ICARUS at the Fermilab Short-Baseline Neutrino program: initial operation

The ICARUS collaboration employed the 760-ton T600 detector in a successful 3-year physics run at the underground LNGS laboratory, performing a sensitive search for LSND-like anomalous ν e appearance in the CERN Neutrino to Gran Sasso beam, which contributed to the constraints on the allowed neutrino oscillation parameters to a narrow region around 1 eV2 . After a significant overhaul at CERN, the T600 detector has been installed at Fermilab. In 2020 the cryogenic commissioning began with detector cool down, liquid argon filling and recirculation. ICARUS then started its operations collecting the first neutrino events from the booster neutrino beam (BNB) and the Neutrinos at the Main Injector (NuMI) beam off-axis, which were used to test the ICARUS event selection, reconstruction and analysis algorithms. ICARUS successfully completed its commissioning phase in June 2022. The first goal of the ICARUS data taking will be a study to either confirm or refute the claim by Neutrino-4 short-baseline reactor experiment. ICARUS will also perform measurement of neutrino cross sections with the NuMI beam and several Beyond Standard Model searches. After the first year of operations, ICARUS will search for evidence of sterile neutrinos jointly with the Short-Baseline Near Detector, within the Short-Baseline Neutrino program. In this paper, the main activities carried out during the overhauling and installation phases are highlighted. Preliminary technical results from the ICARUS commissioning data with the BNB and NuMI beams are presented both in terms of performance of all ICARUS subsystems and of capability to select and reconstruct neutrino events.

Scintillation light detection in the 6-m drift-length ProtoDUNE Dual Phase liquid argon TPC

DUNE is a dual-site experiment for long-baseline neutrino oscillation studies, neutrino astrophysics and nucleon decay searches. ProtoDUNE Dual Phase (DP) is a 6  ×  6  ×  6 m 3 liquid argon time-projection-chamber (LArTPC) that recorded cosmic-muon data at the CERN Neutrino Platform in 2019-2020 as a prototype of the DUNE Far Detector. Charged particles propagating through the LArTPC produce ionization and scintillation light. The scintillation light signal in these detectors can provide the trigger for non-beam events. In addition, it adds precise timing capabilities and improves the calorimetry measurements. In ProtoDUNE-DP, scintillation and electroluminescence light produced by cosmic muons in the LArTPC is collected by photomultiplier tubes placed up to 7 m away from the ionizing track. In this paper, the ProtoDUNE-DP photon detection system performance is evaluated with a particular focus on the different wavelength shifters, such as PEN and TPB, and the use of Xe-doped LAr, considering its future use in giant LArTPCs. The scintillation light production and propagation processes are analyzed and a comparison of simulation to data is performed, improving understanding of the liquid argon properties.

Prospects for beyond the Standard Model physics searches at the Deep Underground Neutrino Experiment: DUNE Collaboration

The Deep Underground Neutrino Experiment (DUNE) will be a powerful tool for a variety of physics topics. The high-intensity proton beams provide a large neutrino flux, sampled by a near detector system consisting of a combination of capable precision detectors, and by the massive far detector system located deep underground. This configuration sets up DUNE as a machine for discovery, as it enables opportunities not only to perform precision neutrino measurements that may uncover deviations from the present three-flavor mixing paradigm, but also to discover new particles and unveil new interactions and symmetries beyond those predicted in the Standard Model (SM). Of the many potential beyond the Standard Model (BSM) topics DUNE will probe, this paper presents a selection of studies quantifying DUNE's sensitivities to sterile neutrino mixing, heavy neutral leptons, non-standard interactions, CPT symmetry violation, Lorentz invariance violation, neutrino trident production, dark matter from both beam induced and cosmogenic sources, baryon number violation, and other new physics topics that complement those at high-energy colliders and significantly extend the present reach.

Overnight switch from rasagiline to safinamide in Parkinson's disease patients with motor fluctuations: a tolerability and safety study

BACKGROUND AND PURPOSE

When switching between monoamine oxidase type B (MAO-B) inhibitors, a 15-day suspension period is a precautionary measure to avoid a serotonin syndrome and hypertensive crisis. However, this indication results in a major inconvenience for parkinsonian patients because of the worsening of their clinical condition. In routine clinical practice, neurologists often perform a substitution of these two drugs without solution of continuity (i.e. overnight), to avoid worsening of fluctuations and prolonged OFF periods. Therefore, a safety open label study was performed to investigate the possible risks of switching overnight from rasagiline to safinamide.

METHODS

The study population included 20 advanced patients with Parkinson's disease on stable treatment with rasagiline and levodopa (alone or in combination with other anti-parkinsonian medication). The possible occurrence of serotonin syndrome and hypertension was monitored through a strict clinical observation and a 24-h Holter recording (ABPM) performed twice, whilst subjects were on rasagiline and immediately after switching to safinamide.

RESULTS

No cases of serotonin syndrome or hypertensive crisis occurred during the study. Changes that were not significant occurred in the primary end-point: 24-h mean blood pressure (BP) had a mild +4.4% increase in the ABPM2 versus ABPM1 (P = 0.17), 24-h systolic and diastolic BP values were slightly higher at ABPM2 compared to ABPM1 (respectively +3.3%, P = 0.13; and 5.4%, P = 0.08) and 24-h systolic BP variability was unchanged between the two ABPM evaluations (from 8.6 ± 2.9 to 8.9 ± 1.8; P = 0.27).

CONCLUSION

The results of the present study confirm that the overnight switch from rasagiline to safinamide is safe and well tolerated by patients.

P286 Inverse relation between systolic blood pressure variability and global longitudinal strain in patients with Parkinson"s disease and autonomic dysfunction

Background

Parkinson"s disease (PD) patients often present cardiac blood pressure (BP) derangement as a result of autonomic dysfunction. However their echocardiography pattern have been poorly investigated yet . Study aim: to evaluate the correlation between indices of left ventricular function ad 24/h blood pressure pattern in patients with PD

Methods We evaluated 20 patients with diagnosed PD and autonomic dysfunction and 15 hypertensive age-matched subjects. All patients performed 24/h blood pressure monitoring (ABPM) and echocardiography. Left ventricular systolic function was evaluated through ejection fraction (EF), tissue doppler S wave and global longitudinal strain (GLS). BP variability (BPV) was evaluated through average real variability.

Results

GLS (17.6 vs 22.8; p = 0.04) was reduced in the PD group compared to hypertensive patients. Conversely EF and S wave was similar between the two groups. Patients with PD had an inverse significant correlation between GLS and 24/h systolic BPV (r= -0.64; p = 0.003) and a trend through significance between S wave and systolic BPV (r= -0.31; p = 0.07). sNocturnal diastolic BP was inversely related to GLS (r= -0.44; p = 0.001) . There were no correlation between GLS and BPV and values in hypertensive patients.

Conclusions

In PD patients GLS is related to indices of poor BP control. GLS appears to be an early detector of LV dysfunction in patients with PD and autonomic dysfunction.

The Lee Silverman Voice Treatment (LSVT®) speech therapy in progressive supranuclear palsy

BACKGROUND

The Lee Silverman Voice Treatment (LSVT®) was specifically created and tested to comply with the needs of individuals with Parkinson's disease (PD) and other neurological problems. This is a high effort intensive treatment that aims at increasing vocal intensity through the increase of subglottal air pressure, i.e. respiratory effort, for a better cordal adduction and vibration, following the motto "think loud".

AIM

The main goal of this study is to inspect the efficacy of LSVT® treatment in progressive supranuclear palsy (PSP) patients.

DESIGN

Longitudinal study.

SETTING

Rehabilitative inpatient unit.

POPULATION

Sixteen patients with PSP and 23 patients with idiopathic PD as control were enrolled in the study.

METHODS

All patients underwent a training consisting in16 sessions of speech therapy following the LSVT® protocol. Initially the two groups of patients had similar voice problems, i.e. low volume and bad articulation of speech.

