Vasodilator-stimulated Phosphoprotein Phosphorylation Research Articles

418 The antiplatelet effects of EPA, an omega-3 fatty acid, are mediated by its 12-lipoxygenase metabolite, 12-HEPE

OBJECTIVES/GOALS: To determine whether cardioprotective effects observed in individuals taking dietary supplementation with eicosapentaenoic acid (EPA), an ω-3 polyunsaturated fatty acid, are realized by altering platelet function, and if these effects are mediated through the 12-lipoxygenase derived metabolite, 12-hydroxyeicosapentaenoic acid (12-HEPE). METHODS/STUDY POPULATION: Washed platelets or platelet rich plasma from healthy human donors were treated with EPA and 12-HEPE to assess their ability to inhibit platelet activation. Platelets were stimulated with agonists targeting different steps of the hemostatic response to vascular injury. Platelet aggregation, dense granule secretion, surface expression of integrin αIIbβ3 and P-selectin, and clot retraction were analyzed. To assess signaling through Gαs-GPCRs and protein kinase A activity, phosphorylation of vasodilator-stimulated phosphoprotein (VASP) was examined via western blot following treatment with EPA or 12-HEPE. RESULTS/ANTICIPATED RESULTS: EPA and 12-HEPE dose-dependently inhibit both collagen and thrombin-induced platelet aggregation. Furthermore, 12-HEPE more potently attenuates dense granule secretion and surface expression of platelet activation markers, integrin αIIbβ3 and P-selectin, in comparison to EPA. Plasma treated with EPA delayed thrombin-induced clot retraction, while 12-HEPE had no effect. Additionally, treatment with 12-HEPE increases phosphorylation of VASP, suggesting it could signal through the activation of the eicosanoid Gαs-GPCRs. DISCUSSION/SIGNIFICANCE: Here, we show for the first time that EPA directly inhibits platelet activation through its 12-LOX metabolite, 12-HEPE. These findings provide further insight into the mechanisms underlying the cardioprotective effects of EPA. A better understanding of current PUFA supplementations can inform treatment and prevention of cardiovascular diseases.

The focal adhesion protein talin is a mechanically gated A-kinase anchoring protein

Protein kinase A (PKA) is a ubiquitous, promiscuous kinase whose activity is specified through subcellular localization mediated by A-kinase anchoring proteins (AKAPs). PKA has complex roles as both an effector and a regulator of integrin-mediated cell adhesion to extracellular matrix (ECM). Recent observations demonstrate that PKA is an active component of focal adhesions (FA), suggesting the existence of one or more FA AKAPs. Using a promiscuous biotin ligase fused to PKA type-IIα regulatory (RIIα) subunits and subcellular fractionation, we identify the archetypal FA protein talin1 as an AKAP. Talin is a large, mechanosensitive scaffold that directly links integrins to actin filaments and promotes FA assembly by recruiting additional components in a force-dependent manner. The rod region of talin1 consists of 62 α-helices bundled into 13 rod domains, R1 to R13. Direct binding assays and NMR spectroscopy identify helix41 in the R9 subdomain of talin as the PKA binding site. PKA binding to helix41 requires unfolding of the R9 domain, which requires the linker region between R9 and R10. Experiments with single molecules and in cells manipulated to alter actomyosin contractility demonstrate that the PKA-talin interaction is regulated by mechanical force across the talin molecule. Finally, talin mutations that disrupt PKA binding also decrease levels of total and phosphorylated PKA RII subunits as well as phosphorylation of VASP, a known PKA substrate, within FA. These observations identify a mechanically gated anchoring protein for PKA, a force-dependent binding partner for talin1, and a potential pathway for adhesion-associated mechanotransduction.

CS585 Demonstrates Favorable Selectivity and Sustained In Vivo Action in Preventing Platelet Activation and Thrombosis Compared to Existing IP Receptor Agonists

