Journal
BRITISH JOURNAL OF HAEMATOLOGY
Volume 148, Issue 3, Pages 416-427Publisher
WILEY
DOI: 10.1111/j.1365-2141.2009.07959.x
Keywords
Wiskott-Aldrich syndrome; platelet disorder; integrins; fibrin clot retraction; phosphatidylserine exposure
Categories
Funding
- National Institutes of Health [AI039574, HL59561, HL081407]
- Jeffrey Modell Foundation
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P>The most consistent feature of Wiskott Aldrich syndrome (WAS) is profound thrombocytopenia with small platelets. The responsible gene encodes WAS protein (WASP), which functions in leucocytes as an actin filament nucleating agent -yet- actin filament nucleation proceeds normally in patient platelets regarding shape change, filopodia and lamellipodia generation. Because WASP localizes in the platelet membrane skeleton and is mobilized by alpha IIb beta 3 integrin outside-in signalling, we questioned whether its function might be linked to integrin. Agonist-induced alpha IIb beta 3 activation (PAC-1 binding) was normal for patient platelets, indicating normal integrin inside-out signalling. Inside-out signalling (fibrinogen, JON/A binding) was also normal for wasp-deficient murine platelets. However, adherence/spreading on immobilized fibrinogen was decreased for patient platelets and wasp-deficient murine platelets, indicating decreased integrin outside-in responses. Another integrin outside-in dependent response, fibrin clot retraction, involving contraction of the post-aggregation actin cytoskeleton, was also decreased for patient platelets and wasp-deficient murine platelets. Rebleeding from tail cuts was more frequent for wasp-deficient mice, suggesting decreased stabilisation of the primary platelet plug. In contrast, phosphatidylserine exposure, a pro-coagulant response, was enhanced for WASP-deficient patient and murine platelets. The collective results reveal a novel function for WASP in regulating pro-aggregatory and pro-coagulant responses downstream of integrin outside-in signalling.
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