The relationship of the active and latent forms of TGF-β1 with marrow fibrosis in essential thrombocythemia and primary myelofibrosis

DARS expression in BCR/ABL1-negative myeloproliferative neoplasms and its association with the immune microenvironment

DARS, encoding for aspartyl-tRNA synthetase, is implicated in the pathogenesis of various cancers, including renal cell carcinoma, glioblastoma, colon cancer, and gastric cancer. Its role in BCR/ABL1-negative myeloproliferative neoplasms (MPNs), however, remains unexplored. This study aimed to elucidate the expression of DARS in patients with MPNs (PV 23, ET 19, PMF 16) through immunohistochemical analysis and to examine the profiles of circulating immune cells and cytokines using flow cytometry. Our findings indicate a significant overexpression of DARS in all MPNs subtypes at the protein level compared to controls (P < 0.05). Notably, elevated DARS expression was linked to splenomegaly in MPNs patients. The expression of DARS showed a negative correlation with CD4+ T cells (R = - 0.451, P = 0.0004) and CD4+ T/CD8+ T cell ratio (R = - 0.3758, P = 0.0040), as well as with CD68+ tumor-associated macrophages (R = 0.4037, P = 0.0017). Conversely, it was positively correlated with IL-2 (R = 0.5419, P < 0.001), IL-5 (R = 0.3161, P = 0.0166), IL-6 (R = 0.2992, P = 0.0238), and IFN-γ (R = 0.3873, P = 0.0029). These findings underscore a significant association between DARS expression in MPNs patients and specific clinical characteristics, as well as immune cell composition. Further investigation into the interplay between DARS and the immune microenvironment in MPNs could shed light on the underlying mechanisms of MPNs pathogenesis and immune dysregulation.

TGF-β signaling in health, disease, and therapeutics

Transforming growth factor (TGF)-β is a multifunctional cytokine expressed by almost every tissue and cell type. The signal transduction of TGF-β can stimulate diverse cellular responses and is particularly critical to embryonic development, wound healing, tissue homeostasis, and immune homeostasis in health. The dysfunction of TGF-β can play key roles in many diseases, and numerous targeted therapies have been developed to rectify its pathogenic activity. In the past decades, a large number of studies on TGF-β signaling have been carried out, covering a broad spectrum of topics in health, disease, and therapeutics. Thus, a comprehensive overview of TGF-β signaling is required for a general picture of the studies in this field. In this review, we retrace the research history of TGF-β and introduce the molecular mechanisms regarding its biosynthesis, activation, and signal transduction. We also provide deep insights into the functions of TGF-β signaling in physiological conditions as well as in pathological processes. TGF-β-targeting therapies which have brought fresh hope to the treatment of relevant diseases are highlighted. Through the summary of previous knowledge and recent updates, this review aims to provide a systematic understanding of TGF-β signaling and to attract more attention and interest to this research area.

Therapeutic activity of GARP:TGF-β1 blockade in murine primary myelofibrosis

Primary myelofibrosis (PMF) is a myeloproliferative neoplasm characterized by the clonal expansion of myeloid cells, notably megakaryocytes (MKs), and an aberrant cytokine production leading to bone marrow (BM) fibrosis and insufficiency. Current treatment options are limited. TGF-β1, a profibrotic and immunosuppressive cytokine, is involved in PMF pathogenesis. While all cell types secrete inactive, latent TGF-β1, only a few activate the cytokine via cell type-specific mechanisms. The cellular source of the active TGF-β1 implicated in PMF is not known. Transmembrane protein GARP binds and activates latent TGF-β1 on the surface of regulatory T lymphocytes (Tregs) and MKs or platelets. Here, we found an increased expression of GARP in the BM and spleen of mice with PMF and tested the therapeutic potential of a monoclonal antibody (mAb) that blocks TGF-β1 activation by GARP-expressing cells. GARP:TGF-β1 blockade reduced not only fibrosis but also the clonal expansion of transformed cells. Using mice carrying a genetic deletion of Garp in either Tregs or MKs, we found that the therapeutic effects of GARP:TGF-β1 blockade in PMF imply targeting GARP on Tregs. These therapeutic effects, accompanied by increased IFN-γ signals in the spleen, were lost upon CD8 T-cell depletion. Our results suggest that the selective blockade of TGF-β1 activation by GARP-expressing Tregs increases a CD8 T-cell-mediated immune reaction that limits transformed cell expansion, providing a novel approach that could be tested to treat patients with myeloproliferative neoplasms.