Anti-platelet therapeutics are common tools in the treatment of thrombotic diseases, decreasing morbidity and mortality resulting from cardiovascular complications. However, many patients remain at risk for a cardiovascular event while others experience bleeding due to hemostatic dysregulation. The need for target specificity and lasting stability presents a major challenge in the development of novel antithrombotic therapeutics. While increasing platelet cAMP levels through activation of the prostacyclin (IP) receptor is a viable therapeutic approach, the IP receptor is currently considered a challenging target due to the non-selectivity and instability of existing IP agonists. Our lab has developed a novel IV and orally available IP receptor agonist, CS585, with selectivity towards the IP receptor and sustained in vivo protection from injury-induced thrombosis without observed bleeding. CS585 demonstrates IP receptor-dependent activity, leading to activation of protein kinase A (PKA), a key player in inhibitory signaling. While indications of current IP receptor agonists are limited to pulmonary arterial hypertension and temporary relief of peripheral artery disease, CS585 presents a new approach to selectively regulate platelet activation and thrombosis. CS585 and other IP receptor agonists, iloprost and selexipag, were assessed by direct comparison to elucidate potential differences in selectivity and sustained action. Selectivity was determined using aggregation and VASP phosphorylation. The effects of CS585 are inhibited by pharmacological inhibition of the IP receptor, but not by inhibition of the DP1, EP2, or EP4 prostaglandin receptors. Meanwhile, the activities of iloprost and selexipag were affected by other prostaglandin inhibitors, supporting the improved selectivity toward activation of the IP receptor with CS585. Arterial thrombosis was measured and quantified in a laser-induced cremaster thrombosis assay in IP agonist-treated WT mice to assess platelet activation and thrombus formation in vivo in mouse models of thrombosis. In WT mice treated with CS585, we observed sustained effects of CS585 following both IV and oral administration. Platelets and fibrin were labeled and accumulation at the site of injury was measured using intravital microscopy. In contrast to the FDA-approved IP receptor agonists (iloprost and selexipag) which showed short-term protection from thrombosis, treatment with CS585 resulted in sustained inhibition of clot and fibrin formation at the site of injury in the same model between 24 and 48 hours post-administration. To determine if the anti-thrombotic effects of CS585 impact coagulation, coagulation parameters were assessed in whole blood using thromboelastography (TEG). Treatment with CS585 did not impact coagulation parameters in whole blood, while a significant increase in lysis was observed with iloprost. Here, we show for the first time a head-to-head comparison of CS585, a novel IP receptor agonist, with selexipag and iloprost. Our preclinical results with CS585 indicate a favorable profile for inhibiting platelet activation and clot formation and demonstrate a sustained duration of action in mice in the ability of CS585 to inhibit platelet activation through multiple routes of administration. Importantly, CS585 does not affect coagulation parameters and previous studies demonstrated no potential for increased bleeding in mouse models. Overall, CS585 provides a new option of activating the IP receptor to decrease platelet reactivity and could represent the first viable option for targeting the IP receptor on platelets for primary inhibition of thrombosis with a reduced risk of bleeding.

Direct and indirect effects of Puumala hantavirus on platelet function

Thrombocytopenia is a cardinal symptom of hantavirus-induced diseases including Puumala virus (PUUV)-induced hemorrhagic fever with renal syndrome (HFRS), which is associated with impaired platelet function, bleeding manifestations and augmented thrombotic risk. However, the underlying mechanisms causing thrombocytopenia and platelet hypo-responsiveness are unknown. Thus, we investigated the direct and indirect impact of PUUV on platelet production, function and degradation.Analysis of PUUV-HFRS patient blood revealed that platelet hypo-responsiveness in PUUV infection was cell-intrinsic and accompanied by reduced platelet-leukocyte aggregates (PLAs) and upregulation of monocyte tissue factor (TF), whereas platelet vasodilator-stimulated phosphoprotein (VASP) phosphorylation was comparable to healthy controls. Plasma CXCL4 levels followed platelet count dynamics throughout disease course. PUUV activated both neutrophils and monocytes in vitro, but platelet desialylation, degranulation and GPIIb/IIIa activation as well as PLA formation and endothelial adhesion under flow remained unaltered in the presence of PUUV. Further, MEG-01 megakaryocytes infected with PUUV displayed unaltered polyploidization, expression of surface receptors and platelet production. However, infection of endothelial cells with PUUV significantly increased platelet sequestration.Our data thus demonstrate that although platelet production, activation or degradation are not directly modulated, PUUV indirectly fosters thrombocytopenia by sequestration of platelets to infected endothelium. Upregulation of immunothrombotic processes in PUUV-HFRS may further contribute to platelet dysfunction and consumption. Given the pathophysiologic similarities of hantavirus infections, our findings thus provide important insights into the mechanisms underlying thrombocytopenia and highlight immune-mediated coagulopathy as potential therapeutic target.

Superiority of CS585 as a selective prostacyclin receptor agonist in prevention of thrombosis

