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Paul DS, Blatt TN, Schug WJ, Clark EG, Kawano T, Mackman N, Murcia S, Poe KO, Mwiza JMN, Harden TK, Bergmeier W, Nicholas RA. Loss of P2Y 1 receptor desensitization does not impact hemostasis or thrombosis despite increased platelet reactivity in vitro. J Thromb Haemost 2023; 21:1891-1902. [PMID: 36958516 PMCID: PMC10809801 DOI: 10.1016/j.jtha.2023.03.013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2022] [Revised: 02/20/2023] [Accepted: 03/09/2023] [Indexed: 03/25/2023]
Abstract
BACKGROUND The hemostatic plug formation at sites of vascular injury is strongly dependent on rapid platelet activation and integrin-mediated adhesion and aggregation. However, to prevent thrombotic complications, platelet aggregate formation must be a self-limiting process. The second-wave mediator adenosine diphosphate (ADP) activates platelets via Gq-coupled P2Y1 and Gi-coupled P2Y12 receptors. After ADP exposure, the P2Y1 receptor undergoes rapid phosphorylation-induced desensitization, a negative feedback mechanism believed to be critical for limiting thrombus growth. OBJECTIVE The objective of this study was to examine the role of rapid P2Y1 receptor desensitization on platelet function and thrombus formation in vivo. METHODS We analyzed a novel knock-in mouse strain expressing a P2Y1 receptor variant that cannot be phosphorylated beyond residue 340 (P2Y1340-0P), thereby preventing the desensitization of the receptor. RESULTS P2Y1340-0P mice followed a Mendelian inheritance pattern, and peripheral platelet counts were comparable between P2Y1340-0P/340-0P and control mice. In vitro, P2Y1340-0P/340-0P platelets were hyperreactive to ADP, showed a robust activation response to the P2Y1 receptor-selective agonist, MRS2365, and did not desensitize in response to repeated ADP challenge. We observed increased calcium mobilization, protein kinase C substrate phosphorylation, alpha granule release, activation of the small GTPase Rap1, and integrin inside-out activation/aggregation. This hyperreactivity, however, did not lead to increased platelet adhesion or excessive plug formation under physiological shear conditions. CONCLUSION Our studies demonstrate that receptor phosphorylation at the C-terminus is critical for P2Y1 receptor desensitization in platelets and that impaired desensitization leads to increased P2Y1 receptor signaling in vitro. Surprisingly, desensitization of the P2Y1 receptor is not required for limiting platelet adhesion/aggregation at sites of vascular injury, likely because ADP is degraded quickly or washed away in the bloodstream.
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Affiliation(s)
- David S Paul
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA; UNC Blood Research Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA. https://twitter.com/David_S_Paul
| | - Tasha N Blatt
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Wyatt J Schug
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA; UNC Blood Research Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Emily G Clark
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA; UNC Blood Research Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Tomohiro Kawano
- UNC Blood Research Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA; Department of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Nigel Mackman
- UNC Blood Research Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA; Department of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Sebastian Murcia
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Kathryn O Poe
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA; UNC Blood Research Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Jean Marie N Mwiza
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA; UNC Blood Research Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - T Kendall Harden
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Wolfgang Bergmeier
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA; UNC Blood Research Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.
| | - Robert A Nicholas
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.
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Inverse agonism at the P2Y12 receptor and ENT1 transporter blockade contribute to platelet inhibition by ticagrelor. Blood 2016; 128:2717-2728. [PMID: 27694321 DOI: 10.1182/blood-2016-03-707844] [Citation(s) in RCA: 66] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2016] [Accepted: 09/22/2016] [Indexed: 12/13/2022] Open
Abstract
Ticagrelor is a potent antagonist of the P2Y12 receptor (P2Y12R) and consequently an inhibitor of platelet activity effective in the treatment of atherothrombosis. Here, we sought to further characterize its molecular mechanism of action. Initial studies showed that ticagrelor promoted a greater inhibition of adenosine 5'-diphosphate (ADP)-induced Ca2+ release in washed platelets vs other P2Y12R antagonists. This additional effect of ticagrelor beyond P2Y12R antagonism was in part as a consequence of ticagrelor inhibiting the equilibrative nucleoside transporter 1 (ENT1) on platelets, leading to accumulation of extracellular adenosine and activation of Gs-coupled adenosine A2A receptors. This contributed to an increase in basal cyclic adenosine monophosphate (cAMP) and vasodilator-stimulated phosphoprotein phosphorylation (VASP-P). In addition, ticagrelor increased platelet cAMP and VASP-P in the absence of ADP in an adenosine receptor-independent manner. We hypothesized that this increase originated from a direct effect on basal agonist-independent P2Y12R signaling, and this was validated in 1321N1 cells stably transfected with human P2Y12R. In these cells, ticagrelor blocked the constitutive agonist-independent activity of the P2Y12R, limiting basal Gi-coupled signaling and thereby increasing cAMP levels. These data suggest that ticagrelor has the pharmacological profile of an inverse agonist. Based on our results showing insurmountable inhibition of ADP-induced Ca2+ release and forskolin-induced cAMP, the mode of antagonism of ticagrelor also appears noncompetitive, at least functionally. In summary, our studies describe 2 novel modes of action of ticagrelor, inhibition of platelet ENT1 and inverse agonism at the P2Y12R that contribute to its effective inhibition of platelet activation.