RESULTS

A statistically significant improvement was found among the data collected before and after treatment in the PSP and Parkinson groups. Increase in maximum phonation duration and volume of voice in reading were similar in the two groups. Improvement in quality of voice and articulation were more significant in the PD group as compared to the PSP group.

CONCLUSION

These results, along with previous findings, add further support to the generalized therapeutic impact of intensive voice treatment on respiratory and laryngeal functions in individuals with PSP.

CLINICAL REHABILITATION IMPACT

The positive results, the absence of dropout and collateral effect following this clinical treatments with LSVT technique encouraged to use this technique in PSP patients.

The proline-rich tyrosine kinase Pyk2 regulates platelet integrin αIIbβ3 outside-in signaling

BACKGROUND

The proline-rich tyrosine kinase Pyk2 is a focal adhesion kinase expressed in blood platelets, and is activated downstream of G-protein coupled receptors as well as integrin α2β1.

OBJECTIVE

In this study we have investigated the involvement of Pyk2 in integrin αIIbβ3 outside-in signaling in human and murine platelets.

METHODS

We analyzed the stimulation of intracellular signaling pathways in platelets from Pyk2 knockout mice adherent to immobilized fibrinogen.

RESULTS

Pyk2 was rapidly phosphorylated and activated in human and murine platelets adherent to fibrinogen through integrin αIIbβ3. Activation of Pyk2 was Src-dependent, but did not require phospholipase Cγ2 activity. Platelets from Pyk2 knockout mice showed a defective ability to adhere and spread on fibrinogen, in association with a dramatic reduction of phosphatidylinositol 3-kinase (PI3K) activation and Akt phosphorylation. Pharmacological and genetic analysis demonstrated that integrin αIIbβ3 engagement selectively stimulated the β-isoform of PI3K (PI3Kβ), and that, as for Pyk2, PI3Kβ activation required Src family kinases activity, but not phospholipase Cγ2. In fibrinogen-adherent platelets, both Pyk2 and PI3Kβ were necessary for stimulation of the small GTPase Rap1b, a regulator of cell adhesion and spreading. Integrin αIIbβ3 engagement triggered the association of the PI3Kβ regulatory subunit p85 with the adaptor protein c-Cbl, which was mediated by the p85 SH3 domain, and was independent of c-Cbl tyrosine phosphorylation. However, p85-associated c-Cbl was tyrosine phosphorylated by activated Pyk2 in fibrinogen adherent platelets.

CONCLUSIONS

These results identify a novel pathway of integrin αIIbβ3 outside-in signaling and recognize the tyrosine kinase Pyk2 as a major regulator of platelet adhesion and spreading on fibrinogen.

Integrin alpha2beta1 induces phosphorylation-dependent and phosphorylation-independent activation of phospholipase Cgamma2 in platelets: role of Src kinase and Rac GTPase

BACKGROUND

Platelet adhesion promoted by integrin alpha2beta1 induces integrin alpha(IIb)beta3 activation through the phospholipase C (PLC)-dependent stimulation of the small GTPase Rap1b.

OBJECTIVE

To analyze the mechanism of PLC activation downstream of alpha2beta1 that is required for regulation of Rap1b and alpha(IIb)beta3.

METHODS

Human and murine platelets were allowed to adhere to immobilized type I monomeric collagen through alpha2beta1. Tyrosine phosphorylation of PLCgamma2, PLC activation, accumulation of GTP-bound Rap1b and fibrinogen binding were measured and compared.

RESULTS

Integrin alpha2beta1 recruitment induced an evident PLC activation that was concomitant with robust tyrosine phosphorylation of PLCgamma2, and was suppressed in platelets from PLCgamma2-knockout mice. Moreover, PLCgamma2(-/-) platelets were unable to accumulate active Rap1b and to activate alpha(IIb)beta3 upon adhesion through alpha2beta1. Inhibition of Src kinases completely prevented tyrosine phosphorylation of PLCgamma2 in adherent platelets, but did not affect its activation, and both Rap1b and alpha(IIb)beta3 stimulation occurred normally. Importantly, alpha(IIb)beta3-induced phosphorylation and activation of PLCgamma2, as well as accumulation of active Rap1b, were totally suppressed by Src inhibition. Integrin alpha2beta1 recruitment triggered the Src kinase-independent activation of the small GTPase Rac1, and activation of Rac1 was not required for PLCgamma2 phosphorylation. However, when phosphorylation of PLCgamma2 was blocked by the Src kinase inhibitor PP2, prevention of Rac1 activation significantly reduced PLCgamma2 activation, GTP-Rap1b accumulation, and alpha(IIb)beta3 stimulation.

CONCLUSIONS

Src kinases and the Rac GTPases mediate independent pathways for PLCgamma2 activation downstream of alpha2beta1.

Proplatelet formation in heterozygous Bernard-Soulier syndrome type Bolzano

BACKGROUND

Although mutations of GPIb alpha are among the most frequent causes of inherited platelet disorders, the mechanisms for the onset of thrombocytopenia and platelet macrocytosis are still poorly defined.

OBJECTIVE

In this work we analyzed in vitro megakaryocyte differentiation and proplatelet formation in six subjects heterozygous for the Ala156Val mutation in the GPIb alpha (Bolzano mutation).

METHODS

Human megakaryocytes were obtained by differentiation of patient cord blood-derived CD34(+) cells and peripheral blood-derived CD45(+) cells. Proplatelet formation was evaluated by phase contrast and fluorescence microscopy.

RESULTS

Megakaryocyte differentiation from both cord blood (one patient) and peripheral blood (five patients) was comparable to controls. However, proplatelet formation was reduced by about 50% with respect to controls. An identical defect of proplatelet formation was observed when megakaryocytes were plated on fibrinogen, von Willebrand factor or grown in suspension. Morphological evaluation of proplatelet formation revealed an increased size of proplatelet tips, which was consistent with the increased diameters of patients' blood platelets. Moreover, alpha-tubulin distribution within proplatelets was severely deranged.

CONCLUSIONS

Megakaryocytes from patients carrying a Bolzano allele of GPIb alpha display both quantitative and qualitative abnormalities of proplatelet formation in vitro. These results suggest that a defect of platelet formation contributes to macrothrombocytopenia associated to the Bolzano mutation, and indicate a key role for GPIb alpha in proplatelet formation.

Adhesive receptors, extracellular proteins and myosin IIA orchestrate proplatelet formation by human megakaryocytes

BACKGROUND

Megakaryocytes release platelets from the tips of cytoplasmic extensions, called proplatelets. In humans, the regulation of this process is still poorly characterized.

OBJECTIVE

To analyse the regulation of proplatelet formation by megakaryocyte adhesion to extracellular adhesive proteins through different membrane receptors.

METHODS

Human megakaryocytes were obtained by differentiation of cord blood-derived CD34(+) cells, and proplatelet formation was evaluated by phase contrast and fluorescence microscopy.

RESULTS

We found that human megakaryocytes extended proplatelets in a time-dependent manner. Adhesion to fibrinogen, fibronectin or von Willebrand factor (VWF) anticipated the development of proplatelets, but dramatically limited both amplitude and duration of the process. Type I, but not type III or type IV, collagen totally suppressed proplatelet extension, and this effect was overcome by the myosin IIA antagonist blebbistatin. Integrin alphaIIbbeta3 was essential for megakaryocyte spreading on fibrinogen or VWF, but was not required for proplatelet formation. In contrast, proplatelet formation was prevented by blockade of GPIb-IX-V, or upon cleavage of GPIbalpha by the metalloproteinase mocarhagin. Membrane-associated VWF was detected exclusively on proplatelet-forming megakaryocytes, but not on round mature cells that do not extend proplatelets.

CONCLUSIONS

Our findings show that proplatelet formation in human megakaryocytes undergoes a complex spatio-temporal regulation orchestrated by adhesive proteins, GPIb-IX-V and myosin IIA.

