| The scavenger receptor class B type I (SR-BI) was the first molecularly well-defined cell-surface high density lipoprotein (HDL) receptor to be described. SR-BI is a multi-ligand receptor that can mediate the binding and bi-direction flux of cholesterol and other lipids between HDLs and cells. Reverse cholesterol transport (RCT) is the HDL-mediated transport of excess cholesterol from peripheral tissues to the liver for excretion or recycling. It involves multiple steps, the first step with the efflux of unesterified cholesterol from macrophages to HDL. Finally, cholesterol ester that remains associated with HDL is delivered directly to the liver by a process called selective lipid uptake. SR-BI is very important in RCT as the receptor of HDL. The present work observed changes of plasma lipid level and SR-BI expressions in atherosclerotic mini swine. Furthermore, the present study also investigated that lipoproteins influenced the expression of SR-BI and cholesterol transport in HepG2 and THP-1 cell lines.Part I: Changes of SR-BI expression in atherosclerotic mini swineAIM: In order to study the expression of SR-BI in liver and abdominal aorta ofatherosclerotic mini swine.METHODS: Chinese mini swine were fed a normal diet or a high fat/high cholesterol diet(HFHC) for 12 months. The sections, which were taken from liver and abdominal aorta, were stained with hematoxylin eosin and oil red O. The expression of SR-BI mRNA and protein in liver and aorta tissue were detected by reverse transcription-polymerase chain reaction (RT-PCR), western blotting and immunohistochemistry respectively.RESULT: At the end of 12 months, there was fatty liver and atherosclerotic plaque in porcine liver and aorta respectively. The expression of SR-BI was upregulated in the liveand aorta tissues of mini swine fed with HFHC diet.CONCLUSIONS: HFHC diet upregulated the expression of SR-BI in the liver and aorta ofmini swine.Part II: Influences of the SR-BI expression by ox-LDL, LDL and HDL in HepG2 and THP-1 cellsAIM: To investigate the influences of the SR-BI expression and cholesterol transport byox-LDL, LDL and HDL in HepG2 and THP-1 cell lines.METHODS: HepG2 cells were cultured in DMEM medium supplemented with 10% fetalbovine serum. THP-1 cells were cultured in RPMI-1640 medium supplemented with 10% fetal bovine serum and induced to differentiation into macrophages by PMA treatment. In the process of this experiment, cells were co-incubated with 50jug/ml ox-LDL, LDL or HDL respectively for 24 hr. Moreover, THP-1 cells were also co-incubated with 50jUg/m\ ox-LDL and different concentration of HDL (50, 100, 150//g/ml). Cellular lipid accumulation was determined by Oil Red O staining and high performance liquid chromatography analysis. [3H]-labeled cholesterol flux was determined by FJ-2107P type liquid scintillator. SRtBI mRNA and protein level were determined by reverse transcription-polymerase chain reaction and western blot, respectively.RESULT: Oil Red O staining showed that HepG2 cells treated with 50/ig/ml ox-LDL, LDLand HDL receptively accumulated more lipid droplet than control group cells. The effect of increased cellular lipid accumulation by HDL was more than by ox-LDL and LDL in HepG2 cells. High performance liquid chromatography analysis demonstrated that ox-LDL, LDL and HDL increased HepG2 cellular total cholesterol. Liquid scintillator showed that ox-LDL, LDL and HDL increased the influx of cholesterol in HepG2 cells. On the other hand, ox-LDL decreased the efflux of cellular cholesterol and HDL increased the efflux of cellular cholesterol in THP-1 macrophages cells by a dose dependent manner. The expression of SR-BI mRNA and protein that was determined by RT-PCR and western blot was increased by ox-LDL, LDL and HDL in HepG2 cells. Moreover, ox-LDL downregulated the expression of SR-BI and HDL upregulated the expression of SR-BI in...
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