Localization of β2-Glycoprotein 1 in Late Endosomes of Human Endothelial Cells

Abstract

SummaryAntiphospholipid antibodies (APLA) are associated with thrombophilia and recurrent pregnancy loss. Different mechanisms have been proposed to explain their pathogenic effects and among them, we have previously shown that APLA accumulate in late endosomes of human umbilical vein endothelial cells (HUVEC) leading to a redistribution of the cation-independent mannose-6-phosphate receptor (CI-M6PR). Because many APLA are directed towards β2-glycoprotein 1 (β2GP1)-phospholipid complexes, we investigated the localisation of β2GP1 in HUVEC. By immunofluorescence analysis, using monoclonal and polyclonal anti- β2GP1 antibodies, we detected β2GP1 at the cell surface and in late endosomes. Incubation of HUVEC with anti- β2GP1 antibodies resulted in antibody accumulation at the cell surface and within late endosomes and in a redistribution of the CI-M6PR from the Golgi apparatus to late endosomes. The anti- β2GP1 antibodies remained detectable in late endosomes even after several days of incubation in antibody-free medium. The accumulation of anti- β2GP1 antibodies in late endosomes of endothelial cells and the resulting modification of intracellular protein trafficking may contribute to the pathogenic effects of these antibodies.

Association of Early Kidney Allograft Failure with Preformed IgA Antibodies to β 2-Glycoprotein I

“…It is localized on the endothelial cell surfaces associated with lipids or membrane proteins as receptors. 41 aB2GPI antibodies can activate endothelial cells, 42 modulating the expression of adhesion molecules and cytokine production. 43 Cell activation seems to be a major pathogenic cause in the pathogenesis of APS.…”

Receptors involved in cell activation by antiphospholipid antibodies

“…These results imply that activation of the vascular endothelium by aPLA is a major thrombogenic mechanism [14]. Several in vitro as well as in vivo studies have shown that aPLA may recognize target antigens, such as β2GP1, bound to the surface of EC [15]. The specific binding of anti-β2GP1 antibodies to EC induces surface expression of pro-coagulant, pro-adhesive and pro-inflammatory molecules that favors the binding of circulating leukocytes.…”

“…In particular, we have previously suggested that the translocation of aPLA into late endosomes may contribute to their pathogenic effects [15,57,70]. Interestingly, annexin A2 appears to be a necessary component of the machinery controlling endosomal membrane dynamics and multivesicular endosome biogenesis, and, in particular the clathrin-dependent endocytosis [71].…”

Aspirin inhibits endothelial cell activation induced by antiphospholipid antibodies

“…These antibodies may bind directly to phospholipids or to phospholipid binding proteins, such as b 2 -glycoprotein I (b 2 GPI), prothrombin and annexin V [4]. Previously we have shown that patients' APLA or rabbit antibodies to b 2 GPI bind to the endothelial cell (EC) surface, are internalized and accumulate in the late endosomes of EC [5,6]. Furthermore, incubation of EC with APLA led to an increased expression of tissue factor, leukocyte adhesion molecules [2,[7][8][9] and monocyte adhesion [10].…”