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Demina OV, Khodonov AA, Sinauridze EI, Shvets VI, Varfolomeev SD. 5-Substituted pyridylisoxazoles as effective inhibitors of platelet aggregation. Russ Chem Bull 2015. [DOI: 10.1007/s11172-014-0707-3] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Yang Y, Wang C, Jin L, Chen G, Li C, Qi K, Kong D, Wang Y, Song M, Ma L. Effectiveness of and risk associated with aspirin therapy in hemodialysis patients with a background of antiplatelet factor 4/heparin complex antibody detection. Thromb Res 2015; 136:61-8. [PMID: 25936230 DOI: 10.1016/j.thromres.2015.04.023] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2014] [Revised: 04/10/2015] [Accepted: 04/18/2015] [Indexed: 10/23/2022]
Abstract
BACKGROUND The optimal prevention measures against hemodialysis (HD)-associated complications, including all-cause thrombotic events and death, are unclear. METHODS This prospective study was designed to assess the effect of aspirin on prevention of HD-associated complications. Patients were divided into four groups according to platelet factor-4/heparin-complex (PF4/H) antibody detection and aspirin prescription: Group 1, antibody(-)/aspirin(+); Group 2, antibody(-)/aspirin(-); Group 3, antibody(+)/aspirin(+); and Group 4, antibody(+)/aspirin(-). Adverse events were compared among all four groups. Cox hazard regression was performed to analyze the effects of anti-PF4/H antibody and aspirin on thrombosis and death. RESULTS This study included 648 patients undergoing HD; 142 were positive for anti-PF4/H antibodies, and 229 had received aspirin before enrollment. During the 4-year follow-up period, 138 patients developed thrombosis, and 63 of these events were anti-PF4/H antibody-associated. A total of 112 patients died; 75 died of coronary heart disease (CHD). Group 4 had a significantly higher incidence of total and anti-PF4/H antibody-associated thrombosis events as well as total and CHD-associated death than did the other three groups. Aspirin had a preventive effect against all adverse events in anti-PF4/H antibody-positive patients, but not in antibody-negative patients. Group 1 patients with baseline D-dimer levels of <0.6μg/mL developed more hemorrhagic events than did patients in the other groups. CONCLUSIONS Aspirin prevention of thrombosis and death in patients undergoing HD might require consideration of the anti-PF4/H antibody status. In antibody-positive individuals, taking aspirin could improve the prognosis and therefore might be recommended. In antibody-negative individuals, prevention was minimal and the bleeding risk was obviously increased; thus, aspirin should be avoided or at least require careful evaluation prior to aspirin treatment.
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Affiliation(s)
- Yang Yang
- Kidney Therapeutic Center of Traditional Chinese and Western Medicine, Beidaihe Sanatorium of Beijing Military Region, Qinhuangdao, China
| | - Chao Wang
- Kidney Therapeutic Center of Traditional Chinese and Western Medicine, Beidaihe Sanatorium of Beijing Military Region, Qinhuangdao, China
| | - Liping Jin
- Kidney Therapeutic Center of Traditional Chinese and Western Medicine, Beidaihe Sanatorium of Beijing Military Region, Qinhuangdao, China
| | - Guanglei Chen
- Kidney Therapeutic Center of Traditional Chinese and Western Medicine, Beidaihe Sanatorium of Beijing Military Region, Qinhuangdao, China
| | - Changchun Li
- Kidney Therapeutic Center of Traditional Chinese and Western Medicine, Beidaihe Sanatorium of Beijing Military Region, Qinhuangdao, China
| | - Ka Qi
- Hemodialysis Centre, Beidaihe Sanatorium of Beijing Military Region, Qinhuangdao, China
| | - Deyang Kong
- Hemodialysis Centre, First Affiliated Hospital of Haerbin Medical University, Haerbin, China
| | - Yaping Wang
- Hemodialysis Centre, General Hospital of Beijing Military Region, Beijing, China
| | - Minghui Song
- Kidney Therapeutic Center of Traditional Chinese and Western Medicine, Beidaihe Sanatorium of Beijing Military Region, Qinhuangdao, China
| | - Lu Ma
- Kidney Therapeutic Center of Traditional Chinese and Western Medicine, Beidaihe Sanatorium of Beijing Military Region, Qinhuangdao, China.
