Reynaert Hendrik, Rombouts Krista, Jia Yutao, Urbain Daniel, Chatterjee Nirjhar, Uyama Naoki, Geerts Albert
Laboratory for Liver Cell Biology, Vrije Universiteit Brussel (VUB), Belgium.
Br J Pharmacol. 2005 Sep;146(1):77-88. doi: 10.1038/sj.bjp.0706298.
Previous studies have shown antifibrotic effects of somatostatin. Since hepatic stellate cells (HSC) express somatostatin receptors and play a key role in hepatic fibrogenesis, we investigated the in vitro antifibrotic effect of somatostatin on rat HSC. At day 12 after isolation, cells were exposed to different concentrations of somatostatin (10(-6)-10(-9) mol l(-1)). mRNA expression of collagen types I and III, and of smooth muscle alpha-actin (alpha-SMA) was analysed by Northern blotting. At 10(-9) mol l(-1), somatostatin significantly reduced mRNA expression of collagen I (72.3 +/- 10.7%; 95% confidence interval (95% CI): 45.5-99.0), collagen III (79.0 +/- 4.5%; 95% CI: 67.6-90.4) and alpha-SMA (65.7 +/- 5.9%; 95% CI: 51.1-80.2), as compared to control normalized at 100%. These results were confirmed by quantitative RT-PCR. Cycloheximide experiments indicated that somatostatin has no direct transcriptional effect.Using immunoprecipitation, we demonstrated that somatostatin also decreased de novo synthesis of collagen I (73 +/-10%; 95% CI: 48-98%), collagen III (65 +/- 13%; 95% CI: 33-97%) and alpha-SMA (47 +/- 9%; 95% CI: 25-69%). Remarkably, at higher concentrations, somatostatin did not suppress collagen mRNA expression nor de novo protein synthesis. We ascribe this observation to desensitization of the cells for somatostatin. Cell proliferation, as measured by 5-bromo-2'-deoxyuridine labelling, was not altered by somatostatin. No significant effect on the intermediate and actin cytoskeleton were detected by immunohistochemistry and Western blotting. Our findings imply that in vivo antifibrotic effects of somatostatin could result partially from a direct action of somatostatin on HSC, but other, in vivo effects are probably also involved.
以往研究表明生长抑素具有抗纤维化作用。由于肝星状细胞（HSC）表达生长抑素受体并在肝纤维化形成中起关键作用，我们研究了生长抑素对大鼠HSC的体外抗纤维化作用。分离后第12天，将细胞暴露于不同浓度的生长抑素（10^(-6)-10^(-9) mol l^(-1)）。通过Northern印迹分析I型和III型胶原以及平滑肌α-肌动蛋白（α-SMA）的mRNA表达。在10^(-9) mol l^(-1)时，与以100%标准化的对照相比，生长抑素显著降低了I型胶原（72.3±10.7%；95%置信区间（95%CI）：45.5-99.0）、III型胶原（79.0±4.5%；95%CI：67.6-90.4）和α-SMA（65.7±5.9%；95%CI：51.1-80.2）的mRNA表达。这些结果通过定量RT-PCR得到证实。放线菌酮实验表明生长抑素没有直接转录作用。通过免疫沉淀，我们证明生长抑素还降低了I型胶原（73±10%；95%CI：48-98%）、III型胶原（65±13%；95%CI：33-97%）和α-SMA（47±9%；95%CI：25-69%）的从头合成。值得注意的是，在较高浓度下，生长抑素既不抑制胶原mRNA表达也不抑制蛋白质从头合成。我们将这一观察结果归因于细胞对生长抑素的脱敏。通过5-溴-2'-脱氧尿苷标记测量的细胞增殖不受生长抑素影响。免疫组织化学和Western印迹未检测到对中间丝和肌动蛋白细胞骨架的显著影响。我们的研究结果表明，生长抑素的体内抗纤维化作用可能部分源于生长抑素对HSC的直接作用，但可能也涉及其他体内作用。