The endocannabinoid 2-arachidonoylglycerol activates human platelets through non-CB1/CB2 receptors

BACKGROUND

The endocannabinoid 2-arachidonoylglycerol (2-AG) is an endogenous lipid that acts through the activation of G-protein-coupled cannabinoid receptors and plays essential roles in many physiological contexts. In the cardiovascular system 2-AG is generated by both activated endothelial cells and platelets, and participates in the regulation of inflammation and thrombosis. Although human platelets actively metabolize endocannabinoids, 2-AG also binds to platelet surface and leads to cell activation.

OBJECTIVE

To investigate the biological consequence of 2-AG interactions with human platelets and to clarify the role of cannabinoid receptors.

METHODS

Gel-filtered platelets were stimulated with 2-AG in the presence or absence of various inhibitors. Platelet aggregation and secretion were measured in a lumiaggregometer. Calcium ion movements were measured in FURA-2 loaded platelets. Thromboxane A(2) (TxA(2)) generation was evaluated as Thromboxane B(2) accumulation with a commercial EIA assay.

RESULTS

2-AG induced platelet shape change, aggregation and secretion with a dose-dependent mechanism that required engagement of platelet TxA(2) receptors. 2-AG caused also cytosolic calcium increase; however, it was totally dependent on availability of TxA(2). Indeed 2-AG was able to induce a robust generation of TxA(2) through the cyclooxygenase pathway. Treatment of platelets with inhibitors of monoacylglycerol lipase and fatty acid amide hydrolase did not affect the activation induced by 2-AG. Moreover, neither CB(1) and CB(2) proteins nor CB(1)/CB(2) mRNAs were detected in platelets.

CONCLUSIONS

2-AG can be considered a new physiologic platelet agonist able to induce full platelet activation and aggregation with a non-CB(1)/CB(2) receptor-mediated mechanism.

Intraplatelet signaling mechanisms of the priming effect of matrix metalloproteinase-2 on platelet aggregation

OBJECTIVE

Platelets contain and release some matrix metalloproteinases (MMPs), enzymes involved in the degradation of extracellular matrix, and one of these (MMP-2) exerts a proaggregatory effect. We explored the signal transduction mechanisms activated by MMP-2 in human blood platelets.

METHODS AND RESULTS

Recombinant, human MMP-2, added before stimulation with subthreshold doses of different agonists, potentiated platelet activation, calcium influx, IP3 formation, and pleckstrin phosphorylation. Wortmannin and LY29400, two PI3-K inhibitors, suppressed the potentiating effects of MMP-2 and preincubation with MMP-2 enhanced the thrombin-induced association of the p85alpha PI3-K subunit with the cytoskeleton and increased the phosphorylation of PKB. Protein tyrosine kinase inhibitors, MAP kinase inhibitors, PLA2 inhibitors, cyclooxygenase inhibitors and antagonists of the P2Y1 and P2Y12 receptors did not affect the potentiating activity of MMP-2 on platelets.

CONCLUSION

Our data show that MMP-2, at a concentration released by activated platelets, facilitates platelet activation acting at the level of a second messenger system common to different agonists and related to the activation of PI3-K. Platelet-released MMP-2 may contribute to platelet activation in vivo.

Altered cytoskeleton organization in platelets from patients with MYH9-related disease

MYH9-related disease (MYH9-RD) is an autosomal dominant disorder deriving from mutations in the MYH9 gene encoding for the heavy chain of non-muscle myosin IIA, and characterized by thrombocytopenia and giant platelets. Isoform IIA of myosin is the only one expressed in platelets, but the possibility that MYH9 mutations affect the organization of contractile structures in these blood elements has never been investigated. In this work we have analyzed the composition and the agonist-induced reorganization of the platelet cytoskeleton from seven MYH9-RD patients belonging to four different families. We found that an increased amount of myosin was constitutively associated with actin in the cytoskeleton of resting MYH9-RD platelets. Upon platelet stimulation, an impaired increase in the total cytoskeletal proteins was observed. Moreover, selected membrane glycoproteins, tyrosine kinases, and small GTPases failed to interact with the cytoskeleton in agonist-stimulated MYH9-RD platelets. These results demonstrate for the first time that mutations of MYH9 result in an alteration of the composition and agonist-induced reorganization of the platelet cytoskeleton. We suggest that these abnormalities may represent the biochemical basis for the previously reported functional alterations of MYH9-RD platelets, and for the abnormal platelet formation from megakaryocytes, resulting in thrombocytopenia and giant platelets.

Activation of the small GTPase Rap2B in agonist-stimulated human platelets

The activation of the small GTPase Rap2B in resting and agonist-stimulated human platelets was investigated. Both thrombin, that stimulates heterotrimeric G-protein-coupled receptors, and the GPVI ligand convulxin, that activates a tyrosine-kinase based signaling pathway, were able to induced the rapid and sustained binding of GTP to Rap2B. Similarly, a number of other agonists tested, previously known to activate the highly related protein Rap1B, were also able to stimulate Rap2B. In contrast, platelet antagonists that increase the intracellular concentration of cAMP did not signal to Rap2B. Thrombin- and convulxin-induced activation of Rap2B was not dependent on thromboxane A2, did not require the interaction of the protein with the cytoskeleton, and was not regulated by integrin alphaIIbbeta3-dependent outside-in signaling. When secreted ADP was neutralized, activation of Rap2B induced by thrombin, but not by convulxin, was significantly reduced. ADP itself was found to induce the rapid and sustained binding of GTP to Rap2B, and this effect was predominantly mediated by stimulation of the Gi-coupled P2Y12 receptor. Activation of Rap2B promoted by both thrombin and convulxin was regulated by intracellular Ca2+, while protein kinase C was found to be involved in convulxin- but not in thrombin-induced activation of Rap2B. Moreover, Rap2B activation induced by thrombin, but not by convulxin, was totally dependent on phosphatidylinositol 3-kinase activity. These results demonstrate that the small GTPase Rap2B is involved in platelet activation, and outline some important differences between the regulation of highly related GTPases Rap2B and Rap1B in human platelets.

Platelet activation by von Willebrand factor requires coordinated signaling through thromboxane A2 and Fc gamma IIA receptor

Interaction of von Willebrand Factor with glycoprotein Ib-IX-V induces platelet activation through a still poorly defined mechanism. Previous studies have suggested a possible role for the low affinity receptor for immunoglobulin, Fc gamma RIIA, in GPIb-IX-V signaling. Here we show that binding of vWF to platelets induces the tyrosine phosphorylation of Fc gamma RIIA by a Src kinase. Treatment of platelets with the anti-Fc gamma RIIA monoclonal antibody IV.3 specifically inhibits vWF-induced but not thrombin-induced pleckstrin phosphorylation and serotonin secretion. Moreover, vWF fails to induce pleckstrin phosphorylation in mouse platelets, lacking Fc gamma RIIA, and serotonin secretion is impaired. Pleckstrin phosphorylation and serotonin secretion in human platelets stimulated with vWF are blocked by the cyclooxygenase inhibitor acetylsalicylic acid. However, release of arachidonic acid and synthesis of TxA(2) induced by vWF are not affected by the anti-Fc gamma RIIA monoclonal antibody IV.3. Similarly, vWF-induced tyrosine phosphorylation of Fc gamma RIIA, as well as of Syk and PLC gamma 2, occurs normally in aspirinized platelets. Inhibition of the tyrosine kinase Syk by piceatannol does not affect vWF-induced tyrosine phosphorylation of Fc gamma RIIA but prevents phosphorylation of PLC gamma 2. Pleckstrin phosphorylation and platelet secretion induced by vWF, but not by thrombin, are also inhibited by piceatannol. Pleckstrin phosphorylation is also sensitive to the phosphatidylinositol 3-kinase inhibitor wortmannin. These results indicate that PLC gamma 2 plays a central role in platelet activation by vWF and that the stimulation of this enzyme requires coordinated signals through endogenous TxA(2) and Fc gamma RIIA.

