Essential role of glycoprotein Ibα in platelet activation.

Glycoprotein (GP) Ib, the ligand-binding subunit of platelet GPIb-IX complex, interacts with von Willebrand factor (VWF) exposed at the injured vessel wall, initiating platelet adhesion, activation, hemostasis, and thrombus formation. The cytoplasmic tail of GPIb interacts with 14-3-3, regulate ng the VWF-GPIb-elicited signal transduction and VWF binding function of GPIb. However, we unexpectedly found that the GPIb-14-3-3 association, beyond VWF-dependent function, is essential for general platelet activation. We found that the GPIb cytoplasmic tail peptide MPC, a potential GPIb inhibitor, by itself induced platelet aggregation, integrin αIIbß3 activation, granule secretion, and phosphatidylserine (PS) exposure. Conversely, the deletion of the cytoplasmic tail of GPIb in mouse platelets (10aa-/-) decreased platelet aggregation, integrin IIb3 activation, granule secretion, and PS exposure induced by various physiological agonists. Phosphoproteome-based kinase activity profiling revealed significantly upregulated protein kinase C (PKC) activity in MPC-treated platelets. MPC-induced platelet activation was abolished by the pan-PKC inhibitor and PKC deletion. Decreased PKC activity was observed in both resting and agonist-stimulated 10aa-/- platelets. GPIb regulates PKC activity by sequestering 14-3-3 from PKC. In vivo, the deletion of the GPIb cytoplasmic tail impaired mouse hemostasis and thrombus formation and protected against platelet-dependent pulmonary thromboembolism. Therefore, our findings demonstrate an essential role for the GPIb cytoplasmic tail in regulating platelet general activation and thrombus formation beyond the VWF-GPIb axis.

Activation of AMPK in platelets promotes the production of offspring.

Platelets are terminally differentiated anucleated cells, but they still have cell-like functions and can even produce progeny platelets. However, the mechanism of platelet sprouting has not been elucidated so far. Here, we show that when platelet-rich plasma(PRP) was cultured at 37°C, platelets showed a spore phenomenon. The number of platelets increased when given a specific shear force. It is found that AMP-related signaling pathways, such as PKA and AMPK are activated in platelets in the spore state. Meanwhile, the mRNA expression levels of genes, such as CNN3, CAPZB, DBNL, KRT19, and ESPN related to PLS1 skeleton proteins also changed. Moreover, when we use the AMPK activator AICAR(AI) to treat washed platelets, cultured platelets can still appear spore phenomenon. We further demonstrate that washed platelets treated with Forskolin, an activator of PKA, not only platelet sprouting after culture but also the AMPK is activated. Taken together, these data demonstrate that AMPK plays a key role in the process of platelet budding and proliferation, suggesting a novel strategy to solve the problem of clinical platelet shortage.

What is new? In this study, we showed that when platelet-rich plasma(PRP) was cultured at 37°C, platelets showed spore phenomenon and increased.It was found that AMP-related signaling pathways, such as PKA and AMPK were activated in platelets in the spore state.In addition, we found that PKA acts as an upstream kinase of AMPK.In the process of platelet sprouting and proliferation, the mRNA expression levels of skeleton protein PLS1 and its related genes, such as CNN3, CAPZB, DBNL, KRT19, andESPN also changed.What is the impact? Our study proposes a new strategy to solve the problem of clinical platelet shortage.

The role of PKC in X-ray-induced megakaryocyte apoptosis and thrombocytopenia.

Thrombocytopenia is a critical complication after radiation therapy and exposure. Dysfunction of megakaryocyte development and platelet production are key pathophysiological stages in ionizing radiation (IR)-induced thrombocytopenia. Protein kinase C (PKC) plays an important role in regulating megakaryocyte development and platelet production. However, it remains unclear how PKC regulates IR-induced megakaryocyte apoptosis. In this study, we found that pretreatment of PKC pan-inhibitor Go6983 delayed IR-induced megakaryocyte apoptosis, and inhibited IR-induced mitochondrial membrane potential and ROS production in CMK cells. Moreover, suppressing PKC activation inhibited cleaved caspase3 expression and reduced p38 phosphorylation levels, and IR-induced PKC activation might be regulated by p53. In vivo experiments confirmed that Go6983 promoted platelet count recovery after 21 days of 3 Gy total body irradiation. Furthermore, Go6983 reduced megakaryocyte apoptosis, increased the number of megakaryocyte and polyploid formation in bone marrow, and improved the survival rate of 6 Gy total body irradiation. In conclusion, our results provided a potential therapeutic target for IR-induced thrombocytopenia.