Lower CXCR3 expression in both patients with neovascular AMD and advanced stages of chronic myeloproliferative blood cancers

Purpose

Peripheral T cell CXCR3 expression has been found uniquely lower in patients having neovascular age-related macular degeneration (nAMD) than in healthy individuals. The CXCR3-axis has been shown to have angiostatic and antifibrotic properties. We have recently investigated systemic markers in patients with myeloproliferative neoplasms (MPNs) because of their higher prevalence of AMD, and we have observed higher systemic chronic low-grade inflammation and immunosenescence signs in MPNs with drusen (MPNd) compared to those with normal retinas (MPNn). The MPNs evolve in a biological continuum from early cancer-stages (essential thrombocytosis, polycythemia vera) to the advanced myelofibrosis stage. Especially myelofibrosis is characterized by bone marrow angiogenesis and fibrosis, similarly to retinal observations in nAMD. We speculate if we can find lower CXCR3 expression in MPNs, particularly myelofibrosis and if differences are seen between MPNd and MPNn. We also wanted to compare expression in nAMD and intermediate (i)AMD.

Methods

Patients in this cross-sectional study were 29 nAMD, 28 iAMD, 35 MPNd, and 27 MPNn. We performed flowcytometry on blood to measure CXCR3 expression.

Results

CD8+CXCR3 expression in nAMD was 6,1%, significantly lower than in iAMD 16%, MPNd 11%, MPNn 12% (p-values<0.05). Similar results were seen for CD4+CXCR3 expression. We also found CXCR3 expression decreasing over the MPN-continuum. For instance, in myelofibrosis, intermediate monocytes expression was 6.2%, significantly lower than 18% in ET and 18% in PV (p-values<0.05).

Conclusions

We find CXCR3 downregulation on T-cells and some monocyte subset in nAMD compared to iAMD, MPNd, and MPNn, in line with previous nAMD studies. We also find CXCR3 downregulation in most monocyte subsets over the MPN continuum. Systemic leukocyte CXCR3 expression could both be involved in changes seen in the retina and the bone marrow. Further understanding the CXCR3-axis in AMD and MPNs may elucidate underlying pathogenic mechanisms and reveal new targets for treatment.

Myeloproliferative Disorders and its Effect on Bone Homeostasis: The Role of Megakaryocytes

Myeloproliferative Neoplasms (MPNs) are a heterogeneous group of chronic hematological diseases that arise from the clonal expansion of abnormal hematopoietic stem cells, of which Polycythemia Vera (PV), Essential Thrombocythemia (ET), and Primary Myelofibrosis (PMF) have been extensively reviewed in context of clonal expansion, fibrosis and other phenotypes. Here, we review current knowledge on the influence of different forms of MPN on bone health. Studies implicated various degrees of effect of different forms of MPN on bone density, and on osteoblast proliferation and differentiation, using murine models and human data. The majority of studies show that bone volume is generally increased in PMF patients, whereas it is slightly decreased or not altered in ET and PV patients, although possible differences between male and female phenotypes were not fully explored in most MPN forms. Osteosclerosis seen in PMF patients is a serious complication that can lead to bone marrow failure, and the loss of bone reported in some ET and PV patients can lead to osteoporotic fractures. Some MPN forms are associated with increased number of megakaryocytes (MKs), and several of the MK-associated factors in MPN are known to affect bone development. Here, we review known mechanisms involved in these processes, with focus on the role of MKs and secreted factors. Understanding MPN-associated changes in bone health could improve early intervention and treatment of this side effect of the pathology.

