Zingariello Maria, Ruggeri Alessandra, Martelli Fabrizio, Marra Manuela, Sancillo Laura, Ceglia Ilaria, Rana Rosa Alba, Migliaccio Anna Rita
Unit of Microscopic and Ultrastructural Anatomy, Department of Medicine, Campus Bio-Medico University Rome Italy.
Biomedical and Neuromotory Sciences, Alma Mater University Bologna, Italy.
Am J Blood Res. 2015 Dec 25;5(2):34-61. eCollection 2015.
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.
尽管有大量间接证据，但转化生长因子-β（TGF-β）在原发性骨髓纤维化（PMF，费城染色体阴性骨髓增殖性肿瘤中最严重的一种）中的致病作用仍不清楚，因为在PMF患者和Gata1（低表达）小鼠模型中观察到其血浆水平仅适度（2倍）升高。骨髓纤维化是否与结合在纤维化纤维上的TGF-β生物利用度增加有关尚不清楚。透射电子显微镜（TEM）观察发现，PMF患者和Gata1（低表达）小鼠的脾脏中含有巨核细胞，其细胞质中TGF-β和胶原纤维水平异常高。对Gata1（低表达）小鼠脾脏的额外免疫电镜观察显示，存在大量活化的成纤维细胞，它们通过突起与巨核细胞建立了一种新的细胞相互作用，称为周缘运动。这些突起侵入巨核细胞细胞质，释放胶原蛋白，最终以其成熟的聚合形式被检测到。被成熟胶原纤维吞噬的巨核细胞获得了准凋亡细胞的形态，在最严重的情况下，被识别为被与TGF-β紧密相关的胶原纤维包围的多叶异染色质核。这些区域中TGF-β金颗粒的浓度比正常情况高约1000倍，并且有大量肌成纤维细胞，这表明TGF-β具有生物活性。功能丧失研究表明，巨核细胞和成纤维细胞之间的周缘运动既需要TGF-β（可能用于诱导成纤维细胞活化），也需要P-选择素（可能用于介导两种细胞类型之间的相互作用）。TGF-β和P-选择素的功能丧失也可预防纤维化。这些观察结果表明，骨髓纤维化与TGF-β生物利用度的病理性增加有关，并提示了一种新的巨核细胞介导的机制，该机制可能在慢性炎症中增加TGF-β的生物利用度。