Abstract Background A major challenge with development of new targets for antithrombotic treatment is the sustained effect on the platelet and the target selectivity. While increasing cAMP in the platelet through activation of the prostacyclin (IP) receptor represents a viable antiplatelet target for prevention of thrombosis, current IP receptor agonists lack stability and selectivity. Development of a selective IP receptor agonist that is stable in the blood and selective for the IP receptor would represent a new approach for prevention of platelet activation and thrombosis in the blood and expand the utility of IP receptor agonists which are currently used for the treatment of pulmonary arterial hypertension (PAH). Purpose Develop an IV and oral IP receptor agonist, CS585, with sustained activity in vivo in the blood and eliminating the off-target effects observed with other IP agonists not having selective activation of the IP receptor. These characteristics would make CS585 an attractive new therapeutic approach for limiting platelet activation and thrombosis. Methods We assessed platelet activation and thrombosis in human blood ex vivo and mouse models in vivo. For mouse models, platelets and fibrin were labelled and accumulation at the site of injury was measured using intravital microscopy. Thrombosis in the vessel was assessed in the laser-induced cremaster thrombosis assay. Selectivity was assessed in human blood pharmacologically using prostaglandin receptor inhibitors and in mouse with an IP receptor knockout mouse. Flow cytometry, aggregometry, and western blot techniques were used to assess selectivity. Results IV and oral administration of CS585 resulted in sustained inhibited clot formation and fibrin formation at the site of injury in the laser-induced cremaster arteriole thrombosis assay in wild-type mice but was unable to alter platelet function in IP knockout mice. CS585 inhibition of platelet activation was fully prevented in platelets from IP knockout mice as assessed by flow cytometry (integrin activation and granule secretion) and by VASP phosphorylation. Inhibition of human platelet activation by CS585 was inhibited by pharmacological inhibition of the IP receptor, but not by inhibition of the DP1, EP2, or EP4 receptors as assessed by aggregation, flow cytometry, and VASP phosphorylation. Conclusions We have shown for the first time that CS585, a novel IP receptor agonist, not only inhibits platelet activation and clot formation, but gives sustained inhibition through multiple routes of administration in an in vivo mouse model of thrombosis. Importantly, the challenge in selectivity observed with other IP receptor agonists is not observed with CS585 supporting its development for a number of diseases in the cardiovascular system including thrombosis, VTE, secondary prevention after MI and stroke, and PAH.CS585 inhibition of thrombosis in vivoCS585 selectively signals through IP

Paracrine cardioprotective signaling by red blood cells through hypoxia-mediated activation of soluble guanylate cyclase and release of cyclic guanosine monophosphate

Abstract Background Red blood cells (RBCs) are known to regulate cardiovascular function under hypoxic conditions and to mediate cardioprotection via nitric oxide (NO)-like bioactivity. However, the molecular signalling behind this effect and the identity of any mediator released by the RBCs remain unknown. Previous studies revealed that NO activates soluble guanylate cyclase (sGC) and increases formation of the second messenger cyclic guanosine monophosphate (cGMP) in RBCs. The functional role of this signalling in RBCs during hypoxia/ischemia is still unclear. Aim To determine the functional role of the NO-sGC-cGMP signalling pathway in RBCs during hypoxia and myocardial ischemia. Method RBCs collected from wild-type and sGC knockout mice were exposed to 1% hypoxia or normoxia for 1 h. The RBCs or the extracellular supernatant were then administered to isolated Langendorff-perfused mouse hearts subjected to 40 min global ischemia and 60 min reperfusion. Afterwards, left ventricular developed pressure and infarct size were determined. Additional groups of mice and patients with mild hypertension were given oral nitrate (10mM in their drinking water) before the collection of RBCs to further increase NO signalling. Result Administration of RBCs or the extracellular supernatant collected from wild-type mouse RBCs exposed to hypoxia to isolated hearts subjected to ischemia-reperfusion improved post-ischemic cardiac function and reduced infarct size (Fig. 1A and B). By contrast, supernatant collected from hypoxic RBCs of sGC knockout mice failed to induce cardioprotection (Fig. 1C). The cardioprotection induced by hypoxic RBCs of wild-type mice was blocked by MK571, an inhibitor of cyclic nucleotide transport (Fig. 1D). Hypoxia increased extracellular export of hate cGMP from mouse RBCs (Fig. 1E), and exogenous cGMP resulted in similar cardioprotection induced by the supernatant. The cardioprotective effect of RBCs was blocked by an inhibitor of cardiac cGMP-dependent protein kinase G (PKG) (Fig. 1F) and was associated with increased cardiac PKG-dependent phosphorylation of vasodilator-stimulated phosphoprotein. Oral administration of nitrate to mice for 4 weeks to increase NO bioactivity further enhanced the cardioprotective effect of hypoxic RBCs. RBCs collected from patients randomized to a 5-week nitrate-rich diet induced cardioprotection in the isolated rat heart via an effect dependent on sGC activation in the RBCs (Fig 2). Conclusion RBCs generate and export cGMP as a physiological response to hypoxia mediating cardioprotection via a paracrine effect. This effect can be further augmented by a simple dietary intervention with nitrate suggesting preventive and therapeutic opportunities in ischemic heart disease.Figure 1Figure 2

