Smooth Muscle-Selective Inhibition of Nuclear Factor-κB Attenuates Smooth Muscle Phenotypic Switching and Neointima Formation Following Vascular Injury

Background-Vascular proliferative diseases such as atherosclerosis are inflammatory disorders involving multiple cell types including macrophages, lymphocytes, endothelial cells, and smooth muscle cells (SMCs). Although activation of the nuclear factor-kappa B (NF-kappa B) pathway in vessels has been shown to be critical for the progression of vascular diseases, the cell-autonomous role of NF-kappa B within SMCs has not been fully understood. Methods and Results-We generated SMC-selective truncated I kappa B expressing (SM22 alpha-Cre/I kappa B Delta N) mice, in which NF-kappa B was inhibited selectively in SMCs, and analyzed their phenotype following carotid injury. Results showed that neointima formation was markedly reduced in SM22 alpha-Cre/I kappa B Delta N mice after injury. Although vascular injury induced downregulation of expression of SMC differentiation markers and myocardin, a potent activator of SMC differentiation markers, repression of these markers and myocardin was attenuated in SM22 alpha-Cre/I kappa B Delta N mice. Consistent with these findings, NF-kappa B activation by interleukin-1 beta (IL-1 beta) decreased expression of SMC differentiation markers as well as myocardin in cultured SMCs. Inhibition of NF-kappa B signaling by BAY 11-7082 attenuated repressive effects of IL-1 beta. Of interest, Kruppel-like factor 4 (Klf4), a transcription factor critical for regulating SMC differentiation and proliferation, was also involved in IL-1 beta-mediated myocardin repression. Promoter analyses and chromatin immunoprecipitation assays revealed that NF-kappa B repressed myocardin by binding to the myocardin promoter region in concert with Klf4. Conclusions-These results provide novel evidence that activation of the NF-kappa B pathway cell-autonomously mediates SMC phenotypic switching and contributes to neointima formation following vascular injury.