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  • 學位論文

氧化性膽固醇在動脈硬化中的角色探討

Effects of Oxysterols on Atherosclerosis

指導教授 : 康照洲

摘要


氧化性低密度脂蛋白會改變脂蛋白的代謝;影響黏滯性分子,生長因子,細胞素等基因的表現;以及造成細胞程序性死亡,細胞移動和細胞增生。因此氧化性低密度脂蛋白被認為與血管動脈粥狀硬化的發生有密切的關聯性,而氧化性的膽固醇則是氧化性低密度脂蛋白的主要組成物質,在過去的研究中也指出,較高濃度之氧化性膽固醇類物質會傷害血管內皮細胞、血管平滑肌細胞、免疫細胞等,並出現微核或核酸片斷化等細胞凋亡指標,同時也觀察到粒線體的異常變化。在動脈硬化病灶形成的過程中,內皮細胞的活化,平滑肌細胞的移行與增生皆扮演了重要的角色。因此,在本項研究當中,我們探討了常見三種氧化性膽固醇7-ketocholesterol (7-keto), Cholesterol-5α, 6α-epoxide (α-poxide)及Cholesterol 3β,5α,6β-triol (α-triol),在人類臍靜脈內皮細胞與大鼠平滑肌細胞所扮演的角色。 結果顯示,α-triol會調控人類臍靜脈內皮細胞當中調控環氧化酶-2 (COX-2) mRNA與蛋白的表現並且進而釋放出前列腺素E2 (PGE2)。此外,α-triol會造成人類臍靜脈內皮細胞當中eNOS1177蛋白的磷酸化而觀察到一氧化氮(NO)的產生。在探討其分子機制上,前處理p38蛋白與PI3K蛋白的抑制劑會抑制α-triol於人類臍靜脈內皮細胞當中所觀察到eNOS1177蛋白的磷酸化,而NO,PI3K,p38與NF-κB的抑制劑則有效地防止了α-triol在人類臍靜脈內皮細胞當中所促進的COX-2 mRNA與蛋白之增加。另外,7-keto與α-poxide會促進大鼠平滑肌的移行與增生。透過抑制劑的處理,我們證實了MMPs, EGFR 與PI3K會參予在7-keto與α-poxide所造成的平滑肌移行,而EGFR,PI3K,ERK以及sphingomyelin的水解在促進7-keto與α-poxide所造成的平滑肌增生中扮演了重要的角色。進一步透過共免疫沉澱法,我們發現7-keto與α-poxide會造成平滑肌中EGFR的磷酸化並與PI3K結合。利用RT-PCR,西方點墨法與酵素螢光受質,我們證實了7-keto與α-poxide會在平滑肌細胞內造成Akt與ERK的活化,並造成MMP-2/9 mRNA與酵素活性的增加。綜合以上的結果,我們證明了這三種常見的氧化性膽固醇對於促進動脈硬化的發生扮演了重要的角色。

並列摘要


Oxidized LDLs (oxLDLs), may induce changes in lipoprotein metabolism, gene expression of adhesion molecules, growth factors, and cytokines, cell viability/apoptosis, migration, and proliferation. There are strong correlation between atherosclerosis and ox-LDL. Oxysterols is the major components of ox-LDL. The cytotoxicity of oxysterol has been widely reported in endothelial cells, smooth muscle cells and macrophages concomitant mitochondria dysfunction and nuclear fragmentation which are the apoptotic marker. The formation of an atherosclerotic lesion occurs through several cellular events that include endothelial cell activation, vascular smooth muscle cell migration and proliferation. Therefore, we investigated the roles of three common oxysterols, cholesterol 3β,5α,6β-triol (α-triol), 7-ketocholesterol (7-keto) and cholesterol-5α,6α-epoxide (α-epoxide) on human umbilical vein endothelial cells (HUVECs) and smooth muscle cells (SMCs). We found that α-triol dose- and time-dependently enhanced COX-2 protein expression and mRNA production followed by PGE2 generation in HUVECs. In addition, α-triol upregulated peNOS1177 protein phosphorylation and dose-dependently increased nitric oxide production. In studying the mechanisms involved in α-Triol-induced COX2/PGE2 production, eNOS1177 phosphorylation was abrogated by the p38 and PI3K inhibitor. Inhibitors of NO, PI3K, p38, and NF-κB, effectively attenuated COX-2 protein induction and mRNA expression, suggesting that the PI3K-Akt-eNOS pathway, p38MAPK, and NF-κB are involved in α-triol-induced COX-2 expression. Also, our results showed that 7-keto and α-epoxide promoted SMC migration by a chemotactic assay, and induced mitogenic effects by MTT assay and BrdU assay. Specific inhibitors confirmed that MMPs, EGFR and PI3K are involved in oxysterol-induced SMC migration, while EGFR, ERK, Akt, and sphingomyelin/ceramide pathways might play a role in SMC proliferation. More, the co-immunoprecipitation study indicated that 7-keto and α-epoxide caused EGFR phosphorylation and there was an interaction between EGFR and PI3K. At protein expression level, Akt and ERK were activated, at messenger RNA level, MMP-2/9 mRNA was transcribed, at enzyme activity level, the MMP-2/9 enzyme activity were increased in SMCs treated with 7-keto and α-epoxide according to Western bolt, RT-PCR and a fluorogenic substrate. Taken together, we concluded that 7-keto and α-epoxide may be an atherogenic factor.

參考文獻


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