Cyclic thrombocytopenia associated with estradiol: a case report.

OBJECTIVES: Cyclic thrombocytopenia (CTP) is a rare blood disorder characterized by periodic fluctuations in platelet counts. CTP usually appears in pre-menopausal women, and these fluctuations of platelets are in phase with the menstrual cycle. CTP is a heterogeneous disease, and the pathogenic mechanism is still unclear. Therefore, it harbors great significance for exploring the association of fluctuations in platelet counts with hormonal-cycle. MATERIALS: Firstly, we washed human platelets from healthy volunteers following the Declaration of Helsinki. Flow cytometer was employed to measure the mitochondrial inner transmembrane potential (ΔΨm) depolarization, PS exposure, P-selectin expression, and GPIIb/IIIa activation in platelets. In addition, western blot detected the related protein expression. The corresponding assay kit measured the caspase-3 and PDE3A activity. Finally, flow cytometry determined mouse platelets labeled with calcein. RESULTS: We find a reverse relationship between the platelet count and serum estradiol (E2) level in a CTP patient. We demonstrated that E2 induces platelet apoptosis in vitro and platelet clearance in vivo. We further discovered that E2 activates phosphodiesterase 3A, which inhibits protein kinase A (PKA), leading to PKA-mediated platelet apoptosis. Activation of PKA protected platelets from E2-induced thrombocytopenia and elevated the number of mice circulatory platelets. CONCLUSIONS: We find that E2 induces platelet apoptosis and clearance through PDE3A-mediated PKA inhibition. Activation of PKA rescues E2-induced thrombocytopenia in mice. Thus, our study reveals a pathogenesis of E2-related CTP and suggests promising therapeutic strategies for the disease.

X-rays Stimulate Granular Secretions and Activate Protein Kinase C Signaling in Human Platelets.

X-rays can induce morphological as well as functional changes in cells. Platelets are anuclear cellular fragments originating from megakaryocytes and are the major regulators in hemostasis and thrombosis. Platelet products are irradiated to avoid medical complications associated with platelet transfusion. So far, gamma, UV, and laser radiation have been used for this purpose. However, scientists are divided about the effects of radiation on platelet quality. The present study was designed to explore the possible effects of X-rays in washed human platelets and understand the molecular mechanism behind them. In the present study, we exposed washed human platelets to 10 or 30 Gy X-rays at 0.25 Gy/min. Flow cytometry, aggregometry, and western blot were performed to investigate the effect of X-rays on platelet degranulation, integrin activation, platelet aggregation, and apoptosis. It was found that X-rays immediately induced granular secretions with no effect on GP IIb/IIIa activation. Not surprisingly, due to granule secretions in irradiated platelets, platelet aggregation was significantly reduced. In contrast to granular secretions and platelet aggregation, X-rays induced mitochondrial transmembrane potential depolarization in a time-dependent manner to induce apoptosis and activated protein kinase C (PKC) signaling. This study revealed and explained the molecular mechanism activated by X-rays in washed human platelets. Here we also introduced Gö 6983, a PKC inhibitor, as an agent that counteracts X-ray-induced changes and maintains the integrity of platelets.

[Regulation of Mitochondria on Platelet Apoptosis and Activation].

OBJECTIVE: To explore the regulation of mitochondria on platelet apoptosis and activation, and the relationship between platelet apoptosis and activation. METHODS: Platelets were isolated from peripheral venous blood of healthy volunteers. Cyclosporin A (CsA), which has a protective effect on the function of platelet mitochondria, BAPTA, which can chelate calcium ions across membranes in platelets, and NAC, an antioxidant that reduces the level of intracellular reactive oxygen species, were selected for coincubation with washed platelets, respectively. By flow cytometry, platelet aggregator was used to detect the changes of platelet mitochondrial function and platelet activation indexes after different interventions. RESULTS: H89, staurosporine, and A23187 led to platelet mitochondrial abnormalities, while CsA could effectively reverse the decline of platelet mitochondrial membrane potential caused by them. Antioxidant NAC could reverse platelet mitochondrial damage correspondingly, and completely reverse platelet shrinkage and phosphatidylserine eversion induced by H89. BAPTA, prostaglandin E1, acetylsalicylic acid and other inhibitors could not reverse the decline of platelet mitochondrial membrane potential. CONCLUSION: Mitochondrial function plays an important role in platelet apoptosis and activation. Abnormal mitochondrial function causes the imbalance of reduction/oxidation state in platelets, which leads to platelet apoptosis. Platelet apoptosis and activation are independent signal processes.

