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Schematic diagram of platelet. The platelet is a 2–3 μm discoid cell that contains α-granules, dense granules, and lysosomes. Platelets also contain mitochondria. Tunnel invaginations of the plasma membrane forms a complex membrane network, termed the open canalicular system, that courses throughout the platelet interior. Platelet granule secretion is thought to occur through fusion of granules with either the plasma membrane or the open canalicular system.
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The rapid secretion of bioactive amines from chromaffin cells constitutes an important component of the fight or flight response of mammals to stress. Platelets respond to stresses within the vasculature by rapidly secreting cargo at sites of injury, inflammation, or infection. Although chromaffin cells derive from the neural crest and platelets fr...
Citations
... Activation leads to the release of alpha granules, dense granules, and lysosomes by platelets [39]. Alpha granules contain a variety of proteins, such as fibrinogen, von Willebrand factor, and platelet-derived growth factor, which are important for platelet function and wound healing [10]. ...
Platelets play crucial roles in cardiovascular diseases (CVDs) by regulating hemostasis and blood coagulation at sites of blood vessel damage. Accumulating evidence indicates daidzein inhibits platelet activation, but the mechanism involved has not been elucidated. Thus, in this study, we investigated the mechanism responsible for the inhibition of collagen-induced platelet aggregation by daidzein. We found that in collagen-induced platelets, daidzein suppressed the production of thromboxane A2 (TXA2), a molecule involved in platelet activation and aggregation, by inhibiting the cytosolic phospholipase A2 (cPLA2) signaling pathway. However, daidzein did not affect cyclooxygenase-1 (COX-1). Furthermore, daidzein attenuated the PI3K/PDK1/Akt/GSK3αβ and MAPK (p38, ERK) signaling pathways, increased the phosphorylation of inositol trisphosphate receptor1 (IP3R1) and vasodilator-stimulated phosphoprotein (VASP), and increased the level of cyclic adenosine monophosphate (cAMP). These results suggest that daidzein inhibits granule release (ATP, serotonin, P-selectin), integrin αIIbβ3 activation, and clot retraction. Taken together, our study demonstrates that daidzein inhibits collagen-induced platelet aggregation and suggests that daidzein has therapeutic potential for the treatment of platelet aggregation-related diseases such as atherosclerosis and thrombosis.
... Serotonin is a lipophilic compound that crosses the platelet membrane by passive diffusion or driven by the 5-HT carrier (SERT) [8]. Once internalized, 5-HT is avidly taken up by -granules through specific uptake mechanisms, which are probably identical to those used by aminergic neurons or by chromaffin, enterochromaffin, and mast cells [9]. These mechanisms involve membrane carriers, as well as granule core factors that bind to soluble factors and create a dense inner matrix [10]. ...
Platelets are probably the most accessible human cells to study exocytosis by amperometry. These cell fragments accumulate biological amines, serotonin in particular, using similar if not the same mechanisms as those employed by sympathetic, serotoninergic, and histaminergic neurons. Thus, platelets have been widely recognized as a model system to study certain neurological and psychiatric diseases. Platelets release serotonin by exocytosis, a process that entails the fusion of a secretory vesicle to the plasma membrane and that can be monitored directly by classic single cell amperometry using carbon fiber electrodes. However, this is a tedious technique because any given platelet releases only 4–8 secretory d-granules. Here, we introduce and validate a diamond-based multielectrode array (MEA) device for the high-throughput study of exocytosis by human platelets. This is probably the first reported study of human tissue using an MEA, demonstrating that they are very interesting laboratory tools to assess alterations to exocytosis in neuropsychiatric diseases. Moreover, these devices constitute a valuable platform for the rapid testing of novel drugs that act on secretory pathways in human tissues.
... In addition to serving as an energy capturing molecule in ATP production, only a small portion of ADP serves as a signaling molecule. In platelets, most of the ADP molecules (653 mM) are compartmentalized into dense granules along with ATP that serve as signaling molecules [9]. Since little free ADP is available, it can be used for making ATP in glycolysis and TCA cycle through substrate level phosphorylation reaction but will not be available for making ATP through OXPHOS. ...
