Platelet SR-BI contributes to increased platelet responses and thrombosis in hyperlipidemic apoE^−/− mice. (A) Platelets in PRP from apoE^−/− mice fed Western-type diet and from matched WT mice were stained with 50 μg/mL filipin to label unesterified cholesterol and analyzed by flow cytometry (n = 4). (B-E) ApoE^−/− mice were reconstructed with either apoE^−/−/SR-BI^−/− bone marrow or apoE^−/− bone marrow. One month later, Western diet feeding was started and continued for 6 weeks, and then mice were used for experiments. (B) Agonist-induced platelet integrin α_IIbβ₃ activation was assessed by flow cytometry in platelet isolated by gel filtration. (n ≥ 3). (C-D) Platelet aggregation in PRP from apoE^−/− mice with apoE^−/− BM or apoE^−/−/SR-BI^−/− BM was induced by PAR4-AP and optically monitored. (C) Representative aggregation curves are shown in response to 120μM PAR4-AP. (D) Quantification of the aggregation data expressed as maximal amplitude of aggregation within 5 minutes after induction (n ≥ 3). (E) Times to thrombotic occlusion of carotid arteries of chimeric apoE^−/− mice with apoE^−/− BM or apoE^−/−/SR-BI^−/− BM were measured 2 minutes after topical application of 7% FeCl₃. n = 11. Data are presented as mean ± SEM. * P < .05, **P < .01.