[The Effect of Ena/VASP Family on the Expression of GPIb-IX Complex in Human Megakaryoblastic Leukemia Dami Cells].

OBJECTIVE: To explore the effects of Ena/VASP gene family on the expression of glycoprotein (GP) Ib-IX complex in human megakaryoblastic leukemia Dami cells. METHODS: SiRNAs targeting Ena/VASP gene family were designed and synthesized to interfere Enah, EVL and VASP gene expression. When the siRNAs were transfected into Dami cells by using LipofectamineTM 2000 for 48 h, the expression of GPIb-IX complex was detected by quantitative real-time PCR, Western blot and flow cytometry. RESULTS: We successfully established siVASP , siEVL and si Enah Dami cell lines. And it was found that the expression of GPIb-IX complex had no evident reduction in siEVL or siVASP Dami cells at both mRNA and protein level, while the total protein and membrane protein of GPIb-IX complex were obviously reduced when Enah was knocked down. CONCLUSION: Enah could affect the expression of GPIb-IX complex in human megakaryoblastic leukemia Dami cells, but the underlying mechanism still needs to be further explored.

Alantolactone induces platelet apoptosis by activating the Akt pathway.

Alantolactone (ALT), a sesquiterpene lactone compound isolated from Inula helenium L., has recently attracted much attention for its anti-tumor properties. ALT reportedly functions by regulating the Akt pathway, which has been shown to be involved in programmed platelet death (apoptosis) and platelet activation. However, the precise effect of ALT on platelets remains unclear. In this study, washed platelets were treated with ALT in vitro, and apoptotic events and platelet activation were detected. In vivo, platelet transfusion experiments were employed to detect the effect of ALT on platelet clearance. Platelet counts were examined after intravenous injection of ALT. We found that ALT treatment induced Akt activation and Akt-mediated apoptosis in platelets. ALT-activated Akt elicited platelet apoptosis by activating phosphodiesterase (PDE3A) and PDE3A-mediated protein kinase A (PKA) inhibition. Pharmacological inhibition of the PI3K/Akt/PDE3A signaling pathway or PKA activation was found to protect platelets from apoptosis induced by ALT. Moreover, ALT-induced apoptotic platelets were removed faster in vivo, and ALT injection resulted in the platelet count decline. Either PI3K/Akt/PDE3A inhibitors or a PKA activator could protect platelets from clearance, ultimately ameliorating the ALT-induced decline in platelet count in the animal model. These results reveal the effects of ALT on platelets and their related mechanisms, suggesting potential therapeutic targets for the prevention and alleviation of possible side effects resulting from ALT treatments.

What is the context? In the past several decades, natural products, including traditional Chinese medicine (TCM), have been developed for the treatment of a variety of diseases.Alantolactone (ALT), a natural herb compound mainly extracted from the root of Inula helenium L., is the essential active component in many TCM formulas. ALT has attracted extensive attention because of its anti-cancer capacity recently.However, adverse events (AEs) induced by drugs are common in chemotherapy, and the side effects of ALT treatment remain unclear.What is new? In this study, experiments were conducted to clarify the precise effect of ALT on platelets. We demonstrated for the first time that ALT induces platelet apoptosis and platelet count decline, suggesting possible side effects of ALT treatment.ALT-activated Akt elicited platelet apoptosis by activating phosphodiesterase (PDE3A) and PDE3A-mediated protein kinase A (PKA) inhibition.Our work provides experimental evidence supporting the hypothesis that the effects of ALT on Akt may vary depending on cell types. Therefore. More research is needed to explore the side effects of ALT on other cells before clinical application.What is the impact? This study reveals possible side effects of ALT treatment, providing the reference for clinic drug administrate and estimation of medicine safety. Significantly, our findings demonstrated relevant molecular mechanisms, providing strategies for controlling or alleviating these side effects in the future.

[Main Factors Influencing the Platelet Spreading].

