β2 glycoprotein I participates in phagocytosis of apoptotic neurons and in vascular injury in experimental brain stroke

Beta-2 Glycoprotein I (beta 2-GPI) is the main target of anti-phospholipid antibodies (aPL) in the autoimmune anti-phospholipid syndrome, characterized by increased risk of stroke. We here investigated the antibody independent role of beta 2-GPI after ischemia/reperfusion, modeled in vivo by transient middle cerebral artery occlusion (tMCAo) in male C57Bl/6J mice; in vitro by subjecting immortalized human brain microvascular endothelial cells (ihBMEC) to 16 h hypoxia and 4 h re-oxygenation. ApoH (coding for beta 2-GPI) was upregulated selectively in the liver at 48 h after tMCAo. At the same time beta 2-GPI circulating levels increased. beta 2-GPI was detectable in brain parenchyma and endothelium at all time points after tMCAo. Parenchymal beta 2-GPI recognized apoptotic neurons (positive for annexin V, C3 and TUNEL) cleared by CD68+ brain macrophages. Hypoxic ihBMEC showed increased release of IL-6, over-expression of thrombomodulin and IL-1 alpha after re-oxygenation with beta 2-GPI alone. beta 2-GPI interacted with mannose-binding lectin in mouse plasma and ihBMEC medium, potentially involved in formation of thrombi. We show for the first time that brain ischemia triggers the hepatic production of beta 2-GPI. beta 2-GPI is present in the ischemic endothelium, enhancing vascular inflammation, and extravasates binding stressed neurons before their clearance by phagocytosis. Thus beta 2-GPI may be a new mediator of brain injury following ischemic stroke.

Automated summary

Beta-2 Glycoprotein I plays a role in brain injury following ischemic stroke by triggering hepatic production, enhancing vascular inflammation, interacting with mannose-binding lectin, and binding stressed neurons for clearance by phagocytosis.