PKCζ phosphorylates VASP to mediate chemotaxis in breast cancer cells

Breast carcinoma (BC) is one of the most common malignant cancers in females, and metastasis remains the leading cause of death in these patients. Chemotaxis plays an important role in cancer cell metastasis and the mechanism of breast cancer chemotaxis has become a central issue in contemporary research. PKCζ, a member of the atypical PKC family, has been reported to be an essential component of the EGF-stimulated chemotactic signaling pathway. However, the molecular mechanism through which PKCζ regulates chemotaxis remains unclear. Here, we used a proteomic approach to identify PKCζ-interacting proteins in breast cancer cells and identified VASP as a potential binding partner. Intriguingly, stimulation with EGF enhanced this interaction and induced the translocalization of PKCζ and VASP to the cell membrane. Further experiments showed that PKCζ catalyzes the phosphorylation of VASP at Ser157, which is critical for the biological function of VASP in regulating chemotaxis and actin polymerization in breast cancer cells. Furthermore, in PKCζ knockdown BC cells, the enrichment of VASP at the leading edge was reduced, and its interaction with profilin1 was attenuated, thereby reducing the chemotaxis and overall motility of breast cancer cells after EGF treatment. In functional assays, PKCζ promoted chemotaxis and motility of BC cells through VASP. Our findings demonstrate that PKCζ, a new kinase of VASP, plays an important role in promoting breast cancer metastasis and provides a theoretical basis for expanding new approaches to tumor biotherapy.

Increased Responsiveness of Stored Platelets after Short-Term Refrigeration

Introduction: Refrigeration of platelets is considered to provide advantages in therapy of acute hemorrhage due to increased platelet responsiveness. The alleviation of inhibitory signaling caused by cold temperature (CT) has been identified as an important mechanism contributing to enhanced platelet reactivity, detectable in freshly prepared platelets within 1 h of cold storage. The aim of this study was to confirm the effects of short-term refrigeration in platelets from apheresis-derived platelet concentrates (APC). Methods: APC were stored under standardized conditions for 1 day or for 2 days at room temperature and then refrigerated for 1 h, followed by sampling of platelets for analysis. Platelet reactivity was measured by aggregation studies using threshold concentrations of different agonists and by detection of fibrinogen binding using flow cytometry. The exploration of inhibitory signaling comprised the detection of VASP phosphorylation using flow cytometry or Western blot and the measurement of cyclic nucleotide levels. Results: Aggregation responses induced with ADP, collagen, or thrombin receptor-activating peptide-6 (TRAP-6) were increased in APC after cold storage for 1 h, associated with elevated TRAP-6-induced fibrinogen binding. VASP phosphorylation levels were decreased after cold exposition, detectable in 1-day- and 2-day-stored APC with flow cytometry, and in 2-day-stored APC with Western blot technique. Induced cGMP levels were lower after storage at CT in APC on day 1 and on day 2, whereas cAMP levels were reduced on 2-day-stored APC. Conclusion: Short-term refrigeration for 1 h is sufficient to induce an attenuation of inhibitory signaling, accompanied with increased aggregation responses in APC stored for up to 2 days. The “on demand” refrigeration of PC may be a reasonable approach for the preparation of platelets with enhanced responsiveness to treat patients with hemorrhage more effectively, which should be further addressed in consecutive studies.

Oncogenic BRAF noncanonically promotes tumor metastasis by mediating VASP phosphorylation and filopodia formation.

BRAF is frequently mutated in various cancer types and contributes to tumorigenesis and metastasis. As an important switch in RAS signaling pathway, BRAF typically enables the activation of MEK and ERK, and its mutation significantly promotes metastasis. However, whether BRAF could stimulate metastasis via a distinct manner is still unknown. Herein, we found that a portion of the BRAF protein localized at the plasma membrane and that the BRAFV600E mutation led to abundant formation of filopodia, which is a hallmark of invasive cancer cells. Mechanistically, BRAF physically interacts with the pseudopod formation-related protein Vasodilator-stimulated phosphoprotein (VASP), and BRAF specifically catalyzes VASP phosphorylation at Ser157. VASP depletion or disruption of Ser157 phosphorylation preferentially reduced the motility, invasion and metastasis of tumor cells harboring oncogenic BRAF or KRAS. Moreover, in clinical cancer tissues, BRAFV600E was positively correlated with the extent of invasion, and tissues with BRAFV600E expression exhibited elevated levels of VASP Ser157 phosphorylation. Our study therefor reveals a noncanonical mechanism by which oncogenic BRAF or KRAS promotes metastasis, suggests that VASP Ser157 phosphorylation might serve as a valuable therapeutic target in BRAF or KRAS mutant cancers.

Prorelaxant E-type Prostanoid Receptors Functionally Partition to Different Procontractile Receptors in Airway Smooth Muscle.