Anorectal function in multiple system atrophy and Parkinson's disease

This study was designed to investigate anorectal function in Parkinson's disease and multiple system atrophy (MSA). After a standardized interview, 17 patients with Parkinson's disease (PD) and 16 patients with multiple system atrophy (MSA) underwent anorectal manometry with a continuously perfused multi-lumen catheter, located to record pressures from the anal canal, and a balloon for rectal distension. Data were analyzed by observers blind to the neurologic diagnosis. Disease duration was shorter in the MSA than in the PD group (6+/-4 versus 10+/-5 yrs, p<0.05). Most patients reported a bowel frequency of less than three evacuations per week and some patients had fecal incontinence. Most manometric recordings disclosed an abnormal pattern during straining (a paradoxic contraction or lack of inhibition) in 13 patients with MSA and 11 patients with PD. Mean anal pressures and rectal sensitivity threshold were not significantly higher in the MSA group, whereas the inhibitory anal reflex and rectal compliance thresholds were within the normal range in both groups. Manometric patterns did not differentiate patients with MSA from patients with PD. Most patients in both groups showed an abnormal straining pattern, decreased anal tone, or both dysfunctions. In conclusion, our findings suggest that although bowel and anorectal dysfunctions do not differentiate MSA from PD, both abnormalities occur earlier and develop faster in MSA than in PD.

The platelet cytoskeleton regulates the aggregation-dependent synthesis of phosphatidylinositol 3,4-bisphosphate induced by thrombin

Pretreatment of intact platelets with cytochalasin D prevented actin polymerization and cytoskeleton reorganization induced by thrombin, but did not affect platelet aggregation. Under these conditions, synthesis of phosphatidylinositol 3,4-bisphosphate (PtdIns(3,4)P2) stimulated by thrombin was strongly inhibited, while production of phosphatidic acid was unaffected. The inhibitory effect of cytochalasin D was not observed when platelet aggregation was prevented by the RGDS peptide. We also found that cytochalasin D did not affect PtdIns(3,4)P2 synthesis induced by concanavalin A (ConA), which is known to occur through an aggregation-independent mechanism. Moreover, thrombin, but not ConA, induced the translocation of phosphatidylinositol 3-kinase to the cytoskeleton. This process was equally inhibited by both the RGDS peptide and cytochalasin D. These results demonstrate that the cytoskeleton represents a functional link between thrombin-induced aggregation and synthesis of PtdIns(3,4)P2.

Anorectal function in multiple system atrophy and Parkinson's disease

This study was designed to investigate anorectal function in Parkinson's disease and multiple system atrophy (MSA). After a standardized interview, 17 patients with Parkinson's disease (PD) and 16 patients with multiple system atrophy (MSA) underwent anorectal manometry with a continuously perfused multi-lumen catheter, located to record pressures from the anal canal, and a balloon for rectal distension. Data were analyzed by observers blind to the neurologic diagnosis. Disease duration was shorter in the MSA than in the PD group (6+/-4 versus 10+/-5 yrs, p<0.05). Most patients reported a bowel frequency of less than three evacuations per week and some patients had fecal incontinence. Most manometric recordings disclosed an abnormal pattern during straining (a paradoxic contraction or lack of inhibition) in 13 patients with MSA and 11 patients with PD. Mean anal pressures and rectal sensitivity threshold were not significantly higher in the MSA group, whereas the inhibitory anal reflex and rectal compliance thresholds were within the normal range in both groups. Manometric patterns did not differentiate patients with MSA from patients with PD. Most patients in both groups showed an abnormal straining pattern, decreased anal tone, or both dysfunctions. In conclusion, our findings suggest that although bowel and anorectal dysfunctions do not differentiate MSA from PD, both abnormalities occur earlier and develop faster in MSA than in PD.

Interaction of the low-molecular-weight GTP-binding protein rap2 with the platelet cytoskeleton is mediated by direct binding to the actin filaments

The interaction of the low-molecular-weight GTP-binding protein rap2 with the cytoskeleton from thrombin-aggregated platelets was investigated by inducing depolymerization of the actin filaments, followed by in vitro-promoted repolymerization. We found that the association of rap2 with the cytoskeleton was spontaneously restored after one cycle of actin depolymerization and repolymerization. Exogenous rap2, but not unrelated proteins, added to depolymerized actin and solubilized actin-binding proteins, was also specifically incorporated into the in vitro reconstituted cytoskeleton. The incorporation of exogenous rap2 was also observed when the cytoskeleton from resting or thrombin-activated platelets was subjected to actin depolymerization-repolymerization. Moreover, such interaction occurred equally well when exogenous rap2 was loaded with either GDP or GTPgammaS. We also found that polyhistidine-tagged rap2 immobilized on Ni(2+)-Sepharose and loaded with either GDP or GTPgammaS, could specifically bind to cytoskeletal actin. Moreover, when purified monomeric actin was induced to polymerize in vitro in the presence of rap2, the small G-protein specifically associated with the actin filaments. Finally, rap2 loaded with either GDP or GTPgammaS was able to bind to purified F-actin immobilized on a plastic surface. These results demonstrate that rap2 interacts with the platelet cytoskeleton by direct binding to the actin filaments and that this interaction is not regulated by the activation state of the protein.

Hydrolysis of NADP+ by platelet CD38 in the absence of synthesis and degradation of cyclic ADP-ribose 2'-phosphate

CD38 is a multifunctional cell surface ectoenzyme that catalyzes both the synthesis of cyclic ADP-ribose from NAD+ and its hydrolysis to ADP-ribose. In this work, we investigated the metabolism of NADP+ by CD38 expressed on human platelets. Incubation of either platelet membranes or intact cells with NADP+ resulted in the rapid and time-dependent accumulation of ADP-ribose 2'-phosphate that paralleled the consumption of the substrate. However, under the same conditions, synthesis of cyclic ADP-ribose 2'-phosphate was not observed. By immunoprecipitation experiments, we identified CD38 as the enzyme responsible for the observed NADP+ glycohydrolase activity. The lack of detection of cyclic ADP-ribose 2'-phosphate was not due to its rapid hydrolysis, since direct incubation of platelet membranes with cyclic ADP-ribose 2'-phosphate did not result in the formation of ADP-ribose 2'-phosphate. By contrast, the same membrane samples expressed a significant ability to hydrolyze cyclic ADP-ribose to ADP-ribose. The absence of cyclic ADP-ribose 2'-phosphate hydrolase activity was also confirmed using high concentrations of substrate and by analysing both intact Jurkat T-lymphocytes and immunoprecipitated CD38. These results indicate that CD38, which is a multifunctional enzyme towards NAD+, displays exclusively a NADP+ glycohydrolase activity and is unable to catalyze both the synthesis and the hydrolysis of cyclic ADP-ribose 2'-phosphate.

Rap1B and Rap2B translocation to the cytoskeleton by von Willebrand factor involves FcgammaII receptor-mediated protein tyrosine phosphorylation

Stimulation of human platelets with von Willebrand factor (vWF) induced the translocation of the small GTPases Rap1B and Rap2B to the cytoskeleton. This effect was specifically prevented by an anti-glycoprotein Ib monoclonal antibody or by the omission of stirring, but was not affected by the peptide RGDS, which antagonizes binding of adhesive proteins to platelet integrins. Association of Rap2B with the cytoskeleton was very rapid, while translocation of Rap1B occurred in a later phase of platelet activation and was totally inhibited by cytochalasin D. vWF also induced the rapid tyrosine phosphorylation of several proteins that was prevented by the tyrosine kinases inhibitor genistein and by cAMP-increasing agents. Under these conditions, also the association of Rap1B and Rap2B with the cytoskeleton was prevented. Translocation of Rap proteins to the cytoskeleton induced by vWF, but not by thrombin, was inhibited by a monoclonal antibody against the FcgammaII receptor. The same antibody inhibited vWF-induced tyrosine phosphorylation of selected substrates with molecular masses of about 75, 95, and 150 kDa. Three of these substrates were identified as the tyrosine kinase pp72(syk), the phospholipase Cgamma2, and the inositol 5-phosphatase SHIP. Our results indicate that translocation of Rap1B and Rap2B to the cytoskeleton is regulated by tyrosine kinases and suggest a novel role for the FcgammaII receptor in the mechanism of platelet activation by vWF.

