Presentation description

Platelets are produced by megakaryocytes, in which process the actin cytoskeleton undergoes dynamic changes but the mechanism remains not well understood. We recently identified L-plastin (encoded by lcp1) as a novel actin bundling protein that inhibits human MK proplatelet formation (PPF) in vitro. We investigated its in vivo significance and the mechanism in platelet production and function, using a lcp1-/- mouse strain in our current study. Lcp1-/- mice have significantly increased platelet count and increased MK PPF as compared to the wildtype (WT) controls. These lcp1-/- mice also had accelerated mortality in a pulmonary embolism model, shortened tail vein bleeding times and increased thrombosis ex vivo. Confocal imaging revealed reduced F-actin filamentous structure in MKs from lcp1-/-, with significantly increased spreading area on fibrinogen. The Biomembrane Force Probe (BFP) tether assay allowed us to measure the MK stiffness at a single cell level for the first time. The stiffness of the WT MKs is about 0.4pN/nm but reduced for more than 70% in the lcp1-/- group. In summary, L-plastin is critical in maintaining F-actin cytoskeleton stiffness and constrains membrane spreading in MKs and platelets. The L-plastin deficiency increases platelet number and promotes thrombosis in vivo.