The Role of Megakaryocytes in Myelofibrosis

Megakaryocytes give rise to platelets, which have a wide variety of functions in coagulation, immune response, inflammation, and tissue repair. Dysregulation of megakaryocytes is a key feature of in the myeloproliferative neoplasms, especially myelofibrosis. Megakaryocytes are among the main drivers of myelofibrosis by promoting myeloproliferation and bone marrow fibrosis. In vivo targeting of megakaryocytes by genetic and pharmacologic approaches ameliorates the disease, underscoring the important role of megakaryocytes in myeloproliferative neoplasms. Here we review the current knowledge of the function of megakaryocytes in the JAK2, CALR, and MPL-mutant myeloproliferative neoplasms.

Cytokines frequently implicated in myeloproliferative neoplasms

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MPN is a chronic inflammation-driven tumor model.

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Many cytokines are involved in pathogenesis and progression of MPN.

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IL-1β, TNF-α, IL-6, IL-8, VEGF, PDGF, TGF-β and IFNs are critical in MPN.

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Cytokine directed therapy could be an alternative treatment for MPN in future.

Classical myeloproliferative neoplasms (MPN) include polycythemia vera (PV), essential thrombocythemia (ET) and primary myelofibrosis (PMF). MPN has been defined as a chronic inflammation-driven tumor model. It is clear that there is a close link between chronic inflammation and MPN pathogenesis. Several studies have demonstrated cytokine profiles in MPN patients. Other studies have used cell lines or animal models aiming to clarify the underlying mechanism of cytokines in the pathogenesis of MPN. However, important questions remain: (1) among all these cytokines, which are more predictive? and (2) which are more critical? In this review, we summarize cytokines that have been investigated in MPN and highlight several cytokines that may be more significant in MPN. We suggest that cytokines are more critical in PMF than PV or ET. These cytokines include IL-1β, TNF-α, IL-6, IL-8, VEGF, PDGF, IFNs and TGF-β, all of which should be more closely investigated in MPN. Based on our extensive literature search, several key factors have emerged in our understanding of MPN: first, TNF-α could correlate with MPN progression including PMF, PV and ET. IL-1β plays a role in PMF progression, while it showed no relation with PV or ET. Second, IL-8 could be a prognostic factor for PMF, and IL-6 could be important for MPN progression. Third, VEGF and PDGF play an indirect role in MPN development and their inhibitors could be effective. Fourth, different subtypes of IFNs could have different effects in MPN. Finally, TGF-β is closely linked to MF, although the data are inconsistent. Agents that have targeted these cytokines described above are already in clinical trials, and some of them have even been used to treat MPN patients. Taken together, it will be critical to continue to investigate the precise role of these cytokines in the pathogenesis and progression of MPN.

GATA1 Expression in BCR/ABL1-negative Myeloproliferative Neoplasms

Background

This study aimed to determine GATA1 expression levels to better characterize subgroups in BCR/ABL1-negative myeloproliferative neoplasms (MPNs).

Methods

This study enrolled 49 patients diagnosed as having BCR/ABL1-negative MPN on the basis of the 2016 World Health Organization classification : nine polycythemia vera (PV), 17 essential thrombocythemia (ET), 12 prefibrotic primary myelofibrosis (prePMF), and 11 overt primary myelofibrosis (PMF). Relevant clinical and laboratory data were retrieved from the medical records. The molecular analysis of CALR and MPL mutations and quantification of JAK2 V617F allele burden were performed. GATA1 expression was assessed by an immunohistochemical assay on bone marrow biopsy. GATA1 expression was analyzed serially in 18 patients.

Results

GATA1 expression decreased significantly in PMF compared with that in other subtypes, while no statistical difference was identified between ET and prePMF. GATA1 expression did not differ according to the mutation profiles or the allele burden of JAK2 V617F, but it decreased significantly in patients with overt fibrosis or leukemic transformation.

Conclusions

Our results suggest that GATA1 expression is significantly low in PMF and decreases with progressive fibrosis and possibly with leukemic transformation, although our attempt to accurately distinguish between subgroups using GATA1 immunohistochemical approach did not achieve statistical significance. A large patient cohort with long term follow-up is required to evaluate the prognostic value of GATA1 expression.

