Regulation of blood platelet function by the AGC family of protein kinases

Upon vascular injury, platelets aggregate at the site of blood vessel injury to form a hemostatic plug maintaining the physiological integrity of the vascular system. Platelets respond to a variety of extracellular stimuli to undergo a rapid aggregation response, releasing active granule contents and leading to a rapidly growing thrombus. During the adhesion, activation, and aggregation of platelets at an injured site, the endothelium responds by limiting the size and growth of the hemostatic plug or thrombus, or even reversing platelet reactivity. These responses are defined as endothelial thromboregulation. There are three primary (and functionally independent) pathways during the early stages of thromboregulation by which the endothelium controls platelet reactivity (1) nitric oxide (NO); (2) prostacyclin (PGI₂ ); and (3) the ectonucleotidase CD39. NO and PGI2 stimulate signalling cascades that result in the activation of the AGC family of Ser/Thr protein kinases (PKA, PKG and PKC). Once activated these kinase blunt platelet function through the phosphorylation of signalling proteins requested for activation. In this study, the role of AGC family kinases and their signaling cascades in regulating platelet function was assessed. The experimental data produced during this study demonstrate new insights in to the regulation of these kinases in platelets. More specifically it was found that1. Peroxynitrite, a derivative of NO, regulated platelet function and particularly cytoskeletal rearrangement through PKC-dependent phosphorylation of VASPSer²³⁹⁄¹⁵⁷2. NO-mediated signalling in platelets had a requirement for PKC.3. Multiple forms of PKA are present in platelets, which are differentially localised.4. The potential regulation of platelet function by PKA is mediated through Akinase anchoring proteins.5. Lipid rafts may play an important role in platelet regulation by NO and PKG.In summary, this studies present insights of the factors regulating AGC kinases in blood platelets

Regulation of blood platelet function by the AGC family of protein kinases

Upon vascular injury, platelets aggregate at the site of blood vessel injury to form a hemostatic plug maintaining the physiological integrity of the vascular system. Platelets respond to a variety of extracellular stimuli to undergo a rapid aggregation response, releasing active granule contents and leading to a rapidly growing thrombus. During the adhesion, activation, and aggregation of platelets at an injured site, the endothelium responds by limiting the size and growth of the hemostatic plug or thrombus, or even reversing platelet reactivity. These responses are defined as endothelial thromboregulation. There are three primary (and functionally independent) pathways during the early stages of thromboregulation by which the endothelium controls platelet reactivity (1) nitric oxide (NO); (2) prostacyclin (PGI₂ ); and (3) the ectonucleotidase CD39. NO and PGI2 stimulate signalling cascades that result in the activation of the AGC family of Ser/Thr protein kinases (PKA, PKG and PKC). Once activated these kinase blunt platelet function through the phosphorylation of signalling proteins requested for activation. In this study, the role of AGC family kinases and their signaling cascades in regulating platelet function was assessed. The experimental data produced during this study demonstrate new insights in to the regulation of these kinases in platelets. More specifically it was found that 1. Peroxynitrite, a derivative of NO, regulated platelet function and particularly cytoskeletal rearrangement through PKC-dependent phosphorylation of VASPSer²³⁹⁄¹⁵⁷ 2. NO-mediated signalling in platelets had a requirement for PKC. 3. Multiple forms of PKA are present in platelets, which are differentially localised. 4. The potential regulation of platelet function by PKA is mediated through Akinase anchoring proteins. 5. Lipid rafts may play an important role in platelet regulation by NO and PKG. In summary, this studies present insights of the factors regulating AGC kinases in blood platelets

Thrombospondin-1 induces platelet activation through CD36-dependent inhibition of the cAMP/protein kinase A signaling cascade

