Xie Shaozhen, Lee Yi-Fen, Kim Eungseok, Chen Lu-Min, Ni Jing, Fang Lei-Ya, Liu Su, Lin Shin-Jen, Abe Jun-Ichi, Berk Bradford, Ho Feng-Ming, Chang Chawnshang
George Whipple Lab for Cancer Research, Department of Pathology, and Cardiovascular Research Institute, University of Rochester Medical Center, Rochester, NY 14642, USA.
Proc Natl Acad Sci U S A. 2009 Aug 11;106(32):13353-8. doi: 10.1073/pnas.0905724106. Epub 2009 Jul 28.
Testicular orphan nuclear receptor 4 (TR4) is an orphan member of the nuclear receptor superfamily with diverse physiological functions. Using TR4 knockout (TR4(-/-)) mice to study its function in cardiovascular diseases, we found reduced cluster of differentiation (CD)36 expression with reduced foam cell formation in TR4(-/-) mice. Mechanistic dissection suggests that TR4 induces CD36 protein and mRNA expression via a transcriptional regulation. Interestingly, we found this TR4-mediated CD36 transactivation can be further enhanced by polyunsaturated fatty acids (PUFAs), such as omega-3 and -6 fatty acids, and their metabolites such as 15-hydroxyeico-satetraonic acid (15-HETE) and 13-hydroxy octa-deca dieonic acid (13-HODE) and thiazolidinedione (TZD)-rosiglitazone. Both electrophoretic mobility shift assays (EMSA) and chromatin immunoprecipitation (ChIP) assays demonstrate that TR4 binds to the TR4 response element located on the CD36 5'-promoter region for the induction of CD36 expression. Stably transfected TR4-siRNA or functional TR4 cDNA in the RAW264.7 macrophage cells resulted in either decreased or increased CD36 expression with decreased or increased foam cell formation. Restoring functional CD36 cDNA in the TR4 knockdown macrophage cells reversed the decreased foam cell formation. Together, these results reveal an important signaling pathway controlling CD36-mediated foam cell formation/cardiovascular diseases, and findings that TR4 transactivation can be activated via its ligands/activators, such as PUFA metabolites and TZD, may provide a platform to screen new drug(s) to battle the metabolism syndrome, diabetes, and cardiovascular diseases.
睾丸孤儿核受体4（TR4）是核受体超家族的一个孤儿成员，具有多种生理功能。利用TR4基因敲除（TR4(-/-)）小鼠研究其在心血管疾病中的功能，我们发现TR4(-/-)小鼠中分化簇（CD）36表达降低，泡沫细胞形成减少。机制分析表明，TR4通过转录调控诱导CD36蛋白和mRNA表达。有趣的是，我们发现这种TR4介导的CD36反式激活可被多不饱和脂肪酸（PUFA），如ω-3和-6脂肪酸，及其代谢产物如15-羟基二十碳四烯酸（15-HETE）、13-羟基十八碳二烯酸（13-HODE）和噻唑烷二酮（TZD）-罗格列酮进一步增强。电泳迁移率变动分析（EMSA）和染色质免疫沉淀（ChIP）分析均表明，TR4与位于CD36 5'-启动子区域的TR4反应元件结合，以诱导CD36表达。在RAW264.7巨噬细胞中稳定转染TR4-siRNA或功能性TR4 cDNA导致CD36表达降低或升高，同时泡沫细胞形成减少或增加。在TR4敲低的巨噬细胞中恢复功能性CD36 cDNA可逆转泡沫细胞形成减少的情况。总之，这些结果揭示了一条控制CD36介导的泡沫细胞形成/心血管疾病的重要信号通路，并且TR4反式激活可通过其配体/激活剂（如PUFA代谢产物和TZD）激活的发现，可能为筛选治疗代谢综合征、糖尿病和心血管疾病的新药提供一个平台。
