Abstract
Beyond their fundamental role in hemostasis, platelets importantly contribute to other processes aimed at maintaining homeostasis. Indeed, platelets are a natural source of growth factors and also release many other substances—such as fibronectin, vitronectin, sphingosine 1-phosphate—that are important in maintaining healthy tissues, and ensuring regeneration and repair. Despite rare thrombotic events have been documented in astronauts, some in vivo and in vitro studies demonstrate that microgravity affects platelet’s number and function, thus increasing the risk of hemorrhages and contributing to retard wound healing. Here we provide an overview about events linking platelets to the impairment of wound healing in space, also considering, besides weightlessness, exposure to radiation and psychological stress. In the end we discuss the possibility of utilizing platelet rich plasma as a tool to treat skin injuries eventually occurring during space missions.
Highlights
INTRODUCTIONApproximately one trillion platelets circulate in the blood. These disc-shaped anucleate cells arise from the fragmentation of the cytoplasm of megakaryocytes, residing in the bone marrow
In the adult, approximately one trillion platelets circulate in the blood
The platelet receptor glycoprotein (GP) Ib-IX-V complex tethers immobilized von Willebrand factor, a multimeric adhesive protein secreted from activated endothelial cells
Summary
Approximately one trillion platelets circulate in the blood. These disc-shaped anucleate cells arise from the fragmentation of the cytoplasm of megakaryocytes, residing in the bone marrow. Alpha granules contain hundreds of proteins such as coagulation factors, growth factors (GFs), adhesive molecules, pro- and anti-angiogenic factors, cytokines and chemokines (Chen et al, 2018) After their release, these proteins potentiate platelet responses in an autocrine fashion or target other cell types through paracrine mechanisms. The platelet receptor glycoprotein (GP) Ib-IX-V complex tethers immobilized von Willebrand factor (vWF), a multimeric adhesive protein secreted from activated endothelial cells. A very low grade platelet activation is likely to occur as a response to rheologic events, accounting for a tonic, controlled release of low amounts of endothelial trophogens-VEGF, angiopoietin 1, Brain-Derived Neurotrophic Factor (BDNF), Sphingosine-1-Phosphate (S1P)- stored in the granules or for their exposure on the cell surface (Randriamboavonjy and Fleming, 2018). The arsenal of GFs stored in platelet’s granules can aid the proliferation of many cellular protagonists in healing, i.e., keratinocytes in case of TABLE 1 | Summary of the studies on platelets in microgravity using different experimental models
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