Impaired thrombin generation in Reelin‐deficient mice: a potential role of plasma Reelin in hemostasis

Abstract

Impaired thrombin generation in Reelin-deficient mice: a potential role of plasma Reelin in hemostasis. J Thromb Haemost 2014; 12: 2054-64.Summary. Background: Reelin is a large extracellular glycoprotein that is present in the peripheral blood. That Reelin interacts with the coagulation components and elicits a functional role in hemostasis has not yet been elucidated. Objectives: The hemostatic activity of Reelin is investigated and defined in this study. Methods: The interplay of Reelin with coagulation components was elucidated by far-Western and liposome/platelet binding assays. In vivo and ex vivo hemostasis-related analyses of Reelin-deficient mice and plasma were also performed. Results: Reelin interacted with the liposomes containing phosphatidylserine (PS) or phosphatidylcholine. Instead of interacting with known Reelin receptors (ApoE receptor 2, very low density lipoprotein receptor and integrin b1), Reelin interacted with PS of the activated platelets. The interaction between Reelin and the coagulation factors of thrombin and FXa was also demonstrated with the Kd of 11.7 and 21.2 nM, respectively. Reelin-deficient mice displayed a prolonged bleeding time and an increase in rebleeding rate. Despite the fact that Reelin deficiency had no significant effect on the clotting time of prothrombin and activated partial thromboplastin time, the fibrin clot formation was abnormal and the fibrin clot structure was relatively loosened with reduced clot strength. Abnormal fibrinogen expression did not account for the hemostatic defects associated with Reelin deficiency.Instead, thrombin generation was impaired concomitant with an altered prothrombin cleavage pattern. Conclusions: By interacting with platelet phospholipids and the coagulation factors, thrombin and FXa, Reelin plays a selective role in coagulation activation, leading to thrombin generation and formation of a normal fibrin clot.

Loss of Reelin protects against atherosclerosis by reducing leukocyte–endothelial cell adhesion and lesion macrophage accumulation

“…Reelin, a regulator of brain development and synaptic neuromodulator that signals through ApoE receptors, is also abundant in the liver and present at substantial concentrations in the circulation (21, 23, 24). In the present work, we employed two distinct types of Reelin conditional knockout mice to determine how Reelin affected atherosclerosis.…”

“…Although atherosclerosis specifically affects arterial vessels, as opposed to the venous system, and is marked by the subendothelial accumulation of lipids and lipid-laden foam cells (40), it shares the recruitment of circulating leukocytes and monocytes to the developing and progressing lesions with other inflammatory processes that involve the vasculature. Reelin has been reported to affect thrombosis and hemostasis (23, 24). Here we have shown that Reelin promotes atherosclerosis by increasing leukocyte adhesion to the vascular endothelium through increased abundance of the major adhesion molecules that are induced during atherogenesis and which promote the accumulation of macrophages in the lesions - ICAM-1, VCAM-1, and E-selectin (34, 35, 41, 42).…”

“…Conceivable alternative strategies involve siRNA- or antisense oligonucleotide-directed ablation of peripheral Reelin production or systemic application of recombinant function-blocking decoy receptors, a strategy that is being successfully employed for anti-TNF therapy (52). In addition, removing or inhibiting circulating Reelin could be expected to further protect against thromobosis by reducing platelet adhesion (23) and clotting propensity (24), factors that also promote atherogenesis. Likewise, suppression of circulating Reelin might also be beneficial in other diseases in which excessive leukocyte/monocyte extravasation contributes to the pathology.…”

“…These include: (i) the Reelin-induced reduction of eNOS and simultaneous increase of NF-kB activity via Apoer2, resulting in (ii) increased leukocyte-endothelial adhesion and (iii) monocyte/macrophage accumulation in expanding atherosclerotic lesions. These cellular mechanisms, combined with a direct prothrombotic function of Reelin (24), represent peripheral proatherogenic effects of this essential regulator of brain development, synaptic plasticity, learning and memory. Reelin and its surprising modes of action in the context of atherosclerosis open up new avenues to pursue in our efforts to combat cardiovascular disease and potentially other disorders that are driven by excessive leukocyte extravasation.…”

“…In the liver, Reelin is produced by stellate cells, not hepatocytes (22). It promotes platelet spreading on fibrinogen and also plays a role in coagulation by enhancing thrombin generation and the formation of fibrin clots (23, 24). There is evidence that the two receptors for Reelin, Apolipoprotein E receptor-2 (Apoer2/Lrp8) and very low-density lipoprotein receptor (Vldlr), influence atherosclerosis severity.…”