Clustering of integrin alphaIIb-beta3 differently regulates tyrosine phosphorylation of pp72syk, PLCgamma2 and pp125FAK in concanavalin A-stimulated platelets

Tyrosine phosphorylation of the non-receptor tyrosine kinases pp72syk and pp125FAK and of the gamma2 isoform of phospholipase C (PLCgamma2) in human platelets stimulated with the lectin Concanavalin A was investigated. Concanavalin A induced the rapid tyrosine phosphorylation of pp72syk and PLCgamma2 with a similar kinetics, while tyrosine phosphorylation of pp125FAK occurred in a later phase of platelet activation. When compared with other platelet agonists, Concanavalin A revealed to be at least as potent as collagen in inducing tyrosine phosphorylation of PLCgamma2 and pp125FAK, while tyrosine phosphorylation of pp72syk induced by the lectin was much stronger than that induced by thrombin or collagen. Concanavalin A-induced tyrosine phosphorylation of pp72syk, PLCgamma2 and pp125FAK was not dependent on platelet aggregation as it occurred normally even in the absence of sample stirring and when fibrinogen binding to integrin alphaIIb-beta3 was inhibited by the peptide RGDS. Tyrosine phosphorylation of pp72syk, PLCgamma2 and pp125FAK required the binding of the lectin to the platelet surface, but was not observed in platelets treated with succinyl-Concanavalin A, a derivative of the lectin that interacts with the same receptors but does not promote clustering of membrane glycoproteins. Moreover, the aggregation-independent tyrosine phosphorylation of pp125FAK and pp72syk induced by Concanavalin A required the expression of integrin alphaIIb-beta3 on the platelet surface as it was strongly inhibited in platelets from patients affected by Glanzmann thrombasthenia. By contrast, tyrosine phosphorylation of PLCalpha2 occurred normally also in thrombasthenic platelets stimulated with Concanavalin A. These results demonstrate that, even in the absence of aggregation, the clustering of integrin alphaIIb-beta3 induced by Concanavalin A on the platelet surface directly promotes tyrosine phosphorylation of pp72syk and pp125FAK and provide further evidence that the oligomerization of the fibrinogen receptor promoted by its natural ligand during platelet aggregation may be responsible for the tyrosine phosphorylation of these proteins induced by physiological agonists.

Cytoskeleton-dependent inhibition of the ADP-ribosyl cyclase activity of CD38 in thrombin-stimulated platelets

Stimulation of human platelets with thrombin caused a 42% inhibition of the ADP-ribosyl cyclase activity of membrane CD38. This effect was mediated by the activation of the platelet thrombin receptor rather than by proteolysis of CD38, and was not due to a different distribution of the synthesised nucleotide or to a reduced accessibility of CD38 to the substrate. The inhibitory effect of thrombin required actin polymerisation and was not observed when interaction of CD38 with the cytoskeleton was prevented by cytochalasin D. Finally, we analysed whether cADPR could play a role as a Ca2+-mobilising agent in human platelets. Using saponin-permeabilised cells, we found that unlike IP3, cADPR did not induce any release of Ca2+ from intracellular stores. These results indicate that the enzymatic activity of membrane CD38 can be modulated by platelet activation, and that the function of this glycoprotein is probably not related to Ca2+ mobilisation.

Arachidonic acid mediates angiotensin II effects on p21ras in renal proximal tubular cells via the tyrosine kinase-Shc-Grb2-Sos pathway

In kidney epithelial cells, an angiotensin II (Ang II) type 2 receptor subtype (AT2) is linked to a membrane-associated phospholipase A2 (PLA2) and the mitogen-activated protein kinase (MAPK) superfamily. However, the intervening steps in this linkage have not been determined. The aim of this study was to determine whether arachidonic acid mediates Ang II's effect on p21ras and if so, to ascertain the signaling mechanism(s). We observed that Ang II activated p21ras and that mepacrine, a phospholipase A2 inhibitor, blocked this effect. This activation was also inhibited by PD123319, an AT2 receptor antagonist but not by losartan, an AT1 receptor antagonist. Furthermore, Ang II caused rapid tyrosine phosphorylation of Shc and its association with Grb2. Arachidonic acid and linoleic acid mimicked Ang II-induced tyrosine phosphorylation of Shc and activation of p21ras. Moreover, Ang II and arachidonic acid induced an association between p21ras and Shc. We demonstrate that arachidonic acid mediates linkage of a G protein-coupled receptor to p21ras via Shc tyrosine phosphorylation and association with Grb2/Sos. These observations have important implications for other G protein-coupled receptors linked to a variety of phospholipases.

Thrombin induces the association of cyclic ADP-ribose-synthesizing CD38 with the platelet cytoskeleton

The effect of platelet stimulation on the subcellular localization of CD38, a membrane glycoprotein that catalyses the synthesis of cyclic ADP-ribose from beta-NAD+ was investigated. Treatment of human platelets with thrombin caused the association of about 40% of the total ADP-ribosyl cyclase activity with the cytoskeleton, through the translocation of the CD38 molecule from the Triton X-100-soluble to the insoluble fraction. The interaction of CD38 with the cytoskeleton was a specific and reversible process, mediated by the binding to the actin-rich filaments and was inhibited by treatment of platelets with cytochalasin D. This event was regulated by integrin alphaIIb beta3 and platelet aggregation as it was prevented by the inhibition of fibrinogen binding and was not observed in platelets from a patient affected by Glanzmann thrombasthenia. These results demonstrate that the subcellular localization of CD38 can be influenced by platelet stimulation with physiological agonists, and that membrane CD38 can interact with intracellular proteins.

Agonist-induced actin polymerization is required for the irreversibility of platelet aggregation

Cytochalasin D was used to investigate the role of intracellular cytoskeleton in the stabilization of platelet aggregation induced by strong platelet agonists. Incubation of gel-filtered platelets with increasing concentrations of cytochalasin D resulted in a dose-dependent inhibition of actin polymerization and association of actin-binding proteins with the Triton X-100-insoluble material induced by the thromboxane analogue, U46619, and the thrombin receptor activating peptide, TRAP. The same concentrations of cytochalasin D did not significantly inhibit platelet aggregation promoted by the two agonists. The addition of the chelating agent EDTA to fully aggregated platelets, that had been treated with cytochalasin D, resulted in the rapid and almost complete disaggregation. EDTA did not cause disaggregation of control, solvent-treated, aggregated platelets. The degree of platelet disaggregation induced by EDTA was dependent on the dose of cytochalasin D used, and was correlated with the inhibition of the cytoskeletal reorganization. Aggregation of cytochalasin D-treated platelets stimulated with U46619 or TRAP was also reverted by the addition of the tetrapeptide RGDS or the fibrinogen gamma-chain dodecapeptide, which competitively interfere with fibrinogen binding to the glycoprotein IIb-IIIa complex. These results indicate that the intracellular cytoskeleton plays an essential role in the stabilization of the fibrinogen-platelet interaction, and is necessary for the irreversibility of platelet aggregation induced by strong agonists.

