Shiraishi Mitsuya, Tani Eisuke, Miyamoto Atsushi
Department of Veterinary Pharmacology, Faculty of Agriculture, Kagoshima University, 1-21-24 Korimoto, Kagoshima 890-0065, Japan.
J Vet Med Sci. 2010 Mar;72(3):285-92. doi: 10.1292/jvms.09-0385. Epub 2009 Dec 1.
Hypercholesterolemia is one of the major contributing factors in atherosclerosis and the development of cardiovascular disease. Platelets from hypercholesterolemic rabbit have an increased cholesterol content and a hypersensitivity to endogenous aggregating agonists. Although rabbit has been widely used in studies of hypercholesterolemia, the precise role of platelet cholesterol in rabbit platelet activation has not been studied. In the present study, to determine the direct role of cholesterol on rabbit platelet activation, we examined the effect of in vitro modulation of cholesterol content on platelet activation. Cholesterol-depleted rabbit platelets by the treatment with methyl-beta-cyclodextrin showed decreased platelet aggregation by physiological agonists such as thrombin, adenosine diphosphate, and collagen. The inhibition of thrombin-induced aggregation in cholesterol-depleted platelets was restored by cholesterol repletion in platelets. The cholesterol depletion also inhibited Ca(2+) mobilization, which plays a pivotal role in the platelet activation induced by physiological agonists. We showed that the Ca(2+) influx pathway is strongly suppressed by cholesterol depletion more than Ca(2+) release from intracellular Ca(2+) stores in platelets stimulated with thrombin. Furthermore, platelet aggregation induced by PMA, a potent protein kinase C activator, was also depressed by cholesterol depletion. On the other hand, cholesterol enrichment in platelets augmented thrombin-induced aggregation and Ca(2+) mobilization. These findings suggest that cholesterol plays a critical role in regulating rabbit platelet activation, and provides fundamental information regarding hypercholesterolemia-mediated effects on cells in the rabbit model.
高胆固醇血症是动脉粥样硬化和心血管疾病发展的主要促成因素之一。高胆固醇血症兔的血小板胆固醇含量增加，且对内源性聚集激动剂过敏。尽管兔已广泛用于高胆固醇血症研究，但血小板胆固醇在兔血小板激活中的精确作用尚未得到研究。在本研究中，为确定胆固醇对兔血小板激活的直接作用，我们检测了体外调节胆固醇含量对血小板激活的影响。用甲基-β-环糊精处理使胆固醇耗竭的兔血小板，对凝血酶、二磷酸腺苷和胶原等生理性激动剂的血小板聚集反应降低。血小板中胆固醇补充可恢复胆固醇耗竭血小板中凝血酶诱导的聚集抑制作用。胆固醇耗竭还抑制了Ca(2+)动员，而Ca(2+)动员在生理性激动剂诱导的血小板激活中起关键作用。我们发现，在用凝血酶刺激的血小板中，Ca(2+)内流途径比细胞内Ca(2+)储存释放Ca(2+)受胆固醇耗竭的抑制作用更强。此外，强力蛋白激酶C激活剂佛波酯诱导的血小板聚集也因胆固醇耗竭而受到抑制。另一方面，血小板中胆固醇富集增强了凝血酶诱导的聚集和Ca(2+)动员。这些发现表明，胆固醇在调节兔血小板激活中起关键作用，并提供了关于高胆固醇血症介导的对兔模型中细胞影响的基础信息。