OBJECTIVE: To explore the main factors of platelet spreading and provide the foundation for related research. METHODS: Platelets (2×107/ml) were draw from C57BL/6J mouse and kept at 22 ℃ for 1-2 hours. Platelets (2×107/ml) were were allowed to adhere and spread on the fibrinogen-coated slides, after staining F-actin in platelets, the platelets were observed with the confocal microscopy. The effects of different concentrations of fibrinogen (10 µg/ml, 30 µg/ml, 100 µg/ml) and kinds of agonists ï¼»thrombin(0.01,0.05,0.1 U/ml), ADP（5,10,20 µmol/L）, U46619（0.125,0.25,0.5 µmol/L）］ on platelets were analyzed. The platelet spreading was successful if the spreading rate was higher after treated with agonists. RESULTS: Compared to the group which coated with 10 µg/ml and 100 µg/ml fibrinogen, the platelet density is optimal when coated with 30 µg/ml fibrinogen. In addition, under the stimulation of thrombin, ADP and U46619, the spreading rate of platelets showed a certain concentration-dependent increasing. CONCLUSION: The platelet spreading is easily influenced by various factors, the platelet spreading can be induced successfully at 0.1 U/ml thrombin, 20 µmol/L ADP and 0.5 µmol/L U46619 on the slide coated with 30 µg/ml fibrinogen.

Actin polymerization regulates glycoprotein Ibα shedding.

Glycoprotein (GP) Ibα shedding mediated by ADAM17 (a disintegrin and metalloproteinase 17) plays an important role in negatively regulating platelet function and thrombus formation. However, the mechanism of GPIbα shedding remains elusive. Here, we show that jasplakinolide (an actin-polymerizing peptide)-induced actin polymerization results in GPIbα shedding and impairs platelet function. Thrombin and A23187-induced GPIbα shedding is increased by jasplakinolide; in contrast, GPIbα shedding is reduced by a depolymerization regent (cytochalasin B). We find that actin polymerization activates calpain leading to filamin A hydrolyzation. We further demonstrate that the interaction of filamin A with the cytoplasmic domain of GPIbα plays a critical role in regulating actin polymerization-induced GPIbα shedding. Taken together, these data demonstrate that actin polymerization regulates ADAM17-mediated GPIbα shedding, suggesting a novel strategy to negatively regulate platelet function.

The binding of autotaxin to integrins mediates hyperhomocysteinemia-potentiated platelet activation and thrombosis in mice and humans.

Hyperhomocysteinemia (HHcy) is associated with an exaggerated platelet thrombotic response at sites of vascular injury. In this study, human medical examination showed that elevated human plasma Hcy levels correlated positively with enhanced blood coagulation and platelet activity, suggesting that humans with HHcy are more prone to thrombus formation at the sites of vascular injury. Accordingly, we observed accelerated platelet activation, primary hemostasis, and thrombus formation in apolipoprotein E-deficient (ApoE-/-) mice with acute or chronic HHcy. Upon homocysteine (Hcy) administration in C57BL/6J mice, platelet aggregation, spreading and clot retraction were markedly induced. More important, Hcy increased the affinity of platelet integrin αIIbß3 with ligands and enhanced integrin outside-in signaling by promoting membrane phosphatidylserine exposure in vitro. Mechanistically, lipidomics analysis showed that lysophosphatidylcholines were the primary metabolites leading to clustering of HHcy-stimulated platelets. Cytosolic phospholipase A2 (cPLA2) activity and autotaxin (ATX, a secreted lysophospholipase D) secretion were upregulated by Hcy, leading to membrane phospholipid hydrolysis and PS exposure. Moreover, secreted ATX directly interacted with integrin ß3. Inhibitors of cPLA2 and ATX activity blocked integrin αIIbß3 outside-in signaling and thrombosis in HHcy ApoE-/- mice. In this study, we identified a novel mechanism by which HHcy promotes platelet membrane phospholipid catabolism and extracellular ATX secretion to activate integrin outside-in signaling, consequently exacerbating thrombosis and the results revealed an innovative approach to treating HHcy-related thrombotic diseases.

Essential role of zyxin in platelet biogenesis and glycoprotein Ib-IX surface expression.

