Platelet integrin activation surfs the calcium waves

Fibrinogen binding to activated platelets and its biomimetic thrombus-targeted thrombolytic strategies

Thrombosis is associated with various fatal arteriovenous syndromes including ischemic stroke, myocardial infarction, and pulmonary embolism. However, current clinical thrombolytic treatment strategies still have many problems in targeting and safety to meet the thrombolytic therapy needs. Understanding the molecular mechanism that underlies thrombosis is critical in developing effective thrombolytic strategies. It is well known that platelets play a central role in thrombosis and the binding of fibrinogen to activated platelets is a common pathway in the process of clot formation. Based on this, a concept of biomimetic thrombus-targeted thrombolytic strategy inspired from fibrinogen binding to activated platelets in thrombosis was proposed, which could selectively bind to activated platelets at a thrombus site, thus enabling targeted delivery and local release of thrombolytic agents for effective thrombolysis. In this review, we first summarized the main characteristics of platelets and fibrinogen, and then introduced the classical molecular mechanisms of thrombosis, including platelet adhesion, platelet activation and platelet aggregation through the interactions of activated platelets with fibrinogen. In addition, we highlighted the recent advances in biomimetic thrombus-targeted thrombolytic strategies which inspired from fibrinogen binding to activated platelets in thrombosis. The possible future directions and perspectives in this emerging area are briefly discussed.

Janus Amphipathic Dressing With Liquid Self-Pumping and Blood-Clot Anti-Adhesion for Satisfactory Hemostasis

Ideal hemostatic materials for the emergency rescue of war and traffic accident sufferers are essential to significantly control hemorrhage, reduce patient discomfort, and improve the survival ratio. However, most hemostats absorb blood quickly in contact with the wound; and then, adhere to blood clots, resulting in breaking scabs and tearing the wound when the materials are removed. Herein, an effective Janus amphipathic hemostatic dressing (Fiber@Gel/Ca2+/KL) with a fiber layer (polylactic acid/carboxymethyl chitosan) and a hydrogel layer (polyvinyl alcohol, carboxymethyl chitosan, Ca2+, and kaolin) is reported. Such a composite dressing unidirectionally drains the excessive serum from its hydrophobic side (fiber layer) to its hydrophilic side (hydrogel layer), so-called self-pumping, thereby further concentrating coagulated factors (including red blood cells and platelets). Further, Ca2+ diffused from the hydrogel layer subsequently activates platelets and coagulation cascade. Besides, the Fiber@Gel/Ca2+/KL exhibits specific blood-clot anti-adhesion property on the fiber layer, making the dressing easily and safely peel off from the wound. It is believed that this novel hemostatic dressing with good hemostatic performance, easy clots removal, and excellent biocompatibility is expected to be used as a safe and efficient hemostatic dressing in clinical applications.

Hemostatic Effect of 20(S)-Panaxadiol by Induced Platelet Aggregation Depending on Calcium Signaling Pathway

Panax notoginseng (Burk.) F.H. Chen is the most traditional hemostatic herb in China. Our previous research found that 20(S)-protopanaxadiol showed the hemostatic effect. And 20(S)-panaxadiol (PD) has a similar structure to 20(S)-protopanaxadiol with a dammarane skeleton. So, this article mainly studies the hemostatic effect of PD. The mouse tail amputation and liver scratch models were used to detect the hemostatic effect of PD. Blood routine and plasma coagulation parameters were measured by using a blood analyzer. The platelet aggregometer analyzed the platelet aggregation rate and adenosine triphosphate (ATP) concentration. Moreover, the intracellular calcium concentration ([Ca²⁺]_i), P-selectin (CD62P), PAC-1 (GP IIb/IIIa receptor marker), and cyclic adenosine monophosphate (cAMP) of platelets were also detected. The results showed that PD obviously shortened the bleeding time of the model mouse, affected the RBC and PLT parameters of rats, reduced APTT and TT, elevated FIB concentration, and promoted human/rat-washed platelet aggregation in vitro. PD promoted the release of ATP and [Ca²⁺]_i and slightly increased the expression of CD62P and PAC-1 of platelets without 1 mM Ca²⁺. After adding 1 mM Ca²⁺, PD obviously increased ATP releasing and CD62P and GP IIb/IIIa expression rate and decreased the cAMP level of platelets. These parameter changes of PD-caused platelet were inhibited by vorapaxar. Besides, PD increased the phosphorylation of phosphoinositide 3-kinase/protein kinase B/glycogen synthase kinase 3β (PI3K/Akt/GSK3β) of human platelets. PD is an important hemostatic ingredient in Panax notoginseng, which induced platelet aggregation by affecting the calcium signaling and activating the PI3K/Akt/GSK3β signaling pathway.

