Platelet glycoprotein VI cluster size is related to thrombus formation and phosphatidylserine exposure in collagen-adherent platelets under arterial shear

Background: Collagen-induced platelet activation is predominantly mediated by glycoprotein (GP) VI through formation of receptor clusters that coincide with the accumulation of signaling molecules and are hypothesized to drive strong and sustained platelet activation. Objectives: To determine the importance of GPVI clusters for thrombus formation in whole blood under shear. Methods: We utilized whole blood microfluidics and an anti-GPVI nanobody (Nb), Nb28, labeled with AlexaFluor 488, to assess the distribution of GPVI on the surface of platelets adhering to a range of collagen-like substrates with different platelet activation potentials. Results: Automated analysis of GPVI surface distribution on platelets supported the hypothesis that there is a relationship between GPVI cluster formation, thrombus size, and phosphatidylserine (PS) exposure. Substrates that supported the formation of macroclusters also induced significantly bigger aggregates, with increased amounts of PS-exposing platelets in comparison to substrates where no GPVI clusters were detected. Furthermore, we demonstrate that only direct inhibition of GPVI binding, but not of downstream signaling, is able to disrupt cluster formation. Conclusion: Labeled anti-GPVI Nb28 permits visualization of GPVI clustering under flow conditions. Furthermore, whilst inhibition of downstream signaling does not affect clustering, it does prevent thrombus formation. Therefore, GPVI macroclustering is a prerequisite for thrombus formation and platelet activation, namely, PS exposure, on highly GPVI-dependent collagen surfaces

Restraining of glycoprotein VI- and integrin α2β1-dependent thrombus formation y platelet PECAM1

The platelet receptors, glycoprotein VI (GPVI) and integrin α2β1 jointly control collagen-dependent thrombus formation via protein tyrosine kinases. It is unresolved to which extent the ITIM (immunoreceptor tyrosine-based inhibitory motif) receptor PECAM1 and its downstream acting protein tyrosine phosphatase PTPN11 interfere in this process. Here, we hypothesized that integrin α2β1 has a co-regulatory role in the PECAM1- and PTPN11-dependent restraint of thrombus formation. We investigated platelet activation under flow on collagens with a different GPVI dependency and using integrin α2β1 blockage. Blood was obtained from healthy subjects and from patients with Noonan syndrome with a gain-of-function mutation of PTPN11 and variable bleeding phenotype. On collagens with decreasing GPVI activity (types I, III, IV), the surface-dependent inhibition of PECAM1 did not alter thrombus parameters using control blood. Blockage of α2β1 generally reduced thrombus parameters, most effectively on collagen IV. Strikingly, simultaneous inhibition of PECAM1 and α2β1 led to a restoration of thrombus formation, indicating that the suppressing signaling effect of PECAM1 is masked by the platelet-adhesive receptor α2β1. Blood from 4 out of 6 Noonan patients showed subnormal thrombus formation on collagen IV. In these patients, effects of α2β1 blockage were counterbalanced by PECAM1 inhibition to a normal phenotype. In summary, we conclude that the suppression of GPVI-dependent thrombus formation by either PECAM1 or a gain-of-function of PTPN11 can be overruled by α2β1 engagement

Examining variation across treatment clinics in cancer patients' psychological outcomes: results of a cross sectional survey

