Abstract 273: Platelet Dense Granule Secretion Plays a Critical Role in Thrombotic Occlusion of Normal and Atherosclerotic Arteries in vivo
Thrombotic vascular occlusion is a prominent cause of cardiovascular events such as myocardial infarction and stroke. Activated platelets secrete pro-thrombotic and pro-inflammatory molecules from intracellular granules that may amplify cell activation, but the contribution of platelet granule secretion (exocytosis) to thrombotic occlusion and vascular remodeling is not well understood. We investigated the hypothesis that platelet dense granule secretion is required for thrombotic occlusion after arterial injury in mice that mimic human Hermansky Pudlak Syndrome-3 (HPS-3) due to a genetic deficiency of HPS3 protein. Platelets from HPS3 coa/coa mice lack dense granules and their ATP secretion is reduced by 99.7% (±0.01%, n=4 mice). Collagen-induced platelet aggregation was also reduced by 90.3% (±1.1%) in HPS3 coa/coa mice (n=4). However, platelet activation and alpha granule secretion in response to thrombin (measured by surface P-selectin expression) was normal in HPS3 coa/coa mice (n=14 mice). We assessed thrombotic occlusion in HPS3 coa/coa mice on normal and atherosclerotic (ApoE-deficient) backgrounds fed a high fat diet for 22–25 weeks. Arterial injury was induced with 5% ferric chloride in the left common carotid artery of anesthetized mice and carotid blood flow was monitored with a miniature Doppler probe for 30 min after injury. Wild-type mice (n=10) displayed complete vessel occlusion 10 min after ferric chloride application while HPS3 coa/coa mice (n=6) displayed no reduction in blood flow during the monitoring period (p<0.001). Similar results were observed in atherosclerotic mice: complete occlusion occurred 10 min after injury in ApoE-deficient mice (n=4) vs. no occlusion after injury in the HPS3 coa/coa mice with ApoE-deficiency (n=6, p<0.001). Histologic sections through the injured carotid arteries indicate extensive atherosclerosis in the ApoE-deficient mice. Normal mice showed complete vessel occlusion while HPS3 coa/coa mice showed minimal mural thrombus in the injured vessels. We conclude that impaired dense granule secretion affects platelet aggregation and markedly protects against thrombotic vascular occlusion in normal and atherosclerotic arteries.