魚油對小鼠脂肪組織基因表現之影響研究

Study on the gene expression profile in adipose tissue of mouse fed fish oil diet.

黃莉婷(Li-Tin Huang)

指導教授 ： 呂紹俊

國立臺灣大學/醫學院/生物化學暨分子生物學研究所/碩士(2005年)

https://doi.org/10.6342/NTU.2005.02157

摘要

摘要
證據顯示肥胖是造成第二型糖尿病的重要因素，然而，究竟是何種機轉連結肥胖與胰島素抗性則仍未明瞭。在動物實驗，魚油曾被發現具有預防高醣飲食及高油飲食所引起的胰島素抗拒的作用，但其機轉仍不清楚。近年來的研究顯示脂肪組織所分泌的一些adipokines與肥胖引起的胰島素抗拒息息相關，因此我們以含20%豬油或含20%魚油之高脂飲食飼料餵養C57BL/6J小鼠及db/db小鼠，分析血糖的變化及脂肪組織組成及adipokines mRNA的表現。在C57BL/6J小鼠觀察到魚油組之小鼠副睪脂肪組織重量明顯低於豬油組(0.17+0.06g vs 0.32+0.05g，p<0.05)，而且血漿三酸甘油酯、膽固醇、游離脂肪酸皆顯著低於豬油組(p<0.05)，但體重及血糖並沒有明顯變化(p>0.05)。由於小鼠脂肪組織太少不易取得足夠的檢體進行mRNA表現的分析工作，而且C57BL/6J小鼠血糖並不因攝食高之飲食而升高，經評估後在第二個實驗改以db/db小鼠進行探討。
在實驗二，我們以低脂飼料(4%大豆油--LF)、高豬油脂飼料(20%豬油+4%大豆油; Lard)或高魚油飼料(20%魚油+4%大豆油; FO)餵養db/db小鼠。餵食三週或五週之FO組小鼠體重及脂肪組織重量明顯低於Lard組的小鼠(p<0.05)，而LF組小鼠又較FO組略低。FO組血漿中葡萄糖、三酸甘油酯、膽固醇濃度皆顯著低於Lard組和LF組(p< 0.05)，FO組游離脂肪酸亦顯著低於Lard組(p<0.05)。餵食三週之FO組血漿胰島素濃度顯著低於其他兩組；在餵養五週後各組的胰島素濃度明顯的降低，且三組之間沒有差異。FO組單位重量脂肪組織中DNA含量較Lard組和LF組高。若以每單位DNA計算細胞TG含量，發現Lard組之TG含量最高，顯示Lard組小鼠脂肪細胞中含最大量的TG。LF組和FO組脂肪組織的ob, TNF-α, interleukin-6 (IL-6)和iNOS mRNA表現量皆較Lard組少，另外FO組脂肪組織的resistin mRNA表現量也較Lard組少。相反的，FO組adiponectin和GLUT-4 mRNA的表現量均較LF組和Lard組明顯的高。相關性分析顯示FO組血糖及胰島素濃度比Lard組及LF組低與脂肪組織GLUT-4及resistin mRNA表現量有明顯的相關性，但與脂肪組織重量、TG/DNA、ob, TNF-α, interleukin-6 (IL-6)、iNOS或adiponectin mRNA的表現量沒有直接關係。這些結果不足以說明魚油是如何改善db/db鼠糖尿病的情況，因此進一步探討魚油改善db/db鼠糖尿病的途徑會是有趣且重要的，因此我們由各組分別取一隻小鼠的脂肪組織RNA進行microarray分析，三隻小鼠脂肪組織基因表現作交叉比較。各組間基因表現的比較發現在FO組表現比Lard組高出2倍以上的基因有176個，而在Lard組表現高於FO組2倍以上的基因有650個。在Lard組表現比LF組高出2倍以上的基因有607個，而在LF組表現高於Lard組2倍以上的基因有90個。在FO組表現比LF組高出2倍以上的基因有275個，而LF組表現高於FO組2倍以上的基因有355個。這些基因的變化提供日後更近一步了解肥胖造成胰島素抗拒的分子機轉的機會。