In platelets, most of the ADP is stored in dense granules and released into extracellular space through exocytosis as a signaling molecule upon platelet activation. Glycolysis and the TCA cycle consume considerable amounts of ADP; however, limiting quantities of available ADP to make ATP through OXPHOS result in failure of ATP production and release of energy as heat
into the surroundings. Thus, body heat may be a potential product of circulating platelets. Furthermore, the incomplete OXPHOS process causes the production of ROS that leads to earlier platelet death resulting in shorter life span. In the future, this new function may have a wide variety of clinical applications.
... Previous studies suggested that mitochondri al hyperpolarization represents a key event in platelet activation and remodeling (21) in addition to increased formation of cytosolic reactive oxygen species (37). Furthermore, numerous studies highlighted a pivotal role for intracellular calcium in exocytosis through the direct activation of synaptic proteins with defined calcium-binding domains and/or the activation of protein kinases controlling granule secretion in activated platelets [e.g (38,39).]. However, these molecular parameters were not adequately addressed in the context of SARS-CoV-2 viral infection. ...
... For example, depressed metabolic activities in critically ill patients may impair the function of calcium channels requiring ATP for their activation. Impaired calcium dynamics leads to impaired nerve transmission and pathology of the peripheral nervous system, with mechanisms shared by platelets and causing bleeding tendency of zinc deficiency (39,61). Consistently, impaired mobilization and significantly lowered levels of intracellular calcium in neonatal platelet has been reported (42) and was suggested more recently to cause impaired granule trafficking and secretion despite signs of platelets hyper activation (41). ...
Roles of platelets during infections surpass the classical thrombus function and are now known to modulate innate immune cells. Leukocyte-platelet aggregations and activation-induced secretome are among factors recently gaining interest but little is known about their interplay with severity and mortality during the course of SARS-Cov-2 infection. The aim of the present work is to follow platelets’ bioenergetics, redox balance, and calcium homeostasis as regulators of leukocyte-platelet interactions in a cohort of COVID-19 patients with variable clinical severity and mortality outcomes. We investigated COVID-19 infection-related changes in platelet counts, activation, morphology (by flow cytometry and electron microscopy), bioenergetics (by Seahorse analyzer), mitochondria function (by high resolution respirometry), intracellular calcium (by flow cytometry), reactive oxygen species (ROS, by flow cytometry), and leukocyte-platelet aggregates (by flow cytometry) in non-intensive care unit (ICU) hospitalized COVID-19 patients (Non-ICU, n=15), ICU-survivors of severe COVID-19 (ICU-S, n=35), non-survivors of severe COVID-19 (ICU-NS, n=60) relative to control subjects (n=31). Additionally, molecular studies were carried out to follow gene and protein expressions of mitochondrial electron transport chain complexes (ETC) in representative samples of isolated platelets from the studied groups. Our results revealed that COVID-19 infection leads to global metabolic depression especially in severe patients despite the lack of significant impacts on levels of mitochondrial ETC genes and proteins. We also report that severe patients’ platelets exhibit hyperpolarized mitochondria and significantly lowered intracellular calcium, concomitantly with increased aggregations with neutrophil. These changes were associated with increased populations of giant platelets and morphological transformations usually correlated with platelets activation and inflammatory signatures, but with impaired exocytosis. Our data suggest that hyperactive platelets with impaired exocytosis may be integral parts in the pathophysiology dictating severity and mortality in COVID-19 patients.
... Lack of TNFR1 or the use of the TNF inhibitor etanercept reduced thrombocytopenia, cytokine expression, lung injury and improved survival of MHV-infected mice. In support of the murine study, etanercept also reduced SARS-CoV-2 replication in human lung epithelial cells (156,157). ...