Platelets are generated from the cytoplasm of megakaryocytes (MKs) via actin cytoskeleton reorganization. Zyxin is a focal adhesion protein and wildly expressed in eukaryotes to regulate actin remodeling. Zyxin is upregulated during megakaryocytic differentiation; however, the role of zyxin in thrombopoiesis is unknown. Here we show that zyxin ablation results in profound macrothrombocytopenia. Platelet lifespan and thrombopoietin level were comparable between wild-type and zyxin-deficient mice, but MK maturation, demarcation membrane system formation, and proplatelet generation were obviously impaired in the absence of zyxin. Differential proteomic analysis of proteins associated with macrothrombocytopenia revealed that glycoprotein (GP) Ib-IX was significantly reduced in zyxin-deficient platelets. Moreover, GPIb-IX surface level was decreased in zyxin-deficient MKs. Knockdown of zyxin in a human megakaryocytic cell line resulted in GPIbα degradation by lysosomes leading to the reduction of GPIb-IX surface level. We further found that zyxin was colocalized with vasodilator-stimulated phosphoprotein (VASP), and loss of zyxin caused diffuse distribution of VASP and actin cytoskeleton disorganization in both platelets and MKs. Reconstitution of zyxin with VASP binding site in zyxin-deficient hematopoietic progenitor cell-derived MKs restored GPIb-IX surface expression and proplatelet generation. Taken together, our findings identify zyxin as a regulator of platelet biogenesis and GPIb-IX surface expression through VASP-mediated cytoskeleton reorganization, suggesting possible pathogenesis of macrothrombocytopenia.

Carbamazepine Induces Platelet Apoptosis and Thrombocytopenia Through Protein Kinase A.

Carbamazepine is extensively used worldwide to treat a wide range of disorders such as epilepsy, peripheral neuralgia and bipolar disorder. Thrombocytopenia and hemorrhage have been identified in multiple carbamazepine-treated patients. However, the underlying mechanism remains poorly understood. Here, we show that platelets undergo apoptosis after carbamazepine treatment. The apoptotic platelets induced by carbamazepine are rapidly removed in vivo, which accounts for thrombocytopenia. We found that carbamazepine treatment attenuates the phosphorylation level of bcl-xl/bcl-2-associated death promoter (BAD), vasodilator-associated stimulated phosphoprotein (VASP) and GPIbß in platelets, indicating an inhibition effect on protein kinase A (PKA). We further demonstrated that carbamazepine reduced PKA activity through PI3K/Akt/PDE3A signaling pathway. Pharmacological activation of PKA or inhibition of PI3K/Akt/PDE3A protects platelets from apoptosis induced by carbamazepine. Importantly, PDE3A inhibitors or PKA activator ameliorates carbamazepine-mediated thrombocytopenia in vivo. These findings shed light on a possible mechanism of carbamazepine-induced thrombocytopenia, designating PDE3A/PKA as a potential therapeutic target in the treatment of carbamazepine-induced thrombocytopenia.

Impact of supervised beego, a traditional Chinese water-only fasting, on thrombosis and haemostasis.

Beego is a traditional Chinese complete water-only fasting practice initially developed for spiritual purposes, later extending to physical fitness purposes. Beego notably includes a psychological induction component that includes meditation and abdominal breathing, light body exercise and ends with a specific gradual refeeding program before returning to a normal diet. Beego has regained its popularity in recent decades in China as a strategy for helping people in subhealthy conditions or with metabolic syndrome, but we are unaware of any studies examining the biological effects of this practice. To address this, we here performed a longitudinal study of beego comprising fasting (7 and 14 day cohorts) and a 7-day programmed refeeding phase. In addition to detecting improvements in cardiovascular physiology and selective reduction of blood pressure in hypertensive subjects, we observed that beego decreased blood triacylglycerol (TG) selectively in TG-high subjects and increased cholesterol in all subjects during fasting; however, the cholesterol levels were normalised after completion of the refeeding program. Strikingly, beego reduced platelet formation, activation, aggregation and degranulation, resulting in an alleviated thrombosis risk, yet maintained haemostasis by sustaining levels of coagulation factors and other haemostatic proteins. Mechanistically, we speculate that downregulation of G6B and MYL9 may influence the observed beego-mediated reduction in platelets. Fundamentally, our study supports that supervised beego reduces thrombosis risk without compromising haemostasis capacity. Moreover, our results support that beego under medical supervision can be implemented as non-invasive intervention for reducing thrombosis risk, and suggest several lines of intriguing inquiry for future studies about this fasting practice (http://www.chictr.org.cn/index.aspx, number, ChiCTR1900027451).

[The Role of Zyxin in Regulating Platelet Cytoskeleton Distribution].

