In addition to their hemostatic function, platelets play an important role in regulating the inflammatory response. The platelet NLRP3 inflammasome not only promotes interleukin-1β secretion, but was also found to be upregulated during platelet activation and thrombus formation in vitro. However, the role of NLRP3 in platelet function and thrombus formation in vivo remains unclear. In this study, we aimed to investigate the role of NLRP3 in platelet integrin αIIbβ3 signaling transduction. Using NLRP3−/− mice, we showed that NLRP3-deficient platelets do not have significant differences in expression of the platelet-specific adhesive receptors αIIbβ3 integrin, GPIba or GPVI; however, NLRP3−/− platelets transfused into wild-type mice resulted in prolonged tail-bleeding time and delayed arterial thrombus formation, as well as exhibiting impaired spreading on immobilized fibrinogen and defective clot retraction, concomitant with decreased phosphorylation of c-Src, Syk and PLCγ2 in response to thrombin stimulation. Interestingly, addition of exogenous recombinant interleukin-1β reversed the defect in NLRP3−/− platelet spreading and clot retraction, and restored thrombin-induced phosphorylation of c-Src/Syk/PLCγ2, whereas an anti-interleukin-1β antibody blocked spreading and clot retraction mediated by wild-type platelets. Using the direct NLRP3 inhibitor, CY-09, we demonstrated significantly reduced human platelet aggregation in response to threshold concentrations of collagen and ADP, as well as impaired clot retraction in CY-09-treated human platelets, supporting a role for NLRP3 also in regulating human platelet αIIbβ3 outside-in signaling. This study identifies a novel role for NLRP3 and interleukin-1β in platelet function, and provides a new potential link between thrombosis and inflammation, suggesting that therapies targeting NLRP3 or interleukin-1β might be beneficial for treating inflammation-associated thrombosis.
All-trans retinoic acid (ATRA) is widely used for induction of complete remission in patients with acute promyelocytic leukemia (APL). ATRA also regulates protein kinase C (PKC) activity. Therapeutic use of ATRA reportedly interferes with hemostatic function in APL patients, including effects on coagulation or other vascular cells, although effects of ATRA on platelets remain unclear. This study aims to investigate the effect of therapeutic-relevant doses of ATRA on platelet function. Human platelets were preincubated with ATRA (0–20 μM) for 1 hour at 37°C, followed by analysis of aggregation, granule secretion, receptor expression by flow cytometry, platelet spreading, or clot retraction. Additionally, ATRA (10 mg/kg) was injected intraperitoneally into mice and tail bleeding time and arterial thrombus formation were evaluated. ATRA inhibited platelet aggregation and adenosine triphosphate release induced by collagen (5 μg/mL) or thrombin (0.05 U/mL) in a dose-dependent manner without affecting P-selectin expression or surface levels of glycoprotein (GP) Ibα, GPVI, or αIIbβ3. ATRA-treated platelets demonstrated reduced spreading on immobilized fibrinogen or collagen and reduced thrombin-induced clot retraction together with reduced phosphorylation of Syk and PLCγ2. In addition, ATRA-treated mice displayed significantly impaired hemostasis and arterial thrombus formation in vivo. Further, in platelets stimulated with either collagen-related peptide or thrombin, ATRA selectively inhibited phosphorylation of PKCßI (Ser661) and PKCδ (Thr505), but not PKCα or PKCßII phosphorylation (Thr638/641). In conclusion, ATRA inhibits platelet function and thrombus formation, possibly involving direct or indirect inhibition of PKCßI/δ, indicating that ATRA might be beneficial for the treatment of thrombotic or cardiovascular diseases.
BackgroundPlatycodin D (PD) is one of the major bioactive components of the roots of Platycodon grandiflorum and possesses multiple biological and pharmacological properties, such as antiviral, anti-inflammatory, and anti-cancer activities. However, whether it affects platelet function remains unclear. This study aims to evaluate the role of PD in platelet function and thrombus formation.MethodsPlatelets were treated with PD followed by measuring platelet aggregation, activation, spreading, clot retraction, expression of glycoprotein receptors. Moreover, mice platelets were treated with PD and infused into wild-type mice for analysis of in vivo hemostasis and arterial thrombosis.ResultsPlatycodin D treatment significantly inhibited platelet aggregation in response to collagen, ADP, arachidonic acid and epinephrine, reduced platelet P-selectin expression, integrin αIIbβ3 activation, spreading on fibrinogen as well as clot retraction, accompanied with decreased phosphorylation of Syk and PLCγ2 in collagen-related peptide or thrombin-stimulated platelets. Moreover, PD-treated mice platelets presented significantly impaired in vivo hemostasis and arterial thrombus formation. Interestingly, PD induced internalization of glycoprotein receptors αIIbβ3, GPIbα and GPVI. However, GM6001, cytochalasin D, BAPTA-AM and wortmannin did not prevent PD-induced internalization of receptors.ConclusionsOur study demonstrates that PD inhibits platelet aggregation, activation and impairs hemostasis and arterial thrombosis, suggesting it might be a potent anti-thrombotic drug.
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