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Kwon SU, Cha JY, Lee HY, Xin M, Ji SJ, Kim DK, Park DS, Pyo MK, Lee YM. Chloroform fraction of Euphorbia maculata has antiplatelet activity via suppressing thromboxane B2 formation. Mol Med Rep 2015; 11:4255-61. [PMID: 25672843 DOI: 10.3892/mmr.2015.3319] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2014] [Accepted: 01/15/2015] [Indexed: 11/06/2022] Open
Abstract
Euphorbia maculata (EM) is a traditionally used antidiarrheal, antibacterial, antifungal and antioxidant agent. However, the effects of EM on platelet activity remain to be elucidated. Therefore, the present study investigated the antiplatelet effect of various EM extract fractions on platelet aggregation in rats. The antiplatelet activity of the EM fractions on collagen or adenosine diphosphate (ADP)‑induced platelet aggregation was evaluated in vitro and ex vivo. Thromboxane B2 (TXB2) formation, rat‑tail bleeding time and coagulation time were also measured. Among the fractions, the chloroform fraction of EM (CFEM) significantly inhibited ADP‑induced platelet aggregation in vitro. Furthermore, oral administration of 50 mg/kg CFEM to rats significantly reduced ADP‑induced platelet aggregation without increasing the tail bleeding time or coagulation time. In addition, EM significantly inhibited the level of TXB2 formation in a dose‑dependent manner. These results suggest that CFEM exhibits antiplatelet activity, without causing bleeding, via the suppression of TXB2 formation. CFEM may be a type of food which has the potential for preventing cardiovascular disease.
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Affiliation(s)
- Se-Uk Kwon
- Department of Oriental Pharmacy, College of Pharmacy, Wonkwang‑Oriental Medicines Research Institute, Wonkwang University, Iksan, Jeonbuk 570‑749, Republic of Korea
| | - Ji-Yoon Cha
- Department of Oriental Pharmacy, College of Pharmacy, Wonkwang‑Oriental Medicines Research Institute, Wonkwang University, Iksan, Jeonbuk 570‑749, Republic of Korea
| | - Hoon-Yeon Lee
- Department of Oriental Pharmacy, College of Pharmacy, Wonkwang‑Oriental Medicines Research Institute, Wonkwang University, Iksan, Jeonbuk 570‑749, Republic of Korea
| | - Mingjie Xin
- Department of Oriental Pharmacy, College of Pharmacy, Wonkwang‑Oriental Medicines Research Institute, Wonkwang University, Iksan, Jeonbuk 570‑749, Republic of Korea
| | - Su-Jeong Ji
- Department of Food Industry Convergence, Wonkwang University, Iksan, Jeonbuk 570‑749, Republic of Korea
| | - Dae-Ki Kim
- Department of Immunology and Institute of Medical Science, Jeonbuk National University Medical School, Jeonju, Jeonbuk 561‑180, Republic of Korea
| | - Do-Sim Park
- Department of Laboratory Medicine, School of Medicine, Wonkwang University, Iksan, Jeonbuk 570‑749, Republic of Korea
| | - Mi-Kyung Pyo
- International Ginseng and Herb Research Institute, Guemsan, Chungbuk 312‑804, Republic of Korea
| | - Young-Mi Lee
- Department of Oriental Pharmacy, College of Pharmacy, Wonkwang‑Oriental Medicines Research Institute, Wonkwang University, Iksan, Jeonbuk 570‑749, Republic of Korea
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Yang Y, Kong D, Wang C, Chen G, Shan F, Qi K, Ma L. Inhibition of platelet activation could decrease thrombotic events in hemodialysis PF4/H antibody-positive patients. Ren Fail 2014; 36:870-6. [PMID: 24665827 DOI: 10.3109/0886022x.2014.899880] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
BACKGROUND Platelet factor 4/heparin (PF4/H) antibody detection is widely used to evaluate the risk of thrombosis in patients undergoing hemodialysis (HD). Most patients who are PF4/H-antibody-positive can survive thrombosis, but the reason has not been clarified. In addition, no valid preventive methods for thrombosis in patients undergoing HD have been confirmed. METHODS A single-center, semi-randomized controlled study was designed. In total, 157 patients fulfilled the inclusion criteria and participated. Patients were first divided according to PF4/H antibody detection and then subdivided randomly according to different anti-platelet agent descriptions. RESULTS (1) PF4/H antibody-positive patients suffered a significantly higher incidence of thrombosis than those who were antibody-negative; (2) PF4/H antibody-positive patients who survived a thrombosis manifested a significantly longer bleeding time and decreased maximum percentage of platelet aggregation inhibition; (3) aspirin and clopidogrel decreased the incidence of thrombosis in PF4/H antibody-positive patients by inhibiting platelet activation. CONCLUSION The PF4/H antibody was effective for prediction of the risk of thrombosis, except in patients with dysfunctional platelets; aspirin manifested effects similar to clopidogrel in terms of prevention of thromboses in PF4/H antibody-positive patients, but costs much less and is therefore recommended.
