Targeting Filamin A Reduces Macrophage Activity and Atherosclerosis

Background: The actin-binding protein FLNA (filamin A) regulates signal transduction important for cell locomotion, but the role of macrophage-specific FLNA during atherogenesis has not been explored. Methods: We analyzed FLNA expression in human carotid atherosclerotic plaques by immunofluorescence. We also produced mice withFlna -deficient macrophages by breeding conditionalFlna -knockout mice (Flna o/fl ) with mice expressingCre from the macrophage-specific lysosome M promoter (LC ). Atherosclerosis in vivo was studied by transplanting bone marrow from maleFlna o/fl /LC mice to atherogenic low-density lipoprotein receptor–deficient (Ldlr –/– ) mice; and by infectingFlna o/fl andFlna o/fl /LC mice with AdPCSK9 (adenoviral vector overexpressing proprotein convertase subtilisin/kexin type 9). Furthermore, C57BL/6 mice were infected with AdPCSK9 and then treated with the calpain inhibitor calpeptin to inhibit FLNA cleavage.Results: We found that macrophage FLNA expression was higher in advanced than in intermediate human atherosclerotic plaques.Flna o/fl /LC macrophages proliferated and migrated less than controls; expressed lower levels of phosphorylated AKT and ERK1/2; exhibited reduced foam cell formation and lipid uptake; and excreted more lipids. The deficiency ofFlna in macrophages markedly reduced the size of aortic atherosclerotic plaques in bothLdlr –/–BMT:Flnao/fl/LC and AdPCSK9-infectedFlna o/fl /LC mice. Intima/media ratios and numbers of CD68-positive macrophages in atherosclerotic plaques were lower inFlna -deficient mice than in control mice. Moreover, we found that STAT3 interacts with a calpain-cleaved carboxyl-terminal fragment of FLNA. Inhibiting calpain-mediated FLNA cleavage with calpeptin in macrophages reduced nuclear levels of phosphorylated STAT3, interleukin 6 secretion, foam cell formation, and lipid uptake. Finally, calpeptin treatment reduced the size of atherosclerotic plaques in C57BL/6 mice infected with AdPCSK9.Conclusions: Genetic inactivation ofFlna and chemical inhibition of calpain-dependent cleavage of FLNA impaired macrophage signaling and function, and reduced atherosclerosis in mice, suggesting that drugs targeting FLNA may be useful in the treatment of atherosclerosis.