CLIC1 Supports Mechanisms Related to Platelet Activation and Thrombosis.

Abstract

Background: Chloride intracellular channel 1 (CLIC1) is expressed in endothelial cells and platelets. Loss-of-function studies suggest that CLIC1 is involved in adhesive interactions in either cell type, but the exact mechanism of CLIC1 action is still a matter of debate.

Methods: Cultured endothelial cells and platelets were probed for CLIC1 function as well as subcellular location using fluorescence microscopy, flow cytometry, and light transmission aggregometry. CLIC1 function in vivo was tested using a mouse dorsal skin fold chamber model to assess thrombus formation.

Results: Knocking down CLIC1 in endothelial cells is associated with the inability of cells to spread after attachment to the extracellular matrix. Critical to this process is the endothelial integrin αvβ3, which mediates the recruitment of CLIC1 into newly formed lamellipodia and subsequent colocalization with F-actin. Inhibiting CLIC1 with siRNA or the synthetic CLIC1 inhibitor IAA94, on the other hand, reduced F-actin formation in nascent adhesions, indicating that CLIC1 supports integrin β3-mediated cytoskeletal dynamics during endothelial cell attachment. In addition to endothelial cells, colocalization of CLIC1 with F-actin was detected in lamellipodia of platelets, which relocate CLIC1 to their cell surface in an integrin-dependent manner. Treatment with the CLIC1 inhibitor IAA94 hindered CLIC1 relocation to the platelet membrane, diminished platelet aggregation, and reduced integrin α_IIbβ₃ activation. Injecting mice with IAA94 delayed vaso-occlusion in a mouse model of photochemical thrombus formation in vivo.

Conclusion: CLIC1 is regulated by adhesive interactions with integrin ligands that cause CLIC1 to relocate to the cell membrane of endothelial cells and platelets. This process in turn appears to be relevant for integrin-mediated functions involved in platelet thrombus formation in vitro and in vivo.