磷脂酰丝氨酸外翻是凋亡“食我”的信号

An apoptotic ＂Eat Me＂ signal： phosphatidylserine exposure

磷脂酰丝氨酸（Phosphatidylserine,PS）在真核细胞膜中广泛存在,具有重要的生物学功能。翻转酶可以将细胞内的PS经过生化反应而使其外翻在细胞表面,如细胞凋亡、血小板活化。细胞凋亡时,细胞内的ATP供应不足会引起胞浆Ca^2＋浓度升高,使得PS外翻。细胞凋亡及凋亡细胞的清除是动物体内基本的生理过程,对于要清除的凋亡细胞,必须显示一个“食我”（“eat me”）的信号来促使吞噬细胞识别进行吞噬,而这一信号最有可能是由PS发出。当PS外翻在细胞表面,凋亡细胞表面的PS就会充当起“食我”的信号,并且能够活化血小板产生血液凝血因子。在早期研究中并没有发现反转录和翻转酶,而近期发现外翻在细胞表面的PS受到越来越多学者的关注,成为研究热点。本文介绍了在血小板活化和凋亡细胞中PS外翻,并讨论清除凋亡细胞的过程。

Phosphatidylserine （PS） is a phospholipid that is abundant in eukaryotic plasma membranes,has crucial biological functions.Under cell apoptosis, cells can not generate enough ATP for energy and the concentration of cytoplasmic Ca ^2 ＋increases, resulting in PS eversion.Apoptosis and the clearance of apoptotic cells are essential processes in animal development and homeostasis.For apoptotic cells to be cleared, they must display an＂eat me＂ signal, most likely PS exposure, which prompts phagocytes to engulf the cells.PS is exposed by the action of scramblase on the cell＇s surface in biological processes such as apoptosis and platelet activation.Once exposed to the cell surface, PS acts as an ＂eat me＂ signal on dead cells, and creates a scaffold for blood-clotting factors on activated platelets.The molecular identities of the flippase and scramblase that work at plasma membranes have long eluded researchers.Indeed, their identity as well as the mechanism of the PS exposure to the cell surface has only recently been revealed.We describe how PS is exposed in activated platelets and in apoptotic cells, and discuss the clearance of apoptotic cells.