Ohata M, Lin M, Satre M, Tsukamoto H
Division of Gastrointestinal and Liver Diseases, University of Southern California School of Medicine and Veterans Affairs Outpatient Clinic, Los Angeles 90033-4581, USA.
Am J Physiol. 1997 Mar;272(3 Pt 1):G589-96. doi: 10.1152/ajpgi.1997.272.3.G589.
Hepatic stellate cells (HSC) participate in liver fibrogenesis via myofibroblastic activation, the extent of which appears to correlate with the loss of cellular vitamin A. The present study has tested a hypothesis that HSC activation is associated with diminished retinoic acid (RA) signaling. Pure HSC were isolated from rats with cholestatic liver fibrosis induced by bile duct ligation (BDL) and sham-operated animals (Sham). Northern blot analysis of HSC RNA from BDL confirmed fibrogenic activation of the cells with enhanced mRNA levels for procollagen-alpha1(I) and transforming growth factor-beta1 (TGF-beta1). Competitive polymerase chain reaction analysis showed selective reductions in the mRNA levels of RA receptor (RAR)-beta and retinoid X receptor (RXR)-alpha to 20 and 17% of the Sham HSC. The mRNA level for cellular retinol binding protein I, a gene with RA responsive element (RARE), was also suppressed by 78% in BDL. The concentrations of all-trans-RA and 9-cis-RA were decreased in HSC from BDL. Nuclear extracts of these cells showed diminished binding activity to the RARE, whereas activity of AP-1, a transcription factor known to be antagonized by RAR and RXR, was enhanced. These results demonstrate diminished RA signaling in HSC from cholestatic liver fibrosis, which appeared to have resulted from RA deficiency and suppressed expression of RAR-beta and RXR-alpha. Furthermore, the reciprocal enhancement of AP-1 activity and coordinately increased expression of an AP-1 responsive gene, TGF-beta1, suggest a permissive role of the diminished RA signaling in promoting AP-1 activity and TGF-beta1 expression.
肝星状细胞（HSC）通过肌成纤维细胞激活参与肝纤维化形成，其激活程度似乎与细胞内维生素A的丢失相关。本研究检验了一个假设，即HSC激活与视黄酸（RA）信号转导减弱有关。从胆管结扎（BDL）诱导的胆汁淤积性肝纤维化大鼠和假手术动物（Sham）中分离出纯HSC。对BDL大鼠的HSC RNA进行Northern印迹分析，证实细胞发生纤维化激活，原胶原α1（I）和转化生长因子β1（TGF-β1）的mRNA水平升高。竞争性聚合酶链反应分析显示，RA受体（RAR）-β和视黄醛X受体（RXR）-α的mRNA水平选择性降低，分别降至假手术组HSC的20%和17%。细胞视黄醇结合蛋白I是一个含有RA反应元件（RARE）的基因，其mRNA水平在BDL组中也被抑制了78%。BDL组HSC中全反式RA和9-顺式RA的浓度降低。这些细胞的核提取物显示与RARE的结合活性减弱，而一种已知受RAR和RXR拮抗的转录因子AP-1的活性增强。这些结果表明，胆汁淤积性肝纤维化的HSC中RA信号转导减弱，这似乎是由于RA缺乏以及RAR-β和RXR-α的表达受抑制所致。此外，AP-1活性的相互增强以及AP-1反应基因TGF-β1表达的协同增加，提示减弱的RA信号转导在促进AP-1活性和TGF-β1表达中起允许作用。