Hemostatic Effect of 20(S)-Panaxadiol by Induced Platelet Aggregation Depending on Calcium Signaling Pathway

Panax notoginseng (Burk.) F.H. Chen is the most traditional hemostatic herb in China. Our previous research found that 20(S)-protopanaxadiol showed the hemostatic effect. And 20(S)-panaxadiol (PD) has a similar structure to 20(S)-protopanaxadiol with a dammarane skeleton. So, this article mainly studies the hemostatic effect of PD. The mouse tail amputation and liver scratch models were used to detect the hemostatic effect of PD. Blood routine and plasma coagulation parameters were measured by using a blood analyzer. The platelet aggregometer analyzed the platelet aggregation rate and adenosine triphosphate (ATP) concentration. Moreover, the intracellular calcium concentration ([Ca2+]i), P-selectin (CD62P), PAC-1 (GP IIb/IIIa receptor marker), and cyclic adenosine monophosphate (cAMP) of platelets were also detected. The results showed that PD obviously shortened the bleeding time of the model mouse, affected the RBC and PLT parameters of rats, reduced APTT and TT, elevated FIB concentration, and promoted human/rat-washed platelet aggregation in vitro. PD promoted the release of ATP and [Ca2+]i and slightly increased the expression of CD62P and PAC-1 of platelets without 1 mM Ca2+. After adding 1 mM Ca2+, PD obviously increased ATP releasing and CD62P and GP IIb/IIIa expression rate and decreased the cAMP level of platelets. These parameter changes of PD-caused platelet were inhibited by vorapaxar. Besides, PD increased the phosphorylation of phosphoinositide 3-kinase/protein kinase B/glycogen synthase kinase 3β (PI3K/Akt/GSK3β) of human platelets. PD is an important hemostatic ingredient in Panax notoginseng, which induced platelet aggregation by affecting the calcium signaling and activating the PI3K/Akt/GSK3β signaling pathway.

Deletion of Grin1 in mouse megakaryocytes reveals NMDA receptor role in platelet function and proplatelet formation

The process of proplatelet formation (PPF) requires coordinated interaction between megakaryocytes (MKs) and the extracellular matrix (ECM), followed by a dynamic reorganization of the actin and microtubule cytoskeleton. Localized fluxes of intracellular calcium ions (Ca2+) facilitate MK-ECM interaction and PPF. Glutamate-gated N-methyl-D--aspartate receptor (NMDAR) is highly permeable to Ca2+. NMDAR antagonists inhibit MK maturation ex vivo, however there is no in vivo data. Using the Cre-loxP system, we generated a platelet lineage-specific knockout mouse model of reduced NMDAR function in MKs and platelets (Pf4-Grin1-/- mice). Effects of NMDAR deletion were examined using well-established assays of platelet function and production in vivo and ex vivo. We found that Pf4-Grin1-/- mice had defects in megakaryopoiesis, thrombopoiesis and platelet function, which manifested as reduced platelet counts, lower rates of platelet production in the immune model of thrombocytopenia, and a prolonged tail bleeding time. Platelet activation was impaired to a range of agonists associated with reduced Ca2+ responses, including metabotropic-like, and defective platelet spreading. MKs showed reduced colony and proplatelet formation. Impaired reorganization of intracellular F-actin and α-tubulin was identified as the main cause of reduced platelet function and production. Pf4-Grin1-/- MKs also had lower levels of transcripts encoding crucial ECM elements and enzymes, suggesting NMDAR signaling is involved in ECM remodeling. In summary, we provide the first genetic evidence that NMDAR plays an active role in platelet function and production. NMDARs regulate PPF through the mechanism that involves MK-ECM interaction and cytoskeletal reorganization. Our results suggest that NMDAR helps guide PPF in vivo.