Expression of cyclic ADP-ribose-synthetizing CD38 molecule on human platelet membrane

CD38 is a cell surface molecule widely used as a marker for immature and activated lymphocytes. It has been recently shown that CD38 displays three enzymatic activities: hydrolysis of NAD+ to ADP-ribose, synthesis of cyclic ADP-ribose from NAD+, and hydrolysis of cyclic ADP-ribose to ADP-ribose. Thus, CD38 plays a key role in the synthesis of cyclic ADP-ribose, a calcium-mobilizing compound. We investigate here the expression and cellular localization of CD38 in human platelets using a specific monoclonal antibody. Results showed that CD38 is expressed by human platelet membranes. Moreover, we show that platelet CD38 possesses NAD glycohydrolase, ADP-ribose cyclase, and cyclic ADP-ribose hydrolase activities. This finding indicates that the calcium-mobilizing agent cyclic ADP-ribose can be synthetized by human platelets and raises the question about the possible role of CD38 expression and enzymatic activities in the signal transduction pathways leading to platelet activation.

Activation of human platelets by lysophosphatidic acid

The biochemical mechanisms of platelet activation by lysophosphatidic acid were investigated. Lysophosphatidic acid interacts with a membrane receptor coupled to the inhibitory GTP-binding protein Gi and produces a rapid decrease of the intracellular concentration of cAMP. Aggregation of gel-filtered platelets by lysophosphatidic acid requires the presence of extracellular CaCl2, as this phospholipid does not induce secretion of platelet dense granules. Platelet activation by lysophosphatidic acid in the absence of extracellular CaCl2 does not involve phospholipase C activation, as evaluated by measuring mobilization of Ca2+ from internal stores and pleckstrin phosphorylation, but causes the rapid tyrosine phosphorylation of several intracellular proteins. Our results indicate that activation of intracellular tyrosine kinases is not secondary to Ca2+ mobilization and protein kinase C activation in lysophosphatidic acid-stimulated platelets.

Evidence for a glycoprotein IIb-IIIa- and aggregation-independent mechanism of phosphatidylinositol 3',4'-bisphosphate synthesis in human platelets

The synthesis of phosphatidylinositol 3',4'-bisphosphate (PtdIns(3,4)P2) in 32P-labeled human platelets induced by the tetrameric lectin concanavalin A and the physiological agonist thrombin were compared. Like thrombin, concanavalin A stimulated a time-dependent accumulation of PtdIns(3,4)P2, which reached maximal levels after 5 min of stimulation. However, while synthesis of PtdIns(3,4)P2 induced by thrombin was dependent on platelet aggregation, the production of PtdIns(3,4)P2 induced by concanavalin A was unchanged when aggregation was prevented by the omission of stirring or when fibrinogen binding to platelets was inhibited by the tetrapeptide RGDS. Accumulation of PtdIns(3,4)P2 was not observed in platelets stimulated with succinyl-concanavalin A, a dimeric derivative of the lectin that binds to the same receptors on the platelet surface but does not promote clustering of membrane glycoproteins. The synthesis of PtdIns(3,4)P2 induced by concanavalin A was also independent of the membrane glycoprotein IIb-IIIa, as normal accumulation of this lipid was observed in platelets from two patients affected by Glanzmann thrombasthenia. In contrast, thrombin showed a strongly reduced ability to stimulate PtdIns(3,4)P2 production in thrombasthenic platelets. Although concanavalin A was able to induce association of the regulatory subunit of the phosphatidylinositol 3-kinase with tyrosine-phosphorylated proteins, the tyrosine kinase inhibitor tyrphostin AG-213 did not inhibit the lectin-induced synthesis of PtdIns(3,4)P2. These results demonstrate the existence of a novel mechanism of PtdIns(3,4)P2 synthesis in human platelets, which is independent of glycoprotein IIb-IIIa and aggregation, but requires clustering of membrane glycoproteins. As clustering events occur during platelet aggregation promoted by physiological agonists, this new mechanism may also be involved in the aggregation-dependent production of PtdIns(3,4)P2 in thrombin-stimulated platelets.

Dual mechanism of protein-tyrosine phosphorylation in concanavalin A-stimulated platelets

Treatment of human platelets with the lectin Concanavalin A (Con A) resulted in the tyrosine phosphorylation of several proteins with molecular masses 65, 80, 85, 95, 120, 135, and 150 kDa. These proteins were divided in two groups: the first group included the 65-, 85-, 95-, and 120-kDa bands, which were tyrosine phosphorylated also in thrombin-stimulated platelets; the second group (80-, 135-, and 150-kDa bands) included proteins whose tyrosine phosphorylation was exclusively promoted by Con A, but not by thrombin. Members of the second group were rapidly dephosphorylated when the lectin was displaced from the cell surface by methyl alpha-D-mannopyranoside. Pretreatment of intact platelets with the prostacyclin analog iloprost, inhibited Con A-induced tyrosine phosphorylation of the first group of proteins, but had no effect on the tyrosine phosphorylation of the proteins of the second group. Succinyl-Con A, a dimeric derivative of the lectin, which binds to the platelet surface but does not promote clustering of the receptor, did not induce tyrosine phosphorylation of the second group of proteins, although phosphorylation of some members of the first group was observed. Our results demonstrate the presence of two different mechanisms leading to protein-tyrosine phosphorylation in Con A-stimulated platelets, and identify a new signal transduction pathway, promoted by the clustering of membrane glycoproteins, that produces tyrosine phosphorylation of specific substrates. This new pathway may be activated by platelet interaction with multivalent ligands, such as adhesive proteins, during adhesion, spreading, and aggregation.

Activation of poly(ADP-ribose)polymerase in apoptotic human cells

We have studied the effect of the chemotherapeutic drug VP-16 (etoposide) on the metabolism of HeLa cells by analysing different cellular parameters considered as markers of apoptosis. Typical features such as chromatin condensation and internucleosomal DNA cleavage are visible in HeLa cells exposed to VP-16. We investigated whether the appearance of small-sized DNA fragments could regulate the ADP-ribosylation process. To this purpose, we have analysed, by means of the activity gel technique; the structural and catalytical properties of poly(ADP-ribose)polymerase. In extracts from cells where etoposide-induced DNA fragmentation occurred, we have shown that the label of the autoribosylated form of the enzyme is greatly increased even if the amount of the protein remains constant. This phenomenon is completely abolished in cells preincubated with poly(ADP-ribose)polymerase inhibitor, 3-aminobenzamide. After VP-16 administration, we have observed that the level of NAD is not heavily decreased. It is widely agreed that zinc exerts an inhibitory effect on the endonuclease(s) responsible for the fragmentation of DNA during apoptosis. After incubation of cells with zinc/VP-16 we have found the occurrence of apoptotic parameters even in the absence of internucleosomal DNA cleavage. The inhibition of DNA fragmentation prevents the activation of poly(ADP-ribose)polymerase activity. These results indicate that the activation of the enzyme towards the automodification reaction is strictly dependent on the appearance of DNA internucleosomal fragments and could represent a way to control enzyme activity.

Glycoprotein IIb-IIIa and the translocation of Rap2B to the platelet cytoskeleton

The stimulation of human platelets with physiological agonists results in the incorporation of several proteins into the cytoskeleton, fibrinogen binding, and platelet aggregation. We recently demonstrated that the Ras-related low molecular weight GTP-binding protein Rap2B associates with the cytoskeleton in activated platelets and that this interaction requires platelet aggregation. In the present study we demonstrate that agonist-induced actin polymerization is necessary for the translocation of Rap2B to the cytoskeleton, suggesting that Rap2B interacts with the newly formed actin filaments. Moreover, the association of Rap2B with Triton X-100-insoluble material from platelets was totally blocked by treatment of intact platelets with monoclonal antibodies against the fibrinogen receptor glycoprotein IIb-IIIa. Platelets from patients affected by Glanzmann thrombastenia, a genetic disorder in which platelet plasma membranes lack glycoprotein IIb-IIIa but possess normal levels of Ras-related proteins, failed to incorporate Rap2B into the cytoskeleton upon activation by thrombin. Comparative immunoblotting revealed that the translocation of Rap2B to the cytoskeleton during platelet aggregation was accompanied by the simultaneous translocation of glycoprotein IIb-IIIa. Moreover, the cytoskeleton from aggregated platelets contained Rap2B and glycoprotein IIb-IIIa in comparable amounts. These results demonstrate the association of Rap2B and glycoprotein IIb-IIIa and their translocation to the cytoskeleton in aggregated human platelets.