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Affiliation(s)
- Yang Yang
- Therapeutic Centre of Kidney Diseases, First Affiliated Hospital of Beidaihe Sanatorium of Beijing Military Region , Qinhuangdao, Hebei Province , P.R. China
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Chlorin e6 Prevents ADP-Induced Platelet Aggregation by Decreasing PI3K-Akt Phosphorylation and Promoting cAMP Production. EVIDENCE-BASED COMPLEMENTARY AND ALTERNATIVE MEDICINE 2013; 2013:569160. [PMID: 23997795 PMCID: PMC3755423 DOI: 10.1155/2013/569160] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/05/2013] [Revised: 06/19/2013] [Accepted: 06/19/2013] [Indexed: 01/07/2023]
Abstract
A number of reagents that prevent thrombosis have been developed but were found to have serious side effects. Therefore, we sought to identify complementary and alternative medicinal materials that are safe and have long-term efficacy. In the present studies, we have assessed the ability of chlorine e6 (CE6) to inhibit ADP-induced aggregation of rat platelets and elucidated the underlying mechanism. CE6 inhibited platelet aggregation induced by 10 µM ADP in a concentration-dependent manner and decreased intracellular calcium mobilization and granule secretion (i.e., ATP and serotonin release). Western blotting revealed that CE6 strongly inhibited the phosphorylations of PI3K, Akt, c-Jun N-terminal kinase (JNK), and different mitogen-activated protein kinases (MAPKs) including extracellular signal-regulated kinase 1/2 (ERK1/2) as well as p38-MAPK. Our study also demonstrated that CE6 significantly elevated intracellular cAMP levels and decreased thromboxane A2 formation in a concentration-dependent manner. Furthermore, we determined that CE6 initiated the activation of PKA, an effector of cAMP. Taken together, our findings indicate that CE6 may inhibit ADP-induced platelet activation by elevating cAMP levels and suppressing PI3K/Akt activity. Finally, these results suggest that CE6 could be developed as therapeutic agent that helps prevent thrombosis and ischemia.
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Través PG, Pimentel-Santillana M, Carrasquero LMG, Pérez-Sen R, Delicado EG, Luque A, Izquierdo M, Martín-Sanz P, Miras-Portugal MT, Boscá L. Selective impairment of P2Y signaling by prostaglandin E2 in macrophages: implications for Ca2+-dependent responses. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2013; 190:4226-35. [PMID: 23479225 DOI: 10.4049/jimmunol.1203029] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Extracellular nucleotides have been recognized as important modulators of inflammation via their action on specific pyrimidine receptors (P2). This regulation coexists with the temporal framework of proinflammatory and proresolution mediators released by the cells involved in the inflammatory response, including macrophages. Under proinflammatory conditions, the expression of cyclooxygenase-2 leads to the release of large amounts of PGs, such as PGE2, that exert their effects through EP receptors and other intracellular targets. The effect of these PGs on P2 receptors expressed in murine and human macrophages was investigated. In thioglycollate-elicited and alternatively activated macrophages, PGE2 selectively impairs P2Y but not P2X7 Ca(2+) mobilization. This effect is absent in LPS-activated cells and is specific for PGE2 because it cannot be reproduced by other PGs with cyclopentenone structure. The inhibition of P2Y responses by PGE2 involves the activation of nPKCs (PKCε) and PKD that can be abrogated by selective inhibitors or by expression of dominant-negative forms of PKD. The inhibition of P2Y signaling by PGE2 has an impact on the cell migration elicited by P2Y agonists in thioglycollate-elicited and alternatively activated macrophages, which provide new clues to understand the resolution phase of inflammation, when accumulation of PGE2, anti-inflammatory and proresolving mediators occurs.