Published online: 4 April 2018Purpose: The majority of research on psychological outcomes for cancer patients has focussed on the role of individual characteristics, and disease and treatment factors. There has been very little exploration of the potential contribution of the treatment clinic to these outcomes. This study explored whether there is variation among clinics in cancer patients’ psychological outcomes. Methods: Cancer outpatients were recruited from 22 medical oncology and haematology clinics in Australia. Participants completed a pen and paper survey including the Hospital Anxiety and Depression Scale (HADS), as well as sociodemographic, disease and treatment characteristics. Results: Of those eligible to participate, 4233 (82%) consented and 2811 (81% of consenters) returned the completed survey. There was no statistically significant variation in HADS depression scores across clinics. Some difference in anxiety scores derived from the HADS questionnaire between clinics (p = 0.03) was found with the percentage of between-clinic variation estimated to be 1.11%. However, once all demographic, disease and treatment predictors were adjusted for there was no statistical differences between clinics (percent of between-clinic variation = 0.53%; p = 0.1415). Conclusions: Psychological outcomes were not found to vary between clinics. Other sources of variation including patient characteristics may over-ride between-clinic variability, if it exists.Mariko Carey, Robert Sanson-Fisher, Tara Clinton-McHarg, Allison Boyes, Ian Olver, Christopher Oldmeadow, Christine Paul, Catherine D'Este, Frans Hensken

Antibodies against Platelet Glycoproteins in Clinically Suspected VITT Patients

Vaccine-induced thrombotic thrombocytopenia (VITT) is a rare but severe complication following COVID-19 vaccination, marked by thrombocytopenia and thrombosis. Analogous to heparin-induced thrombocytopenia (HIT), VITT shares similarities in anti-platelet factor 4 (PF4) IgG-mediated platelet activation via the FcγRIIa. To investigate the involvement of platelet-antibodies in VITT, we analyzed the presence of platelet-antibodies directed against glycoproteins (GP)IIb/IIIa, GPV and GPIb/IX in the serum of 232 clinically suspected VITT patients determined based on (suspicion of) occurrence of thrombocytopenia and/or thrombosis in relation to COVID-19 vaccination. We found that 19% of clinically suspected VITT patients tested positive for anti-platelet GPs: 39%, 32% and 86% patients tested positive for GPIIb/IIIa, GPV and GPIb/IX, respectively. No HIT-like VITT patients (with thrombocytopenia and thrombosis) tested positive for platelet-antibodies. Therefore, it seems unlikely that platelet-antibodies play a role in HIT-like anti-PF4-mediated VITT. Platelet-antibodies were predominantly associated with the occurrence of thrombocytopenia. We found no association between the type of vaccination (adenoviral vector vaccine versus mRNA vaccine) or different vaccines (ChAdOx1 nCoV-19, Ad26.COV2.S, mRNA-1273, BTN162b2) and the development of platelet-antibodies. It is essential to conduct more research on the pathophysiology of VITT, to improve diagnostic approaches and identify preventive and therapeutic strategies.</p

Reply to: New Meta- and Mega-analyses of Magnetic Resonance Imaging Findings in Schizophrenia: Do They Really Increase Our Knowledge About the Nature of the Disease Process?

This work was supported by National Institute of Biomedical Imaging and Bioengineering Grant No. U54EB020403 (to the ENIGMA consortium)

Aortic stiffness is associated with cardiac function and cerebral small vessel disease in patients with type 1 diabetes mellitus: assessment by magnetic resonance imaging

To evaluate, with the use of magnetic resonance imaging (MRI), whether aortic pulse wave velocity (PWV) is associated with cardiac left ventricular (LV) function and mass as well as with cerebral small vessel disease in patients with type 1 diabetes mellitus (DM). We included 86 consecutive type 1 DM patients (49 male, mean age 46.9 +/- 11.7 years) in a prospective, cross-sectional study. Exclusion criteria included aortic/heart disease and general MRI contra-indications. MRI of the aorta, heart and brain was performed for assessment of aortic PWV, as a marker of aortic stiffness, systolic LV function and mass, as well as for the presence of cerebral white matter hyperintensities (WMHs), microbleeds and lacunar infarcts. Multivariate linear or logistic regression was performed to analyse the association between aortic PWV and outcome parameters, with covariates defined as age, gender, mean arterial pressure, heart rate, BMI, smoking, DM duration and hypertension. Mean aortic PWV was 7.1 +/- 2.5 m/s. Aortic PWV was independently associated with LV ejection fraction ( = -0.406, P = 0.006), LV stroke volume ( = -0.407, P = 0.001), LV cardiac output ( = -0.458, P = 0.001), and with cerebral WMHs (P < 0.05). There were no independent associations between aortic stiffness and LV mass, cerebral microbleeds or lacunar infarcts. Aortic stiffness is independently associated with systolic LV function and cerebral WMHs in patients with type 1 DM.Neuro Imaging Researc

