低溫緊迫下斑馬魚腦內抗氧化機制與解偶聯蛋白相關研究

對於變溫脊椎動物（包含魚類）而言，環境溫度的改變除了會加速粒線體的呼吸作用，同時也會增加粒線體內活性氧化物（Reactive oxygen species, ROS）的形成。密集的呼吸作用下所產生的過量ROS會導致細胞損害。但是藉由粒線體解偶聯蛋白（Uncoupling proteins, UCPs）所引起的緩和性解偶聯作用（Mild uncoupling），與抗氧化酵素的調節，則能夠抑制ROS所造成的氧化壓力。然而至今對於魚類腦部處於低溫緊迫下的抗氧化機制仍不清楚。本研究偵測模式動物-斑馬魚在急性寒冷緊迫下（28 °C 轉移至18 °C），腦內氧化壓力相關指標因子的變化。其中，斑馬魚五個UCP亞型（zUCP1, -2, -2l, -4, -5）被清楚註解與確認，並偵測低溫下其mRNA在斑馬魚腦內的表現。同時，亦測量在低溫緊迫下，斑馬魚腦部蛋白質羰基(氧化壓力的生物標記)的濃度，和細胞內的抗氧化分子，諸如過氧化氫酵素(Catalase, CAT)的mRNA表現量與超氧化歧化酵素(SOD)的活性。實驗結果顯示，除了zucp1外，其餘四型zucps皆會受到低溫刺激而有不同的表現趨勢；蛋白質羰基的濃度在低溫刺激下則有顯著增加，另外腦部SOD活性與cat的mRNA在低溫緊迫下亦會增加。另一方面，目前哺乳類研究已知過氧化酶活化增生受體（PPAR）可調控UCPs和抗氧化酵素的轉錄。本研究中發現五型的zppar mRNA在低溫下各有不同的表現趨勢，由此推論低溫緊迫下，神經細胞可能會藉由PPAR轉錄調控解偶聯蛋白的基因表現，導致粒線體緩和性解偶聯作用，進而降低ROS累積。此外，研究中也發現抗氧化酶與PPAR有類似的表現量變化趨勢。另一方面，細胞氧化還原狀態的指標：穀胱甘肽氧化還原率（2GSSG/GSH）和穀胱甘肽含量（Glutathione content），在低溫緊迫下均維持不變。综合以上推論：斑馬魚腦內除了抗氧化酶的作用外，PPAR-UCP可能是低溫緊迫下腦部細胞抵抗氧化壓力的另一途徑，同時並參與了代謝平衡的調控與體內平衡的維持。

關鍵字

解偶聯蛋白；活性氧；低溫；抗氧化

並列摘要

Exposure to fluctuating temperatures accelerates the mitochondrial respiration and increases the formation of mitochondrial reactive oxygen species (ROS) in ectothermic vertebrates including fish. Excess ROS production by intensively respiring mitochondria results in cellular damages, but mild uncoupling mechanism and enzymatically antioxidant adjustments can defense the oxidative stress. However, neuronal defense pathway against oxidative stress in fish brain upon cold stress is unclear so far. In this study, five members of uncoupling proteins (UCPs) of zebrafish (Danio rerio) were clearly annotated and identified. Effects of acute cold exposure (from 28 °C to 18 °C) on brains’ zucp mRNA expressions and oxidative stress parameters were measured. Except the zucp1, transcripts of other four zucps would be affected by acute 18 °C exposure. Concentrations of cellular protein carbonyl groups (biomarkers of oxidative stress) were significantly increased after cold exposure. Following the cold exposure, anti-oxidative stress parameters, activities of superoxide dismutase (SOD) and transcripts of catalase (CAT), were increased. All the mRNA levels of zppar homologs were also found to change after 18 °C exposure. The axis of peroxisome proliferator-activated receptor (PPAR) and UCPs is involved in the defense pathways against ROS. In addition, the similar expression patterns of PPAR and antioxidant enzymes were also found in this study. Furthermore, indicators of the cellular redox situation, glutathione redox ratio and glutathione content, were maintained constant. Taken all together, stimulation of the PPAR-UCP axis results in mitochondrial mild uncoupling, biogenesis activation, and reduction of ROS. Apart from the antioxidant enzymes, this mechanism may be one of the defense pathways for anti-oxidative stress, regulating metabolic balance, and maintaining cellular homeostasis in ectothermic zebrafish brain upon stressful cold exposure.

並列關鍵字

uncoupling protein ； antioxidant ； cold exposure ； ROS

參考文獻

Abele, D., and Puntarulo, S. (2004). Formation of reactive species and induction of antioxidant defence systems in polar and temperate marine invertebrates and fish. Comp Biochem and Physiol A Mol Integr Physiol 138, 405-415.

Amo, R., Aizawa, H., Takahoko, M., Kobayashi, M., Takahashi, R., Aoki, T., and Okamoto, H. (2010). Identification of the Zebrafish Ventral Habenula As a Homolog of the Mammalian Lateral Habenula. J Neurosci 30, 1566-1574.

Andrews, Z.B., Diano, S., and Horvath, T.L. (2005). Mitochondrial uncoupling proteins in the CNS: in support of function and survival. Nat Rev Neurosci 6, 829-840.

Arsenijevic, D., Onuma, H., Pecqueur, C., Raimbault, S., Manning, B., Miroux, B., Couplan, E., Alves-Guerra, M., Goubern, M., and Surwit, R. (2000). Disruption of the uncoupling protein-2 gene in mice reveals a role in immunity and reactive oxygen species production. Nat genet 26, 435-439.

Azzu, V., and Brand, M.D. (2010). The on-off switches of the mitochondrial uncoupling proteins. Trends Biochem Sci 35, 298-307

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低溫緊迫下斑馬魚腦內抗氧化機制與解偶聯蛋白相關研究

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