母親高膽固醇血症對小鼠子代代謝性和心血管疾病的影響

Abstract

發展規劃 (developmental programming) 為當某件事情發生在子宮或是嬰兒期可能會對個體健康造成長久的影響。過去研究指出，出生前過多營養物質的供應，會使子代成年後得到胰島素阻抗、第二型糖尿病、代謝性疾病和心血管疾病的風險增加。目前普遍認為表觀遺傳的調控在發展規劃中可能扮演重要角色，但其中相關機制尚未有定論。故本研究假說為：以高油脂高膽固醇飲食誘導母鼠孕期高膽固醇血症，會改變子代脂質代謝，導致非酒精性脂肪肝及動脈粥狀硬化發生。 本研究使用 8 周齡的 ApoE -/- 母鼠，懷孕前以西方飲食 (Western diet, WD) (23% 脂肪及0.15% 膽固醇) 誘導母鼠產生高膽固醇血症，對照組給予低脂控制組飲食 (control diet, CD) (7% 脂肪)，懷孕期及哺乳期維持孕前相同飲食。後續實驗分為兩部分，第一部份子代離乳後餵食 CD (CC & WC 組)，兩組子代在體重上雖無差異，但在第 15 周齡時 WC 組雄鼠出現葡萄糖不耐情形，在第 16 周齡犧牲時也觀察到 WC 組雄雌鼠子代脂肪組織重量較 CC 組重。另外 WC 組雄鼠肝臟中三酸甘油酯及膽固醇堆積顯著較 CC 組多，顯示有肝臟脂肪變性 (hepatic steatosis)，在肝臟 mRNA 表現量也可以看到 WC 組負責脂肪酸運輸的 Cd36 明顯上升，推測可能有較多脂肪酸運送到肝臟，造成脂質堆積；而脂質生成的相關基因 Srebf1、Fasn 和 Dgat2 表現量下降，可能為肝臟啟動的保護機制。另外，為了研究後天西方飲食是否會加遽疾病發展，在第二部分實驗子代離乳後改餵食 WD 誘導動脈粥狀硬化發生 (CW & WW 組)，雄鼠子代兩組在肝臟以及血管的病變程度相當，而雌鼠因 CW 組較不嚴重所以可以觀察到 WW 組可能有胰島素阻抗，且在主動脈弓區域斑塊堆積情形較 CW 組嚴重，顯示母體西方飲食攝取會加遽子代成年後胰島素阻抗以及動脈粥狀硬化的發生。 綜合兩部份實驗可知，母鼠孕期西方飲食會使子代成年後較易得到非酒精性脂肪肝及動脈粥狀硬化等疾病。後續研究將會著重在探討母體效應 (maternal effect) 是否藉由影響子代基因甲基化的程度，造成發展規劃的現象。

Increasing evidence suggests that the intrauterine environment has an important impact on lifelong health. Epidemiological and animal studies have showed that poor maternal nutrition status increases the risk of type 2 diabetes, metabolic syndrome and cardiovascular diseases in adult offspring. However, the molecular mechanisms underlying the fetal programming are not yet conclusive, and may involve in epigenetic regulation. Our study is aimed to investigate if maternal high fat/high cholesterol Western-typed diet intake impair lipid metabolism in their offspring, which may lead to the development of nonalcoholic fatty liver diseases (NAFLD) and atherosclerosis later in life. Apolipoprotein E-deficient (ApoE -/-) mice are highly susceptible to developing dyslipidemia and atherosclerosis, and were chosen to induce hypercholesterolemia. Eight-week-old ApoE -/- female mice were fed with either a Western diet (WD) (23% fat and 0.15% cholesterol) or a low-fat control diet (CD) (7% fat) prior to and during pregnancy and lactation. In the first study, the offspring were weaned onto CD for 16 weeks, generating two experimental groups: C-C and W-C. At 15-week of age, W-C male offspring exhibited reduced glucose tolerance compared to C-C groups. Although female mice in both groups showed a similar blood glucose response, W-C female offspring showed a higher fat mass than C-C mice, suggesting obesity. In addition, W-C male offspring revealed increased hepatic steatosis, as evidenced by accumulation of hepatic cholesterol and triglycerides. Probing mechanism, we found that several genes involved in lipid metabolism and transport are dysregulated. While the expression of fatty acid translocase Cd36 was significantly increased, the expression of few lipogenic genes, such as Srebf1, Fasn and Dgat2, was markedly downregulated in W-C male liver compared to C-C livers. Collectively, our results suggest that increased hepatic lipid accumulation in W-C offspring is likely mediated in part through upregulation of hepatic fatty acid uptake. To examine if a post-weaning Western-style diet exacerbates disease progression, the offspring were all fed with a WD after weaning. Two experimental groups, C-W and W-W, were generated in the second study. We showed that W-W female offspring may display insulin resistance compared to C-W groups. Notably, when compared to C-W mice, W-W female offspring developed significant atherosclerotic lesion. Our results suggest that maternal Western-typed diet exaggerates insulin resistance and atherosclerosis in adult offspring. Taken together, maternal Western-typed diet may increase susceptibility to not only NAFLD, but also atherosclerosis in their adult offspring. Future research will be focused on whether the maternal effect is mediated by epigenetic regulation.