Cyclic adenosine monophosphate (cAMP)-dependent signaling modulates platelet function at sites of vascular injury. Here we show that thrombospondin-1 (TSP-1) prevents cAMP/protein kinase A (PKA) signaling through a CD36-dependent mechanism. Prostaglandin E 1 (PGE 1 ) induced a robust inhibition of both platelet aggregation and platelet arrest under physiologic conditions of flow. Exogenous TSP-1 reduced significantly PGE 1 -mediated inhibition of both platelet aggregation and platelet arrest. TSP-1 prevented PGE 1 -stimulated cAMP accrual and phosphorylation of PKA substrates, through a mechanism requiring phosphodiesterase3A. TSP-1 also inhibited VASP phosphorylation stimulated by the nonhydrolyzable cAMP analog, 8-bromocAMP, indicating that it may regulate cAMPmediated activation of PKA. The inhibitory effect of TSP-1 on cAMP signaling could be reproduced with a peptide possessing a CD36 binding sequence of TSP-1, while the effects of TSP-1 were prevented by a CD36 blocking antibody. TSP-1 and the CD36 binding peptide induced phosphorylation of Src kinases, p38 and JNK. More-over, inhibition of Src kinases blocked TSP-1-mediated regulation of cAMP concentrations and the phosphorylation of VASP, indicating that TSP-1 modulated the cAMP/PKA signaling events through a tyrosine kinase-dependent pathway downstream of CD36. These data reveal a new role for TSP-1 in promoting platelet aggregation through modulation of the cAMP-PKA signaling pathway. © 2010 by The American Society of Hematology

Regulation of blood platelet function by the AGC family of protein kinases

Upon vascular injury, platelets aggregate at the site of blood vessel injury to form a hemostatic plug maintaining the physiological integrity of the vascular system. Platelets respond to a variety of extracellular stimuli to undergo a rapid aggregation response, releasing active granule contents and leading to a rapidly growing thrombus. During the adhesion, activation, and aggregation of platelets at an injured site, the endothelium responds by limiting the size and growth of the hemostatic plug or thrombus, or even reversing platelet reactivity. These responses are defined as endothelial thromboregulation. There are three primary (and functionally independent) pathways during the early stages of thromboregulation by which the endothelium controls platelet reactivity (1) nitric oxide (NO); (2) prostacyclin (PGI2 ); and (3) the ectonucleotidase CD39. NO and PGI2 stimulate signalling cascades that result in the activation of the AGC family of Ser/Thr protein kinases (PKA, PKG and PKC). Once activated these kinase blunt platelet function through the phosphorylation of signalling proteins requested for activation. In this study, the role of AGC family kinases and their signaling cascades in regulating platelet function was assessed. The experimental data produced during this study demonstrate new insights in to the regulation of these kinases in platelets. More specifically it was found that 1. Peroxynitrite, a derivative of NO, regulated platelet function and particularly cytoskeletal rearrangement through PKC-dependent phosphorylation of VASPSer239/157 2. NO-mediated signalling in platelets had a requirement for PKC. 3. Multiple forms of PKA are present in platelets, which are differentially localised. 4. The potential regulation of platelet function by PKA is mediated through Akinase anchoring proteins. 5. Lipid rafts may play an important role in platelet regulation by NO and PKG. In summary, this studies present insights of the factors regulating AGC kinases in blood platelets.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Regulation of blood platelet function by the AGC family of protein kinases

Upon vascular injury, platelets aggregate at the site of blood vessel injury to form a hemostatic plug maintaining the physiological integrity of the vascular system. Platelets respond to a variety of extracellular stimuli to undergo a rapid aggregation response, releasing active granule contents and leading to a rapidly growing thrombus. During the adhesion, activation, and aggregation of platelets at an injured site, the endothelium responds by limiting the size and growth of the hemostatic plug or thrombus, or even reversing platelet reactivity. These responses are defined as endothelial thromboregulation. There are three primary (and functionally independent) pathways during the early stages of thromboregulation by which the endothelium controls platelet reactivity (1) nitric oxide (NO); (2) prostacyclin (PGI2 ); and (3) the ectonucleotidase CD39. NO and PGI2 stimulate signalling cascades that result in the activation of the AGC family of Ser/Thr protein kinases (PKA, PKG and PKC). Once activated these kinase blunt platelet function through the phosphorylation of signalling proteins requested for activation. In this study, the role of AGC family kinases and their signaling cascades in regulating platelet function was assessed. The experimental data produced during this study demonstrate new insights in to the regulation of these kinases in platelets. More specifically it was found that 1. Peroxynitrite, a derivative of NO, regulated platelet function and particularly cytoskeletal rearrangement through PKC-dependent phosphorylation of VASPSer239/157 2. NO-mediated signalling in platelets had a requirement for PKC. 3. Multiple forms of PKA are present in platelets, which are differentially localised. 4. The potential regulation of platelet function by PKA is mediated through Akinase anchoring proteins. 5. Lipid rafts may play an important role in platelet regulation by NO and PKG. In summary, this studies present insights of the factors regulating AGC kinases in blood platelets.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Globular adiponectin increases cGMP formation in blood platelets independently of nitric oxide

