Effects of polyunsaturated fatty acids on the regulation and expression of peroxisome proliferator-activated receptors in smooth muscle cells, macrophages, and hepatocytes

• Main Authors: Tse-Chun Kuo, 郭則君
• Other Authors: An-Na Chiang
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/30461917759926074179

碩士 === 國立陽明大學 === 生物化學研究所 === 91 === Peroxisome proliferator-activated receptors (PPARs) are a family of ligand-activated nuclear transcriptional factors that include three membranes, PPARα, γ, and β/δ. Defined functions for these receptors mainly concerned their ability to regulate lipid metabolism, adipocytes differentiation, and keratinocyte differentiation, respectively. In addition, many researches indicated that PPARα and PPARγ have protective actions on vascular disease, especially on atherosclerosis. Several experimental studies have been shown that polyunsaturated fatty acids (PUFAs) are ligands of PPARs. Many researches also demonstrated that the expressions of nuclear hormone receptors can be influenced by their ligands. In this study, we are interested to address whether PUFAs, such as arachidonic acid (AA), linoleic acid (LA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) are involved in regulating expressions of PPARα and PPARγ. To investigate the effects of PUFAs on PPAR expression, we used RT-PCR and Western blot analysis to demonstrate the expression of PPARα and PPARγin human coronary artery smooth muscle cells and macrophages treated with different kinds of PUFAs. The result showed that both PPARα and PPARγ mRNA were induced in smooth muscle cells with different kinds of PUFA and synthetic ligand treatment. The ligand-induced protein expression of PPARγ was considered to be mediated through the PKC pathway in smooth muscle cells. In macrophages, the expression of PPARα and PPARγ mRNA was inhibited by different kinds of PUFA and synthetic ligands. The mechanism seems to be involved in ROS generation and is mediated via MAP Kinase activation, because pretreatment with NAC and MEK inhibitor PD98059 reversed the inhibitory effects on PPARγ protein expression. In addition, we investigated whether PUFAs contribute to the trans-activation of gene expression by using transcient transfection experiments. The results indicated that the PPRE of LXRα promoter could be trans-activated by all polyunsaturated fatty acids we used, but DHA had the greatest ligand-activation effect. In conclusion, we found that PUFAs play differential effects on the expression of PPARα and PPARγin coronary artery smooth muscle cells and macrophages. The different effects may probably due to the extent of ROS generation in the two cell lines. The result of transfection study indicates that DHA may enhance cholesterol efflux in vascular cells during the process of atherosclerosis. However, detail molecular mechanisms still need further studies to delineate.