Hunt P, Hokom M M, Wiemann B, Leven R M, Arakawa T
Laboratory of Stem Cell Biology, Amgen Center, Thousand Oaks, CA 91320.
Exp Hematol. 1993 Feb;21(2):372-81.
The process of platelet shedding from megakaryocytes is incompletely understood, due in part to the impossibility of studying this dynamic process in vivo. Megakaryocytes in situ and in in vitro cultures display extended cytoplasmic processes constricted at platelet-sized intervals which presumably are the structural intermediates between megakaryocytes and platelets. This study describes the establishment of a serum-free culture system of purified guinea pig megakaryocytes in which extensive cytoplasmic process formation can be observed on 21 to 29% of the cells. The addition of as little as 0.05% pooled human serum to the cultures will completely but reversibly block process development. The serum inhibitor was identified as residual prothrombin, which upon contact with megakaryocytes is converted to the serine esterase thrombin. Thrombin directly prevents the formation of new processes and also induces retraction of existing processes. When megakaryocytes are cultured on Matrigel, process formation occurs even in an excess of thrombin. This potentiation of process development in the presence of inhibitory factors is mediated by the glycosaminoglycan content of Matrigel. The physiological implications of these observations are discussed.
巨核细胞释放血小板的过程尚未完全明确，部分原因是难以在体内研究这一动态过程。原位和体外培养的巨核细胞呈现出延长的细胞质突起，这些突起以血小板大小的间隔收缩，推测它们是巨核细胞和血小板之间的结构中间体。本研究描述了一种纯化豚鼠巨核细胞的无血清培养系统的建立，在该系统中，21%至29%的细胞可观察到广泛的细胞质突起形成。向培养物中加入低至0.05%的混合人血清将完全但可逆地阻断突起的发育。血清抑制剂被鉴定为残留的凝血酶原，其与巨核细胞接触后会转化为丝氨酸酯酶凝血酶。凝血酶直接阻止新突起的形成，并诱导现有突起的回缩。当巨核细胞在基质胶上培养时，即使存在过量的凝血酶，也会发生突起形成。在抑制因子存在的情况下，这种突起发育的增强是由基质胶的糖胺聚糖含量介导的。讨论了这些观察结果的生理学意义。
