- 學位論文
探討 HLJ1 蛋白在脂肪組織生成與產熱功能所扮演之角色與機制
Investigate the Role of HLJ1 in Adipose Tissue Adipogenesis and Thermogenesis
摘要
隨著生活習慣改變與飲食的精緻化，肥胖等代謝性疾病，漸漸成為最為普遍並受矚目的健康議題，研究脂肪組織調控代謝的議題，是我們感興趣的。 人體脂肪組織按照分佈位置與功能可以分為：白色脂肪(White)、棕色脂肪(Brown)，白色脂肪為人體主要儲存多餘能量的場所，透過三酸甘油質的型態將多餘能量儲存，需要時再分解、釋放，白色脂肪主要分布於皮下與臟器周圍，因此也有隔熱與保護臟器等功能；棕色脂肪是身體重要的產熱器官，透過UCP1表達，產出熱能維持體溫，同時增強葡萄糖的利用與脂肪分解；白色脂肪也有產熱的功能，當身體受到冷刺激時，去甲基腎上腺素便會分泌刺激白色脂肪棕化，形成在形態和功能上都和棕色脂肪相似的棕化(Beige)細胞。 近期許多研究證明，刺激體內棕化細胞生成或活化棕色脂肪，都能有效調控身體代謝，促進血糖與脂肪代謝，進而達到減肥的效果。在過去實驗室的研究中，我們發現HLJ1剔除小鼠的白色脂肪組織相較於野生型有較大的油滴，而在受到冷刺激時，白色脂肪組織棕化現象較為明顯，產熱基因Ucp1較WT小鼠表現量高，我們也透過RNA-seq資料進行GSEA和MetaCore分析，發現HLJ1剔除小鼠的白色脂肪組織，在脂肪生成和氧化途徑相關基因表現較WT高，種種結果證明HLJ1參與在脂肪生成和產熱功能當中，但機制尚未釐清，因此本篇研究專注在，探討HLJ1與脂肪生成以及產熱功能的機制研究。 我們利用primary iWAT preadipocyte, primary BAT preadipocyte, 3T3-L1三種脂肪幹細胞建立脂肪細胞分化模型，在三種模型中都可以發現，相較於野生型細胞株，HLJ1默化的細胞中有較高比例的幹細胞分化為成熟脂肪細胞，接著透過基因表現和蛋白表達量證明，HLJ1表達減少會促進轉錄因子PPARγ表達與活化，並刺激下游脂肪生成相關基因轉錄：Leptin, Glut4, AdipoQ隨之上升。我們進一步探討HLJ1對PPARγ的調控機轉，發現HLJ1缺失的細胞胰島素訊號途徑活化較不明顯，而mTOR表現量卻增加，推測HLJ1缺失透過某種機制促進mTOR以及PPARγ表達，而負向回饋抑制胰島素訊號傳遞途徑，進而對生物體造成脂肪組織增生以及胰島素抗性升高等影響。另一方面，HLJ1缺乏也促使粒線體生成基因Pgc1α表達增加，所生成的脂肪細胞相較於HLJ1表現正常的脂肪細胞具有較高的產熱基因(Ucp1)表現，而細胞功能上，粒線體功能、脂肪分解與產熱功能、醣類代謝功能等仍待進一步實驗釐清。
並列摘要
Obesity constitutes a public health issue of major proportion especially in the development countries. It has been related to a strong risk towards numerous disease such as cardiovascular disease, diabetes, and cancer. White adipose tissue (WAT) stores excess energy as triglycerides and brown adipose tissue (BAT) is specialized in the dissipation of energy through non-shivering thermogenesis. HLJ1, a member of the DnaJ-like Hsp40 family, has been characterized as a tumor suppressor and a vital gene in unfolded protein response (UPR) system. Previously, our group observed enlarged adipocyte size in iWAT of HLJ1 knockout (KO) mice with higher Fatty Acid Synthase expression levels than wild-type mice. Ucp1, the major thermogenic protein, was up-regulated significantly in the HLJ1-KO iWAT after cold-induction comparing to WT sample. Those findings guide us to further understand the role of HLJ1 in adipogenesis and thermogenesis. We established in vitro system for adipocyte differentiation and thermogenic function study. We demonstrated that depletion of HLJ1 in preadipocyte enhanced adipogenesis by improving PPARγ and adipocyte genes, Leptin and Adiponectin expression. Otherwise, HLJ1-silenced adipocyte showed upregulated thermogenic genes such as Pgc1α and Ucp1. We also observed that silence of HLJ1 enhanced mTOR expression and exhibit a reduction in Akt phosphorylation, which indicated that reduction of HLJ1 might give rise to insulin resistant in both preadipocyte and mature adipocyte. In summary, we demonstrated reduced HLJ1 expression contributed in adipogenesis and thermogenic function in adipocyte. In the near future, we look forward to specifically silence HLJ1 in adipose tissue to improve whole body metabolic capacity and thermogenesis function, thus controlling body weight and health.