Kolb S, Vranckx R, Huisse M-G, Michel J-B, Meilhac O
INSERM, U698 Haematology, Bio-engineering and Cardiovascular Remodelling, Paris F-75018, France.
J Pathol. 2007 Jul;212(3):249-59. doi: 10.1002/path.2190.
Apoptosis participates in every step of atherogenesis, but the process of clearance of apoptotic cells by phagocytosis has been underestimated. Rapid removal of apoptotic cells is critical for tissue homeostasis, in order to avoid accumulation of necrotic material and subsequent inflammation in the pathological vascular wall. We have demonstrated by RT-PCR, western blot and immunocytofluorescence that vascular smooth muscle cells (VSMCs) express the phosphatidylserine receptor (PSR). We then tested the involvement of PSR in the ability of VSMCs to bind and engulf apoptotic cells. We used a model of senescent erythrocytes, which expose PS after 4 days of culture (85% of cells relative to 8% in freshly isolated erythrocytes). The pseudo-peroxidase activity of haemoglobin contained within erythrocytes allowed us to quantify per se both binding and phagocytosis by VSMCs. We have also shown by light and confocal microscopy that VSMCs were able to ingest aged erythrocytes. Addition of a blocking antibody or transfection of VSMCs by a siRNA directed against PSR reduced the binding and engulfment of aged erythrocytes by more than 90%. These results suggest that PSR is involved in phagocytosis of PS-presenting cells. Incubation of aged erythrocytes with VSMCs also significantly increased the expression of PSR, suggesting that the tethering/ingestion of apoptotic cells triggers this process. Immunostaining for PSR in complicated atherosclerotic plaques shows positivity in the media and macrophage-rich areas. The mechanisms underlying phagocytosis and involving PSR in vivo, within the pathological arterial wall, deserve further investigation.
细胞凋亡参与动脉粥样硬化形成的每一个步骤，但吞噬作用清除凋亡细胞的过程一直被低估。快速清除凋亡细胞对于组织稳态至关重要，以避免坏死物质的积累以及病理血管壁中随后发生的炎症。我们通过逆转录聚合酶链反应（RT-PCR）、蛋白质印迹法和免疫细胞荧光法证明，血管平滑肌细胞（VSMC）表达磷脂酰丝氨酸受体（PSR）。然后，我们测试了PSR在VSMC结合和吞噬凋亡细胞能力中的作用。我们使用了衰老红细胞模型，培养4天后这些红细胞会暴露磷脂酰丝氨酸（相对于新鲜分离的红细胞，85%的细胞会暴露，而新鲜分离的红细胞中这一比例为8%）。红细胞内所含血红蛋白的假过氧化物酶活性使我们能够对VSMC的结合和吞噬作用进行定量分析。我们还通过光学显微镜和共聚焦显微镜观察到，VSMC能够摄取衰老红细胞。添加阻断抗体或用针对PSR的小干扰RNA（siRNA）转染VSMC，可使衰老红细胞的结合和吞噬作用降低90%以上。这些结果表明，PSR参与了呈现磷脂酰丝氨酸的细胞的吞噬作用。衰老红细胞与VSMC共孵育也显著增加了PSR的表达，这表明凋亡细胞的拴系/摄取触发了这一过程。在复杂动脉粥样硬化斑块中对PSR进行免疫染色显示，在中膜和富含巨噬细胞的区域呈阳性。在病理动脉壁内，体内吞噬作用以及涉及PSR的机制值得进一步研究。
