Apheresis and Dialysis Center, School of Medicine, Keio University, Tokyo, 160-8582, Japan.
J Am Heart Assoc. 2014 Jan 27;3(1):e000622. doi: 10.1161/JAHA.113.000622.
Krüppel-like factor 4 (Klf4) is involved in a variety of cellular functions by activating or repressing the transcription of multiple genes. Results of previous studies showed that tamoxifen-inducible global deletion of the Klf4 gene in mice accelerated neointimal formation following vascular injury, in part via enhanced proliferation of smooth muscle cells (SMCs). Because Klf4 is also expressed in non-SMCs including endothelial cells (ECs), we determined if Tie2 promoter-dependent deletion of Klf4 in ECs and hematopoietic cells affected injury-induced neointimal formation.
Klf4 conditional knockout (cKO) mice were generated by breeding Tie2-Cre mice and Klf4 floxed mice, and their phenotype was analyzed after carotid ligation injury. Results showed that injury-induced repression of SMC differentiation markers was unaffected by Tie2 promoter-dependent Klf4 deletion. However, of interest, neointimal formation was significantly enhanced in Klf4-cKO mice 21 days following carotid injury. Moreover, Klf4-cKO mice exhibited an augmented proliferation rate, enhanced accumulation of macrophages and T lymphocytes, and elevated expression of cell adhesion molecules including vascular cell adhesion molecule-1 (Vcam1) and E-selectin in injured arteries. Mechanistic analyses in cultured ECs revealed that Klf4 inhibited tumor necrosis factor-α-induced expression of Vcam1 through blocking the binding of nuclear factor-κB to the Vcam1 promoter.
These results provide evidence that Klf4 in non-SMCs such as ECs regulates neointimal formation by repressing arterial inflammation following vascular injury.
Krüppel 样因子 4（Klf4）通过激活或抑制多个基因的转录，参与多种细胞功能。先前的研究结果表明，在小鼠中，通过他莫昔芬诱导的 Klf4 基因全局缺失可加速血管损伤后的新生内膜形成，部分原因是平滑肌细胞（SMCs）的增殖增强。由于 Klf4 也在包括内皮细胞（ECs）在内的非 SMCs 中表达，我们确定内皮细胞和造血细胞中依赖 Tie2 启动子的 Klf4 缺失是否会影响损伤诱导的新生内膜形成。
通过繁殖 Tie2-Cre 小鼠和 Klf4 floxed 小鼠，生成 Klf4 条件性敲除（cKO）小鼠，并在颈动脉结扎损伤后分析其表型。结果表明，Tie2 启动子依赖性 Klf4 缺失对 SMC 分化标志物的损伤诱导抑制无影响。然而，有趣的是，在颈动脉损伤 21 天后，Klf4-cKO 小鼠的新生内膜形成明显增强。此外，Klf4-cKO 小鼠表现出增殖率增加、巨噬细胞和 T 淋巴细胞积累增加以及细胞黏附分子（包括血管细胞黏附分子-1（VCAM1）和 E-选择素）表达升高。在培养的 ECs 中的机制分析表明，Klf4 通过阻断核因子-κB 与 VCAM1 启动子的结合，抑制肿瘤坏死因子-α诱导的 VCAM1 表达。
这些结果提供了证据，表明非 SMC 中的 Klf4（如 ECs）通过抑制血管损伤后的动脉炎症来调节新生内膜形成。