關鍵字

魚油 ； 小鼠脂肪組織

並列摘要

Abstract
Obesity, which leads to insulin resistance, is a strong risk factor for the development of type 2 diabetes. But the connection between obesity and type 2 diabetes remains mostly unknown. Several studies have demonstrated that fish oil supplement can prevent high-sucrose diet or high-fat diet induced insulin resistance. In the present study, C57BL/6J mice were fed with high fat diets containing 20% lard or 20% fish oil (FO) for 6 weeks. Mice fed with FO diet had lower adipose tissue mass (0.17+0.06g vs 0.32+0.05g, p<0.05), and lower plasma triacylglycerol(TG), cholesterol and non-esterified fatty acid(NEFA) concentrations than that in mice fed with lard diet. But plasma glucose and body weight were not significantly different between the two groups. Because the adipose tissues of C57BL/6J were too small to be enough for further experiments, we then screened the differentially expressed genes in mouse liver by Suppression Subtraction Hybridization-PCR (SSH-PCR). Some of these clones were checked by sequencing and the results showed that most clones were from ribosomal RNAs. This could be due to that the poly(A)-RNA used for SSH-PCR was not pure enough. After thoughtful discussion we decided to discontinue sequencing more clones.
In the second experiment, 28 genetically obese db/db mice, from Jackson Lab, were used. Mice were randomly divided into three groups and were fed with low-fat diet (LF, 4% soybean oil), lard diet (Lard, 20% lard + 4% soybean oil) or fish oil diet (FO, 20% fish oil + 4% soybean oil). After feeding for three or five weeks, FO and LF groups had lower body weight and adipose weight than the Lard group. However, plasma glucose, TG and insulin concentrations were lower in FO group than in the LF and Lard groups. That the amount of DNA per gram of adipose tissue significantly higher in the FO group than in the LF and Lard groups indicated higher cell numbers in the FO group than the other 2 groups. FO group also showed lower TG/DNA content than the other two groups. The results suggest that adipocytes of the FO group were smaller in size. Adipose ob, tumor necrosis factor-α), interleukin-6 (IL-6) and inducible nitric oxide synthase (iNOS) mRNA levels were significantly lower in the FO and LF groups than in the Lard group. Compared with the LF and Lard groups, FO group has significantly higher adipose adiponectin and GLUT-4 mRNA. Correlation analyses show that lower plasma glucose and insulin concentrations in FO group were well correlated with levels of GLUT-4 or resistin mRNA, however, the mechanism that fish oil improves diabetes in db/db mice is still not clear. But apparently it is not associated with the weight, TG/DNA, levels of ob, TNF-α IL-6, iNOS or adiponectin mRNA of adipose tissue. Further investigation of mechanism(s) that fish oil improves diabetes in db/db mice would be very important and interesting. We then randomly picked adipose tissue mRNA from one mouse in each group and analyzed the gene expression profile by microarray. There are 176 genes up-regulated and 650 genes down-regulated over 2 fold in mouse fed FO diet compared with the mouse fed Lard diet; and 607 genes up-regulated and 90 genes down-regulated over 2 fold in mouse fed Lard diet compared with the mouse fed LF diet; 275 genes up-regulated and 355 genes down-regulated over 2 fold in mouse fed FO diet compared with the mouse fed LF diet. Further analyses of the expression profile may help us know more about the molecular mechanism that link obesity to insulin resistance

並列關鍵字

adipose tissue ； fish oil diet

參考文獻

Chee, M., Yang, R., Hubbell, E., Berno, A., Huang, X.C., Stern, D., Winkler, J., Lockhart, D.J., Morris, M.S., and Fodor, S.P. (1996) Accessing genetic information with high-density DNA arrays. Science 274, 610-614.

Khan, S., Minihane, A.M., Talmud, P.J., Wright, J.W., Murphy, M.C., and Williams, C.M. (2002) Dietary long-chain n-3 PUFAs increase LPL gene expression in adipose tissue of subjects with an atherogenic lipoprotein phenotype. J. Lipid Res. 43, 979-985.

Ahima, R.S. and Flier, J.S. (2000) Adipose tissue as an endocrine organ. Trends Endocrinol Metab 11, 327-332.

Alberti, K.G. and Zimmet, P.Z. (1998) Definition, diagnosis and classification of diabetes mellitus and its complications. Part 1: Diagnosis and classification of diabetes mellitus, provisional report of a WHO consultation. Diabetic Med 15, 539-553.

Allison, D.B., Fontaine, K.R., and Manson, J.E. (1999) Annual deaths attributable to obesity in the United States. JAMA 284, 1530-1538.