A novel pathway for human endothelial cell activation by antiphospholipid/anti-β2 glycoprotein I antibodies

• Published in: Blood Vol. 119; no. 3; pp. 884 - 893
• Main Authors: Allen, Kristi L., Fonseca, Fabio V., Betapudi, Venkaiah, Willard, Belinda, Zhang, Jainwei, McCrae, Keith R.
• Format: Journal Article
• Language: English
• Published: Washington, DC Elsevier Inc 19.01.2012; Americain Society of Hematology; American Society of Hematology
• Subjects: Annexin A2 - genetics; Annexin A2 - metabolism; Antibodies, Antiphospholipid - pharmacology; beta 2-Glycoprotein I - immunology; Biological and medical sciences; Blotting, Western; Calbindin 2; Cells, Cultured; Endothelium, Vascular - cytology; Endothelium, Vascular - metabolism; General aspects; Hematologic and hematopoietic diseases; Humans; Immunoenzyme Techniques; Immunopathology; Immunoprecipitation; Luciferases - metabolism; Medical sciences; Membrane Microdomains; Nucleolin; Phospholipids - metabolism; Phosphoproteins - genetics; Phosphoproteins - metabolism; Real-Time Polymerase Chain Reaction; RNA, Messenger - genetics; RNA, Small Interfering - genetics; RNA-Binding Proteins - genetics; RNA-Binding Proteins - metabolism; S100 Calcium Binding Protein G - genetics; S100 Calcium Binding Protein G - metabolism; Signal Transduction; Thrombosis; Thrombosis and Hemostasis; Toll-Like Receptor 4 - antagonists & inhibitors; Toll-Like Receptor 4 - genetics; Toll-Like Receptor 4 - metabolism; Umbilical Veins - cytology; Umbilical Veins - metabolism; Vascular Biology; Autoimmunity; Human; Immunopathology; Endothelial cell; Antiphospholipid antibody syndrome; Hematology; Antibody; Autoantibody; Autoimmune disease; Cardiovascular disease; Hemopathy; Vascular disease; β2 acid-Glycoprotein; Platelet
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood-2011-03-344671

Antiphospholipid Abs (APLAs) are associated with thrombosis and recurrent fetal loss. These Abs are primarily directed against phospholipid-binding proteins, particularly β2GPI, and activate endothelial cells (ECs) in a β2GPI-dependent manner after binding of β2GPI to EC annexin A2. Because annexin A2 is not a transmembrane protein, the mechanisms of APLA/anti-β2GPI Ab–mediated EC activation are uncertain, although a role for a TLR4/myeloid differentiation factor 88–dependent pathway leading to activation of NF-κB has been proposed. In the present study, we confirm a critical role for TLR4 in anti-β2GPI Ab–mediated EC activation and demonstrate that signaling through TLR4 is mediated through the assembly of a multiprotein signaling complex on the EC surface that includes annexin A2, TLR4, calreticulin, and nucleolin. An essential role for each of these proteins in cell activation is suggested by the fact that inhibiting the expression of each using specific siRNAs blocked EC activation mediated by APLAs/anti-β2GPI Abs. These results provide new evidence for novel protein-protein interactions on ECs that may contribute to EC activation and the pathogenesis of APLA/anti-β2GPI–associated thrombosis and suggest potential new targets for therapeutic intervention in antiphospholipid syndrome.