Transmission Electron Microscopy of Platelets FROM Apheresis and Buffy-Coat-Derived Platelet Concentrates

Abstract

Platelet concentrates are produced in order to treat bleeding disorders. They can be provided by apheresis machines or by pooling of buffy coats from four blood donations. During their manufacturing and storage, morphological alterations of platelets occur which can be demonstrated by transmission electron microscopy. Alterations range from slight and reversible changes, such as formation of small cell protrusions and swelling of the surface-connected open canalicular system, to severe structural changes, where platelets undergo transitions from discoid to ameboid shapes as a consequence of platelet activation. These alterations end in delivery of the contents of platelet granules as well as platelet involution caused by apoptosis and necrosis processes denoted as the platelet release reaction. Hereby, the involvement of the network of the open canalicular system, helping to deliver the contents of platelet granules into the surrounding milieu via pores, is distinctly shown by electron tomography. As a consequence of platelet activation, a delivery of differently sized microparticles takes place which is thought to play an important role in the adverse reactions in some recipients of platelet concentrates. In this article, the formation and delivery of platelet microparticles is illustrated by electron tomography. Above all, the ultrastructural features of platelets and megakaryocytes are discussed in the context of the molecular characteristics of the plasma membrane and organelles including the different granules and the expression of receptors engaged in signaling during platelet activation. Starting from the knowledge of the ultrastructure of resting and activated platelets, a score classification is presented, allowing the evaluation of different activation stages in a reproducible manner. Examples of evaluations of platelet concentrates using electron microscopy are briefly reviewed. In the last part,

Electron tomography—a tool for ultrastructural 3D visualization in cell biology and histology

“…The interaction of platelets (PLTs) with bacteria has been shown in PLT concentrates after spiking with Staphylococcus aureus . The uptake of these bacteria into the open canalicular system (OCS) was visualized by using ET [ 49 , 50 ]. Bacterial contamination leads to activation of PLTs and to the formation of platelet microparticles (PMPs; Fig.…”

Investigating the effect of age on platelet ultrastructure using transmission electron microscopy

“…Mitochondria and glycogen provide the energy required for secretory functions. Upon activation, platelets change their shape dramatically, acquiring an amoeboid form due to the rearrangement of organelles, and secrete various bioactive components involved in haemostasis, regeneration, repair, and inflammation …”

“…Previous research has demonstrated that people of different age groups show different platelet and fibrin morphologies . Furthermore, several studies have demonstrated that transmission electron microscopy (TEM) is an appropriate tool for evaluating platelet quality . TEM can be used to clearly identify a large number of platelet structural elements, including the open canalicular system (OCS), the dense tubular system (DTS), and various organelles, such as α‐granules, dense granules, lysosomal granules, and mitochondria.…”

A model of the PI cycle reveals the regulating roles of lipid-binding proteins and pitfalls of using mosaic biological data

“…Based on published observations, the size of the cytoplasm was reduced as the observed volume of platelets is filled by organelles such as vesicles, ER remnant, mitochondria and the OCS estimated to occupy up to 40% of the internal volume. Most of the remaining volume contains cytoskeletal proteins and glycogen granules and is calculated to occupy around 1 to 2 fl 37,41,42 . We estimated the mouse platelet plasma membrane and cytosol volumes to be around 0.25 fl each while the nucleated cells average plasma membrane and reaction cytosol volumes at around 17 fl each based on a 2000 fl overall cell volume.…”