Institute of Physiology, Center for Physiology & Pharmacology, Medical University of Vienna, Schwarzspanierstr. 17, A-1090 Vienna, Austria.
Atherosclerosis. 2010 Nov;213(1):129-34. doi: 10.1016/j.atherosclerosis.2010.07.018. Epub 2010 Jul 22.
OxLDL represents a central player in atherogenesis and has been shown to activate human blood platelets. In light of the pivotal role of CD40L in inflammation, it was the aim of this work to clarify if platelet-activating effects of oxidized LDL result in surface exposure and liberation of CD40L and to explore the role of platelet scavenger receptor CD36 in this process.
Binding and functional studies were performed with hypochlorite-oxidized LDL in absence and presence of (potential) competitors in normal and CD36-deficient human platelets. To determine functional effects of hypochlorite-oxidized LDL on human platelets, formation of reactive oxygen species, intraplatelet calcium, CD40L and CD62P as well as platelet aggregation were quantified.
Addition of OxLDL to resting human platelets results in intracellular calcium flux, platelet aggregation and surface expression of CD62P. OxLDL triggers the formation of intracellular reactive oxygen species and surface exposure of CD40L, with both being sensitive to the NADPH oxidase inhibitor apocynin. In CD36-deficient human platelets, functional effects as well as high affinity binding of hypochlorite-oxidized LDL appears to be significantly reduced compared with platelets positive for CD36.
Our results prove a prominent--however, not exclusive--role of CD36 in platelet binding of hypochlorite-oxidized LDL. CD36 appears to be the major receptor responsible for hypochlorite-oxidized LDL-induced platelet activation that accumulates in the release of CD40L. As platelets represent the major source of CD40L, our findings emphasize an important pro-inflammatory role of platelets, especially in conditions of oxidative stress.
氧化低密度脂蛋白（OxLDL）是动脉粥样硬化形成过程中的核心因子，并且已经证实其可以激活人血小板。鉴于 CD40L 在炎症反应中的关键作用，本研究旨在阐明氧化型 LDL 是否通过激活血小板而导致 CD40L 表面暴露和释放，并进一步探讨血小板清道夫受体 CD36 在这一过程中的作用。
采用次氯酸氧化 LDL 方法，在正常和 CD36 缺陷的人类血小板中，通过加入（潜在）竞争物，进行 OxLDL 的结合和功能研究。为了确定次氯酸氧化 LDL 对人类血小板的功能影响，我们对活性氧形成、血小板内钙离子、CD40L 和 CD62P 的表达以及血小板聚集进行了定量分析。
将 OxLDL 加入静止的人血小板中会导致细胞内钙离子流、血小板聚集和 CD62P 表面表达。OxLDL 触发细胞内活性氧的形成和 CD40L 的表面暴露，这两种反应都对 NADPH 氧化酶抑制剂 apocynin 敏感。与 CD36 阳性血小板相比，CD36 缺陷的人类血小板中，次氯酸氧化 LDL 的功能效应以及高亲和力结合似乎明显降低。
我们的研究结果证明了 CD36 在血小板结合次氯酸氧化 LDL 中具有重要作用（尽管不是唯一作用）。CD36 似乎是负责次氯酸氧化 LDL 诱导的血小板激活的主要受体，这种激活导致 CD40L 的释放增加。由于血小板是 CD40L 的主要来源，我们的发现强调了血小板在炎症反应中的重要作用，尤其是在氧化应激条件下。
