| Summary: | 碩士 === 國立臺灣大學 === 醫學檢驗暨生物技術學研究所 === 94 === Hypertriglyceridemia（HTG）is a common metabolic disorder resulted from multiple determinants. It may arise from either over-production or defective clearance of triglyceride-rich lipoproteins in circulation. Furthermore, HTG is also an independent risk factor for coronary heart disease. Plasma lipid is known to be carried by lipoproteins and to undergo further hydrolysis. Meanwhile, diverse-functioned apolipoproteins on lipoproteins modulate metabolism of lipid and lipoprotein. ApoAV was discovered as a new member of the apolipoprotein. Early studies indicated that the concentration of apoAV exerted an inverse correlation with the level of plasma triglyceride（TG）in genetically engineered mice. The studies also revealed that the APOA5 gene polymorphism in human was statistically correlated with the incidence of HTG. Recently studies have shown that apoAV can modulate the triacylglycerol hydrolase activity of lipoprotein lipase（LPL）through direct activation or indirect effects to reduce the plasma TG.
We have identified a c.553G>T polymorphism, resulting in the substitution of cysteine for glycine at residue 185. To gain insight into the mechanism of the effect of APOA5 185C variant, we constructed the vector carrying APOA5 185C variant cDNA, and then expressed and purified the recombinant apoAV. Using in vitro LPL activity assay, we initially showed that both apoAV wild type and 185C variant significantly increased LPL activity, but the later was less effective（26% lower compared to apoAV wild type. p＜0.001）. But this result could not be reproduced using recombinant apoAV purified at different batch. Meanwhile, we also found other factors, such as urea, temperature and the stability of apoAV activity, would cause variation of results. Furthermore, in order to reflect the physiological situation in which LPL is bound to cell surface through HSPG, we examined the effect of apoAV on the LPL activity in the presence of HSPG. Although both wild type and variant significantly increased lipolysis ability of HSPG-bound LPL, there was no statistical difference between them.
According to results of this study, the mechanism of the effect of APOA5 185C variant on triglyceride metabolism remains uncertain. Further animal studies using apoa5 knockout mice will be necessary in order to explore the mechanism in the future.
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