不同能量狀態下肝臟SIRT1對動物能量代謝之調控

The role of hepatic SIRT1 on metabolic regulation under different energy status

劉佳欣(Chia-Hsin Liu)

指導教授 ： 陳靜宜

共同指導教授 ： 丁詩同(Shih-Torng Ding)

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(2012年)

https://doi.org/10.6342/NTU.2012.02910

摘要

Sirtuin 1，又稱之為SIRT1，是屬於Sirtuin哺乳動物蛋白質家族成員之一。SIRT1與其非脊椎動物同源蛋白Sir2 (silent information regulator 2 gene) 皆為菸鹼醯胺腺嘌呤二核苷酸依賴型去乙醯酵素，以菸鹼醯胺腺嘌呤二核苷酸 (NAD+) 與蛋白質上乙醯態之離胺酸為受質，進行去乙醯化作用。先前研究發現，此二種酵素都可因低能量情況或能量限制時而增加其表現量。後續其他研究發現，哺乳動物之SIRT1可以藉由調控其目標蛋白而改變身體代謝、神經及免疫功能，進而產生抗老化與延長壽命之效果。本研究目的在於了解不同代謝能濃度對於豬隻組織中SIRT1及其相關基因表現之影響，並探討高脂飼糧下對於豬隻與小鼠體內SIRT1與能量代謝之影響。
在試驗第一部分，使用十週齡蘭嶼豬進行十週的營養試驗，於期間分別餵飼每公斤2500 (L) 、2700 (M) 及2900 (H) 大卡之飼糧。結果顯示，三組間體重、飼料轉換率及平均日增重皆無差異。而L組別血液中具有較高之三酸甘油酯、高密度脂蛋白及血糖，並且在肝臟中發現其具有較高之SIRT1與脂質合成基因表現。L組別肝臟中合成較多三酸甘油酯，並在血液中觀察到具有較高的血脂現象，於此推斷其具有較高的能量利用效率。另一部分，使用五月齡蘭嶼豬進行六個月的營養試驗，於期間分別餵飼每公斤2700 (CON) 與3700 (HFD) 大卡之飼糧。結果顯示，HFD組具有較高的體重與背脂厚度，但試驗後兩組血脂分析則無出現差異。同時在肝臟中發現HFD組別具有較高的SIRT1與脂質分解基因表現，其餘基因表現皆無差異。據此推斷SIRT1在HFD餵飼下具有避免肥胖造成傷害之功能。
為了更加確定SIRT1是否可以保護身體在肥胖初期避免肥胖飼糧下造成之代謝傷害。此部分利用七週齡小鼠飼食一般飼糧 (CON) 與肥胖飼糧 (HFD) 探討各時期的結果。結果顯示，在試驗初期 (兩週) 肝臟中SIRT1於HFD組有增加的現象，但在長期間餵飼之下則沒有顯著差異，然而在年紀較大之動物上發現SIRT1有增加的現象。體重與血脂分析部分，在第二週時便可發現體重、三酸甘油酯、總膽固醇與血糖皆有顯著提升的效果。於此試驗推論，SIRT1可能在肥胖初期扮演保護的角色，隨著年紀增加其作用活性降低或無法抵禦老化造成之影響，因此仍然出現老化與肥胖現象。
綜觀上述，本研究指出豬隻肝臟中SIRT1表現在能量限制的情況下增加，此點與其他物種具有相同的結果。高能量飼糧餵飼兩週，小鼠肝臟中SIRT1也有提升的現象，在此推斷，SIRT1在肥胖初期具有保護的效果。然而，延長餵飼時間SIRT1的功效則失去保護，其相關機制有待進一步釐清。

關鍵字

SIRT1 ； 能量限制 ； 高脂飼糧 ； 能量代謝 ； 蘭嶼豬 ； 小鼠

並列摘要

Sirtuin 1, also called SIRT1, is one member of sirtuin family proteins in mammals. SIRT1 and its invertebrate homologue, silencing information regulator 2 (Sir2), both are nicotinamide adenine dinucleotide (NAD+) -dependent enzymes that exert deacetylating action on acetyl-Lysine of proteins. Previous studies showed that SIRT1 and Sir2 were up-regulated under low energy conditions or calorie restriction (CR). Furthermore, increasing SIRT1 expression regulated its target proteins to modulate metabolic, neuronal and immunological functions, and therefore lead to anti-aging and longevity. This study was focused on the link between metabolic energy (ME) level and related gene expressions SIRT1 in various tissues of swine, and in mouse models in response to high fat diet (HFD).
In the first part of this study, 10-week-old Lanyu miniature pigs were fed with diet with various ME levels (2500 (L), 2700 (M) or 2900 (H) kcal/kg) for 10 weeks. There was no difference on body weight, feed conversion ratio and average daily gain among three groups. L group had a higher plasma level of triglyceride (TG), high density high density lipoprotein (HDL) and glucose than H group. Increased mRNA expression of SIRT1 and lipogenic genes were found in liver of L group. And hepatic triglyceride content was no different among three groups. These results suggested that low energy diet induced high efficiency by SIRT1, and fluxed to peripheral tissues for further use. In the second part of this study, 5-month-old Lanyu miniature pigs were fed with control (CON) or HFD, as 2700 or 3700 (HFD) kcal ME/kg, for 6-month period. HFD pigs had a higher body weight and backfat thickness, but no difference in blood parameters, including TG, total cholesterol, HDL and LDL level between two groups was observed. After 6 month experiment period, Lanyu pig was not induced obesity. HFD pigs had an increase in hepatic transcript and protein levels of SIRT1 and lipolytic genes, suggesting a protective role of SIRT1 in HFD-induced metabolic damage of porcine model.
In order to elucidate whether SIRT1 protects mice from HFD-induced metabolic damages in early stage of obesity, the third experiment was designed using 7-week-old mice as an animal model in response to high fat diet (HFD) for various duration. Results showed that SIRT1 mRNA expression increased with advancing age. Compared with CON mice, HFD mice had higher hepatic SIRT1 mRNA expression at 2-week period, while there was no difference after 25-week feeding. In addition, body weight, plasma TG, total cholesterol and glucose level were elevated since 2 week by HFD. These results suggested that SIRT1 might play a protective role in early obesity stage, and its activity and protection decline with advancing age.
Taken together, this study indicated that porcine hepatic SIRT1 expression was induced in CR as well as the rodent model. While in the high energy status induced by HFD-feeding 2 weeks, the hepatic SIRT1 expression of mice was elevated as well. These results suggest a protective role of SIRT1 in early obesity stage. However, the related mechanism needs further elucidation.

並列關鍵字

SIRT1 ； calorie restriction ； high fat diet ； energy metabolism ； Lanyu pig ； mice

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