Anaplerosis阻礙aminooxyacetate所引發之早發性細胞老化的機制探討

Abstract

細胞增生(cell proliferation)就是細胞的自我複製，而自我複製最重要的原則就是忠實性(fidelity)。在細胞自我複製的過程中，細胞將會隨時的檢驗忠實性，一旦由於細胞內部因素或者外部環境因素造成細胞自我複製的忠實性無法得到保證時，細胞自我複製將隨時停止，直到忠實性再次的得到保證為止；而當細胞判斷其忠實性無法再次得到保證時，細胞會進行細胞凋亡(apoptosis)或者細胞老化(senescence)以避免失去忠實性的細胞大量增生而放大失去忠實性的部分。 細胞增生的驅動力來自於細胞生長(cell growth)，細胞生長是細胞有組織的將外界營養分子合成大量巨分子來增加細胞質量。為了達到細胞快速累積細胞質量的目的，細胞的代謝途徑需進行代謝重整(metabolic reprogram)，代謝重整主要就是粒線體在細胞角色的改變，粒線體由能量提供的角色，轉變成為巨分子合成中心；而細胞能量提供的角色則由細胞質所進行的糖解作用取代。而細胞生長過程的忠實性檢驗就在動態複雜的代謝途徑中，當物質來源缺乏或者代謝途徑流動不順暢時，細胞生長的忠實性將無法保證。 在人類纖維母細胞WI38中，處理粒線體malate-aspartate shuttle 的抑制物AOA (aminooxyacetate)改變粒線體代謝途徑，阻礙粒線體與細胞質間物質的流動，造成細胞中心調節者(mTOR)活性平衡改變、細胞生長停止和細胞老化的現象。而這些AOA所造成的效應會在分別將AOA共同處理α-ketoglutarate、aspartate、pyruvate或oxaloacetate之下受到阻礙，其中詳細阻礙AOA效應的機制仍待未來研究得到，可幫助我們思考補充機制及物質流動與細胞生長的關係。 本研究透過許多代謝物質與AOA共同處理顯示，當代謝物質流動受到阻礙，細胞立即反應系統忠實性受到挑戰，細胞增生停止；此時，可透過改變營養環境恢復代謝物質的流動，忠實性再次獲得保證後，細胞恢復增生；而粒線體在代謝重整與營養感知均扮演重要角色，視為細胞生長時忠實性的檢驗與調控中心。

Cell proliferation is the process of cell self-replication, and the most important principle of self-replication is fidelity. During cell self-replicating process, cells will be continuously monitored for its fidelity. When cells are challenged with intrinsic or extrinsic environment changes, the self-replicating fidelity will no longer be guaranteed. Then, cell cycle arrests until the fidelity is again ensured. If cell senses fidelity being challenged, the cell will enter apoptosis or cellular senescence process to avoid enlargement the loss of fidelity. Cell proliferation is driven by cell growth. Proliferating cells often take up nutrients in excess of bioenergetic needs and shunt metabolites into pathways that support a platform for biosynthesis. In order to rapidly accumulate biomass, cell must engage in the metabolic reprogramming. Mitochondria play a crucial role in cell growth. When metabolic reprogram proceeds, mitochondria will switch the role of TCA cycle from producing energy to exporting much of the intermediates for biomass synthesis. The fidelity checking during cell growth process lies in the dynamic complex metabolic pathways. When the metabolic flow is blocked. Cell growth fidelity will not be guaranteed. In human embryonic fibroblast WI38 cell system, the malate-aspartate shuttle inhibitor, AOA (aminooxyacetate), impeded the metabolic flow and induced cell cycle arrest and senescence, and changed cell the growth center (mTOR) activity balance. These AOA-induced effects were blocked by co-treatment with NEAA (non-essential amino acid), α-ketoglutarate, aspartate, pyruvate or oxaloacetate. The molecular mechanism of this AOA effect remains to be explored to gain further insight into the interaction between metabolic flow and cell growth. In this study, we explore the important role of mitochondria in reprogramming the metabolic pathway and controlling the cell growth fidelity.