Prostaglandin E2 imparts diverse physiological effects on multiple airway cells through its actions on four distinct E-type prostanoid (EP) receptor subtypes (EP1-EP4). Gs-coupled EP2 and EP4 receptors are expressed on airway smooth muscle (ASM), yet their capacity to regulate the ASM contractile state remains subject to debate. We used EP2 and EP4 subtype-specific agonists (ONO-259 and ONO-329, respectively) in cell- and tissue-based models of human ASM contraction-magnetic twisting cytometry (MTC), and precision-cut lung slices (PCLSs), respectively-to study the EP2 and EP4 regulation of ASM contraction and signaling under conditions of histamine or methacholine (MCh) stimulation. ONO-329 was superior (<0.05) to ONO-259 in relaxing MCh-contracted PCLSs (log half maximal effective concentration [logEC50]: 4.9 × 10-7 vs. 2.2 × 10-6; maximal bronchodilation ± SE, 35 ± 2% vs. 15 ± 2%). However, ONO-259 and ONO-329 were similarly efficacious in relaxing histamine-contracted PCLSs. Similar differential effects were observed in MTC studies. Signaling analyses revealed only modest differences in ONO-329- and ONO-259-induced phosphorylation of the protein kinase A substrates VASP and HSP20, with concomitant stimulation with MCh or histamine. Conversely, ONO-259 failed to inhibit MCh-induced phosphorylation of the regulatory myosin light chain (pMLC20) and the F-actin/G-actin ratio (F/G-actin ratio) while effectively inhibiting their induction by histamine. ONO-329 was effective in reversing induced pMLC20 and the F/G-actin ratio with both MCh and histamine. Thus, the contractile-agonist-dependent differential effects are not explained by changes in the global levels of phosphorylated protein kinase A substrates but are reflected in the regulation of pMLC20 (cross-bridge cycling) and F/G-actin ratio (actin cytoskeleton integrity, force transmission), implicating a role for compartmentalized signaling involving muscarinic, histamine, and EP receptor subtypes.

Daidzein Inhibits Human Platelet Activation by Downregulating Thromboxane A2 Production and Granule Release, Regardless of COX-1 Activity.

Platelets play crucial roles in cardiovascular diseases (CVDs) by regulating hemostasis and blood coagulation at sites of blood vessel damage. Accumulating evidence indicates daidzein inhibits platelet activation, but the mechanism involved has not been elucidated. Thus, in this study, we investigated the mechanism responsible for the inhibition of collagen-induced platelet aggregation by daidzein. We found that in collagen-induced platelets, daidzein suppressed the production of thromboxane A2 (TXA2), a molecule involved in platelet activation and aggregation, by inhibiting the cytosolic phospholipase A2 (cPLA2) signaling pathway. However, daidzein did not affect cyclooxygenase-1 (COX-1). Furthermore, daidzein attenuated the PI3K/PDK1/Akt/GSK3αβ and MAPK (p38, ERK) signaling pathways, increased the phosphorylation of inositol trisphosphate receptor1 (IP3R1) and vasodilator-stimulated phosphoprotein (VASP), and increased the level of cyclic adenosine monophosphate (cAMP). These results suggest that daidzein inhibits granule release (ATP, serotonin, P-selectin), integrin αIIbβ3 activation, and clot retraction. Taken together, our study demonstrates that daidzein inhibits collagen-induced platelet aggregation and suggests that daidzein has therapeutic potential for the treatment of platelet aggregation-related diseases such as atherosclerosis and thrombosis.

Systemic Review of Clot Retraction Modulators.

Through a process termed clot retraction, platelets cause thrombi to shrink and become more stable. After platelets are activated via inside-out signaling, glycoprotein αIIbβIII binds to fibrinogen and initiates a cascade of intracellular signaling that ends in actin remodeling, which causes the platelet to change its shape. Clot retraction is also important for wound healing. Although the detailed molecular biology of clot retraction is only partially understood, various substances and physiological conditions modulate clot retraction. In this review, we describe some of the current literature pertaining to clot retraction modulators. In addition, we discuss compounds from Cudrania trucuspidata, Arctium lappa, and Panax ginseng that diminish clot retraction and have numerous other health benefits. Caffeic acid and diindolylmethane, both common in plants and vegetables, likewise reduce clot retraction, as do all-trans retinoic acid (a vitamin A derivative), two MAP4K inhibitors, and the chemotherapeutic drug Dasatinib. Conversely, the endogenous anticoagulant Protein S (PS) and the matricellular protein secreted modular calcium-binding protein 1 (SMOC1) both enhance clot retraction. Most studies aiming to identify mechanisms of clot retraction modulators have focused on the increased phosphorylation of vasodilator-stimulated phosphoprotein and inositol 1,4,5-triphosphate receptor I and the decreased phosphorylation of various phospholipases (e.g., phospholipase A2 (PLA2) and phosphatidylinositol-specific phospholipase Cγ2 (PLCγ2), c-Jun N-terminal kinase, and (PI3Ks). One study focused on the decreased phosphorylation of Sarcoma Family Kinases (SFK), and others have focused on increased cAMP levels and the downregulation of inflammatory markers such as thromboxanes, including thromboxane A2 (TXA2) and thromboxane B2 (TXB2); prostaglandin A2 (PGE2); reactive oxygen species (ROS); and cyclooxygenase (COX) enzyme activity. Additionally, pregnancy, fibrinolysis, and the autoimmune condition systemic lupus erythematosus all seem to affect, or at least have some relation with, clot retraction. All the clot retraction modulators need in-depth study to explain these effects.

