Thrombospondin-1 controls vascular platelet recruitment and thrombus adherence in mice by protecting (sub)endothelial VWF from cleavage by ADAMTS13

Abstract

The function of thrombospondin-1 (TSP-1) in hemostasis was investigated in wild-type (WT) and Tsp1 ؊/؊ mice, via dynamic platelet interaction studies with A23187-stimulated mesenteric endothelium and with photochemically injured cecum subendothelium. Injected calcein-labeled WT platelets tethered or firmly adhered to almost all A23187-stimulated blood vessels of WT mice, but Tsp1 ؊/؊ platelets tethered to 45% and adhered to 25.8% of stimulated Tsp1 ؊/؊ vessels only. Stimulation generated temporary endothelium-associated ultralarge von Willebrand factor (VWF) multimers, triggering platelet string formation in 48% of WT versus 20% of Tsp1 ؊/؊ vessels. Injection of human TSP-1 or thrombotic thrombocytopenic purpura (TTP) patient-derived neutralizing anti-ADAMTS13 antibodies corrected the defective platelet recruitment in Tsp1 ؊/؊ mice, while having a moderate effect in WT mice. Photochemical injury of intestinal blood vessels induced thrombotic occlusions with longer occlusion times in Tsp1 ؊/؊ venules (1027 ؎ 377 seconds) and arterioles (858 ؎ 289 seconds) than in WT vessels (559 ؎ 241 seconds, P < .001; 443 ؎ 413 seconds, P < .003) due to defective thrombus adherence, resulting in embolization of complete thrombi, a defect restored by both human TSP-1 and anti-ADAMTS13 antibodies. We conclude that in a shear field, soluble or local plateletreleased TSP-1 can protect unfolded endothelium-bound and subendothelial VWF from degradation by plasma ADAMTS13, thus securing platelet tethering and thrombus adherence to inflamed and injured endothelium, respectively. (Blood. 2006;107: 955-964)

Thrombotic Thrombocytopenic Purpura: A Thrombotic Disorder Caused by ADAMTS13 Deficiency

“…In vitro, thrombin, plasmin, and perhaps hemoglobin may inactivate ADAMTS13 [15;16]. Thrombospondin may also protect VWF from cleavage by ADAMTS13 [17]. Based on observations following infusion of normal plasma in patients with genetic deficiency of ADAMTS13, the elimination half-life of ADAMTS13 is approximately 2 days.…”

Purinergic receptor P2RY12-dependent microglial closure of the injured blood–brain barrier

“…Average velocity and flux per image were calculated by Matlab software (MathWorks) with custom software by detecting the movement of red blood cells as black lines devoid of Texas Reddextran (53). Platelet aggregation in vivo was imaged with Texas Red-dextran and Calcein AM (100 μL of 5 mM; Invitrogen) administered through a femoral vein before the imaging (54,55). Collagen (10-50 μL of 1 mg/mL dissolved in saline; Gibco) was administered through a catheter inserted into the external carotid artery to induce platelet aggregation.…”

ADAMTS13 and microvascular thrombosis

“…Some studies have reported that when endothelial cells are exposed to cytoactive molecules such as histamine or calcium ionophore A23187, the secreted VWF may remain anchored to endothelial surface, providing a substrate to support platelet adhesion under flowing conditions (26)(27)(28). ADAMTS13 causes detachment of the platelets, presumably by cleaving the anchored VWF.…”