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Affiliation(s)
- Paqui G Través
- Departamento de Bioquímica y Biología Molecular IV, Facultad de Veterinaria e Instituto Universitario de Investigación en Neuroquímica, Instituto de Investigación Sanitaria del Hospital Clínico San Carlos, Universidad Complutense Madrid, 28040 Madrid, Spain
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Eriksson AC, Whiss PA. Nanomolar concentrations of adrenaline induce platelet adhesion in vitro. Platelets 2012; 24:129-35. [PMID: 22471400 DOI: 10.3109/09537104.2012.672780] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Adrenaline is a platelet activator having a resting plasma concentration of <1 nmol/l that increases to a few nmol/l during stress. However, most in vitro assays only detect effects of adrenaline in micromolar concentrations. This makes it difficult to estimate the relevance of in vitro data for the in vivo situation. The aim of this study was to investigate experimental conditions in vitro that could detect platelet effects of adrenaline in nanomolar concentrations. Platelet adhesion to albumin and collagen was evaluated with a static platelet adhesion assay. Our results show that 10 nmol/l adrenaline induced platelet adhesion to albumin in platelet-rich plasma (PRP) prepared at 140 × g, while 100 nmol/l was necessary in order to increase adhesion of platelets prepared at 220 × g. The mean platelet volume was increased after preparation at 140 × g, suggesting that large reactive platelets contributed to the increased adrenaline sensitivity. At optimal Mg(2+)-concentration, adhesion to collagen was increased by 10 nmol/l adrenaline irrespective of centrifugal force applied during PRP preparation. More specifically, we defined two populations where adhesion to collagen was increased by 10 nmol/l adrenaline either upon centrifugation at 140 × g but not 220 × g or vice versa. In some experiments, platelet adhesion to collagen was induced by 3 nmol/l adrenaline, which corresponds to concentrations achieved during stress in vivo. In summary, the static adhesion assay is able to detect platelet activating effects of adrenaline very close to physiological concentrations. This is rare for in vitro assays and motivates further research about adrenergic signalling in platelets.
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Affiliation(s)
- Andreas C Eriksson
- Division of Drug Research/Pharmacology, Department of Medical and Health Sciences, Linköping University , SE-581 85 Linköping , Sweden.
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Bynagari-Settipalli YS, Lakhani P, Jin J, Bhavaraju K, Rico MC, Kim S, Woulfe D, Kunapuli SP. Protein kinase C isoform ε negatively regulates ADP-induced calcium mobilization and thromboxane generation in platelets. Arterioscler Thromb Vasc Biol 2012; 32:1211-9. [PMID: 22362759 DOI: 10.1161/atvbaha.111.242388] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
OBJECTIVE Members of the protein kinase C (PKC) family are shown to positively and negatively regulate platelet activation. Although positive regulatory roles are extensively studied, negative regulatory roles of PKCs are poorly understood. We investigated the mechanism and specific isoforms involved in PKC-mediated negative regulation of ADP-induced functional responses. METHODS AND RESULTS A pan-PKC inhibitor, GF109203X, potentiated ADP-induced cPLA(2) phosphorylation and thromboxane generation as well as ERK activation and intracellular calcium (Ca(2+)(i)) mobilization, 2 signaling molecules, upstream of cPLA(2) activation. Thus, PKCs inhibit cPLA(2) activation by inhibiting ERK and Ca(2+)(i) mobilization. Because the inhibitor of classic PKC isoforms, GO-6976, did not affect ADP-mediated thromboxane generation, we investigated the role of novel class of PKC isoforms. ADP-induced thromboxane generation, calcium mobilization, and ERK phosphorylation were potentiated in PKCε null murine platelets compared with platelets from wild-type littermates. Interestingly, when thromboxane release is blocked, ADP-induced aggregation in PKCε knockout and wild-type was similar, suggesting that PKCε does not affect ADP-induced aggregation directly. PKCε knockout mice exhibited shorter times to occlusion in an FeCl(3)-induced arterial injury model and shorter bleeding times in tail-bleeding experiments. CONCLUSIONS We conclude that PKCε negatively regulates ADP-induced thromboxane generation in platelets and offers protection against thrombosis.
