title: A novel interaction between megakaryocytes and activated fibrocytes increases TGF-β bioavailability in the Gata1(low) mouse model of myelofibrosis.
abstract: Despite numerous circumstantial evidences, the pathogenic role of TGF-β in primary myelofibrosis (PMF), the most severe of the Philadelphia-negative myeloproliferative neoplasms, is still unclear because of the modest (2-fold) increases in its plasma levels observed in PMF patients and in the Gata1(low) mouse model. Whether myelofibrosis is associated with increased bioavailability of TGF-β bound to fibrotic fibres is unknown. Transmission electron-microscopy (TEM) observations identified that spleen from PMF patients and Gata1(low) mice contained megakaryocytes with abnormally high levels of TGF-β and collagen fibres embedded in their cytoplasm. Additional immuno-TEM observations of spleen from Gata1(low) mice revealed the presence of numerous activated fibrocytes establishing with their protrusions a novel cellular interaction, defined as peripolesis, with megakaryocytes. These protrusions infiltrated the megakaryocyte cytoplasm releasing collagen that was eventually detected in its mature polymerized form. Megakaryocytes, engulfed with mature collagen fibres, acquired the morphology of para-apoptotic cells and, in the most advanced cases, were recognized as polylobated heterochromatic nuclei surrounded by collagen fibres strictly associated with TGF-β. These areas contained concentrations of TGF-β-gold particles ~1000-fold greater than normal and numerous myofibroblasts, an indication that TGF-β was bioactive. Loss-of-function studies indicated that peripolesis between megakaryocytes and fibrocytes required both TGF-β, possibly for inducing fibrocyte activation, and P-selectin, possibly for mediating interaction between the two cell types. Loss-of-function of TGF-β and P-selectin also prevented fibrosis. These observations identify that myelofibrosis is associated with pathological increases of TGF-β bioavailability and suggest a novel megakaryocyte-mediated mechanism that may increase TGF-β bioavailability in chronic inflammation.
authors.affiliation: Unit of Microscopic and Ultrastructural Anatomy, Department of Medicine, Campus Bio-Medico University Rome Italy.
authors.forename: Maria
authors.initials: M
authors.lastname: Zingariello
authors.affiliation: Biomedical and Neuromotory Sciences, Alma Mater University Bologna, Italy.
authors.forename: Alessandra
authors.initials: A
authors.lastname: Ruggeri
authors.affiliation: Hematology, Oncology and Molecular Medicine and Department of Cell Biology and Neuroscience, Istituto Superiore di Sanità Rome, Italy.
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Martelli
authors.affiliation: Hematology, Oncology and Molecular Medicine and Department of Cell Biology and Neuroscience, Istituto Superiore di Sanità Rome, Italy.
authors.forename: Manuela
authors.initials: M
authors.lastname: Marra
authors.affiliation: Medicine and Aging Science, University G. D'Annunzio of Chieti-Pescara Italy.
authors.forename: Laura
authors.initials: L
authors.lastname: Sancillo
authors.affiliation: Tisch Cancer Institute, Ichan School of Medicine at Mount Sinai New York, NY, USA.
authors.forename: Ilaria
authors.initials: I
authors.lastname: Ceglia
authors.affiliation: Medicine and Aging Science, University G. D'Annunzio of Chieti-Pescara Italy.
authors.forename: Rosa Alba
authors.initials: RA
authors.lastname: Rana
authors.affiliation: Biomedical and Neuromotory Sciences, Alma Mater UniversityBologna, Italy; Tisch Cancer Institute, Ichan School of Medicine at Mount SinaiNew York, NY, USA.
authors.forename: Anna Rita
authors.initials: AR
authors.lastname: Migliaccio
keywords: Megakaryocytes; P-selectin; TGF-β; activated fibrocytes; myelofibrosis; neutrophils