Studies on the expression and regulation of adipokines：1. Triacylglycerol-rich lipoproteins effects on ob gene expression in adipose cells.2. LPS and H2O2 effects on resistin mRNA expression in macrophages and monocytes.

• Main Authors: Mei-Ling Chang, 張美鈴
• Other Authors: 呂紹俊
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/06630152934539006387

博士 === 國立臺灣大學 === 微生物與生化學研究所 === 93 === Obesity is the most common cause of metabolic syndrome. Adipocytes produce a variety of biologically active molecules, collectively known as adipokines,including leptin, resistin, TNF-α and adiponectin. These adipokines participates in the metablic syndrome. Leptin acts as an satiety factor and anti-obesity hormone, to control appetite and energy expenditure. The present studies, examine the possible role of triacylglycerol-rich lipoproteins in the down-regulation of adipose obese gene expression in rats re-fed a high-fat diet. Because inflammation and oxidative stress are also believed to be implicated in the pathophysiology of insulin resistance in metabolic diseases, the effect of LPS and H2O2 on resistin mRNA expression was studied in monocytes and macrophages. The large amount of absorbed dietary lipid after feeding a high-fat diet is mainly transported as triacylglycerol (TG)-rich lipoproteins (TRL) in the post-prandial blood and is subsequently distributed to peripheral tissues including adipose and muscle tissues. An in vivo and an in vitro study were conducted to investigate the possible role of post-prandial TRL after high fat feeding in the regulation of obese (ob) gene expression. Adult male Wistar rats were fasted for 48 h and re-fed with either a fat-free/high-carbohydrate diet or a high-fat diet for 2, 4, or 8 h. Rats re-fed the high-fat diet had significantly higher plasma TG (p < 0.05) and lower plasma leptin and adipose ob mRNA (p < 0.05) than those fed the fat-free/high-carbohydrate diet; however, plasma glucose and insulin concentrations were not significantly different between the two groups. Plasma lipid analysis found large amount of TRL in rats fed with the high-fat diet; however, only very small amount of the TRL was found in rats fed with the fat-free/high-carbohydrate diet. We speculated that TRL might be involved in regulation of ob gene expression. To further examine the after of TRL on ob mRNA expression, differentiated 3T3-L1 adipocytes were treated with TRL collected from rats fed 5 mL soybean oil by gastric intubations. TRL down-regulated ob mRNA not only in a dose and time dependent manner but also in the presence of insulin in 3T3-L1 adipocytes. These results suggest a possible role of TRL in the down-regulation of adipose ob mRNA expression and may account, at least in part, for the previous observations that short-term high fat feeding resulted in lower plasma leptin. Adipocyte-derived resistin is a circulating protein implicated in insulin resistance in rodents, but the role of human resistin is uncertain. In human, resistin is mainly expressed in monocytes, it may be involved in insulin resistance which induced by inflammation and oxidative stress. Therefore the effect of LPS and H2O2 on resistin mRNA expression was examined in monocytes and macrophages. LPS led to a significant increase of resistin mRNA in a dose and time dependent manner in RAW264.7 cells and Kuffer’s cells. Induction of resistin mRNA was attenuated by anti-inflammatory reagents, such as dexametasone, genistein and PPARγ agonists (ciglitazone, pioglitazone and 15d-PGJ2), which suggest that resistin is involved in inflammation process. Actinomycin D inhibit the resistin mRNA activation by LPS, indicated that the LPS increased resistin mRNA through the transcriptional activation. LPS-induced increase of resistin mRNA was blocked by U0126 (2.5 μM) and Ly294002 (25 nM). These results suggest that the MEK and PI3K are involved in the LPS-induced increase of resistin mRNA. NF-κB translocation inhibitor, CAPE (10 μg/mL), inhibited translocation of NF-κB to nucleus and blocked LPS-induced increase of resistin mRNA. These results suggest that NF-κB activation is necessary for resistin induction by LPS. Resistin mRNA expression was induced by H2O2 treatment in THP-1 cells and human’s PBMC. Induction of resistin was also attenuated by transcriptional inhibitor drugs, actinomycin D. Treatment of the cells with NF-κB inhibitor, CAPE (10 μg/mL), prevented increase of resistin mRNA upon H2O2 treatment. The p50 subunit was translocated to nucleus after H2O2 administration. These results suggest that the NF-κB is involved in the H2O2-induced increase of resistin mRNA expression. TNF-α is not involved in H2O2 induction of resistin mRNA, but involved in LPS induction process.