Effect of cAMP on the association of small GTP-binding proteins with the cytoskeleton of human platelets

Following activation of human platelets changes in cytoskeletal organization occur: some proteins, which are present in the cytosol or membrane-associated in resting platelets, are recovered in the Triton-insoluble residue in activated cells. Assembly and disassembly of complex effector units on the membrane and inside cells is under the control of low molecular weight GTP-binding proteins, particularly those in the ras family. We investigated the interaction of small GTP-binding proteins with the platelet cytoskeleton and the effect of high cAMP levels on these interactions. At least two GTP-binding proteins of 24 and 28 kDa were detected in the Triton-insoluble residue of resting platelets. Stimulation of platelets with thrombin or concanavalin A (Con A), under non-aggregating conditions, resulted in increased 24 kDa protein-bound GTP, which also contained a significant amount of rap1B. High cAMP levels differently affected this interaction depending on the type of agonist used. cAMP increased association of G-proteins with the cytoskeleton following Con A-activation, while it decreased G-proteins interaction after thrombin stimulation. The activation did not influence the cAMP-dependent phosphorylation of rap1B. No phosphoprotein corresponding to rap1B could be detected in the Triton-insoluble residues, however. These findings could be related to the different mechanisms of cytoskeletal protein recruitment in platelets activated with either thrombin or Con A.

Intracellular calcium mobilization is triggered by clustering of membrane glycoproteins in concanavalin A-stimulated platelets

Stimulation of human platelets with concanavalin A resulted in a significant increase in the concentration of cytoplasmic free Ca2+. This effect was due to two different processes: Ca2+ mobilization from internal stores and Ca2+ influx from the extracellular medium. Kinetic analysis revealed that the release of Ca2+ from internal storage sites occurred sooner than the opening of plasma membrane Ca2+ channels. The ability of concanavalin A to induce a sustained increase in cytoplasmic Ca2+ concentration was antagonized and reversed by methyl alpha-D-mannopyranoside, demonstrating that it was promoted by the interaction of the lectin with cell surface glycoproteins. Succinyl-concanavalin A, a dimeric derivative of the lectin, that does not promote patching/capping of the receptor, was able to bind to the platelet surface, and antagonized the effects of native concanavalin A. In addition, succinyl-concanavalin A, per se, was unable to induce Ca2+ mobilization in human platelets. Therefore, the action of the native concanavalin A was mediated by receptor clustering events. Concanavalin A mobilized Ca2+ from the same internal stores from which Ca2+ was mobilized in response to strong platelet agonists, such as thrombin and arachidonic acid. However, while thrombin was ineffective in inducing Ca2+ release after stimulation of platelets with ConA, ConA was able to cause a full discharge of Ca2+ from internal stores even in platelets previously stimulated with thrombin. These results demonstrate for the first time that the clustering of specific membrane glycoproteins can trigger platelet activation. The physiological implications during platelet aggregation are discussed.

Association of the low molecular weight GTP-binding protein rap2B with the cytoskeleton during platelet aggregation

The intracellular distribution of the low-molecular-weight GTP-binding protein rap2B was investigated in resting and agonist-activated human platelets. In both cases, platelets were lysed by Triton X-100, and cell fractions were obtained by differential centrifugations. Using a specific polyclonal antiserum, we found that rap2B in resting platelets was completely detergent-soluble. When platelets were aggregated with thrombin, the thromboxane analogue U46619, or the Ca(2+)-ATPase inhibitor thapsigargin, a significant amount of rap2B became associated with the cytoskeleton. This association was paralleled by a decrease of rap2B in the Triton X-100-soluble fraction. Translocation of rap2B to the cytoskeleton strictly depended on platelet aggregation, and maximal incorporation was found when approximately 50% aggregation was measured. Inhibition of fibrinogen binding to the glycoprotein IIb-IIIa complex completely prevented the interaction of rap2B with the cytoskeleton. These results clearly demonstrate that changes in the intracellular localization of rap2B occur during platelet activation and represent evidence that this low molecular weight GTP-binding protein may be involved in platelet function.

Cryopreservation of human platelets using dimethyl sulfoxide and glycerol-glucose: effects on "in vitro" platelet function

BACKGROUND

The technique of freezing blood platelets could be very useful in the transfusion support of thrombocytopenic patients. The best method of platelet cryopreservation still remains an object of debate, though it has been suggested that dimethyl sulfoxide (DMSO) is more effective than glycerol-glucose as a cryopreservative. However, few studies have directly compared platelets cryopreserved with different methods.

METHODS

We compared "in vitro" function of platelets cryopreserved with 5% dimethyl sulfoxide (DMSO) or 3% glycerol-glucose at -140 degrees C. Platelet aggregation and release reaction were studied with a Lumi aggregometer, thromboxane B2 (TxB2) production by radioimmunoassay, and Ca++ movement by the Fura 2 method.

RESULTS

Cryopreservation with both of the methods dramatically reduced the ability of platelets to release ATP and to aggregate in response to single agonists. In contrast, cryopreserved platelets maintained their ability to aggregate after stimulation with paired agonists and to produce TxB2. Cytoplasmic Ca++ increase induced by thrombin was observed in the glycerol-preserved platelets, while it was nearly absent in the DMSO-preserved ones.

CONCLUSIONS

We suggest that cryopreservation with glycerol-glucose or DMSO induces similar defects of platelet function. The damage is severe, but platelets are still able to respond to strong stimulation.

Role of rap1B and p21ras GTPase-activating protein in the regulation of phospholipase C-gamma 1 in human platelets

Thrombin activates phospholipase C in human platelets, but the specific isoenzymes activated and the signal pathway used are unknown. Using specific antibodies, we found that phospholipase C-gamma 1 and the p21ras GTPase-activating protein, rasGAP, are present in human platelets. Furthermore, phospholipase C-gamma 1 was detectable, based on enzyme activity and Western blot analysis, in immunoprecipitates of rasGAP, suggesting that these two proteins form tight complexes. The pool of phospholipase C-gamma 1 associated with rasGAP was phosphorylated but not through tyrosine phosphorylation. Although thrombin stimulation had no effect on the level of phosphorylation of phospholipase C-gamma 1 and only slightly increased the tyrosine phosphorylation of rasGAP, the agonist induced the association of rasGAP with rap1B, as indicated by the appearance of rap1B on a Western blot of rasGAP immunoprecipitates. Our results suggest the formation of a signaling complex involving rasGAP, phospholipase C-gamma 1, and rap1B that might be important in the cascade leading to platelet activation.

Defect of platelet aggregation and adhesion induced by autoantibodies against platelet glycoprotein IIIa

A young patient developed chronic idiopathic thrombocytopenic purpura. Prednisone therapy normalized platelet number, but bleeding symptoms did not disappear. Platelet function was severely impaired, since platelet aggregation, ATP release and adhesion to collagen and subendothelial matrix were significantly reduced. Plasma and purified immunoglobulins of the patient reproduced the functional defects in normal platelets. Immunoblotting revealed that patient's plasma contained an antibody reacting with a component of platelets with the same electrophoretic mobility of glycoproteins IIIa of normal platelets. Moreover, patient's plasma inhibited the binding of an anti-GPIIb/IIIa monoclonal antibody to platelet surface. Additional immunosuppressive therapy with prednisone and azathioprine normalized platelet function and induced the disappearance of bleeding symptoms.

