Department of Pediatrics, Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA.
Int J Radiat Oncol Biol Phys. 2011 Aug 1;80(5):1533-40. doi: 10.1016/j.ijrobp.2011.03.039.
Factors affecting the severity of radiation-induced thrombocytopenia (RIT) are not well described. We address whether platelet factor 4 (PF4; a negative paracrine for megakaryopoiesis) affects platelet recovery postradiation.
Using conditioned media from irradiated bone marrow (BM) cells from transgenic mice overexpressing human (h) PF4 (hPF4+), megakaryocyte colony formation was assessed in the presence of this conditioned media and PF4 blocking agents. In a model of radiation-induced thrombocytopenia, irradiated mice with varying PF4 expression levels were treated with anti-hPF4 and/or thrombopoietin (TPO), and platelet count recovery and survival were examined.
Conditioned media from irradiated BM from hPF4+ mice inhibited megakaryocyte colony formation, suggesting that PF4 is a negative paracrine released in RIT. Blocking with an anti-hPF4 antibody restored colony formation of BM grown in the presence of hPF4+ irradiated media, as did antibodies that block the megakaryocyte receptor for PF4, low-density lipoprotein receptor-related protein 1 (LRP1). Irradiated PF4 knockout mice had higher nadir platelet counts than irradiated hPF4+/knockout litter mates (651 vs. 328 × 106/mcL, p = 0.02) and recovered earlier (15 days vs. 22 days, respectively, p <0.02). When irradiated hPF4+ mice were treated with anti-hPF4 antibody and/or TPO, they showed less severe thrombocytopenia than untreated mice, with improved survival and time to platelet recovery, but no additive effect was seen.
Our studies show that in RIT, damaged megakaryocytes release PF4 locally, inhibiting platelet recovery. Blocking PF4 enhances recovery while released PF4 from megakaryocytes limits TPO efficacy, potentially because of increased release of PF4 stimulated by TPO. The clinical value of blocking this negative paracrine pathway post-RIT remains to be determined.
目前尚未充分阐明影响放射性诱导性血小板减少症（RIT）严重程度的因素。本研究旨在探讨血小板因子 4（PF4；巨核细胞生成的负性旁分泌因子）是否会影响放射后血小板的恢复。
利用过表达人 PF4（hPF4+）的转基因小鼠辐照骨髓细胞的条件培养基，评估在存在该条件培养基和 PF4 阻断剂的情况下巨核细胞集落的形成。在 RIT 诱导的血小板减少症模型中，用抗 hPF4 和/或血小板生成素（TPO）处理表达水平不同的 PF4 的辐照小鼠，观察血小板计数恢复和生存情况。
hPF4+ 小鼠辐照骨髓的条件培养基抑制巨核细胞集落形成，提示 PF4 是 RIT 中释放的负性旁分泌因子。用抗 hPF4 抗体阻断可恢复在 hPF4+辐照培养基中生长的 BM 的集落形成，阻断 PF4 巨核细胞受体（低密度脂蛋白受体相关蛋白 1 [LRP1]）的抗体也有同样作用。与辐照 hPF4+/+ 同窝仔鼠相比，辐照 PF4 敲除小鼠的血小板计数最低值更高（651 与 328×106/μL，p=0.02），血小板恢复更早（分别为 15 天与 22 天，p<0.02）。当用抗 hPF4 抗体和/或 TPO 处理辐照 hPF4+小鼠时，与未处理小鼠相比，它们的血小板减少症程度较轻，生存改善，血小板恢复时间缩短，但未观察到相加效应。
我们的研究表明，在 RIT 中，受损的巨核细胞局部释放 PF4，抑制血小板恢复。阻断 PF4 可增强恢复，而巨核细胞释放的 PF4 限制了 TPO 的疗效，这可能是因为 TPO 刺激 PF4 的释放增加。阻断 RIT 后这条负性旁分泌途径的临床价值仍有待确定。
