McKay S, de Jongste J C, Saxena P R, Sharma H S
Department of Pharmacology, Erasmus University, Rotterdam, The Netherlands.
Am J Respir Cell Mol Biol. 1998 Jun;18(6):823-33. doi: 10.1165/ajrcmb.18.6.2924.
Increased smooth muscle mass due to hyperplasia and hypertrophy of airway smooth muscle (ASM) cells is a common feature in asthma. Angiotensin II (Ang II), a potent vasoconstrictor and mitogen for a wide variety of cells, has recently been implicated in bronchoconstriction in asthmatics. However, a possible mitogenic role as well as underlying molecular mechanisms of this octapeptide in human ASM cells are not yet known. We studied the effects of Ang II on ASM cell proliferation and growth and on the expression of three transcription factors, egr-1, c-fos, and c-jun, as well as a cytokine, transforming growth factor-beta1 (TGF-beta1). Human ASM cells were isolated by enzymatic digestion of bronchial smooth muscle obtained from lung resection tissue. Confluent cells were growth-arrested and subsequently incubated with Ang II (100 nM) for different time periods and processed for the measurement of cell growth and gene expression. Ang II significantly induced DNA and protein synthesis in human ASM cells at 8 h, resulting in a net increase in the accumulation of protein over DNA (i.e., cellular hypertrophy) at 16 h of incubation. Cell counts and MTT-reduction assay, however, showed no increase in cell number as a result of Ang II stimulation. Ang II stimulated the expression of egr-1 and c-fos as early as 15 min, reaching maximum levels at 45 min, whereas the expression of c-jun peaked at 2 h of Ang II exposure. Furthermore, steady-state mRNA levels of TGF-beta1 were upregulated by Ang II after 4 h and reached peak levels at 16 h of incubation. Secretion of biologically active TGF-beta1 from human ASM cells was significantly (P <= 0.02) enhanced by Ang II incubation after 8 h, which remained elevated until 24 h. Our results suggest that the Ang II-induced transient early expression of transcription factors may regulate autocrine genes like TGF-beta1, of which the subsequent late upregulation could contribute to cellular hypertrophy during, for example, airway remodeling in asthma.
由于气道平滑肌（ASM）细胞的增生和肥大导致的平滑肌质量增加是哮喘的一个常见特征。血管紧张素II（Ang II）是一种强大的血管收缩剂和多种细胞的促有丝分裂原，最近被认为与哮喘患者的支气管收缩有关。然而，这种八肽在人ASM细胞中可能的促有丝分裂作用及其潜在的分子机制尚不清楚。我们研究了Ang II对ASM细胞增殖和生长以及三种转录因子egr-1、c-fos和c-jun以及一种细胞因子转化生长因子-β1（TGF-β1）表达的影响。通过酶消化从肺切除组织获得的支气管平滑肌来分离人ASM细胞。将汇合的细胞进行生长抑制，随后用Ang II（100 nM）孵育不同时间段，并进行细胞生长和基因表达的测量。Ang II在8小时时显著诱导人ASM细胞中的DNA和蛋白质合成，在孵育16小时时导致蛋白质相对于DNA的积累净增加（即细胞肥大）。然而，细胞计数和MTT还原试验显示，Ang II刺激后细胞数量没有增加。Ang II早在15分钟时就刺激了egr-1和c-fos的表达，在45分钟时达到最高水平，而c-jun的表达在Ang II暴露2小时时达到峰值。此外，TGF-β1的稳态mRNA水平在4小时后被Ang II上调，并在孵育16小时时达到峰值水平。在8小时的Ang II孵育后，人ASM细胞中生物活性TGF-β1的分泌显著（P<=0.02）增强，并一直升高到24小时。我们的结果表明，Ang II诱导的转录因子短暂早期表达可能调节像TGF-β1这样的自分泌基因，其随后的晚期上调可能在例如哮喘气道重塑期间导致细胞肥大。
