Figure 1

Multiparameter assessment of platelet activation and aggregation under arterial flow of Apoe−/− and Ldlr−/− mouse blood in the absence of coagulation. Blood was used from young (9–12 weeks) and aged (37–42 weeks) Apoe−/−, Ldlr−/− and corresponding wild-type mice, held on normal chow diet. PPACK-anticoagulated blood was perfused over collagen type I at wall shear rate of 1000 s−1. Brightfield images were captured, after which the deposited platelets were stained for integrin αIIbβ3 activation, P-selectin expression and PS exposure in different colors (see “Methods”). (A) Representative images from young mice are shown for each color per genotype. Bars indicate 20 μm. (B) Quantification (% SAC) of brightfield images of platelet deposition and fluorescence images of platelet activation parameters: phosphatidylserine (PS) exposure, P-selectin expression and integrin αIIbβ3 activation of (i) young mice and (ii) aged mice. Mean ± SEM (n = 6–15 animals/group). *P < 0.05, **P < 0.01 and ***P < 0.001 vs. wild-type (Mann–Whitney U test). (C) Platelet activation parameters were obtained from brightfield and fluorescence images after 3.5 min: P1, morphological score; P2, platelet surface area coverage (% SAC); P3, aggregate contraction score; P4, aggregate multilayer score; P5, aggregate multilayer coverage (% SAC); P6, PS exposure (% SAC); P7, P-selectin expression (% SAC); P8, integrin αIIbβ3 activation (% SAC). Values per parameter were linearly scaled to 0–10 and a scaled heatmap with integration of age groups was generated. (D) Scaled heatmap of effect sizes per genotype. Effect size per parameter was calculated from the pooled standard deviation, Cohen’s d and regression coefficient r. Analysis based on relevant changes restricted to differences with P < 0.05 (t test, 2-sided, equal variance). Means (n = 15–20 animals/group). (E) Isolated platelets were activated by thrombin (0.5–4 nM) or cross-linked collagen-related peptide (CRP-XL, 0.5–5 μg/ml); exposure of phosphatidylserine (PS), P-selectin and activation of integrin αIIbβ3 were determined by flow cytometry using AF647-labeled annexin A5, FITC-labeled anti-CD62P mAb, and PE-labeled JON/A mAb, respectively. Means ± SEM (n = 8–12), *P < 0.05, #P < 0.01, $P < 0.001 compared to WT (Kruskall–Wallis test).