{'fraction_non_alphanumeric': 0.03676913803496082, 'fraction_numerical': 0.0, 'mean_word_length': 5.360153256704981, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Vitronectin stabilizes thrombi and vessel occlusion but plays a dual role in platelet aggregation

Summary.  The role of vitronectin (Vn) in thrombosis is currently controversial; both inhibitory and supportive roles have been reported. To monitor directly the function of Vn in thrombotic events at the site of vascular injury, we studied Vn‐deficient (Vn–/–) and wild‐type (WT) control mice with two real‐time intravital microscopy thrombosis models. In the mesenteric arteriole model, vessel injury was induced by ferric chloride. We observed unstable thrombi and a significantly greater number of emboli in Vn–/– mice. Vessel occlusion was also delayed and frequent vessel re‐opening occurred. In the cremaster muscle arteriole model, vessel injury was induced by a nitrogen dye laser. We observed significantly fewer platelets, lower fibrin content, and unstable fibrin within the thrombi of Vn–/– mice. To define further the role of Vn in thrombus growth, we studied platelet aggregation in vitro. Consistent with our in vivo data, the second wave of thrombin‐induced aggregation of gel‐filtered platelets was abolished at a low concentration of thrombin in Vn–/– platelets. Interestingly, adenosine diphosphate (ADP)‐induced platelet aggregation was significantly increased in Vn–/– platelet‐rich plasma (PRP) and this effect was attenuated by adding purified plasma Vn. We also observed increased platelet aggregation induced by shear stress in Vn–/– whole blood. These data demonstrate that Vn is a thrombus stabilizer. However, in contrast to released platelet granule Vn which enhances platelet aggregation, plasma Vn inhibits platelet aggregation.