Takehara Tetsuo, Tatsumi Tomohide, Suzuki Takahiro, Rucker Edmund B, Hennighausen Lothar, Jinushi Masahisa, Miyagi Takuya, Kanazawa Yoshiyuki, Hayashi Norio
Department of Molecular Therapeutics, Osaka University Graduate School of Medicine, Osaka, Japan.
Gastroenterology. 2004 Oct;127(4):1189-97. doi: 10.1053/j.gastro.2004.07.019.
BACKGROUND & AIMS: Recent research has suggested that apoptosis could be involved in the development of fibrosis, although it is generally considered to be a mechanism of cell removal without consequences to the tissue. Bcl-xL , an antiapoptotic member of the Bcl-2 family, is expressed in hepatocytes and up-modulated during various pathologic conditions. The aim of this study was to explore the function of Bcl-xL in hepatocytes using the Cre-loxP system and to analyze the consequences of long-term apoptosis in hepatocytes.
Hepatocytes isolated from mice homozygous for a floxed bcl-x allele (bcl-x fl/fl) were infected with recombinant adenovirus expressing the Cre recombinase gene (AdexCre). Bcl-x fl/fl mice were crossed with Alb-Cre transgenic mice, which express Cre under regulation of the albumin gene promoter to generate hepatocyte-specific Bcl-xL-deficient mice.
On AdexCre infection, primary cultured bcl-x fl/fl hepatocytes reduced their expression of Bcl-xL and rapidly underwent apoptosis associated with mitochondrial damage. In vivo hepatocyte-specific disruption of Bcl-xL resulted in spontaneous apoptosis of hepatocytes for more than 6 months. The Bcl-xL -deficient mice showed liver fibrosis with advanced age that was preceded by an increase in hepatic transforming growth factor beta production. In vitro, macrophages and hepatocytes produced transforming growth factor beta on exposure to apoptotic hepatocytes.
The present study identified Bcl-xL as a critical apoptosis antagonist in hepatocytes. Furthermore, it offers proof that persistent apoptosis of parenchymal cells is sufficient to induce fibrotic responses and suggests a mechanistic link between apoptosis and fibrosis.
近期研究表明，细胞凋亡可能参与纤维化的发展，尽管通常认为它是一种细胞清除机制，对组织并无影响。Bcl-xL是Bcl-2家族的抗凋亡成员，在肝细胞中表达，并在各种病理条件下上调。本研究的目的是利用Cre-loxP系统探索Bcl-xL在肝细胞中的功能，并分析肝细胞长期凋亡的后果。
从纯合的floxed bcl-x等位基因（bcl-x fl/fl）小鼠中分离出肝细胞，用表达Cre重组酶基因的重组腺病毒（AdexCre）感染。将bcl-x fl/fl小鼠与Alb-Cre转基因小鼠杂交，后者在白蛋白基因启动子的调控下表达Cre，以产生肝细胞特异性Bcl-xL缺陷小鼠。
感染AdexCre后，原代培养的bcl-x fl/fl肝细胞降低了Bcl-xL的表达，并迅速发生与线粒体损伤相关的凋亡。体内肝细胞特异性破坏Bcl-xL导致肝细胞自发凋亡超过6个月。Bcl-xL缺陷小鼠随着年龄增长出现肝纤维化，其之前肝转化生长因子β的产生增加。在体外，巨噬细胞和肝细胞在接触凋亡肝细胞时产生转化生长因子β。
本研究确定Bcl-xL是肝细胞中的关键凋亡拮抗剂。此外，它证明了实质细胞的持续凋亡足以诱导纤维化反应，并提示了凋亡与纤维化之间的机制联系。
