| Summary: | 碩士 === 國立陽明大學 === 生化暨分子生物研究所 === 99 === Abstract
Decrease in the ability of cholesterol efflux has been observed in patients with type 2 diabetes mellitus. During the cholesterol transportation, ATP-binding cassette transporter A1 (ABCA1) functions as a pivotal regulator of lipid efflux from cells to apolipoprotein A1 (apoAI). However, the cellular and molecular mechanism of ABCA1 expression varied in hyperglycemia is still unclear. The present study aimed to understand the effect of hyperglycemia on ABCA1 expression in RAW264.7 macrophages and its underlying mechanisms. The levels of ABCA1 mRNA and protein expression were decreased in a dose-dependent manner after glucose stimulation by Western blot and reverse transcription polymerase chain reaction (RT-PCR). Our study showed that glucose down-regulated ABCA1 mRNA, protein and cholesterol efflux, but enhanced reactive oxygen species (ROS) production in RAW264.7 macrophages. AP-1 is a redox-sensitive transcription factor involved in the regulation of signaling pathways in hyperglycemia. The 5'-flanking regions containing AP-1 cis-elements upstream of ABCA1 gene were cloned into luciferase plasmids. The promoter activity of ABCA1 was analyzed by transient transfection in RAW264.7 macrophages by luciferase assay. It shows that promoter activities of ABCA1 gene were down-regulated by glucose. Glucose significantly increased the translocation of transcription factor c-fos to nucleus, and was reversed by ERK inhibitor. In addition, the in vivo binding of c-fos to the ABCA1 promoter was increased in the presence of glucose. Together, these results indicate that glucose-induced suppression of glucose-mediated ABCA1 expression is mainly mediated by ERK-MAPK pathway activated by ROS. This study provides an insight to the mechanism of ABCA1 suppression, and a possible explanation for the accelerated atherosclerosis in hyperglycemia.
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