血清澱粉狀蛋白A增進脂肪分解作用之訊息傳遞路徑

Serum amyloid A induced lipolysis signal transduction pathway

劉利儒(Li-Ru Liu)

指導教授 ： 丁詩同

共同指導教授 ： 林劭品

國立臺灣大學/生物資源暨農學院/動物科學技術學研究所/碩士(2009年)

https://doi.org/10.6342/NTU.2009.02846

摘要

血清澱粉狀蛋白A ( serum amyloid A, SAA) 不只是載脂蛋白，也是具有促進脂肪分解能力的脂肪細胞激素，但SAA促進脂肪分解作用的訊息傳遞路逕目前尚無研究，因此本文研究目的為研究SAA調控脂肪分解作用機制。在添加豬SAA重組蛋白和不同訊息傳遞抑制劑於豬脂肪細胞實驗中，發現SAA降低油滴包被蛋白(perilipin)、荷爾蒙敏感性解脂酶 (hormone sensitive lipase, HSL)及脂肪組織三酸甘油酯酶(adipose triacylglycerol lipase, ATGL) 的表現，且這些效應會被細胞外訊息調節蛋白激酶 (extracellular signal regulated kinase, ERK)及蛋白質激酶A (protein kinase A, PKA) 之抑制劑回復。SAA亦於猪脂肪細胞中增加ERK與PKA 之磷酸化，而且SAA增加脂肪分解的效應會被ERK與PKA之抑制劑中止。此外，SAA抑制過氧化體增生活化受體γ (peroxisome proliferator-activated receptor-gamma, PPARγ) mRNA表現之效應亦受ERK抑制劑回復。 為釐清PPARγ是否參與SAA經由活化ERK降低perilipin表現之訊息路徑，於添加SAA和不同抑制劑在已轉染猪perilipin啟動子之3T3L1脂肪細胞實驗中，發現SAA降低perilipin啟動子活性主要序列位置在PPARγ反應子 (peroxisome proliferator-activated receptor response element, PPRE) ，而且ERK也參與其中。綜合以上，證明SAA藉由ERK/PPARγ 與 PKA 訊息傳遞路徑降低perilipin表現，使三酸甘油酯分解成游離脂肪酸及甘油釋出脂肪細胞，達脂肪分解目的。

關鍵字

SAA ； 脂肪分解作用 ； perilipin ； HSL ； ERK ； PPARγ ； PKA

並列摘要

Serum amyloid A protein (SAA) is not only an apolipoprotein, but also a member of adipokines with potentials to enhance lipolysis in human and porcine adipocytes. The purpose of this study was to explore how SAA facilitates lipolysis in porcine adipocytes. Several predict signal transducer inhibitors and porcine SAA recombinant protein were used to treat porcine adipocytes in primary cell culture. We found SAA decreased the expression of perilipin, hormone sensitive lipase (HSL), and adipose triacylglycerol lipase (ATGL) mRNA and such effect could be recovered by extracellular signal-regulated kinase (ERK) and/or protein kinase A (PKA) inhibitors. The SAA also activates ERK and PKA via phosphorylating these kinases in porcine adipocytes. Moreover, SAA increased porcine adipocyte glycerol release, which was abrogated by ERK (PD98059) and PKA (H89) inhibitor, suggesting that ERK and PKA involve in mediating the SAA enhanced lipolysis. On the other hand, SAA down-regulated the expression of peroxisome proliferator-activated receptors gamma (PPARγ) mRNA which was recovered by ERK inhibitor. To understand whether PPARγ participates in SAA promoted lipolysis via ERK, we performed the porcine perilipin promoter assay with luciferase as promoter in differentiated 3T3L1 adipocytes. We found that SAA reduced porcine perilipin promoter specifically through the function of its PPARγ response element (PPRE), and this effect was recovered by ERK inhibitor. However, PKA did not have a role in the SAA regulated PPRE activity. These findings demonstrate that SAA induced lipolysis is a result of down-regulation of perilipin via ERK/PPARγ and PKA signaling pathways which are novel pathways by which SAA directly stimulates lipolysis to liberate glycerol efflux from adipocytes.

並列關鍵字

SAA ； lipolysis ； perilipin ； HSL ； ERK ； PPARγ ； PKA

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