Yan Z, Hansson G K
Center for Molecular Medicine, Karolinska Hospital, Karolinska Institute, Stockholm, Sweden.
Circ Res. 1998;82(1):21-9. doi: 10.1161/01.res.82.1.21.
The formation of a neointima represents an important repair mechanism in response to vascular injury. It is associated with the expression of a specific set of genes by the intimal smooth muscle cells. Recently, expression of the inducible isoform of NO synthase (iNOS) has been identified in injured arteries during neointimal formation, suggesting that intimal SMCs have a unique mechanism for regulating NO production. Therefore, we have analyzed the expression of iNOS in intimal SMCs. Although first expressed in the media within 1 day after injury, iNOS was confined to neointimal smooth muscle cells at 1 to 2 weeks after injury. Isolated intimal SMCs were found to consistently reexpress iNOS in reaction to proinflammatory mediators. This was associated with a 5- to 8-fold higher output of NO in comparison with SMCs derived from the media of uninjured arteries. Western blot and Northern blot analyses likewise revealed that the high production of NO by intimal SMCs was due to overexpression of iNOS. Moreover, the same stimuli induced a higher transcriptional activity in intimal than in medial SMCs, as detected by transfection of a reporter gene under the iNOS promoter. Induction of iNOS led to a reduced proliferation in both medial and intimal SMCs. This inhibitory effect was, however, less pronounced in intimal than in medial SMCs. Similarly, intimal cells were less sensitive to NO-induced inhibition of mitochondrial respiration. When SMC clones were analyzed, there was no correlation between iNOS expression and growth pattern, suggesting that iNOS expression is independent of the morphological phenotype of SMCs. Together, our data show that the intimal SMC is the main iNOS-expressing cell type in the injured artery, that it responds more vividly to iNOS-inducing cytokines because of a more efficient activation of the iNOS promoter, and that it is more resistant to the actions of NO compared with medial SMCs. Intimal production of NO via the inducible pathway may be important for the restoration of vascular homeostasis after injury.
新生内膜的形成是血管损伤后的一种重要修复机制。它与内膜平滑肌细胞中一组特定基因的表达相关。最近，在新生内膜形成过程中，已在损伤动脉中鉴定出诱导型一氧化氮合酶（iNOS）同工型的表达，这表明内膜平滑肌细胞具有调节一氧化氮产生的独特机制。因此，我们分析了iNOS在内膜平滑肌细胞中的表达。尽管iNOS在损伤后1天内首先在中膜表达，但在损伤后1至2周局限于新生内膜平滑肌细胞。发现分离的内膜平滑肌细胞在对促炎介质的反应中持续重新表达iNOS。与来自未损伤动脉中膜的平滑肌细胞相比，这与高出5至8倍的一氧化氮产量相关。蛋白质印迹和RNA印迹分析同样表明，内膜平滑肌细胞中一氧化氮的高产量是由于iNOS的过表达。此外，如通过在iNOS启动子下转染报告基因所检测到的，相同刺激在内膜平滑肌细胞中诱导的转录活性高于中膜平滑肌细胞。iNOS的诱导导致中膜和平滑肌细胞的增殖均减少。然而，这种抑制作用在内膜平滑肌细胞中不如在中膜平滑肌细胞中明显。同样，内膜细胞对一氧化氮诱导的线粒体呼吸抑制较不敏感。当分析平滑肌细胞克隆时，iNOS表达与生长模式之间没有相关性，这表明iNOS表达与平滑肌细胞的形态表型无关。总之，我们的数据表明，内膜平滑肌细胞是损伤动脉中主要表达iNOS的细胞类型，由于iNOS启动子的更有效激活，它对诱导iNOS的细胞因子反应更活跃，并且与中膜平滑肌细胞相比，它对一氧化氮的作用更具抗性。通过诱导途径在内膜产生一氧化氮可能对损伤后血管稳态的恢复很重要。
