探討老化過程對雌性小鼠生殖健康及卵母細胞粒線體功能的影響

Abstract

根據內政部110年人口統計資料顯示，35歲以上的高齡產婦已佔全體產婦的三成，較10年前增加了1.8倍，反映出生育年齡隨著社會發展而逐漸延後。隨著生產高齡化情況日益普遍，越來越多女性面臨生育困難，而卵母細胞品質下降與卵巢功能退化，已被視為導致高齡女性不孕症的主要因素之一。研究指出，女性生育能力會隨年齡明顯下降，特別是在35歲之後，卵巢濾泡數目快速減少，卵母細胞品質惡化，加上氧化壓力的累積，均加速生殖功能的衰退，並對生育能力產生深遠影響。儘管小鼠 (Mus musculus) 廣泛被應用於生殖老化相關研究，其生命週期短、可控性高的特性有助於進行長期追蹤與機制探討，但目前文獻中對小鼠與人類在生殖老化進程上的對應關係仍缺乏一致性的標準化認定，特別是在粒線體功能變化的層面，系統性研究相對有限。本研究選用2月齡、6月齡、8月齡與10月齡的小鼠作為模型，系統性分析其卵巢濾泡庫存、氧化壓力指標、粒線體數量與功能等變化。結果顯示，隨年齡增加，小鼠卵巢內的濾泡數量明顯下降，尤以6月齡與8月齡小鼠之間的濾泡數量下降幅度最為明顯。同時，生殖老化使得卵母細胞中氧化壓力顯著升高，粒線體功能亦呈現衰退現象。8月齡的小鼠卵母細胞中，粒線體數目顯著減少，能量代謝能力降低，且活性氧 (reactive oxygen species, ROS) 累積明顯增加。上述變化不僅影響卵母細胞的形態與可用卵母細胞的數量，也對其受精能力與發育潛能產生不利影響。體外培養過程中發現，由6月齡小鼠卵母細胞發育而成的胚胎，其囊胚形成率顯著較低；而8月齡小鼠卵母細胞所發育而成的胚胎的高品質囊胚比例更是大幅減少。透過本研究的實證數據，系統性建立小鼠生殖老化進程，冀能提供小鼠年齡對應人類生殖年齡的建設性參考架構，以作為未來研究高齡女性生殖力及改善的最佳動物模式。

According to the Ministry of the Interior's 2021 demographic statistics, women aged 35 and above accounted for 30% of all births in Taiwan, a 1.8-fold increase compared to a decade ago. This trend reflects a societal shift toward delayed childbearing, resulting in a growing prevalence of age-related infertility. Declines in oocyte quality and ovarian function have become recognized as key contributors to reduced fertility in older women. Studies have shown that female fertility significantly declines with age, particularly after the age of 35, with a rapid decrease in ovarian follicle numbers, deterioration in oocyte quality, and the accumulation of oxidative stress, all of which accelerate the decline in reproductive function and profoundly affect fertility. Although mice (Mus musculus) are widely used in reproductive aging research due to their short lifespan and high controllability, which facilitate long-term tracking and mechanistic exploration, a standardized and consistent framework for correlating reproductive aging processes between mice and humans remains lacking, especially in the context of mitochondrial function, where systematic studies are still limited. This research used 2-, 6-, 8-, and 10-month-old mice as experimental models to systematically analyze changes in ovarian follicle reserve, oxidative stress indicators, mitochondrial quantity, and function. The results showed a significant age-related decline in follicle numbers, with the steepest drop observed between 6 and 8 months of age. Concurrently, oxidative stress in oocytes markedly increased, while mitochondrial function progressively deteriorated. In 8-month-old mouse oocytes, mitochondrial number was reduced significantly compared to the 2-month-old group, accompanied by elevated levels of reactive oxygen species (ROS). These changes not only affect oocyte morphology and availability but also have an adverse impact on their fertilization ability and developmental potential. During in vitro culture, embryos derived from 6-month-old mouse oocytes exhibited a significantly lower blastocyst formation rate, while those from 8-month-old oocytes showed a further reduction in blastocyst quality. Through these experimental findings, our study establishes a systematic framework for understanding reproductive aging in mice, aiming to provide a constructive reference for correlating mouse age with human reproductive age and to serve as a reliable animal model for future investigations into fertility decline and its potential interventions in older women.