Yanagida Atsuko, Iwaisako Keiko, Hatano Etsuro, Taura Kojiro, Sato Fumiaki, Narita Masato, Nagata Hiromitsu, Asechi Hiroyuki, Uemoto Shinji, Kinoshita Makoto
Department of Surgery, Graduate School of Medicine, Kyoto University, 54 Kawahara-cho, Shogoin, Sakyo-ku, Kyoto 606 8507, Japan.
Biochim Biophys Acta. 2011 Nov;1812(11):1403-11. doi: 10.1016/j.bbadis.2011.06.015. Epub 2011 Jul 6.
BACKGROUND/AIMS: Sept4, a subunit of the septin cytoskeleton specifically expressed in quiescent hepatic stellate cells (HSCs), is downregulated through transdifferentiation to fibrogenic and contractile myofibroblastic cells. Since Sept4(-/-)mice are prone to liver fibrosis, we aimed to identify the unknown molecular network underlying liver fibrosis by probing the association between loss of Sept4 and accelerated transdifferentiation of HSCs.
We compared the transcriptomes of Sept4(+/+) and Sept4(-/-) HSCs undergoing transdifferentiation by DNA microarray and quantitative reverse transcription polymerase chain reaction (RT-PCR) analysis. Because Dickkopf2 (Dkk2) gene expression is reduced in Sept4(-/-) HSCs, we tested whether supplementing Dkk2 could suppress myofibroblastic transformation of Sept4(-/-) HSCs. We tested the involvement of the canonical Wnt pathway in this process by using a lymphoid enhancer-binding factor/transcription factor-luciferase reporter assay.
We observed consistent upregulation of Dkk2 in primary cultured HSCs and in a carbon tetrachloride liver fibrosis in mice, which was decreased in the absence of Sept4. Supplementation with Dkk2 suppressed the induction of pro-fibrotic genes (α-smooth muscle actin and 2 collagen genes) and induced an anti-fibrotic gene (Smad7) in Sept4(-/-) HSCs. In human liver specimens with inflammation and fibrosis, Dkk2 immunoreactivity appeared to be positively correlated with the degree of fibrotic changes.
Pro-fibrotic transformation of HSCs through the loss of Sept4 is, in part, due to reduced expression of Dkk2 and its homologues, and the resulting disinhibition of the canonical Wnt pathway.
背景/目的：Sept4是一种在静止肝星状细胞（HSC）中特异性表达的septin细胞骨架亚基，在向纤维化和收缩性肌成纤维细胞转分化过程中表达下调。由于Sept4基因敲除小鼠易患肝纤维化，我们旨在通过探究Sept4缺失与HSC加速转分化之间的关联，来确定肝纤维化潜在的未知分子网络。
我们通过DNA微阵列和定量逆转录聚合酶链反应（RT-PCR）分析，比较了正在进行转分化的Sept4(+/+)和Sept4(-/-) HSC的转录组。由于Dickkopf2（Dkk2）基因在Sept4(-/-) HSC中表达降低，我们测试了补充Dkk2是否能抑制Sept4(-/-) HSC的肌成纤维细胞转化。我们通过使用淋巴细胞增强因子/转录因子-荧光素酶报告基因检测，测试了经典Wnt信号通路在此过程中的作用。
我们观察到，在原代培养的HSC和小鼠四氯化碳肝纤维化模型中，Dkk2持续上调，而在缺乏Sept4的情况下Dkk2表达降低。补充Dkk2可抑制Sept4(-/-) HSC中促纤维化基因（α-平滑肌肌动蛋白和2种胶原基因）的诱导，并诱导抗纤维化基因（Smad7）表达。在有炎症和纤维化的人肝标本中，Dkk2免疫反应性似乎与纤维化变化程度呈正相关。
HSC因Sept4缺失而发生的促纤维化转化，部分原因是Dkk2及其同源物表达降低，以及由此导致的经典Wnt信号通路抑制解除。
