RESUMO
Advanced chronic idiopathic myelofibrosis (IMF) with osteosclerosis and increase and thickening of bone trabeculae is typically contrasted by the absence or sparse presence of osteoclasts. Because osteoclast formation can be inhibited by osteoprotegerin (OPG) we investigated OPG expression in IMF with severe fibrosis and osteosclerosis, which expressed significantly higher (up to 71-fold) OPG mRNA levels when compared with prefibrotic cellular IMF and control cases. The receptor activator of nuclear factor kappaB ligand (RANKL), a positive regulator of osteoclast differentiation and putative antagonist of OPG was overexpressed by up to 34-fold exclusively in advanced IMF. Case-specific calculation of the RANKL/OPG ratio in advanced IMF showed a wide range without significant differences when compared with the prefibrotic IMF and non-neoplastic haematopoiesis. Immunohistochemical detection of OPG protein revealed strong labelling of endothelial cells within proliferating vessels in fibrotic IMF and heterogeneously labelled megakaryocytes, and fibroblasts. Osteosclerosis and impaired osteoclast function in IMF appears to be associated with upregulated endothelial OPG expression but concomitant reduction of the antagonist RANKL could not be demonstrated. We conclude that osteosclerosis in IMF is associated with increased endothelial OPG expression without concomitant RANKL downregulation.
Assuntos
Células Endoteliais/metabolismo , Glicoproteínas/metabolismo , Osteosclerose/etiologia , Mielofibrose Primária/complicações , Receptores Citoplasmáticos e Nucleares/metabolismo , Receptores do Fator de Necrose Tumoral/metabolismo , Adulto , Idoso , Idoso de 80 Anos ou mais , Exame de Medula Óssea , Proteínas de Transporte/genética , Células Endoteliais/química , Feminino , Fibroblastos/química , Glicoproteínas/genética , Humanos , Imuno-Histoquímica/métodos , Masculino , Megacariócitos/química , Glicoproteínas de Membrana/genética , Pessoa de Meia-Idade , Osteoclastos/patologia , Osteoprotegerina , Osteosclerose/metabolismo , Osteosclerose/patologia , Mielofibrose Primária/metabolismo , Mielofibrose Primária/patologia , Ligante RANK , RNA Mensageiro/análise , Receptor Ativador de Fator Nuclear kappa-B , Receptores Citoplasmáticos e Nucleares/genética , Receptores do Fator de Necrose Tumoral/genética , Reação em Cadeia da Polimerase Via Transcriptase ReversaRESUMO
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.
Assuntos
Biomarcadores Tumorais/metabolismo , Transtornos Mieloproliferativos/metabolismo , Fator de Crescimento Transformador beta/metabolismo , Adulto , Idoso , Idoso de 80 Anos ou mais , Biomarcadores Tumorais/genética , Células da Medula Óssea/metabolismo , Doença Crônica , Diagnóstico Diferencial , Feminino , Expressão Gênica , Glicoproteínas/biossíntese , Glicoproteínas/genética , Hematopoese , Humanos , Leucemia Mieloide Crônica Atípica BCR-ABL Negativa/metabolismo , Masculino , Megacariócitos/metabolismo , Microdissecção/métodos , Pessoa de Meia-Idade , Transtornos Mieloproliferativos/diagnóstico , Osteoprotegerina , Policitemia Vera/metabolismo , Mielofibrose Primária/diagnóstico , Mielofibrose Primária/metabolismo , Análise Serial de Proteínas/métodos , RNA Mensageiro/genética , Receptores Citoplasmáticos e Nucleares/biossíntese , Receptores Citoplasmáticos e Nucleares/genética , Receptores do Fator de Necrose Tumoral , Reação em Cadeia da Polimerase Via Transcriptase Reversa/métodos , Trombocitemia Essencial/metabolismo , Fator de Crescimento Transformador beta/genética , Fator de Crescimento Transformador beta1RESUMO
The expression of members of the platelet-derived growth factor (PDGF) system in bone marrow cells derived from Idiopathic myelofibrosis (IMF) has been investigated by real-time RT-PCR. Increased expression of PDGFs and the corresponding PDGF receptor a could be demonstrated to be a feature of advanced fibrosis in IMF that is not demonstrable in the prefibrotic phase of the disease.