Efficacy of ALK5 inhibition in myelofibrosis

Myelofibrosis (MF) is a bone marrow disorder characterized by clonal myeloproliferation, aberrant cytokine production, extramedullary hematopoiesis, and bone marrow fibrosis. Although somatic mutations in JAK2, MPL, and CALR have been identified in the pathogenesis of these diseases, inhibitors of the Jak2 pathway have not demonstrated efficacy in ameliorating MF in patients. TGF-β family members are profibrotic cytokines and we observed significant TGF-β1 isoform overexpression in a large cohort of primary MF patient samples. Significant overexpression of TGF-β1 was also observed in murine clonal MPL^W515L megakaryocytic cells. TGF-β1 stimulated the deposition of excessive collagen by mesenchymal stromal cells (MSCs) by activating the TGF-β receptor I kinase (ALK5)/Smad3 pathway. MSCs derived from MPL^W515L mice demonstrated sustained overproduction of both collagen I and collagen III, effects that were abrogated by ALK5 inhibition in vitro and in vivo. Importantly, use of galunisertib, a clinically active ALK5 inhibitor, significantly improved MF in both MPL^W515L and JAK2^V617F mouse models. These data demonstrate the role of malignant hematopoietic stem cell (HSC)/TGF-β/MSC axis in the pathogenesis of MF, and provide a preclinical rationale for ALK5 blockade as a therapeutic strategy in MF.

Cytokine Regulation of Microenvironmental Cells in Myeloproliferative Neoplasms

The term myeloproliferative neoplasms (MPN) refers to a heterogeneous group of diseases including not only polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF), but also chronic myeloid leukemia (CML), and systemic mastocytosis (SM). Despite the clinical and biological differences between these diseases, common pathophysiological mechanisms have been identified in MPN. First, aberrant tyrosine kinase signaling due to somatic mutations in certain driver genes is common to these MPN. Second, alterations of the bone marrow microenvironment are found in all MPN types and have been implicated in the pathogenesis of the diseases. Finally, elevated levels of proinflammatory and microenvironment-regulating cytokines are commonly found in all MPN-variants. In this paper, we review the effects of MPN-related oncogenes on cytokine expression and release and describe common as well as distinct pathogenetic mechanisms underlying microenvironmental changes in various MPN. Furthermore, targeting of the microenvironment in MPN is discussed. Such novel therapies may enhance the efficacy and may overcome resistance to established tyrosine kinase inhibitor treatment in these patients. Nevertheless, additional basic studies on the complex interplay of neoplastic and stromal cells are required in order to optimize targeting strategies and to translate these concepts into clinical application.

The secret life of a megakaryocyte: emerging roles in bone marrow homeostasis control

Megakaryocytes are rare cells found in the bone marrow, responsible for the everyday production and release of millions of platelets into the bloodstream. Since the discovery and cloning, in 1994, of their principal humoral factor, thrombopoietin, and its receptor c-Mpl, many efforts have been directed to define the mechanisms underlying an efficient platelet production. However, more recently different studies have pointed out new roles for megakaryocytes as regulators of bone marrow homeostasis and physiology. In this review we discuss the interaction and the reciprocal regulation of megakaryocytes with the different cellular and extracellular components of the bone marrow environment. Finally, we provide evidence that these processes may concur to the reconstitution of the bone marrow environment after injury and their deregulation may lead to the development of a series of inherited or acquired pathologies.

Increased angiogenesis in primary myelofibrosis: latent transforming growth factor-β as a possible angiogenic factor

Objective

The aim of this work was to demonstrate a possible relationship between anti-latency-associated peptide human latent transforming growth factor beta 1 (latent TGF-β1) expression in megakaryocytes and microvascular density in bone marrow biopsies from patients with essential thrombocythemia and primary myelofibrosis.

Methods

Microvascular density was evaluated by immunohistochemical analysis and the expression of latent TGF-β1 in samples (100 megakaryocytes per bone marrow sample) from 18 essential thrombocythemia and 38 primary myelofibrosis (19 prefibrotic and 19 fibrotic) patients. Six bone marrow donor biopsies were used as controls. Fibrosis in the bone marrow biopsies was evaluated according to the European Consensus.

