryocyte biogenesis. Indeed, absence of NFE2 led to severely impaired platelet production. A series of recent data, also summarized here, shed new light on the various functional roles of NFE2 and the regulation of its activity. NFE2 is part of a complex regulatory network, including transcription factors such as GATA1 and RUNX1, controlling megakaryocytic and/or erythroid cell function. Surprisingly, it was recently found that NFE2 also has a role in non-hematopoietic tissues, such as the trophoblast, in which it is also expressed, as well as the bone, opening the door to new research areas for this transcription factor. Additional data showed that NFE2 function is controlled by a series of posttranslational modifications. Important strides have been made with respect to the clinical significance of NFE2, linking this transcription factor to hematological disorders such as polycythemias.

Nuclear factor-erythroid 2, nerve growth factor receptor, and CD34-microvessel density are differentially expressed in primary myelofibrosis, polycythemia vera, and essential thrombocythemia

Because of the presence of various overlapping findings, the discrimination of polycythemia vera (PV) from prefibrotic/fibrotic primary myelofibrosis (PF/F-PMF) and essential thrombocythemia (ET) may be challenging, particularly in suboptimal bone marrow biopsy specimens. In this study, we assessed whether differences in the expression of nuclear factor-erythroid 2 (NF-E2), nerve growth factor receptor (NGFR; CD271), CD34, CD68, p53, CD3, CD20, and CD138 by immunohistochemistry could be useful in separating among them. Higher frequencies of nuclear positive erythroblasts with NF-E2 were observed in ET and PV cases (50% ± 13.3% and 41.5% ± 9.4%, respectively) when compared with both PF-PMF (21% ± 11.7%) and F-PMF (28.5% ± 10.8%). We found that with a cutoff level of at least 30% nuclear staining for NF-E2 in erythroblasts, we could reliably exclude the possibility of PMF. Conversely, NGFR+ stromal cells per high-power field (HPF) was significantly increased in F-PMF (53.5 ± 19.1/HPF) and PF-PMF (13.5 ± 3.8/HPF) compared with ET (4.4 ± 2.2/HPF) and PV (6.6 ± 3.3/HPF). Similarly, differences in CD34-microvessel density was remarkable in F-PMF and PF-PMF cases in comparison with PV and ET (49.9 ± 12.1/HPF, 29.3 ± 12.4/HPF, 13.7 ± 4.6/HPF, and 11.9 ± 5.1/HPF, respectively). Thus, the assessment of NF-E2 and NGFR expression and the evaluation of CD34-microvessel density may provide additional support in reaching a correct diagnosis in these cases of myeloproliferative neoplasms.

A feeder-free differentiation system identifies autonomously proliferating B cell precursors in human bone marrow

The peripheral B cell compartment is maintained by homeostatic proliferation and through replenishment by bone marrow precursors. Because hematopoietic stem cells cycle at a slow rate, replenishment must involve replication of precursor B cells. To study proliferation of early human B cell progenitors, we established a feeder cell-free in vitro system allowing the development of B cells from CD34(+) hematopoietic stem cells up to the stage of immature IgM(+) B cells. We found that pro-B and pre-B cells generated in vitro can proliferate autonomously and persist up to 7 wk in culture in the absence of signals induced by exogenously added cytokines. Nevertheless, addition of IL-7 enhanced pre-B cell expansion and inhibited maturation into IgM(+) B cells. The B cell precursor subsets replicating in vitro were highly similar to the bone marrow B cell precursors cycling in vivo. The autonomous proliferation of B cell precursor subsets in vitro and their long-term persistence implies that proliferation during pro-B and pre-B cell stages plays an important role in the homeostasis of the peripheral B cell compartment. Our in vitro culture can be used to study defects in B cell development or in reconstitution of the B cell pool after depletion and chemotherapy.

World Health Organization-defined classification of myeloproliferative neoplasms: morphological reproducibility and clinical correlations--the Danish experience

We examined inter- and intraobserver reproducibility and concordance between histological diagnosis and independently collected clinical findings in a large series of patients with the major subtypes of myeloproliferative neoplasms (MPNs) and controls. Seven hematopathologists reviewed 272 bone marrow biopsies including 43 controls. Diagnoses were determined according to the 2008 criteria of the World Health Organization (WHO). The participants were blinded to all clinical data except patient age. After initial evaluation all hematopathologists participated in a 3-day meeting with a leading clinician chaired by an expert hematopathologists. In cases with lack of consensus on fiber grading (n = 57), a new evaluation was performed. In cases with discordance on morphological diagnosis (n = 129), an additional nonblinded evaluation taking clinical data into consideration was carried out. For remaining cases with a lack of concordance between morphological diagnosis and clinical diagnosis (n = 33), a similar nonblinded evaluation was performed. Consensus on final histological diagnosis and concordance with clinical diagnosis were determined. Blinded histological evaluation resulted in a 53% consensus rate. After re-evaluation of fiber content, consensus was reached in 60% of cases. Adding clinical data increased the histological consensus to 83%. For cases with a histological consensus, we found a concordance of 71% with the clinician's diagnoses. This is the first study to present a larger cohort of MPN patients mimicking the diagnostic challenges that hematopathologists face in their daily practice. The results support the postulates of the WHO that both morphological and clinical findings are essential for a valid diagnosis

A role of NF-E2 in chronic inflammation and clonal evolution in essential thrombocythemia, polycythemia vera and myelofibrosis?

A novel murine model for myeloproliferative neoplasms (MPNs) generated by overexpression of the transcription factor NF-E2 has recently been described. Sustained overexpression of NF-E2 in this model induced myeloid expansion with anemia, leukocytosis and thrombocytosis. Herein, it is debated if NF-E2 overexpression also might have induced a sustained state of in vivo leukocyte and platelet activation with chronic and self-perpetuating production of inflammatory products from activated leukocytes and platelets. If so, this novel murine model also may excellently describe the deleterious impact of sustained chronic NF-E2 overexpression during uncontrolled chronic inflammation upon the hematopoietic system--the development of clonal myeloproliferation. Accordingly, this novel murine model may also have delivered the proof of concept of chronic inflammation as a trigger and driver of clonal evolution in MPNs.