Plasma membrane repair, blebbing and microvesiculation: parallels and relationships
Cellular automaton modelling of platelet aggregation
Platelet aggregation plays an important role in hemostasis, as it prevents blood loss upon vessel wall disruption. Computational modelling is one of the useful approaches to study this system. The use of a cellular automaton as a model makes it possible both to study the dynamics of individual aggregates and to investigate the behaviour of the system as a whole. The aim of this research is to study platelet aggregation using a model based on a cellular automaton. As a result, a model of platelet aggregation in the basic approximation and with flow condition was constructed. It was shown that under flow conditions, the most number of the aggregates are dimers and trimers, whereas aggregates of large sizes are much less presented.
On calcium fluorophore’s impact in platelet signaling studies
Observation of calcium signaling in platelets - blood cells designed to be involved in stopping bleeding and forming blood clots - is an important part of fundamental research in hemostasis. However, such a study is possible only with the use of calcium fluorophores - small molecules that penetrate the platelet membrane due to their hydrophobic -AM part, which is then hydrolyzed by cytosol esterases. In this work, we consider the phenomenon of inhomogeneous loading of calcium fluorophores into platelets.
We used platelets from healthy adult donors loaded with various fluorescent probes (CalBryte590, DiOC6 (3), Fura Red, Fluo-4 and CellTracker Violet BMQC) and immobilized on antibodies to CD31 in parallel plane flow chambers. Total internal reflection fluorescence (TIRF) microscopy was used for observations.
We demonstrated that all studied probes are loaded heterogeneously, with 30% platelets being loaded with a probe 2-6 times higher than the population median value. Using the CalBryte590 probe as an example, we have shown that a decrease in the incubation temperature, the addition of Pluronic 127 to the incubation medium, or membrane cholesterol depletion significantly reduces the heterogeneity of the probe distribution in the population. By looking at platelet activation from the surface, we have shown that the probability of experiencing strong activation, as measured by the intensity of calcium oscillations, correlates with the amount of probe in the platelet.
Thus, we conclude that the type of fluorophore used and the conditions of its loading into platelets can significantly affect the results of experiments on the observation of calcium signaling in platelets.
Presence of PI-rich vesicles is required for the PLC ζ activation according to mathematical modeling
Phospholipase Cζ (PLCζ) is an enzyme found in the cytoplasm and acrosome of mammalian spermatozoa. It catalyzes the reaction of phosphatidylinositol-4,5-phosphate hydrolysis into inositol-3-phosphate and diacylglycerol. PLCζ is present in the sperm cell acrosome and cytosol but doesn’t significantly affect its metabolism. However, after the fusion of sperm and egg membranes, its activity increases as it begins to bind membranes of the egg. It is unknown why PLCζ is inactive in spermatozoa or any type of somatic cell.
In this work, the modeling approach explains the reasons for the absence of PLCζ activity in any type of mammalian cells but eggs. A model describing the activity of PLCζ in physiological calcium concentrations was developed. It was shown that the presence of phosphoinositide-rich vesicles is required for the PLCζ activity in mature mammalian eggs.