肝X受体上调糖尿病小鼠肾脏脂肪酸合成酶的表达

Activation of liver X receptor upregulates fatty acid synthase expression in diabetic kidney

目的探讨肝X受体（liver X receptor，LXR）对糖尿病小鼠肾脏脂肪酸合成酶（fatty acid synthase，FAS）表达的影响及可能机制。方法在体研究部分：糖尿病db／db小鼠和对照的db／m小鼠分别予以LXR激动剂T0901317（3mg·kg^-1·d^-1）灌胃处理7d，采用免疫组织化学、实时荧光定量PCR、蛋白印迹法检测FAS和活化型固醇调节元件结合蛋白（sterol regulatory element—binding protein-1，SREBP-1）的表达水平。离体研究部分：T0901317（10μmol／L）刺激小鼠近曲小管上皮细胞系（MCT细胞）24h，或转染SREBP-1c表达质粒。LXR或SREBP-1c表达质粒转染人胚。肾细胞系（HEK293细胞）12h，分别采用实时荧光定量PCR、转染荧光素酶报告基因等方法，检测FAS表达和FAS启动子活性水平。结果免疫组化结果显示FAS蛋白主要表达在肾皮质，肾小球表达量较少。同对照组db／m小鼠相比．db／db小鼠肾脏FASmRNA和蛋白水平均明显降低（P〈0．05）；T0901317处理可使db／db小鼠。肾脏FASmRNA表达升高1．3倍（P〈0．01）；db／m小鼠肾脏SREBP-1的mRNA升高5．1倍（P〈0．01），db／db小鼠肾脏SREBP．1的mRNA升高17倍（P〈0．01）；T0901317也能上调MeT细胞FAS的mRNA表达水平，升高1．5倍（P〈0．05）；过表达SREBP-1c也可使MCT细胞中FASmRNA的表达量增加1．8倍（P〈0．05）：不仅如此，LXR的激活、过表达LXR或SREBP-1c能增加HEK293细胞FAS基因启动子活性（P〈0．01）。结论LXR能够通过其本身的直接作用和SREBP-1c的间接作用上调肾脏FAS的表达，LXR可能介导了糖尿病肾脏的脂质代谢紊乱过程。

Objective To investigate the effect and mechanism of liver X receptor （ LXR ） agonist on expression of fatty acid synthase （FAS） in diabetic kidney. Methods In the part of in vivo study, immanostaining was used to detect the FAS protein expression in kidney. 16-week-old male db/db mice on C57BL/6 background were administered via gavage a LXR synthetic agonist, TO901317, at a dose of 3 mg·kg^-1·d^-1 or vehicle （0. 5% Carboxymethyl Cellulose Sodium, CMC-Na）alone for 7 d; Quantitative RT-PCR and Western blot were used to detect mRNA and protein levels of FAS and SREBP-1. In the part of in vitro study, MCT cell （ a mouse murine proximal tubule cell line ） was treated with l0 txmol/L TO901317 for 24 h or transfected with active SREBP-1 c expression vector （SREBP-lcN）. HEK293 cells（ a human renal tubule cell line） were transfected with mFAS-（ 1.7 kb） -luc, LXR expression vector or SREBP-lcN for 12 h. Quantitative RT-PCR and luciferase reproter assay were utilized to examine FAS mRNA level and FAS promoter activity. Results FAS was abundantly expressed in renal cortex, with low expresson in renal glomeruli. Tbe mRNA and protein expressious of FAS in kidney of db/db mice were lowered compared with db/m mice. TO90137 treatment increased FAS mRNA expression by 1.3-fold. TO901317 increased expression of SREBP-1 in kidneys of db/m and db/db mice by 5.1-fold and 17-fold, respectively. TO901317 and overexpression of SREBP-lc increased expression of FAS in MCT cells by 1.5-fold and 1.8-h）ld. Transcription activity of FAS were induced by TO901317, LXR, and SREBP-lcN overexpressions in HEK293 cells. Conclusions Both direct （ LXRE ） and indirect （ SREBP-1 c ） mechanisms may contribute to the up-regulation of FAS expression by LXR in renal proximal tubule cells.