In the broad range of human diseases, thrombo-inflammation appears as a clinical manifestation. Clinically, it is well characterized in context of superficial thrombophlebitis that is recognized as thrombosis and inflammation of superficial veins. However, it is more hazardous when developed in the microvasculature of injured/inflamed/infected tissues and organs. Several diseases like sepsis and ischemia-reperfusion can cause formation of microvascular thrombosis subsequently leading to thrombo-inflammation. Thrombo-inflammation can also occur in cases of antiphospholipid syndrome, preeclampsia, sickle cell disease, bacterial and viral infection. One of the major contributors to thrombo-inflammation is the loss of normal anti-thrombotic and anti-inflammatory potential of the endothelial cells of vasculature. This manifest itself in the form of dysregulation of the coagulation pathway and complement system, pathologic platelet activation, and increased recruitment of leukocyte within the microvasculature. The role of platelets in hemostasis and formation of thrombi under pathologic and non-pathologic conditions is well established. Platelets are anucleate cells known for their essential role in primary hemostasis and the coagulation pathway. In recent years, studies provide strong evidence for the critical involvement of platelets in inflammatory processes like acute ischemic stroke, and viral infections like Coronavirus disease 2019 (COVID-19). This has encouraged the researchers to investigate the contribution of platelets in the pathology of various thrombo-inflammatory diseases. The inhibition of platelet surface receptors or their intracellular signaling which mediate initial platelet activation and adhesion might prove to be suitable targets in thrombo-inflammatory disorders. Thus, the present review summarizes the concept and mechanism of platelet signaling and briefly discuss their role in sterile and non-sterile thrombo-inflammation, with the emphasis on role of platelets in COVID-19 induced thrombo-inflammation. The aim of this review is to summarize the recent developments in deciphering the role of the platelets in thrombo-inflammation and discuss their potential as pharmaceutical targets.
... Moreover, platelets also accommodate several secretory cytoplasmic and lysosomal granules, microparticles, and exosomes,which release various factors as platelets secretome (GFs, cytokines, adhesive molecules, chemokines, and other signalling molecules) that significantlyparticipatein wound repair mechanism (Anitua et al. 2004(Anitua et al. , 2006Pietrzak and Eppley 2005;Fitch-Tewfik and Flaumenhaft 2013;Golebiewska and Poole 2015;Heijnen and van der Sluijs 2015). These secretomes regulate diverse biochemical, molecular, and cellular aspects of wound niche, such as inflammation, recruitment of neutrophils and macrophages, promoting angiogenesis, ECM formation, and tissue remodelling (Etulain et al. 2014;Burnouf et al. 2016a;Gresele et al. 2017;Etulain 2018;Nurden 2018;Everts et al. 2020). ...
Rise in the incidences of chronic degenerative diseases with aging makes wound care a socio-economic burden and unceasingly necessitates a novel, economical, and efficient wound healing treatment. Platelets have a crucial role in hemostasis and thrombosis by modulating distinct mechanistic phases of wound healing, such as promoting and stabilizing the clot. Platelet-rich plasma (PRP) contains a high concentration of platelets than naïve plasma and has an autologous origin with no immunogenic adverse reactions. As a consequence, PRP has gained significant attention as a therapeutic to augment the healing process. Since the past few decades, a robust volume of research and clinical trials have been performed to exploit extensive role of PRP in wound healing/tissue regeneration. Despite these rigorous studies and their application in diversified medical fields, efficacy of PRP-based therapies is continuously questioned owing to the paucity of large samplesizes, controlled clinical trials, and standard protocols. This review systematically delineates the process of wound healing and involvement of platelets in tissue repair mechanisms. Additionally, emphasis is laid on PRP, its preparation methods, handling, classification,application in wound healing, and PRP as regenerative therapeutics combined with biomaterials and mesenchymal stem cells (MSCs).
... First, the interaction of Ca v 3.2 with SNARE proteins governs low-threshold exocytosis, as observed in chromaffin cells.55 Both platelets and chromaffin cells share similar exocytosis mechanisms mediated by calcium influx, which could be an explanation.56 Future studies are required to unveil such association. ...
Background:
Cav 3.2 is a T-type calcium channel that causes low-threshold exocytosis. T-type calcium channel blockers reduce platelet granule exocytosis and aggregation. However, studies of the T-type calcium channel in platelets is lacking.