Crosstalk between diacylglycerol kinase and protein kinase A in the regulation of airway smooth muscle cell proliferation

BackgroundDiacylglycerol kinase (DGK) regulates intracellular signaling and functions by converting diacylglycerol (DAG) into phosphatidic acid. We previously demonstrated that DGK inhibition attenuates airway smooth muscle (ASM) cell proliferation, however, the mechanisms mediating this effect are not well established. Given the capacity of protein kinase A (PKA) to effect inhibition of ASM cells growth in response to mitogens, we employed multiple molecular and pharmacological approaches to examine the putative role of PKA in the inhibition of mitogen-induced ASM cell proliferation by the small molecular DGK inhibitor I (DGK I).MethodsWe assayed cell proliferation using CyQUANT™ NF assay, protein expression and phosphorylation using immunoblotting, and prostaglandin E2 (PGE2) secretion by ELISA. ASM cells stably expressing GFP or PKI-GFP (PKA inhibitory peptide-GFP chimera) were stimulated with platelet-derived growth factor (PDGF), or PDGF + DGK I, and cell proliferation was assessed.ResultsDGK inhibition reduced ASM cell proliferation in cells expressing GFP, but not in cells expressing PKI-GFP. DGK inhibition increased cyclooxygenase II (COXII) expression and PGE2 secretion over time to promote PKA activation as demonstrated by increased phosphorylation of (PKA substrates) VASP and CREB. COXII expression and PKA activation were significantly decreased in cells pre-treated with pan-PKC (Bis I), MEK (U0126), or ERK2 (Vx11e) inhibitors suggesting a role for PKC and ERK in the COXII-PGE2-mediated activation of PKA signaling by DGK inhibition.ConclusionsOur study provides insight into the molecular pathway (DAG-PKC/ERK-COXII-PGE2-PKA) regulated by DGK in ASM cells and identifies DGK as a potential therapeutic target for mitigating ASM cell proliferation that contributes to airway remodeling in asthma.

Characterization of 2 Novel Phosphodiesterase 2 Inhibitors Hcyb1 and PF-05180999 on Depression- and Anxiety-Like Behavior.

Phosphodiesterase 2A (PDE2A) represents a novel target for new therapies addressing psychiatric disorders. To date, the development of PDE2A inhibitors suitable for human clinical evaluation has been hampered by the poor brain accessibility and metabolic stability of the available compounds. Corticosterone (CORT)-induced neuronal cell lesion and restraint stress mouse model were used to measure the neuroprotective effect in cells and antidepressant-like behavior in mice. The cell-based assay showed that both Hcyb1 and PF were potent in protecting cells against stress hormone CORT insults by stimulating cAMP and cGMP signaling in hippocampal cells (HT-22). Administration of both compounds before treatment of CORT to cells increased cAMP/cGMP, VASP phosphorylation at Ser239 and Ser157, cAMP response element binding protein phosphorylation at Ser133, and brain derived neurotrophic factor BDNF expression. Further in vivo study showed that both Hcyb1 and PF displayed -antidepressant- and anxiolytic-like effects against restraint stress as indicated by reduced immobility time in the forced swimming and tail suspension tasks as well as increased open arm entries and time spent in open arms and holes visit in elevated plus maze and hole-board tests, respectively. The biochemical study confirmed that these antidepressant- and anxiolytic-like effects of Hcyb1 and PF were related to cAMP and cGMP signaling in the hippocampus. The results extend the previous studies and validate that PDE2A is a tractable target for drug development in the treatment of emotional disorders such as depression and anxiety.

Anti-thrombotic effects of ginsenoside Rk3 by regulating cAMP and PI3K/MAPK pathway on human platelets

