Reduced responsiveness of bone marrow megakaryocyte progenitors to platelet‐derived transforming growth factor β1, produced in normal amount, in patients with essential thrombocythaemia

Abstract

In this study we evaluated the amount of transforming growth factor-beta 1 (TGF-beta 1) in platelet lysates obtained from 12 patients affected by essential thrombocythaemia (ET) in comparison with five patients affected by myelofibrosis with myeloid metaplasia (MMM) and 15 healthy donors. The levels of both bioactive and latent TGF-beta 1, evaluated in a bioassay on CCL64 cells, before and after transient acidification, were similar in platelet lysates from ET patients and normal donors and significantly (P < 0.01) elevated in platelet lysates from MMM patients. Moreover, platelet lysates from ET patients and normal controls, showed a similar degree of colony suppression when tested on haematopoietic progenitor (CD34+) cells, purified from normal bone marrows, whereas platelet lysates from MMM patients showed a higher (P < 0.01) inhibitory activity on normal CFU-meg and BFU-E growth. In parallel, platelet lysates form ET patients and normal controls were tested on CD34+ cells, purified from ET bone marrows. ET bone marrow BFU-E, similarly to normal bone marrow BFU-E, were markedly inhibited by platelet lysates, whereas ET bone marrow CFU-meg were significantly (P < 0.05) less responsive to the inhibitory activity of platelet lysates than normal bone marrow CFU-meg. The main factor responsible for the inhibitory activity contained in platelet lysates was transforming growth factor-beta 1 (TGF-beta 1), as demonstrated by the ability of a polyclonal neutralizing anti-TGF-beta 1 antibody to almost completely reverse the suppressive effect of platelet lysates on CFU-meg and BFU-E growth. Our data demonstrate that the amount of intraplatelet TGF-beta 1 is similar in ET patients and normal controls, whereas it is increased in platelets from MMM patients. Moreover, megakaryocyte progenitors in ET show a reduced sensitivity to platelet-derived inhibitors and, in particular, to TGF-beta 1.

Cellular Distribution of Platelet-Derived Growth Factor, Transforming Growth Factor-β, Basic Fibroblast Growth Factor, and Their Receptors in Normal Bone Marrow

“…Our demonstration of receptors for all the study cytokines (PDGF, TGF-β, bFGF) in hematopoietic precursor cells is consistent with the currently known regulatory function of these cytokines in physiologic [14, 20, 33, 34, 35]and clonal [30, 31]hematopoiesis. PDGF stimulates erythropoiesis [33, 36, 37, 38]and megakaryocytopoiesis [34], whereas TGF-β suppresses hematopoiesis, in general [20, 35].…”

“…The study of cytokines is often implicated in the regulation of bone marrow fibrosis [22, 23, 24, 25, 26, 27, 28, 29]and clonal hematopoiesis [30, 31]. In mice, increased PDGF and TGF-β levels have been demonstrated in thrombopoietin-induced myelofibrosis [22, 23].…”

“…Furthermore, increased levels of all 3 cytokines have been demonstrated in the plasma, platelets, and megakaryocytes of patients with MMM, suggesting their pathogenetic role [26, 27, 28, 29]. In regard to clonal hematopoiesis, the biologic effects of bFGF (stimulatory) and TGF-β (inhibitory) are believed to be antagonistic, and there is differential cellular expression of these cytokines and their receptors [30, 31]. …”

Osteomyelosclerosis, anemia and extramedullary hematopoiesis in mice lacking the transcription factor NFATc2

“…aberrant production Role of NFATc2 in steady-state hematopoiesis haematologica | 2011; 96 (11) 1585 [29][30][31] About 50 % of patients with primary myelofibrosis carry a mutation of the JAK2 gene, which confers cytokine-independent proliferation and expansion of the hematopoietic clone. In turn, cytokines and growth factors produced by these cells (including osteoprotegerin, 32,33 transforming growth factor-b, 34,35 and platelet-derived growth factor 36 ) alter the bone marrow microenvironment in such a way that large deposits of fibrous and osseous tissue are formed.…”

Does primary myelofibrosis involve a defective stem cell niche? From concept to evidence

“…This accumulation is thought to be the consequence of an excessive release/leakage of growth factors within the bone marrow by cells from the pathological hematopoietic clone and especially by necrotic megakaryocytes. [44][45][46][47][48] Among them, platelet factor 4 (PF4), platelet-derived growth factor (PDGF), basic fibroblast growth factor (bFGF), transforming growth factorbeta (TGF-␤), [49][50][51][52] and vascular endothelial growth factor (VEGF) 53,54 are thought to activate mesenchymal cells, leading to myelofibrosis, as well as endothelial cells, contributing to angiogenesis. It has been recently hypothesized that an increased production of osteoprotegerin by stromal and endothelial cells might also contribute to the unbalanced osteoblast production, resulting in the osteosclerosis frequently associated with myelofibrosis in patients 55,56 and in murine models.…”