Objective:
To examine the expression and role of Cav 3.2 in platelet function.
Methods:
Global Cav 3.2-/- and platelet-specific Cav 3.2-/- mice and littermate controls were used for the study. Western blot analysis was used to detect the presence of Cav 3.2 and activation of the calcium-responsive protein extracellular signal-regulated kinase (ERK). Fura-2 dye was used to assess platelet calcium. Flow cytometry and light transmission aggregometry were used to evaluate platelet activation markers and aggregation, respectively. FeCl3 -induced thrombosis and a microfluidic flow device were used to assess in vivo and ex vivo thrombosis, respectively.
Results:
Cav 3.2 was expressed in mouse platelets. As compared with wild-type controls, Cav 3.2-/- mouse platelets showed reduced calcium influx. Similarly, treatment with the T-type calcium channel inhibitor Ni2+ decreased the calcium influx in wild-type platelets. As compared with controls, both Cav 3.2-/- and Ni2+ -treated wild-type platelets showed reduced activation of ERK. ATP release, P-selectin exposure and αIIb β3 activation were reduced in Cav 3.2-/- and Ni2+ -treated wild-type platelets, as was platelet aggregation. On in vivo and ex vivo thrombosis assay, Cav3.2 deletion caused delayed thrombus formation. However, tail bleeding assay showed intact hemostasis.
Conclusion:
These results suggest that Cav 3.2 is required for the optimal activation of platelets.
... 62-65 Activated platelets expressing CD40L and P-selectin interact with neutrophils and release α-granules along with complement C3 and different cytokines like CC-chemokine ligand 2 (CCL2), CCL3, CCL7, IL-7, IL-8, IL-1β. 66,67 These findings correlate with the clinical data of COVID-19 patients, as the level of these cytokines have been reported to be significantly elevated in these patients compared with healthy controls. 68 Previous studies with dengue virus show that platelets release IL-1β that results in increased permeability. ...
Coronavirus disease 2019 (COVID-19) is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and may result in an overactive coagulative system, thereby resulting in serious cardiovascular consequences in critically affected patients. The respiratory tract is a primary target for COVID-19 infection, which is manifested as acute lung injury in the most severe form of the viral infection, leading to respiratory failure. A proportion of infected patients may progress to serious systemic disease including dysfunction of multiple organs, acute respiratory distress syndrome (ARDS), and coagulation abnormalities, all of which are associated with increased mortality, additionally depending on age and compromised immunity. Coagulation abnormalities associated with COVID-19 mimic other systemic coagulopathies otherwise involved in other severe infections, such as disseminated intravascular coagulation (DIC) and may be termed COVID-19 induced coagulopathy (CIC). There is substantial evidence that patients with severe COVID-19 exhibiting CIC can develop venous and arterial thromboembolic complications. In the initial stages of CIC, significant elevation of D-dimer and fibrin/fibrinogen degradation products is observed. Alteration in prothrombin time, activated partial thromboplastin time, and platelet counts are less common in the early phase of the disease. In patients admitted to intensive care units (ICUs), coagulation test screening involving the measurement of D-dimer and fibrinogen levels, has been recommended. Prior established protocols for thromboembolic prophylaxis are also followed for CIC, including the use of heparin and other standard supportive care measures. In the present review, we summarize the characteristics of CIC and its implications for thrombosis, clinical findings of coagulation parameters in SARS-CoV-2 infected patients with incidences of thromboembolic events and plausible therapeutic measures.
... On the other hand, studies showed that activated platelets can directly regulate leukocyte function and their cytokine release during infections [222], where the direct interaction between platelet P-selectin and CD40L with neutrophil causes the release of their granules contents, complement C3, a variety of cytokines such as CCL2, CCL3, CCL7, IL-1, IL-7, IL-8, and hepatocyte growth factor [223,224]. These cytokines are substantially higher in COVID-19 patients than in healthy individuals [225]. More specifically, the soluble CD40L released from platelets in COVID-19 may be involved in activating CD40-coated cells including different type of lymphocytes while regulating their function and affecting cytokine release [226]. ...
