出生前與哺乳期西式飲食暴露對 ApoE-/- 小鼠脂質代謝之影響

Abstract

子代的代謝狀態會受母親所提供的子宮環境而影響，且這樣的影響可能會造成子代成年後健康，也就是所謂胎兒規劃 (fetal programming) 假說。 過去的文獻指出，懷孕期間母體若攝入過多脂肪及膽固醇而引起高血脂症，會提高子代成年後出現心血管疾病以及脂肪肝的發生率，但詳細的機制目前還不清楚。故本實驗欲建立一個穩定的高膽固醇血症動物模式，研究母體營養對其子代成年期健康之影響及其可能分子機制。我們選用對於高油脂高膽固醇飲食有高敏感性的 apolipoprotein E 剔除 (ApoE-/-) 小鼠做為模式動物，在母鼠孕期前、孕期及哺乳期進行高油脂高膽固醇飲食處理，並在子代斷奶後持續以飲食誘導，欲觀察子代在發育早期處於高膽固醇的環境所造成的健康影響。 本研究中將孕鼠分為高油脂高膽固醇 (Western diet, WD) 組及正常飲食組 (Control diet, CD)。WD 組及 CD 組子代斷奶後皆餵食 Western diet，分別為 W-W 組以及 C-W 組，一共生 3 胎子代。本研究測量動脈粥狀硬化及脂質代謝評量指標: 主動脈弓粥狀硬化斑塊、體重組織重量、血液及肝臟脂肪含量、肝臟及脂肪之病理切片。W-W 組子代在 3 週齡斷奶時，血清膽固醇及三酸甘油酯濃度顯著高於 C-W 組，但 8 周齡後兩組間沒有差異。23 周齡犧牲時，第一、二胎兩組肝臟脂肪含量無顯著差異，但 W-W 組子代有較嚴重的脂肪肝，其餘生理指標如動脈粥狀硬化斑塊面積比例、脂肪細胞大小的差異則不明顯。之後第三胎子代於 16 周齡犧牲，W-W 組子代比起 C-W 組，肝臟及脂肪重量顯著增加，肝臟膽固醇及三酸甘油酯含量顯著增加，肝臟中脂質合成的相關基因 Fasn、Acacb、Srebf1、Srebf2、Lipe 和Chpt1，以及脂質運輸相關基因 Abcg5 和 Abcg8 在 W-W 組子代比 C-W 組有較高的表現量。 綜合以上結果，母鼠孕期前後的高血膽固醇會造成子代成年後脂質在脂肪組織以及肝臟堆積，隨著年齡增長還可能演化為脂肪肝。而肝臟脂質堆積可能是與脂質合成以及運輸相關基因表現量提升有關。後續的研究將會著重於表觀遺傳如何影響此現象。

In utero environment during embryonic and fetal development is associated with risk of diseases later in life. This concept of fetal programming is further supported by clinical and experimental studies. Previous studies demonstrate that maternal high fat diet intake during early development increase susceptibility to cardiovascular diseases and liver diseases in offspring. However, little is known about the molecular mechanisms underlying the impacts of maternal diet on offspring. We aim to setup a mouse model to characterize the effects of maternal hypercholesterolemia on the lipid metabolism of adult offspring. Apolipoprotein E knockout (ApoE-/-) female mice were fed either a Western diet (WD) or a low-fat control diet (CD) before and during gestation and lactation. At weaning, the ApoE-/- offspring were all fed WD, generating two experimental groups: W-W and C-W offspring. Female mice gave birth to three litters. Among them, the offspring of litter 1 and 2 were analyzed at 23 weeks of age, and the offspring of litter 3 were investigated at 16 weeks of age. Biochemical analysis showed that the W-W offspring from litter 1 and 2 have a higher serum triglycerides (TG) and cholesterol levels than C-W offspring at weaning. However, there are no significant differences on hepatic TG and cholesterol levels, adipocyte area as well as the severity of atherosclerotic lesions between W-W and C-W offspring at 23 weeks of age. In contrast to the results from litter 1, and 2, more profound differences between two groups were observed in litter 3. The relative weight of liver, inguinal white adipose tissue (iWAT) and interscapular brown adipose tissue (iBAT) was significantly higher in W-W than in C-W offspring. Although there were no significant differences on the development of atherosclerotic lesions, W-W offspring from litter 3 showed hepatic steatosis combined with accumulation of hepatic TG and cholesterol in comparison with C-W group. This accumulation was associated with up-regulation of de novo lipid synthesis. Increased expressions of lipid synthesis related genes, including Fasn, Acacb, Lipe, Chpt1, Srebf1 and Srebf2 were observed in the livers of W-W offspring. In addition, the expression of cholesterol transport related genes, such as Abcg5 and Abcg8 was significantly higher in the livers of W-W in those of C-W offspring. Taken together, our findings demonstrate that maternal hypercholesterolemia increase susceptibility to lipid accumulation in their adult offspring by augmenting hepatic lipid synthesis, which is mediated at least in part by increased expression of lipid synthesis and transport related genes. Future research will concentrate on epigenetic changes involved in this programming process.