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Korporaal SJA, Meurs I, Hauer AD, Hildebrand RB, Hoekstra M, Cate HT, Praticò D, Akkerman JWN, Van Berkel TJC, Kuiper J, Van Eck M. Deletion of the high-density lipoprotein receptor scavenger receptor BI in mice modulates thrombosis susceptibility and indirectly affects platelet function by elevation of plasma free cholesterol. Arterioscler Thromb Vasc Biol 2010; 31:34-42. [PMID: 21051668 DOI: 10.1161/atvbaha.110.210252] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
OBJECTIVE Scavenger receptor BI (SR-BI) is a cell surface receptor that promotes the selective uptake of cholesteryl esters from high-density lipoprotein (HDL) by the liver. In mice, SR-BI deficiency results in increased plasma HDL cholesterol levels and enhanced susceptibility to atherosclerosis. The aim of this study was to investigate the role of SR-BI deficiency on platelet function. METHODS AND RESULTS SR-BI-deficient mice were thrombocytopenic, and their platelets were abnormally large, probably because of an increased cholesterol content. The FeCl(3) acute injury model to study arterial thrombosis susceptibility showed that SR-BI wild-type mice developed total arterial occlusion after 24±2 minutes. In SR-BI-deficient mice, however, the time to occlusion was reduced to 13±1 minutes (P=0.02). Correspondingly, in SR-BI-deficient mice, platelets circulated in an activated state and showed increased adherence to immobilized fibrinogen. In contrast, platelet-specific disruption of SR-BI by bone marrow transplantation in wild-type mice did not alter plasma cholesterol levels or affect platelet count, size, cholesterol content, or reactivity, suggesting that changes in plasma cholesterol levels were responsible for the altered responsiveness of platelets in SR-BI-deficient mice. CONCLUSIONS The function of SR-BI in HDL cholesterol homeostasis and prevention of atherosclerosis is indirectly also essential for maintaining normal platelet function and prevention of thrombosis.
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Affiliation(s)
- Suzanne J A Korporaal
- Leiden/Amsterdam Center for Drug Research, Division of Biopharmaceutics, Gorlaeus Laboratories, Einsteinweg 55, 2333 CC, Leiden, the Netherlands.
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Young JP, Beckerman J, Vicini S, Myers A. Acetylsalicylic acid enhances purinergic receptor-mediated outward currents in rat megakaryocytes. Am J Physiol Cell Physiol 2010; 298:C602-10. [DOI: 10.1152/ajpcell.00422.2009] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Purinergic receptor activation increases cytosolic Ca2+concentration in a fluctuating fashion, triggering oscillatory outward Ca2+-activated K+currents in rat megakaryocytes (MKs). Whole cell and nystatin-perforated patch-clamp techniques were used to analyze changes in ionic conductance in MK with acetylsalicylic acid (ASA), a cyclooxygenase-1 inhibitor and antithrombotic agent. MKs are a model for platelet reactivity, particularly in ASA treatment failure (ASA resistance). Freshly isolated MKs were incubated 30 min in the absence or presence of 1 mM ASA. Using a K+-rich internal solution, we recorded outward currents in response to 10 μM ATP, 10 μM ADP, and 5 μM 2-methyl-thio-ADP (2MeSADP) in the voltage-clamp mode. Agonist-induced currents decreased in amplitude over time, but this decline was attenuated by ASA in both continuous and repeated agonist challenge, indicating increased MK reactivity with ASA treatment. In separate experiments, heterologous desensitization was observed when MKs were stimulated with ADP after exposure to a thromboxane receptor agonist (U46619), indicating cross talk between thromboxane and purinergic pathways. Different cells, treated with ASA or MRS2179 (P2Y1 receptor antagonist), were stimulated with 2MeSADP. The dose-response curve was shifted to the left in both cases, suggesting increased MK reactivity. ASA also caused an increased interval between currents (delay). ASA attenuated desensitization of purinergic receptors and increased delay, again suggesting cross talk between purinergic and thromboxane pathways. These findings may be relevant to ASA resistance, because individual variations in sensitivity to the multiple effects of ASA on signaling pathways could result in insensitivity to its antiplatelet effects in some patients.
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Affiliation(s)
| | - Jacob Beckerman
- Biology, Georgetown University, Washington, District of Columbia
| | | | - Adam Myers
- Departments of 1Physiology and Biophysics and
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