Background and objectiveThe ability to inhibit aggregation has been demonstrated with synthetically derived ginsenoside compounds G-Rp (1, 3, and 4) and ginsenosides naturally found in Panax ginseng 20(S)-Rg3, Rg6, F4, and Ro. Among these compounds, Rk3 (G-Rk3) from Panax ginseng needs to be further explored in order to reveal the mechanisms of action during inhibition. MethodologyOur study focused to investigate the action of G-Rk3 on agonist-stimulated human platelet aggregation, inhibition of platelet signaling molecules such as fibrinogen binding with integrin αIIbβ3 using flow cytometry, intracellular calcium mobilization, dense granule secretion, and thromboxane B2 secretion. In addition, we checked the regulation of phosphorylation on PI3K/MAPK pathway, and thrombin-induced clot retraction was also observed in platelets rich plasma. Key ResultsG-Rk3 significantly increased amounts of cyclic adenosine monophosphate (cAMP) and led to significant phosphorylation of cAMP-dependent kinase substrates vasodilator-stimulated phosphoprotein (VASP) and inositol 1,4,5-trisphosphate receptor (IP3R). In the presence of G-Rk3, dense tubular system Ca2+ was inhibited, and platelet activity was lowered by inactivating the integrin αIIb/β3 and reducing the binding of fibrinogen. Furthermore, the effect of G-Rk3 extended to the inhibition of MAPK and PI3K/Akt phosphorylation resulting in the reduced secretion of intracellular granules and reduced production of TXA2. Lastly, G-Rk3 inhibited platelet aggregation and thrombus formation via fibrin clot. Conclusions and implicationsThese results suggest that when dealing with cardiovascular diseases brought upon by faulty aggregation among platelets or through the formation of a thrombus, the G-Rk3 compound can play a role as an effective prophylactic or therapeutic agent.

Identification of High Platelet Reactivity Despite ADP P2Y12 Inhibitor Treatment: Two Populations in the Vasodilator-Stimulated Phosphoprotein Assay and Variable PFA-P2Y Shapes of Curve

Introduction Response to ADP P2Y12 receptor inhibition by clopidogrel can be evaluated by various techniques. Here, we compared a functional rapid point-of-care technique (PFA-P2Y) with the degree of biochemical inhibition assessed by the VASP/P2Y12 assay. Methods Platelet response to clopidogrel was investigated in 173 patients undergoing elective intracerebral stenting (derivation cohort n = 117; validation cohort n = 56). High platelet reactivity (HPR) was defined as PFA-P2Y occlusion time &lt;106 seconds or VASP/P2Y12 platelet reactivity index (PRI) &gt;50%. Results In the derivation cohort, receiver operator characteristics analysis for the ability of PFA-P2Y to detect biochemical HPR showed high specificity (98.4%) but poor sensitivity (20.0%) and a very low area under the curve (0.59). The VASP/P2Y12 assay revealed two coexisting platelet populations with different levels of vasodilator-stimulated phosphoprotein (VASP) phosphorylation: a fraction of highly phosphorylated, inhibited platelets and another of poorly phosphorylated, reactive platelets. Analysis of the PFA-P2Y curve shape revealed different types, categorized by time of occlusion (&lt;106 seconds, 106 to 300 seconds, &gt;300 seconds), and pattern (regular, irregular, and atypical). Noteworthy, curves with late occlusion and permeable curves with an irregular or atypical pattern correlated with VASP-PRI &gt;50% and smaller sizes of the inhibited platelet subpopulation. Considering the PFA-P2Y shape of the curve for the detection of HPR improved sensitivity (72.7%) and preserved specificity (91.9%), with a rather high AUC (0.823). The validation cohort confirmed the VASP/P2Y12 assay data and the usefulness of considering the PFA-P2Y curve shape. Conclusion In patients treated with acetylsalicylic acid and clopidogrel for 7-10 days, the VASP/P2Y12 assay reveals two coexisting subpopulations of differentially inhibited platelets, whose relative sizes predict global PRI and distinct PFA-P2Y curve patterns, indicating incomplete clopidogrel efficacy. The detailed analysis of both VASP/P2Y12 and PFA-P2Y is necessary for optimal detection of HPR.

Bioactive Nanogels Mimicking the Antithrombogenic Nitric Oxide-Release Function of the Endothelium.

Nitric oxide (NO) plays a significant role in controlling the physiology and pathophysiology of the body, including the endothelial antiplatelet function and therefore, antithrombogenic property of the blood vessels. This property of NO can be exploited to prevent thrombus formation on artificial surfaces like extracorporeal membrane oxygenators, which when come into contact with blood lead to protein adsorption and thereby platelet activation causing thrombus formation. However, NO is extremely reactive and has a very short biological half-life in blood, so only endogenous generation of NO from the blood contacting material can result into a stable and kinetically controllable local delivery of NO. In this regards, highly hydrophilic bioactive nanogels are presented which can endogenously generate NO in blood plasma from endogenous NO-donors thereby maintaining a physiological NO flux.It is shown that NO releasing nanogels could initiate cGMP-dependent protein kinase signaling followed by phosphorylation of vasodilator-stimulated phosphoprotein in platelets. Thisprevents platelet activation and aggregation even in presence of highly potent platelet activators like thrombin, adenosine 5'-diphosphate, and U46619 (thromboxane A2 mimetic).

