Drebrin attenuates atherosclerosis by limiting smooth muscle cell transdifferentiation

Aims The F-actin-binding protein Drebrin inhibits smooth muscle cell (SMC) migration, proliferation, and pro-inflammatory signalling. Therefore, we tested the hypothesis that Drebrin constrains atherosclerosis. Methods and results SM22-Cre(+)/Dbn(flox/flox)/Ldlr(-)(/)(-) (SMC-Dbn(-)(/)(-)/Ldlr(-)(/)(-)) and control mice (SM22-Cre(+)/Ldlr(-)(/)(-), Dbn(flox/flox)/Ldlr(-)(/)(-), and Ldlr(-)(/)(-)) were fed a western diet for 14-20 weeks. Brachiocephalic arteries of SMC-Dbn (-)(/)(-)/Ldlr(-)(/)(-) mice exhibited 1.5- or 1.8-fold greater cross-sectional lesion area than control mice at 14 or 20 weeks, respectively. Aortic atherosclerotic lesion surface area was 1.2-fold greater in SMC-Dbn(-)(/)(-)/Ldlr(-)(/)(-) mice. SMC-Dbn(-)(/)(-)/Ldlr(-)(/)(-) lesions comprised necrotic cores that were two-fold greater in size than those of control mice. Consistent with their bigger necrotic core size, lesions in SMC-Dbn(-)(/)(-) arteries also showed more transdifferentiation of SMCs to macrophage-like cells: 1.5- to 2.5-fold greater, assessed with BODIPY or with CD68, respectively. In vitro data were concordant: Dbn(-)(/)(-) SMCs had 1.7-fold higher levels of KLF4 and transdifferentiated to macrophage-like cells more readily than Dbn(flox/flox) SMCs upon cholesterol loading, as evidenced by greater up-regulation of CD68 and galectin-3. Adenovirally mediated Drebrin rescue produced equivalent levels of macrophage-like transdifferentiation in Dbn(-)(/)(-) and Dbn(flox/flox) SMCs. During early atherogenesis, SMC-Dbn(-)(/)(-)/Ldlr(-)(/)(-) aortas demonstrated 1.6-fold higher levels of reactive oxygen species than control mouse aortas. The 1.8-fold higher levels of Nox1 in Dbn(-)(/)(-) SMCs were reduced to WT levels with KLF4 silencing. Inhibition of Nox1 chemically or with siRNA produced equivalent levels of macrophage-like transdifferentiation in Dbn(-)(/)(-) and Dbn(flox/flox) SMCs. Conclusion We conclude that SMC Drebrin limits atherosclerosis by constraining SMC Nox1 activity and SMC transdifferentiation to macrophage-like cells.