The Actin Bundling Protein L-Plastin Mediates Platelet Force Generation and Thrombosis

• Published in: Blood 2023-11, Vol.142 (Supplement 1), p.2560-2560
• Main Authors: Bhatlekar, Seema, Jacob, Shancy, Tistao, Marina, Mollica, Molly Y, Rhoads, Nicole, Chen, Lili, Manne, Bhanu Kanth, Murray, Darian, Guo, Siqi, Morley, Sharon Celeste, Rowley, Jesse W, Rondina, Matthew T., Adili, Raymond, Lopez, Jose A., Guo, Li
• Format: Article
• Language: English
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood-2023-178052

Within minutes of activation, platelets dramatically change their shape, forming filopodia and lamellipodia, aggregate with other platelets or different cells, and can increase their surface area up to 4 times. This relies on a dynamic actin cytoskeleton, regulated by many actin binding proteins in a time- and spatial-specific manner. Deficiency or inhibition of several actin binding proteins in platelets have been shown with impaired platelet spreading and reduced thrombosis. Recently, we found that an actin bundling protein, L-plastin, is expressed in platelets. Its function in platelets has not been studied. In megakaryocytes, we showed that L-plastin is responsible for maintaining cytoskeletal stiffness; in this study we sought to determine L-plastin's role in platelet functions, including thrombosis. We examined the role of L-plastin in platelets in vivo and ex vivo using L-plastin deficient ( Lcp1 -/-) male and female mice. First, we used the collagen/epinephrine induced pulmonary embolism (PE) model and found that survival times were significantly shorter in Lcp1 -/- mice than in their littermate wildtype (WT) controls (Mean±SEM WT 202±12 sec, Lcp1 -/- 139.5±14 sec, P=0.004), suggesting accelerated thrombosis upon L-plastin deficiency in vivo. Second, we examined L-plastin's role in arterial thrombosis in vivo using the laser-induced cremaster arteriole thrombosis mode. Platelets were labeled with anti-GPIb IgG derivative X488 and the thrombosis formation after laser injury was recorded. Preliminary data indicate that thrombi in Lcp1 -/- mice are larger than those in WT mice. Third, we examined L-plastin's role in platelet adhesion using a microfluidics assay with DiOC6-labelled whole blood. At a shear rate of 200/s, the Lcp1 -/- mice had significantly increased platelet adhesion to both collagen and fibrinogen matrices. Fourth, to evaluate the effect of L-plastin on platelet aggregation in vitro, we stimulated washed platelets with 3 different concentrations of thrombin and measured the platelet aggregation (i.e., 0.1, 0.5 and 1 U/mL). When platelets are stimulated with 0.5U/mL or 1U/mL thrombin, platelets from WT and Lcp1 -/- mice showed comparable aggregation kinetics. At 0.1U/mL thrombin, however, preliminary data showed increased aggregation in the Lcp1 -/- group. The difference between the low and high concentration of thrombin indicates potential regulation of the GPIba mediated actin cytoskeleton rearrangement during platelet aggregation. We