OBJECTIVE: To investigate the regulatory effect of zyxin on the distribution of platelet cytoskeleton. METHODS: Platelets were isolated from zyxin-knockout (Zyx-/-) and wild type (WT) mice respectively and corresponding platelet cytoskeleton components were separated. The expressions of ß-actin, α-actinin, filamin A and myosin ⅡA in cytoskeleton components were detected by Western blot. Actin polymerization was induced by the actin polymerization inducer Jasplakinolide (Jas) in WT and Zyx-/- platelets. Also, the expressions of the cytoskeleton proteins in cytoskeleton components were detected by Western blot. WT and Zyx-/- platelets were allowed to spread on fibrinogen-coated surface. Platelet F-actin was labeled with Alexa Fluor 488-conjugated phalloidin and the fluorescent intensity was compared between WT and Zyx-/- platelets. RESULTS: After zyxin gene was knockout, the expressions of cytoskeleton proteins ß-actin, α-actinin, filamin A, and myosin Ⅱ A in resting and Jas-induced platelets were significantly increased. In the platelet spreading on fibrinogen surface, F-actin was increased in Zyx-/- platelets as compared with that in WT platelets. CONCLUSION: Zyxin significantly regulates the distribution of platelet cytoskeleton, which plays an important role in maintaining platelet cytoskeleton homeostasis.

Identification of seven tumor-educated platelets RNAs for cancer diagnosis.

BACKGROUND: Tumor-educated platelets (TEPs) may enable blood-based cancer diagnosis. This study aimed to identify diagnostic TEPs genes involved in carcinogenesis. MATERIALS AND METHODS: The TEPs differentially expressed genes (DEGs) between healthy samples and early/advanced cancer samples were obtained using bioinformatics. Gene ontology (GO) analysis and Kyoto encyclopedia of genes and genomes (KEGG) pathway enrichment analysis were used to identify the pathways and functional annotation of TEPs DEGs. Protein-protein interaction of these TEPs DEGs was analyzed based on the STRING database and visualized by Cytoscape software. The correlation analysis and diagnostic analysis were performed to evaluate the diagnostic value of TEPs mRNAs expression for early/advanced cancers. Quantitative real-time PCR (qRT-PCR) was applied to validate the role of DEGs in cancers. RESULTS: TEPs mRNAs were mostly involved in protein binding, extracellular matrix, and cellular protein metabolic process. RSL24D1 was negatively correlated to early-stage cancers compared to healthy controls and may be potentially used for early cancer diagnosis. In addition, HPSE, IFI27, LGALS3BP, CRYM, HBD, COL6A3, LAMB2, and IFITM3 showed an upward trend in the expression from early to advanced cancer stages. Moreover, ARL2, FCGR2A, and KLHDC8B were positively associated with advanced, metastatic cancers compared to healthy controls. Among the 12 selected DEGs, the expression of 7 DEGs, including RSL24D1, IFI27, CRYM, HBD, IFITM3, FCGR2A, and KLHDC8B, were verified by the qRT-PCR method. CONCLUSION: This study suggests that the 7-gene TEPs liquid-biopsy biomarkers may be used for cancer diagnosis and monitoring.

A novel method to detect autoantibodies against platelets in patients with immune thrombocytopenia.

BACKGROUND AND OBJECTIVES: To examine anti-platelet autoantibodies in patients with immune thrombocytopenia (ITP) not only provides solid evidence for diagnosis, and also helps to select an individualized strategy for the treatment. The aim of this study is to develop a novel cell-based assay to detect autoantibodies in ITP patients. METHODS/PATIENTS: The DNA sequences of human platelet membrane protein GPIbα, GPIbß, GP IX, GPIIb and GPIIIa subunits were obtained from NCBI database and synthesized. The synthetic fragments were ligated into pcDNA 3.3 and constructed the recombinant plasmids and transfected into Chinese hamster ovary (CHO) cells to establish cell lines stable expressing GPIb-IX and/or GPIIb/IIIa complexes. One hundred and two ITP patients with different anti-platelet autoantibodies, 57 patients with other kinds of autoimmune diseases and 104 healthy control were selected to examine sensitivity, specificity and accuracy of this method. RESULTS: CHO cells stable expressing GPIb-IX and/or GPIIb/IIIa proteins were established. The cells were fixed with 4% paraformaldehyde and stored at -80 ℃, more than 80% of the cells were still expressed target proteins after 180 days of storage. The concentrations of target antibody from 0.1 to 100 µg/ml were detectable by this method, and 10-50 µg/ml antibody binding to the CHO cells yielded higher distinguishable fluorescent intensities. Inter-assay and intra-assay coefficients of variation and receiver operating characteristic curve analysis showed that this method had relatively higher reproducibility and specificity. Compared with Flow Cytometric Immunobead Array, this method has relatively higher specificity (95.2%) and accuracy (90.8%) in detection of 102 ITP patients. CONCLUSION: A novel cell-based assay to detect autoantibodies in ITP patients is established, which appears to be a promising method to diagnose ITP.