Platelet-leukocyte crosstalk is commonly manifested by reciprocal links between thrombosis and inflammation. Platelet thrombus acts as a reactive matrix that recruits leukocytes to the injury site where their massive accumulation, activation and migration promote thrombotic events while triggering inflammatory responses. As a life-threatening condition with the associations between inflammation and thrombosis, COVID-19 presents diffuse alveolar damage due to exaggerated macrophage activity and cytokine storms. These events, together with direct intracellular virus invasion lead to pulmonary vascular endothelialitis, cell membranes disruption, severe endothelial injury, and thrombosis. The developing pre-alveolar thrombus provides a hyper-reactive milieu that recruits circulating leukocytes to the injury site where their activation contributes to thrombus stabilization and thrombosis propagation, primarily through the formation of Neutrophil extracellular trap (NET). NET fragments can also circulate and deposit in further distance where they may disseminate intravascular thrombosis in severe cases of disease. Thrombi may also facilitate leukocytes migration into alveoli where their accumulation and activation exacerbate cytokine storms and tissue damage, further complicating the disease. Based on these mechanisms, whether an effective anti-inflammatory protocol can prevent thrombotic events, or on the other hand; efficient antiplatelet or anticoagulant regimens may be associated with reduced cytokine storms and tissue damage, is now of interests for several ongoing researches. Thus shedding more light on platelet-leukocyte crosstalk, the review presented here discusses the detailed mechanisms by which platelets may contribute to the pathogenesis of COVID-19, especially in severe cases where their interaction with leukocytes can intensify both inflammatory state and thrombosis in a reciprocal manner.
... The content, or cargo, of EVs consists of lipids, nucleic acids, and proteins-specifically proteins associated with the plasma membrane, cytosol (Borges et al., 2013;Yanez-Mo et al., 2015;Zaborowski et al., 2015;Bebelman et al., 2018). Activation of platelets and the endothelium leads to the release of small EVs or exosomes (Heijnen et al., 1999;Fitch-Tewfik and Flaumenhaft, 2013;Alique et al., 2017;Banizs et al., 2018). EVs from the platelets and endothelium, share specific surface markers indicative of their origin, and present in abundance in the circulation. ...
While platelets are the essential mediators of hemostasis, they are being increasingly recognized for their potential of contributing to host defenses. Here, using immunofluorescent microscopy, western blot, and ELISA, we found that human β-defensin 3 (hBD-3), an important antimicrobial peptide produced by epithelial cells, can be detected in human platelets and megakaryocytes. Flow cytometry and immuno-electron microscopy revealed hBD-3 on the surface of thrombin activated platelets. Moreover, hBD-3 was also found in platelet derived extracellular vesicles (p-EVs), isolated from platelet poor plasma and from platelet supernatants following thrombin stimulation. Incubation of platelets with hBD-3 peptide resulted in modest platelet activation and pre-incubation of platelets with synthetic hBD-3 prior to exposure to thrombin appeared to increase hBD-3 content in platelet lysates as well as in p-EVs, suggesting that hBD-3 can be initially taken up by platelets, perhaps via their open canalicular system. Interestingly, in vitro exposure of primary human endothelial cells to either hBD-3 peptide or purified p-EVs, caused significant endothelial dysfunction as documented by diminished levels of phosphorylated endothelial nitric oxide synthase (eNOS), Krüppel like factor-2 (KLF-2), and elevated relative expression of von Willebrand Factor (vWF). Pre-incubation of platelets with hBD-3 appeared to augment endothelial dysfunction caused by p-EVs. Overall, the current study provides evidence that hBD-3 enriched EVs can be released by activated platelets and may play a role in positive feedback of platelet activation as well as in endothelial dysfunction. Theoretically, these effects could contribute to both cellular recruitment to the endothelium creating a pro-thrombotic vascular microenvironment which serve as a bridge between innate immunity and hemostasis.
