Histological study of megakaryocytogenesis and thrombocytogenesis in the guinea pig bone marrow with reference to the role of adipocytes

Introduction Blood platelets play a pivotal role in hemostasis and participate directly in thrombosis and atherosclerosis. Aim of the work The aim of the study was to investigate the steps of platelet production, the morphological changes that occur during proplatelet production, the cytoskeletal mechanics that drive these transformations, and the possible role of stromal cells in platelet formation. Materials and methods Red bone marrow fragments were harvested from ten adult male guinea pigs. Toluidine blue-stained semithin sections were prepared for light microscopic examination, and ultrathin sections were examined by transmission electron microscope. Results In the semithin sections of the bone marrow, nearly half of the area contained hematopoietic cells, whereas the remainder was occupied by adipocytes that showed unusual bridging connections between them. In addition, the megakaryocytic lineage cells assumed a unique close association with the neighboring adipocytes. Under transmission electron microscope, the surface of the immature megakaryocytes was characteristically smooth, whereas mature megakaryocytes developed characteristic proplatelets in the form of coarse surface cytoplasmic processes that bulged to the outside and detached as preplatelets. Granules and membranes associated with microtubules were translocated from the base of proplatelets to appear in their cytoplasm, and the invaginated membrane system became extensive in the mature megakaryocytes. Sometimes, these cells extended large proplatelets through the attenuated sinusoidal walls, where they discharged preplatelets that further fragmented into platelets. Conclusion The formation of proplatelets and the elaboration of granules into the newly formed preplatelets and platelets were largely dependent on the efficiency of microtubular cytoskeletal elements. Marrow stromal cells, especially adipocytes, might be involved in megakaryocytic lineage development.