Aberrant expression of transforming growth factor β‐1 (TGFβ‐1) per se does not discriminate fibrotic from non‐fibrotic chronic myeloproliferative disorders

Abstract

Transforming growth factor beta-1 (TGF beta-1) is a potent inducer of fibrosis and has been shown to be essential for the development of bone marrow fibrosis in an animal model of idiopathic myelofibrosis (IMF). IMF belongs to the Philadelphia chromosome negative chronic myeloproliferative disorders (Ph(-) CMPD). Megakaryocytes and platelets have been suggested as the major cellular source of TGF beta-1 in IMF. The osteoclastogenesis inhibitory factor osteoprotegerin (OPG) seems to be regulated by TGF beta-1 and substantial involvement of OPG expression in the process of osteosclerosis in IMF has recently been suggested. In order to determine TGF beta-1 expression in IMF and other Ph(-) CMPD, total bone marrow cells as well as laser-microdissected megakaryocytes were quantitatively analysed by real-time RT-PCR. OPG mRNA expression in fibrotic IMF was correlated with TGF beta-1 mRNA expression in a case-specific manner. Both OPG and TGF beta-1 were detected immunohistochemically in order to delineate cellular origin. When total bone marrow cells were investigated, TGF beta-1 mRNA expression was increased in some but not all cases of IMF (n = 21), with highest values in fibrotic cases. Unexpectedly, increased values were also observed in essential thrombocythaemia (ET, n = 11) when compared to non-neoplastic haematopoiesis (n = 38). Megakaryocytes isolated by laser microdissection displayed elevated TGF beta-1 mRNA levels in most of the CMPD samples with no significant differences discernible between fibrotic IMF, polycythaemia vera (PV) and ET. TGF beta-1 protein was predominantly expressed by the myeloid lineage in Ph(-) CMPD and non-neoplastic haematopoiesis, which, however, displayed lower expression. IMF cases with advanced fibrosis concomitantly overexpressed TGF beta-1 and OPG. Immunohistochemically, OPG expression was found in different stromal cells and a subfraction of megakaryocytes. In conclusion, enhanced TGF beta-1 expression occurs in megakaryocytes as well as myeloid cells in Ph(-) CMPD. TGF beta-1 may be necessary, but is not sufficient, to induce bone marrow fibrosis in IMF because non-fibrotic Ph(-) CMPD entities share this feature with IMF and cannot be discriminated from each other on the basis of TGF beta-1 expression.

Bone Morphogenetic Proteins Are Overexpressed in the Bone Marrow of Primary Myelofibrosis and Are Apparently Induced by Fibrogenic Cytokines

“…4 autocrine stimulation of cellular lineages. 7,28,29 In fact, megakaryocytes contain large amounts of nuclear bFGF, suggesting an autocrine mechanism. 30 Megakaryocytes in PMF per se were shown to be involved in fibrogenesis because of either active secretion or decay-associated passive efflux of cellular cytokines into the bone marrow stroma.…”

Stem Cell Defects in Philadelphia Chromosome Negative Chronic Myeloproliferative Disorders: A Phenotypic and Molecular Puzzle?

“…Several important investigations on aberrant processing and expression of growth factor receptors such as Mpl (Myeloproliferative leukaemia virus oncogene) and growth factors such as Transforming growth factor β-1 (TGFβ-1), growth factor hypersensitivity, endogenous erythroid colony (EEC) formation in PV, and introduction of diagnostic markers such as the Polycythaemia vera rubra receptor-1 (PRV-1) mRNA expression in granulocytes from peripheral blood but not bone marrow cells contributed substantially to expanding knowledge on the pathogenesis of Ph -CMPD [12][13][14][15][16][17][18][19]. In the process of myelofibrosis in Ph -CMPD, a series of studies demonstrated that apparently a cocktail of growth factors like TGFβ-1, basic fibroblast growth factor (bFGF) and platelet derived growth factor (PDGF) act in concert to induce and maintain fibrogenesis.…”

P38 Kinase, SGK1 and NF-κB Dependent Up-Regulation of Na+/Ca2+ Exchanger Expression and Activity Following TGFß1 Treatment of Megakaryocytes

“…TGFß1 is produced by megakaryocytes [58, 59] and required for megakaryocyte maturation and platelet formation [19]. The growth factor stimulates expression of bone marrow stromal thrombopoietin [19], which in turn stimulates the expression of megakaryocytic TGF-beta receptors [19].…”