[Inducing Effect of PKA Inhibitor at Different Concentrations on Platelet Apoptosis and Its Mechanism].

OBJECTIVE: To investigate the inducing effect of PKA inhibitor H89 of different concentrations on platelet apoptosis and its mechanism. METHODS: Platelets were isolated from peripheral venous blood of healthy volunteers. Different concentrations gradient PKA inhibitor H89 were co-incubated with washing platelets, and the effects of PKA inhibitor H89 at different concentrations on platelet mitochondrial membrane potential, phosphatidylserine and reactive oxygen species(ROS) were determined by ELISA and flow cytometry. RESULTS: Different concentration of PKA inhibitor H89 could induce the depolarization of mitochondrial membrane potential and PS exposure of platelet. However, high concentration(100 µmol/L) PKA inhibitor H89 could induce the production of ROS in platelets, but medium and low concentrations did not induce the production of ROS in platelets. And several ROS inhibitors could inhibit the apoptosis induced by high concentration PKA inhibitor H89. CONCLUSION: High concentration H89 can induce platelet apoptosis, however the mechanism of platelet apoptosis caused by H89 of high concentration is different from H89 at medium and low concentrations.

[Regulatory Role of Mitochondria in the Shedding of Platelet Membrane Protein GPIbα].

OBJECTIVE: To investigate the role of mitochonaria in the regulation of platelet membrane protein GPIbα shedding and its mechanisms. METHODS: The washed platelets were obtained from peripheral blood in healthy volunteers and co-incubated with mitochondrial inhibitor carbonyl cyanide m-chlorophenyl hydrazone (CCCP), mitochondrial protector cyclosporin A (CsA) or matrix metalloproteinases inhibitor GM6001. After the platelets was stimulated, the effect of mitochondria to the shedding in platelet membrane protein GPIbα was detected by flow cytometry. RESULTS: Depolarization of mitochondrial membrane potential and the respiratory function of mitochondrial could be induced and destroyed by the uncoupling agent CCCP. At the same time, the shedding of GPIbα was detected out, and the result showed a statistical significance, which showed that the shedding of GPIbα could be activated by the damaged of mitochondrial in platelets. After the mitochondrial was protected by CsA, the shedding of GPIbα was inhibited significantly. GM6001 could only inhibited the shedding of GPIbα, but showed no inhibitation to the function of mitochondrial, which showed that the shedding of GPIbα was regulated at the mitochondrial, and the regulatory enzyme of receptor shedding (ADAM17) was located in the pathway of downstream of mitochondria. After the oxidative damage in cells was inhibited by NAC, and the changes of GPIbα shedding was detected, the result showed that the GPIbα shedding could be inhibited by NAC, which showed a dose-dependent manner. CONCLUSION: The GPIbα shedding could be caused by abnormality function of metabolic, and the metabolic imbalance of ROS is caused by the abnormallity function of mitochondria.

[Effect of Protein Kinase A Activation on Aggregation Function of Platelets].

OBJECTIVE: To investigate the effect of protein kinase A (PKA) activation on aggregation funetion of platelets in vitro. METHODS: The peripheral blood of healthy adults were collected, and the washed platelets were gained from collected peripheral blood. The washed platelets were treated with PKA activator Forskolin, then the platelet aggregation was induced by using Ristocetin, Thrombin, Collagen and ADP respectively, the platelet aggregation level was detected by the platelet aggregator. RESULTS: Compared with the controls, 5 µmol/L forskolin significantly inhibited ADP and collagen-induced platelet aggregation (P＜0.001), and showed mild inhibiting effect on Thrombin-induced platelet aggregation (P＜0.05). 2.5-10 µmol/L forskolin significantly inhibited ADP and Collagen -induced platelet aggregation (P＜0.001); but not showed significantly inhibitory effects on Ristocetin-induced platelet aggregation (P＞0.05). CONCLUSION: PKA activation inhibits agonists-induced platelet aggregation.