Lnk regulates integrin αIIbβ3 outside-in signaling in mouse platelets, leading to stabilization of thrombus development in vivo
Hitoshi Takizawa, … , Satoshi Takaki, Koji Eto
Hitoshi Takizawa, … , Satoshi Takaki, Koji Eto
Published December 21, 2009
Citation Information: J Clin Invest. 2010;120(1):179-190. https://doi.org/10.1172/JCI39503.
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Research Article Hematology

Lnk regulates integrin αIIbβ3 outside-in signaling in mouse platelets, leading to stabilization of thrombus development in vivo

Abstract

The nature of the in vivo cellular events underlying thrombus formation mediated by platelet activation remains unclear because of the absence of a modality for analysis. Lymphocyte adaptor protein (Lnk; also known as Sh2b3) is an adaptor protein that inhibits thrombopoietin-mediated signaling, and as a result, megakaryocyte and platelet counts are elevated in Lnk–/– mice. Here we describe an unanticipated role for Lnk in stabilizing thrombus formation and clarify the activities of Lnk in platelets transduced through integrin αIIbβ3–mediated outside-in signaling. We equalized platelet counts in wild-type and Lnk–/– mice by using genetic depletion of Lnk and BM transplantation. Using FeCl3- or laser-induced injury and in vivo imaging that enabled observation of single platelet behavior and the multiple steps in thrombus formation, we determined that Lnk is an essential contributor to the stabilization of developing thrombi within vessels. Lnk–/– platelets exhibited a reduced ability to fully spread on fibrinogen and mediate clot retraction, reduced tyrosine phosphorylation of the β3 integrin subunit, and reduced binding of Fyn to integrin αIIbβ3. These results provide new insight into the mechanism of αIIbβ3-based outside-in signaling, which appears to be coordinated in platelets by Lnk, Fyn, and integrins. Outside-in signaling modulators could represent new therapeutic targets for the prevention of cardiovascular events.

Authors

Hitoshi Takizawa, Satoshi Nishimura, Naoya Takayama, Atsushi Oda, Hidekazu Nishikii, Yohei Morita, Sei Kakinuma, Satoshi Yamazaki, Satoshi Okamura, Noriko Tamura, Shinya Goto, Akira Sawaguchi, Ichiro Manabe, Kiyoshi Takatsu, Hiromitsu Nakauchi, Satoshi Takaki, Koji Eto

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Figure 3

In vivo thrombus formation was impaired in Lnk-chimeras and Lnk–/– mice in a laser-induced injury model.

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In vivo thrombus formation was impaired in Lnk-chimeras and Lnk–/– mice ...
(A, C, and D) Video stills of mesenteric capillaries (A and C) and arterioles (D) obtained using intravital fluorescence microscopy before and 20 seconds after laser-induced injury. The numbers of platelets in developing thrombi after laser injury to capillaries (A and C, lower panel) and arterioles (D, lower panel) were calculated. In A, C, and D, y axes represent the numbers of platelets per micrometer of observed vessel length. In A, results from WT-chimeras 8 weeks after transplantation (16 weeks old) and Lnk-chimeras 4 weeks after transplantation (12 weeks old) are shown (n = 5 each). (B) Relationship between platelet counts and laser-induced thrombosis. All recipient mice were studied 2, 4, 6, or 8 weeks after transplantation (n = 17 animals for each groups). For each mouse, the numbers of platelets per micrometer contributing to thrombi after 20-second injuries to 10 mesenteric capillaries are shown as mean ± SEM along with platelet count. Black and gray dotted lines are fitted to the data from the Lnk- and WT-chimeras, respectively. (C and D) Results from 12-week-old WT and Lnk–/– mice (n = 5 each). See Supplemental Videos 1–6 for original movies. Note the impaired thrombus formation in Lnk–/– mice in both capillaries and arterioles. Scale bars: 10 μm. Horizontal lines indicate the median values in A, C, and D.