Poujol Christel, Ware Jerry, Nieswandt Bernhard, Nurden Alan T, Nurden Paquita
UMR 5533 CNRS, Laboratoire d'Hématologie, Hôpital Cardiologique, Avenue de Magellan, 33604 Pessac, France.
Exp Hematol. 2002 Apr;30(4):352-60. doi: 10.1016/s0301-472x(02)00774-9.
The glycoprotein Ib/IX/V complex (GPIb-IX-V) mediates platelet attachment to von Willebrand factor in exposed subendothelium. Molecular defects in the genes for GPIbalpha, GPIbbeta, and GPIX give rise to the Bernard-Soulier syndrome, in which thrombocytopenia and giant platelets suggest that this receptor also is involved in platelet production. To study how giant platelets are produced in vivo, we used a model of GPIbalpha-deficient mice (GPIbalpha(null)) and mice rescued with the human GPIbalpha transgene (GPIbalpha(null;hTg)).
Using electron microscopy and immunogold labeling, we examined megakaryocytopoiesis in the bone marrow of these mice and developed a method to quantify the membranes of megakaryocytes (MK) and proplatelets by computer analysis.
Abnormal membrane development in the perinuclear zone was found in immature MK of GPIbalpha(null) mice. This led to a poorly developed demarcation membrane system and other ultrastructural changes. As a result, well-organized platelet territories were rarely seen within the cytoplasm of mature MK. Membrane quantification confirmed that MK of GPIbalpha(null) mice had a reduced internal membrane pool. Whereas these MK normally crossed the endothelial barrier, their migration was accompanied by the production of unusually large MK fragments or proplatelets in the vascular sinus with an approximately 50% decrease in internal membrane content compared to wild-type. In the rescued GPIbalpha(null;hTg) model, GPIbalpha was normally localized in MK, and there was a total correction of the ultrastructural defects.
GPIbalpha is essential for membrane development and distribution in maturing MK. Its absence leads to abnormal partitioning of the membrane systems and abnormal proplatelet production.
糖蛋白Ib/IX/V复合物（GPIb-IX-V）介导血小板与暴露的内皮下层的血管性血友病因子结合。GPIbalpha、GPIbbeta和GPIX基因的分子缺陷会导致伯纳德-索利尔综合征，其中血小板减少和巨大血小板提示该受体也参与血小板生成。为了研究体内巨大血小板是如何产生的，我们使用了GPIbalpha缺陷小鼠（GPIbalpha(null)）模型和用人GPIbalpha转基因拯救的小鼠（GPIbalpha(null;hTg)）。
我们使用电子显微镜和免疫金标记检查了这些小鼠骨髓中的巨核细胞生成，并开发了一种通过计算机分析定量巨核细胞（MK）和前血小板膜的方法。
在GPIbalpha(null)小鼠的未成熟MK中发现核周区膜发育异常。这导致分界膜系统发育不良和其他超微结构变化。结果，在成熟MK的细胞质内很少见到组织良好的血小板区域。膜定量证实GPIbalpha(null)小鼠的MK内膜池减少。虽然这些MK通常穿过内皮屏障，但它们的迁移伴随着在血管窦中产生异常大的MK片段或前血小板，与野生型相比内膜含量减少约50%。在拯救的GPIbalpha(null;hTg)模型中，GPIbalpha正常定位于MK，超微结构缺陷得到完全纠正。
GPIbalpha对成熟MK中的膜发育和分布至关重要。其缺失导致膜系统的异常分配和前血小板生成异常。
