熱量限制增加錯誤配對修復缺陷細胞於老化期間基因的穩定性

Calorie restriction promotes genome stability in mismatch repair defected cells during aging

羅云君(Yun-Jun Lo)

指導教授 ： 羅翊禎

國立臺灣大學/生物資源暨農學院/食品科技研究所/碩士(2013年)

https://doi.org/10.6342/NTU.2013.01730

摘要

過去研究指出熱量限制能延長不同實驗模式中個體的平均壽命，且減少多種與老化相關的疾病。錯誤配對修復(Mismatch repair，MMR)在細胞中是維持基因穩定性重要的DNA修復系統。臨床研究顯示遺傳性非瘜肉型大腸直腸癌(Hereditary Nonpolyposis Colorectal Cancer，HNPCC)的患者，約在50歲前發病，而此類患者細胞中具有錯誤配對修復基因的缺陷。出芽酵母菌(Saccharomyces cerevisiae)，因與人類MMR基因具有高度的保守性，故可做為研究癌症的模式生物。因此本研究以酵母菌為模式探討熱量限制延長錯誤配修復缺陷細胞於老化期間基因的穩定性。實驗結果顯示，熱量限制能夠增加錯誤配對修復缺陷的細胞(msh2∆、msh3∆、msh6∆、msh2∆msh3∆、msh2∆msh6∆和msh3∆msh6∆)壽命和降低老化期間細胞的突變率並增加基因穩定性。除此之外，相對於熱量限制組(0.5%葡萄糖)可推測正常老化(正常組2.0%葡萄糖)情況下，Msh3扮演著重要的角色，且發現點突變型態的DNA損傷明顯的增加，是否熱量限制亦影響細胞另一負責修復點突變的修復系統Base excision repair(BER)有待進一步探討。根據氧化壓力老化理論(Oxidative stress theory of aging)，我推測熱量限制可以延長於老化期間錯誤配對缺陷細胞的壽命和增加其基因的穩定性是透過調控細胞內的氧化壓力。測定細胞內ROS (Reactive oxygen species)含量的結果指出正常培養條件下的野生型細胞 ROS含量高但與突變率並沒有明顯的正相關，因此我推測熱量限制增加錯誤配修復缺陷細胞於老化期間基因的穩定性並非透過調控ROS路徑。我建議熱量限制能增加錯誤配對修復缺陷細胞於老化期間基因穩定性的機制可能是透過調控TOR路徑促進基因修復的能力。此一假說有待之後進一步地驗證。

關鍵字

錯誤配對修復 ； 老化 ； 熱量限制 ； 基因穩定性 ； 遺傳性非瘜肉型大腸癌

並列摘要

Previously studies indicate calorie restriction (CR) can extend life span in different experimental model organisms and decrease many age-associated diseases. Mismatch repair (MMR) is a DNA repair system which is critical for maintaining genome stability. Clinical shows patients defect in MMR genes often develop Hereditary nonpolyposis colorectal cancer (HNPCC) before the age of 50. Because genes of MMR in Saccharomyces cerevisiae are highly conservative with human, used been as a model for cancer studies . Therefore we used Saccharomyces cerevisiae as a model for studying this topic of calorie restriction promotes genomic stability in MMR-defected cells during aging. The results show CR can extend life span and promote genomic stability in MMR-defected cells during aging (msh2∆, msh3∆, msh6∆, msh2∆ msh3∆, msh2∆ msh6∆, msh3∆ msh6∆). Compare to CR group (0.5% Glucose), normal group (2.0% Glucose) show significantly high mutation rate in HOM revertant mutation assay during aging especially in msh2∆ msh3∆ and msh3∆ msh6∆ which implied Msh3 may be a special role under normal aging and we speculate calorie restriction can up-regulate Base excision repair to complement high point mutation caused of MMR dysfunction. Based on oxidative stress theory of aging, we postulate calorie restriction can extend life span and promote genomic stability in MMR-defected cells during aging is through regulating reactive oxygen species (ROS) levels. The results of ROS levels detection indicate there is no positive correlation between ROS levels and Hom revertant mutation rate in wild type under normal culture condition (2.0% Glucose). We propose CR can extend life span and promote genomic stability in MMR-defected cells during aging which is through regulating nutrition response signal pathway, target of rapamycin (TOR) to increase DNA repair capacity. This hypothesis must be further confirmed.

並列關鍵字

mismatch repair system ； aging ； calorie restriction ； genome stability

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