Department of Pharmacology, Trinity College Dublin, Dublin 2, Ireland.
J Pathol. 2011 Aug;224(4):461-72. doi: 10.1002/path.2870. Epub 2011 Apr 4.
Transforming growth factor β (TGF-β) is known to play a key role in intestinal fibrosis; however, the underlying mechanisms are not well understood. TGF-β signal transduction is through TGF-β receptors, including the TGF-β type 1 receptor. Most cell types contain a TGF-β type 1 receptor form known as activin receptor-like kinase 5 (ALK5), which propagates the signal to the nucleus through the phosphorylation of Smad2 and Smad3 proteins. Therefore, we assessed the effect of the disruption of TGF-β/ALK5/Smad signalling by an ALK5 inhibitor (SD-208) in two experimental animal models of intestinal fibrosis: anaerobic bacteria- and trinitrobenzensulphonic acid-induced colitis. In addition, isolated myofibroblasts were pretreated with SD-208 and exposed to recombinant TGF-β1. Finally, myofibroblasts were transfected with ALK5, Smad2, and Smad3-specific siRNA. Up-regulation of ALK5 and TIMP-1, phosphorylation of Smad2 and Smad3 proteins, and increased intestinal wall collagen deposition were found in both experimental animal models. These effects were decreased by SD-208. TGF-β1 treatment also induced phosphorylation of Smad2 and Smad3 and up-regulation of ALK5 protein, TIMP-1, and α2 type 1 collagen gene expression in isolated myofibroblasts. Again these effects were inhibited by SD-208. Also, ALK5, Smad2, and Smad3 siRNA abolished the induction of TIMP-1 and α2 type 1 collagen. Our findings provide evidence that the TGF-β/ALK5/Smad pathway participates in the pathogenesis of experimental intestinal fibrosis. These data show promise for the development of an effective therapeutic intervention in this condition.
转化生长因子 β（TGF-β）被认为在肠道纤维化中发挥关键作用；然而，其潜在机制尚不清楚。TGF-β信号转导是通过 TGF-β受体进行的，包括 TGF-β 型 1 受体。大多数细胞类型都含有一种称为激活素受体样激酶 5（ALK5）的 TGF-β 型 1 受体形式，该受体通过磷酸化 Smad2 和 Smad3 蛋白将信号传递到细胞核。因此，我们评估了 ALK5 抑制剂（SD-208）在两种肠道纤维化实验动物模型中的 TGF-β/ALK5/Smad 信号转导中断的效果：厌氧细菌和三硝基苯磺酸诱导的结肠炎。此外，用 SD-208 预处理分离的肌成纤维细胞，并使其暴露于重组 TGF-β1。最后，用 ALK5、Smad2 和 Smad3 特异性 siRNA 转染肌成纤维细胞。在两种实验动物模型中均发现 ALK5 和 TIMP-1 的上调、Smad2 和 Smad3 蛋白的磷酸化以及肠壁胶原沉积增加。这些作用通过 SD-208 减少。TGF-β1 处理还诱导了 Smad2 和 Smad3 的磷酸化以及 ALK5 蛋白、TIMP-1 和α2 型 1 胶原基因表达的上调，在分离的肌成纤维细胞中。SD-208 再次抑制了这些作用。此外，ALK5、Smad2 和 Smad3 siRNA 消除了 TIMP-1 和α2 型 1 胶原的诱导。我们的研究结果提供了证据，证明 TGF-β/ALK5/Smad 通路参与了实验性肠道纤维化的发病机制。这些数据为该疾病的有效治疗干预措施的发展提供了希望。