Background: Platelet-derived nitric oxide (NO) has been shown to play conflicting roles in platelet function, although it is accepted that NO mediates its actions through soluble guanylyl cyclase (sGC). This confusion concerning the roles of platelet NO may have arisen because of an uncharacterized mechanism for activation of sGC. Objectives: To examine the ability of the novel platelet agonist globular adiponectin (gAd) to stimulate the NO-independent cGMP-protein kinase G (PKG) signaling cascade. Methods: We used three independent markers of NO signaling, [ 3 H]l-citrulline production, cGMP accrual, and immunoblotting of vasodilator-stimulated phosphoprotein (VASP), to examine the NO signaling cascade in response to gAd. Results: gAd increased platelet cGMP formation, resulting in a dose- and time-dependent increase in phospho-VASP 157/239 . Phosphorylation of VASP in response to gAd was mediated by both protein kinase A and PKG. Importantly, cGMP formation occurred in the absence of NO synthase (NOS) activation and in the presence of NOS inhibitors. Indeed, inhibition of the NOS signaling cascade had no influence on gAd-mediated platelet aggregation. Exploration of the mechanism demonstrated that NO-independent cGMP formation, phosphorylation of VASP and association of sGCα 1 with heat shock protein-90 induced by gAd were blocked under conditions that inhibited Src kinases, implying a tyrosine kinase-dependent mechanism. Indeed, sGCα1 was reversibly tyrosine phosphorylated in response to gAd, collagen, and collagen-related peptide, an effect that required Src kinases and downstream Ca 2+ mobilization. Conclusions: These data demonstrate activation of the platelet cGMP signaling cascade by a novel tyrosine kinase-dependent mechanism in the absence of NO. © 2008 International Society on Thrombosis and Haemostasis

SARS-CoV-2 vaccination modelling for safe surgery to save lives: data from an international prospective cohort study

Background: Preoperative SARS-CoV-2 vaccination could support safer elective surgery. Vaccine numbers are limited so this study aimed to inform their prioritization by modelling. Methods: The primary outcome was the number needed to vaccinate (NNV) to prevent one COVID-19-related death in 1 year. NNVs were based on postoperative SARS-CoV-2 rates and mortality in an international cohort study (surgical patients), and community SARS-CoV-2 incidence and case fatality data (general population). NNV estimates were stratified by age (18-49, 50-69, 70 or more years) and type of surgery. Best- and worst-case scenarios were used to describe uncertainty. Results: NNVs were more favourable in surgical patients than the general population. The most favourable NNVs were in patients aged 70 years or more needing cancer surgery (351; best case 196, worst case 816) or non-cancer surgery (733; best case 407, worst case 1664). Both exceeded the NNV in the general population (1840; best case 1196, worst case 3066). NNVs for surgical patients remained favourable at a range of SARS-CoV-2 incidence rates in sensitivity analysis modelling. Globally, prioritizing preoperative vaccination of patients needing elective surgery ahead of the general population could prevent an additional 58 687 (best case 115 007, worst case 20 177) COVID-19-related deaths in 1 year. Conclusion: As global roll out of SARS-CoV-2 vaccination proceeds, patients needing elective surgery should be prioritized ahead of the general population