Effect of sialylation on leukocyte transmigration through endothelial cells

我们想知道唾液酸缺乏会如何影响内皮细胞的表型。为此，我们从野生型和ST6Ga1基因缺失的小鼠制备了肝窦内皮细胞。胶原酶灌流后，分离肝脏，切成小片。然后用磁珠分离LSEC。我们发现ST6Ga1 I缺陷小鼠的LSECs表面特异性细胞黏附分子水平显著降低。细胞表面生物素化实验表明，细胞表面黏附分子的半衰期缩短。有趣的是，sislylateion缺陷细胞对线粒体依赖的凋亡刺激更敏感。我们阐明了BACE1切割ST6GalI的生物学意义。通过BACE1的过表达，可溶性糖蛋白(如转铁蛋白)的唾液酸化显著增加(J.Biol.化学。282、34896-34903)。在肝脏急性反应过程中，肝脏产生大量的血浆糖蛋白，其中大部分是唾液酸化的。非唾液酸糖蛋白被去唾液酸糖蛋白受体捕获在肝脏中进行降解。我们目前的假设是，通过BACE1的过度表达，可溶性唾液酸基转移酶可以有效地分解血浆糖蛋白。我们的发现揭示了糖基转移酶裂解-分泌的功能意义。

We wanted to know how sialylation deficiency would affect on the phenotype of endothelial cells. To do so, we prepared liver sinudoidal endothelial cells (LSECs) from wild type and ST6Ga1 I defieicnt mice. After collagenase perfusion, liver was isolated and cut into small pieces. LSECs were then separated by magnetic beads. We found that cell surface level of particular cell adhesion molecule was significantly decreased in LSECs from ST6Ga1 I deficient mice. We did cell surface biotinylation experiment and showed that half life of cell surface adhesion molecule was decreased. Interestingly, sislylateion deficient cells were more sensitive to mitochondrial-dependent apoptotic stimuli.We elucidate the biological significance of ST6Gal I cleavage by BACE1. By BACE1 over-expression, sialylation of soluble glycoproteins (e.g. transferrin) were significantly increased (J. Biol. Chem. 282, 34896-34903). During hepatic acute reaction, liver produces a large amount of plasma glycoproteins, most of which are sialylated. Non-sialylated glycoproteins are trapped by asialoglycoprotein receptor in livers for degradation. Our current hypotheis is that plasma glycoproteins are effectively sialylated by soluble sialyltransferases by BACE1 over-expression. Our finding shed light on the functional siginificance of the cleavage-secretion of glycosyltransferase.