Results

The average fibrosis grade differed between essential thrombocythemia and primary myelofibrosis groups when compared to the control group. Latent TGF-β1 expression differed significantly between the fibrotic primary myelofibrosis (PMF) group and the control group (p-value < 0.01). A high degree of neo-angiogenesis (demonstrated by analysis of CD34 expression) was detected in patients with myelofibrosis. There were correlations between latent TGF-β1 expression and microvascular density (r = 0.45; p-value < 0.0009) and between degree of microvascular density and fibrosis grade (r = 0.80; p-value < 0.0001). Remarkable differences for neo-angiogenesis were not observed between patients with essential thrombocythemia and controls.

Conclusion

Angiogenesis participates in the pathogenesis of primary myelofibrosis, in both the prefibrotic and fibrotic stages, while latent TGF-β is differentially expressed only in the prefibrotic stage.

The expression of lysyl-oxidase gene family members in myeloproliferative neoplasms

Myeloproliferative neoplasms (MPNs) are malignant disorders originating from clonal expansion of a single neoplastic stem cell and characteristically show an increase in bone marrow reticulin fibers. Lysyl oxidases (LOXs) are copper-dependent amine oxidases that play a critical role in the biogenesis of connective tissue by crosslinking extracellular matrix proteins, collagen and elastin. Expression of LOX gene family members is increased in disorders associated with increased fibrosis. To evaluate involvement of LOX gene family in various MPNs. In-situ hybridization was used to detect Lysyl-Oxidase family members in bone marrow biopsies from patients with different MPNs. We compared normal bone marrows and those from patients with polycythemia vera, essential thrombocythemia, chronic myeloid leukemia, and primary myelofibrosis (PMF). Serum levels of lysyl-oxidase from patients with PMF and healthy controls were also examined. LOX gene family was not detected in normal bone marrows. All members of the LOX gene family were over expressed in PMF. In other MPNs a differential pattern of expression was observed. Differences in gene expression were statistically significant (P < 0.010). The medianserum LOX levels in normal controls was 28.4 ± 2.5 ng\ml and 44.6 ± 9.44 ng\ml in PMF (P = 0.02). The varying pattern of expression of LOX genes may reflect differences in the pathophysiology of bone marrow fibrosis in these MPNs. These observations could be used as the basis for future targeted therapy directed against bone marrow fibrosis.

The complex regulation of TGF-β in cardiovascular disease

Transforming growth factor β (TGF-β1) is a pleiotropic cytokine with many and complex effects in cell and tissue physiology. This is made possible by a very complex and interwoven signaling system, whose regulation continues to be the focus of a growing line of research. This complex regulation translates to a key role in cardiovascular physiology, hemostasis, and the blood–vessel interface. In accordance with this, the TGF-β1 pathway appears to be deregulated in related disorders, such as atherosclerotic vascular disease and myeloproliferative syndromes. It is expected that the growing amount of experimental and clinical research will yield medical advances in the applications of knowledge of the TGF-β1 pathway to diagnosis and therapeutics.

Megakaryocyte pathology and bone marrow fibrosis: the lysyl oxidase connection

Megakaryocytes (MKs), the platelet precursors, are capable of accumulating DNA greater than a diploid content as part of their cell cycle. MKs have been recognized as mediating fibrosis in a subset of hematologic malignancies, including acute megakaryoblastic leukemia and a subset of myeloproliferative neoplasms. The mechanisms responsible for fibrosis remain only partially understood. Past studies highlighted the role of growth factors in such pathologies, and recently, the protein lysyl oxidase (LOX) has been implicated in proliferation of MKs, ploidy and deposition of fibers. LOX was initially characterized as a protein responsible for the intermolecular cross-linking of elastin and collagen, and in recent years it has been identified as regulator of various pathologies, such as cancer and inflammation. Here, we review recent advances in the understanding of the contribution of MKs to the progression of myelofibrosis, highlighting the newly identified role of LOX.