Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, AB T6G-2E1, Canada.
Neurochemical Research Unit, Department of Psychiatry, University of Alberta, Edmonton, AB T6G-2R3, Canada.
Cardiovasc Res. 2017 Dec 1;113(14):1719-1731. doi: 10.1093/cvr/cvx179.
In addition to maintaining haemostasis, circulating blood platelets are the cellular culprits that form occlusive thrombi in arteries and veins. Compared to blood leucocytes, which exist as functionally distinct subtypes, platelets are considered to be relatively simple cell fragments that form vascular system plugs without a differentially regulated cellular response. Hence, investigation into platelet subpopulations with distinct functional roles in haemostasis/thrombosis has been limited. In our present study, we investigated whether functionally distinct platelet subpopulations exist based on their ability to generate and respond to nitric oxide (NO), an endogenous platelet inhibitor.
Utilizing highly sensitive and selective flow cytometry protocols, we demonstrate that human platelet subpopulations exist based on the presence and absence of endothelial nitric oxide synthase (eNOS). Platelets lacking eNOS (approximately 20% of total platelets) fail to produce NO and have a down-regulated soluble guanylate cyclase-protein kinase G (sGC-PKG)-signalling pathway. In flow chamber and aggregation experiments eNOS-negative platelets primarily initiate adhesion to collagen, more readily activate integrin αIIbβ3 and secrete matrix metalloproteinase-2, and form larger aggregates than their eNOS-positive counterparts. Conversely, platelets having an intact eNOS-sGC-PKG-signalling pathway (approximately 80% of total platelets) form the bulk of an aggregate via increased thromboxane synthesis and ultimately limit its size via NO generation.
These findings reveal previously unrecognized characteristics and complexity of platelets and their regulation of adhesion/aggregation. The identification of platelet subpopulations also has potentially important consequences to human health and disease as impaired platelet NO-signalling has been identified in patients with coronary artery disease.
除了维持止血作用外，循环血液中的血小板还是在动脉和静脉中形成闭塞性血栓的罪魁祸首。与作为功能不同亚型存在的白细胞相比，血小板被认为是相对简单的细胞碎片，它们在没有差异调节的细胞反应的情况下形成血管系统塞子。因此，对在止血/血栓形成中具有不同功能作用的血小板亚群的研究受到限制。在本研究中，我们研究了是否存在基于其生成和对一氧化氮（NO）反应能力的不同功能的血小板亚群，NO 是一种内源性血小板抑制剂。
利用高度敏感和选择性的流式细胞术方案，我们证明了根据是否存在内皮型一氧化氮合酶（eNOS），人血小板亚群是存在的。缺乏 eNOS 的血小板（约占总血小板的 20%）不能产生 NO，并且可溶性鸟苷酸环化酶-蛋白激酶 G（sGC-PKG）信号通路被下调。在流室和聚集实验中，eNOS 阴性血小板主要起始与胶原蛋白的黏附，更易于激活整合素αIIbβ3并分泌基质金属蛋白酶-2，并形成比其 eNOS 阳性对应物更大的聚集物。相反，具有完整 eNOS-sGC-PKG 信号通路的血小板（约占总血小板的 80%）通过增加血栓素合成形成聚集物的大部分，并最终通过生成 NO 限制其大小。
这些发现揭示了血小板以前未被认识的特征和复杂性及其对黏附和聚集的调节。血小板亚群的鉴定也可能对人类健康和疾病具有重要意义，因为在冠心病患者中已经发现血小板 NO 信号受损。
