營養、代謝和跳躍子的調控與行為的關連

Abstract

跳躍子的適度調控在發育、生理與心智行為上扮演重要的角色。跳躍子調控機制的損害將會造成不孕、老化、老化相關的神經退化疾病與癌症的發生。飲食的組成與多寡會透過表觀遺傳的修飾作用去進一步調控染色體結構，而染色體結構的改變將會影響跳躍子的表現。飲食節制具有延緩老化相關疾病並且具有延長壽命甚至於更好的生理機能，而在小鼠與果蠅的研究上，也觀察到了飲食節制可以抑制跳躍子的表現。此外，類三號DNA甲基化酶(DNMT3L) 在發育中的生殖細胞具有抑制跳躍子表現的作用，其在體細胞的功能性還未有人紀載，但唐氏症患者由於額外的第21染色體造成過量DNMT3L表現，已被連結到造成心智能力受損的可能原因之一。在我的研究中，主要探討飲食的組成、質量對於跳躍子的表現與行為測試的結果有什麼樣的影響，也會對跳躍子的表現與行為實驗的結果進行分析來判斷血液裡的跳躍子表現量是否與腦部功能有所關聯，以及類三號DNA甲基化酶的基因型對與飲食調控的血液跳躍子表現和體細胞的表現型有何影響。 在實驗中，我使用高脂飼料與育種飼料搭配飲食節制與時間的調控來觀察小鼠血液中跳躍子表現的變化與行為的改變。結果顯示兩種飼料在飲食節制的情況下，皆能夠抑制血液中跳躍子的表現。但是進行飲食節制與任意飲食的轉換之後，採食育種飼料的小鼠會隨著飲食的改變而調控血液中跳躍子的表現，但食用高脂飼料的小鼠不論有無進行飲食節制，對於跳躍子表現的調控都需要較長的時間作出調整。而在行為測試中，以育種飼料飼育的小鼠在轉換至飲食節制之後可以提升對新物件的偏好性，而採食高脂飼料的小鼠在轉換至節制飲食之後，在曠野試驗中的運動活性會有顯著的改善。而現階段血液中跳躍子的表現和腦部功能的連結仍不夠明確，需要更深入的研究與探討。另一方面，飲食節制引起的抑制跳躍子表現作用，同樣可以在類三號DNA甲基化酶剔除的老鼠中觀察到。此外，類三號DNA甲基化酶剔除的老鼠在餵飼高脂飼糧與時區轉換的複合實驗中，肝臟中的脂質新生基因、醣類代謝基因以及粒線體數目也皆有顯著的下降。 總結來說，血液中跳躍子的靜默與食物組成、採食量有關，飲食節制可提升老鼠在行為實驗中的表現，不過這些反應具有性別差異性。而因為類三號DNA甲基化酶在成鼠體細胞中的表現尚未完全明朗，我以大家熟知的類三號DNA甲基化酶主要於胚胎發育時期協助DNA甲基化的建立為基礎，來假設類三號DNA甲基化酶剔除鼠在胚胎發育的過程中，由於喪失了類三號DNA甲基化酶主導的表觀遺傳特徵，而造成類三號DNA甲基化酶剔除鼠對不良環境與飲食的組成有更為顯著的反應。

Proper regulation of transposable elements (TEs) is critical for development, physiology and mental activities. Impairment of TE modulation resulted in infertility, aging, aging related neurodegenerative disorders and cancer formation. Dietary composition and quantity could regulate chromatin structure via epigenetic modulation, and that contribute in part to the dynamics of TE expression. In mouse and Drosophila, dietary restriction (DR) has also been introduced to alleviate aging related disease, and to increase lifespan and heath span, correlating to repress TEs. DNA methyltransferase 3 like (DNMT3L) is required for TE repression in developing germ cells. However, no obvious phenotype in somatic lineages have been documented in Dnmt3l KO mice, despite the suggestion that excessive DNMT3L expression from the extra chromosome 21 may be responsible for impaired cognition ability for Down syndrome patients. In my study, I aim to clarify the effect of dietary composition, quantity and duration on TE expression and behavior outcome. Furthermore, I wanted to exam the potential link between peripheral blood TEs expression and behavior test result in order to evaluate the feasibility of using whole blood TEs expression as brain diseases biomarker. Lastly, I wanted to know whether Dnmt3l genotype would influence the dietary effect on TE modulation and phenotype in somatic lineages. For these purposes, I used a 2-month-switching between DR and ad libitum (AL) with high fat diet (HFD) or breeding diet to observe TEs expression in mouse whole blood. I also used behavior test to demonstrate cognitive function. The result showed that DR with both HFD and breeding diet resulted in repressing TEs expression in whole blood. However, only switching between AL and DR with breeding diet demonstrated fluctuation of food quantity-associated TEs expression pattern. After taking HFD without limitation (AL) for 2-month resulted in resistance of TEs re-repression in blood after switching to DR treatment. In behavior test, DR with breeding diet improved novel object preference and DR with HFD improved locomotorability in open filed test. But I could not associate whole blood TEs expression with brain function so far. On the other hand, DR-mediated TEs expression were also demonstrated in Dnmt3l mutant mice as it did in the wild type (WT) littermate. In addition, Dnmt3l KO mice after 6 weeks of time zone shifting and HFD treatment demonstrated decreased expression level of lipogenesis and carbohydrate metabolism related genes, and decreased mitochondrial copy number in liver. In conclusion, modulation of whole blood TEs expression is associated with dietary choice. DR in general improves cognition and motor related behavior test results. In addition, gender differences are clearly demonstrated in diet associated TEs regulation and behavior test results. Since the expression of DNMT3L is not easily detectable in somatic cells, I hypothesize that loss of DNMT3L dependent epigenetic signature in embryonic stem cells/progenitor cells may eventually enhanced the sensitivity of metabolic genes and transposable elements in adult DNMT3L mutants.