Vasoactive intestinal peptide receptor 2 signaling promotes breast cancer cell proliferation by enhancing the ERK pathway

Vasoactive intestinal peptide (VIP) receptor 2 (VIPR2) is a class B G protein-coupled receptor with the neuropeptide VIP as a ligand. Increased VIPR2 mRNA expression and/or VIPR2 gene copy number has been documented in several cancers including breast carcinoma. However, the pathophysiological role of increased VIPR2 in the proliferation of breast cancer cells remains largely unknown. In this study, we found that VIPR2 overexpression in MCF-7 and MDA-MB-231 cells, human breast cancer cell lines, promoted cell proliferation. Increased VIPR2 also exacerbated intraperitoneal proliferation of breast cancer MDA-MB-231 cells in a tumor nude mouse model in vivo. Treatment with KS-133, a VIPR2-selective antagonist peptide, significantly inhibited VIP-induced cell proliferation in VIPR2-overexpressing MCF-7 and MDA-MB-231 cells. Overexpressed VIPR2 caused increases in the levels of cAMP and phosphorylated extracellular signal-regulated kinase (ERK), which involves a VIPR2 signaling pathway through Gs protein. Additionally, phosphorylation of vasodilator-stimulated phosphoprotein (Ser157) and cAMP response element binding protein (Ser133) in VIPR2-overexpressing MCF-7 cells was greater than that in control cells, suggesting the increased PKA activity. Moreover, an inhibitor of mitogen-activated protein kinase kinase, U0126, attenuated tumor proliferation in exogenous VIPR2-expressing MCF-7 and MDA-MB-231 cells at the same level as observed in EGFP-expressing cells treated with U0126. Together, these findings suggest that VIPR2 controls breast tumor growth by regulating the cAMP/PKA/ERK signaling pathway, and the excessive expression of VIPR2 may lead to an exacerbation of breast carcinoma.

High On-Treatment Platelet Reactivity in Patients Undergoing Complex Percutaneous Coronary Interventions.

Patient response to P2Y12 inhibitor therapy is heterogeneous, and those with high on-treatment platelet reactivity (HTPR) are at an increased risk of thrombotic complications. The aim of our study was to determine whether selecting a high-risk patient group of individuals after complex percutaneous coronary intervention (PCI) would show the clinical benefit of HTPR testing for preventing thrombotic complications. Blood samples of patients after complex PCI were acquired 1 day and 1 month after the intervention. The samples were tested using vasodilator-stimulated phosphoprotein phosphorylation (VASP-P) and platelet function assay (PFA). The occurrence of clinically significant stent thrombosis with repeated revascularization of the target vessel was observed over a 1-year period. One day after PCI, 37% of patients had HTPR as established by VASP-P. One month after PCI, the percentage of patients with HTPR decreased to 30.9%. According to PFA, 1 day after PCI, 33.3% of patients had HTPR. This percentage declined to 19.8% after 1 month. All measurements identified a significantly higher proportion of HTPR in patients on clopidogrel compared to ticagrelor and prasugrel. Two cases of early stent thrombosis and 1 case of late stent thrombosis were identified. Further study of adenosine diphosphate receptor blocker on-treatment response in patients undergoing complex PCI is necessary.

Impaired Platelet Function and Thrombus Formation in PDE5A-Deficient Mice.

Intracellular cyclic GMP (cGMP) inhibits platelet function. Platelet cGMP levels are controlled by phosphodiesterase 5A (PDE5A)-mediated degradation. However, the exact role of PDE5A in platelet function and thrombus formation remains poorly understood. In this study, we characterized the role of PDE5A in platelet activation and function. Platelets were isolated from wild type or PDE5A-/- mice to measure platelet aggregation, activation, phosphatidylserine exposure (annexin-V binding), reactive oxygen species (ROS) generation, platelet spreading as well as clot retraction. Cytosolic calcium mobilization was measured using Fluo-4 AM by a microplate reader. Western blot was used to measure the phosphorylation of VASP, ERK1/2, p38, JNK, and AKT. FeCl3-induced arterial thrombosis and venous thrombosis were assessed to evaluate the in vivo hemostatic function and thrombus formation. Additionally, in vitro thrombus formation was assessed in a microfluidic whole-blood perfusion assay. PDE5A-deficient mice presented significantly prolonged tail bleeding time and delayed arterial and venous thrombus formation. PDE5A deficiency significantly inhibited platelet aggregation, ATP release, P-selectin expression, and integrin aIIbb3 activation. In addition, an impaired spreading on collagen or fibrinogen and clot retraction was observed in PDE5A-deficient platelets. Moreover, PDE5A deficiency reduced phosphatidylserine exposure, calcium mobilization, ROS production, and increased intracellular cGMP level along with elevated VASP phosphorylation and reduced phosphorylation of ERK1/2, p38, JNK, and AKT. In conclusion, PDE5A modulates platelet activation and function and thrombus formation, indicating that therapeutically targeting it might be beneficial for the treatment of thrombotic diseases.