Stress as a determinant of saliva-mediated adherence and coadherence of oral and nonoral microorganisms

Objective:: The mucosal secretory proteins, such as the salivary proteins, play a key role in the acquisition and regulation of the mucosal microflora. Most notably, some microorganisms utilize the host's secretory proteins to adhere to the mucosa; a first step in colonization and infection. The secretory proteins also influence colonization by affecting the binding among microorganisms, a process denoted as coadherence. Previously we reported that acute stressors cause specific changes in saliva composition. The present study investigated to what extent these changes influence saliva-mediated microbial adherence and coadherence (ex vivo). Methods:: Thirty-two male undergraduates provided unstimulated saliva before and during a control condition and two stressors: A memory test and a surgery video presentation. We used saliva-coated microplates to test the adherence of bacteria for which the oral cavity is either a natural reservoir (eg, viridans streptococci) or a portal of entry (eg, Helicobacter pylori). We also tested the saliva-mediated co-adherence between Streptococcus gordonii and the yeast Candida albicans. Correlation analyses were performed to determine the relationships between changes in microbial adherence and the concentrations of potential salivary ligands, viz. cystatin S, the mucins MUC5B and MUC7, S-IgA, lactoferrin, [alpha]-amylase, and total salivary protein. Results:: During the memory test, saliva-mediated adhesion of Streptococcus sanguis, Streptococcus gordonii, and H. pylori increased, whereas the coadherence of C. albicans with S. gordonii decreased. During the surgical video presentation the saliva-mediated adherence of H. pylori, S. sanguis, and Streptococcus mitis increased. These changes were independent of salivary flow rate, but correlated with specific changes in salivary protein composition. Conclusion:: The results show that even moderate stressors, by altering the activity of the mucosal secretory glands, may affect microbial colonization processes such as adherence and coadherence. This study hereby presents a mechanism by which stress may affect the mucosal microflora and susceptibility to infectious disease

Association between Carotid Plaque Characteristics and Cerebral White Matter Lesions: One-Year Follow-Up Study by MRI

Objective: To prospectively assess the relation between carotid plaque characteristics and the development of new cerebral white matter lesions (WMLs) at MRI. Methods: Fifty TIA/stroke patients with ipsilateral 30-69% carotid stenosis underwent MRI of the plaque at baseline. Total plaque volume and markers of vulnerability to thromboembolism (lipid-rich necrotic core [LRNC] volume, fibrous cap [FC] status, and presence of intraplaque hemorrhage [IPH]) were assessed. All patients also underwent brain MRI at baseline and after one year. Ipsilateral cerebral WMLs were quantified with a semiautomatic method. Results: Mean WML volume significantly increased over a one-year period (6.52 vs. 6.97 mm3, P = 0.005). WML volume at baseline and WML progression did not significantly differ (P>0.05) between patients with 30-49% and patients with 50-69% stenosis. There was a significant correlation between total plaque volume and baseline ipsilateral WML volume (Spearman ¿ = 0.393, P = 0.005). There was no significant correlation between total plaque volume and ipsilateral WML progression. There were no significant associations between LRNC volume and WML volume at baseline and WML progression. WML volume at baseline and WML progression did not significantly differ between patients with a thick and intact FC and patients with a thin and/or ruptured FC. WML volume at baseline and WML progression also did not significantly differ between patients with and without IPH. Conclusion: The results of this study indicate that carotid plaque burden is significantly associated with WML severity, but that there is no causal relationship between carotid plaque vulnerability and the occurrence of WMLs. © 2011 Kwee et al