| Summary: | 博士 === 國立陽明大學 === 生物化學研究所 === 90 === Abstract
Oxidative modification of low density lipoproteins (LDL) and uptake of oxidized LDL (oxLDL) by macrophages are key steps in the early stage of atherogenesis. Apoptosis of macrophages and smooth muscle cells (SMC), located in the fibrous plaque, is an important factor in the late stage of atherosclerosis. Apolipoproteins are known to play a central role in lipid transport and metabolism and are intimately associated with the pathogenesis of atherosclerosis. The distribution of apoH in atherosclerotic lesions was examined by immunohistochemical analysis. The data revealed that apoH was located in the coronary arteries with atherosclerotic lesions. In this study, LDL was oxidized by copper ion, 2, 2’-azobis(2-amidio-propane)dihydrochloride (a free radical generator) or macrophages in the absence or presence of apoH to delineate the correlation between apoH and LDL peroxidation,. It was shown that the formation of thiobarbituric acid reactive substances and conjugated dienes was decreased and the electrophoretic mobility of LDL was reduced in the presence of apoH. It suggests that apoH exerts an antioxidative effect. Furthermore, cultured macrophages were treated with labeled oxLDL and the radioactivity in the cells and medium was detected. It was found that apoH could inhibit cholesterol influx and enhance cholesterol efflux. Intracellular cholesterol and 7-ketocholesterol, determined by high-performance liquid chromatography, were also decreased in the presence of apoH. It implies that apoH may inhibit the oxidation of cholesterol in macrophages. ApoH could also decrease lipid accumulation in macrophages by oil red O staining.
Immunostaining with antibodies specific to apoH revealed that apoH was localized within apoptotic macrophages and smooth muscle cells. It is suggested that apoH may be involved in the apoptosis of vascular cells. Cultured macrophages and SMCs were treated with nitric oxide donors to induce apoptosis. The results showed that the cytotoxicity was decreased and DNA fragmentation was inhibited in the presence of apoH. Furthermore, the induction of some apoptosis-related proteins, such as caspase-3, c-Fos and c-Jun, was suppressed by apoH. It indicates that apoH can inhibit apoptosis of vascular cells.
In conclusion, the present study reveals several physiological functions of apoH in vascular cells. First, apoH plays as an antioxidant from its protective effect on LDL oxidation. Second, apoH exerts a significant effect on the decrease of cholesterol influx and increase of cholesterol efflux as well as the decrease of lipid accumulation. Third, apoH can inhibit the apoptosis of macrophages and SMCs. It is suggested that apoH may participate in the prevention of atherogenesis.
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