Epinephrine induces association of pp60src with Gi alpha in human platelets

Using specific antibodies against the alpha subunit of the inhibitory GTP-binding protein Gi, we analyzed the association of Gi alpha with other cellular components in human platelets. Three tyrosine phosphorylated proteins with molecular mass of 63, 58, and 55 kDa were specifically associated with Gi alpha in resting platelets. Stimulation of platelets with epinephrine, but not with thrombin, induced an increase of the reactivity of the 63- and 55-kDa proteins to anti-phosphotyrosine antibodies on western blotting. By in vitro kinase assay we found that epinephrine induced the association of kinase activity with Gi alpha and that the 63-kDa protein was phosphorylated by this activity. The association of kinase activity with Gi alpha in epinephrine-stimulated platelets paralleled the association of pp60src with Gi alpha, as detected by western blotting analysis using specific anti-pp60src monoclonal antibodies. The interaction of pp60src with Gi alpha may play a role in the mechanism of platelet activation by epinephrine or in the epinephrine-induced potentiation of the action of other platelet agonists.

Erythropoietin rapidly induces tyrosine phosphorylation in the human erythropoietin-dependent cell line, UT-7

UT-7 is a human megakaryoblastic cell line capable of growing in interleukin-3, granulocyte-macrophage colony-stimulating factor, or erythropoietin (Epo) (Cancer Res 51:341, 1991). We used this cell line and a selected Epo-dependent subcell line (UT-7/Epo) to study the early signal transduction events induced by Epo. When UT-7 cells were exposed to Epo, tyrosine phosphorylation of several proteins (with molecular weight equivalent to that of p85, p110, and p145) was observed. Protein phosphorylation occurred in both a dose- and time-dependent manner. p85 showed a marked increase in phosphotyrosine content within 30 seconds; maximal phosphorylation was observed at 1 minute. Subsequently, tyrosine phosphorylation of p110 and p145 was observed, beginning at 1 minute and reaching plateau at 5 minutes. The degree of phosphorylation of these three proteins gradually decreased thereafter. In addition, in UT-7/Epo cells, Epo induced tyrosine phosphorylation of other proteins that were not observed in Epo-induced UT-7 cells. The concentration of Epo required to induce tyrosine phosphorylation was in the same range of concentration required to stimulate cell growth. Epo was also able to activate p21ras as measured by exchange of guanosine diphosphate for guanosine triphosphate. These data show that tyrosine phosphorylation and P21ras activation are early signals in the Epo-induced mitogenic pathway.

Erythropoietin induces p21ras activation and p120GAP tyrosine phosphorylation in human erythroleukemia cells

Erythropoietin is the major regulator of the proliferation and differentiation of erythroid precursors, but little is known about its molecular mechanism of action. Using a human erythroleukemic cell line (HEL), we investigated whether p21ras is involved in erythropoietin signal transduction. We found that stimulation of HEL cells with erythropoietin induces a 5-fold increase in the amount of GTP bound to the endogenous p21ras. This effect is dose-dependent and occurs very rapidly. We also observed that erythropoietin causes tyrosine phosphorylation of several proteins in a time-dependent manner that correlates with the p21ras activation. Moreover, inhibition of tyrosine kinases by genistein totally prevents the erythropoietin-induced accumulation of a p21ras.GTP complex. By using an antiserum against the GTPase-activating protein, we found that p120GAP is rapidly phosphorylated in tyrosine in response to erythropoietin. Furthermore, the ability of a lysate from erythropoietin-stimulated HEL cells to induce in vitro hydrolysis of GTP bound to p21ras was strongly reduced. These results demonstrate that activation of p21ras is an early event in the erythropoietin signal transduction pathway, and they suggest that accumulation of the p21ras.GTP complex may be triggered by inhibition of GTPase-activating protein activity.

Stimulation of human platelets with concanavalin A involves phospholipase C activation

In response to concanavalin A, cytoplasmic calcium movement was observed in human platelets, both in the presence of 1 mM Ca2+ or 1 mM EGTA in the medium. Concanavalin A also caused the activation of inositide turnover and the production of inositol phosphates, suggesting that activation of phospholipase C occurs. The mechanism by which concanavalin A stimulates phospholipase C does not depend on GTP-binding transducers, because it was not inhibited by GDP beta S, while experiments performed in the presence of cytochalasin B suggested a role for membrane glycoprotein IIb-IIIa-cytoskeleton interaction in this process. Ca(2+)-proteases and Na+/H+ antiport also seemed to be related to concanavalin A-induced phospholipase C activation, as suggested by experiments performed in the presence of leupeptin and amiloride.

Platelet glycoprotein IIb-IIIa is associated with 21-kDa GTP-binding protein

Platelet membrane glycoprotein IIb-IIIa has been widely studied in the last years because of its role as an activation-dependent, adhesive protein receptor. Recently we demonstrated that occupancy of glycoprotein IIb-IIIa-receptor sites by specific ligands exerts an inhibitory effect on platelet responses induced by mild stimulation, leading us to suppose that this event may interact with activation pathways. Although the mechanisms of signal transduction in human platelets are not completely elucidated, the hypothesis that GTP-binding proteins are involved is generally accepted. Our results demonstrate that platelet ConA receptors, known to be located mainly on GP IIb-IIIa, are able to bind [35S]GTP gamma S; the GTP-binding activity is specific and is due to the association with the receptors of two G-proteins, with apparent molecular masses of 25 and 21 kDa, respectively. After the purification of GP IIb-IIIa, a glycoprotein complex electrophoretically pure was obtained that was still associated with a GTP-binding activity, migrating in SDS-polyacrylamide gel electrophoresis as a narrow band of about 21 kDa.

Fibronectin modulates the activation of human platelets

In this paper we studied the effect of plasma fibronectin on platelet responsiveness to low doses of thrombin or ADP. Fibronectin causes: (i) a significant lowered cytoplasmic calcium movement in platelets activated both with low doses of thrombin and with ADP, (ii) a lowered decrease of the cAMP level induced by low thrombin, but not by ADP, (iii) a dramatic decrease of protein phosphorylation in low thrombin-treated platelets. The results reported here demonstrate that plasma fibronectin behaves like an inhibitor of mild activations of human platelets; its effect is probably mediated by the glycoprotein llb-llla complex in thrombin activated platelets, whereas a different and unknown mechanism must be supposed to explain the results obtained with ADP-activated platelets.

The occupancy of glycoprotein IIb-IIIa complex modulates thrombin activation of human platelets

Platelet membrane glycoprotein (GP IIb-IIIa), besides its activity as adhesive protein receptor, displays a number of properties supporting its involvement in the mechanisms of transduction of the activation signal. Recently we have observed that GP IIb-IIIa ligands, mostly fibrinogen, inhibit Ca2+ movement and cytoskeleton reorganization caused by mild platelet activation. These findings led us to investigate the effect of GP IIb-IIIa ligands on agonist-induced platelet responses, with particular attention to the two major messenger generating systems, involving the activation of phospholipase C and the inhibition of cAMP production. In this paper we demonstrate that the occupancy of the major adhesive protein receptor on the platelet surface modulates the phosphatidylinositol cycle decreasing the amount of IP3, IP2 and IP produced after mild platelet activation as well as the pattern of protein phosphorylation. The platelet cAMP content of activated platelets was also affected and kept higher when evaluated under the same experimental conditions. Our data provide evidence for a role of fibrinogen binding in regulating the degree of activation of circulating platelets.

Interrelation of platelet aggregation, release reaction and thromboxane A2 production

Aggregation of platelets, stimulated by different agonists, was inhibited by omitting sample stirring or by preincubation of platelets with a monoclonal antibody against glycoproteins IIb-IIIa or with a pentapeptide containing the sequence Arg-Gly-Asp-Ser. In platelets stimulated by collagen, ADP and epinephrine, the inhibition of aggregation paralleled a reduction of both release reaction and thromboxane A2 formation. When thrombin was the stimulus, ATP release and thromboxane A2 production were unaffected (or only slightly modified) by the inhibition of platelet aggregation. These data add further evidence to the hypothesis that aggregation supports the activation of platelets stimulated by weak agonists.