Department of Pharmacology and Therapeutics, McGill University, Montréal, Québec, Canada.
Biol Reprod. 2013 Dec 26;89(6):147. doi: 10.1095/biolreprod.113.112995. Print 2013 Dec.
A strong correlation exists between increasing paternal age and a decline in reproductive function. Testis aging is associated with testicular atrophy, increased DNA damage, and de novo mutations. It is unclear whether these problems arise from the spermatogonial stem cells (SSCs), a buildup of anomalies as older germ cells progress through spermatogenesis, or both. We hypothesize that with the continual divisions of SSCs that maintain the germ cell population, an alteration of these cells occurs over time. To test this, we utilized young (4-mo-old) and aged (18- and 21-mo-old) transgenic rats that express GFP in germ cells only. We first examined the number and activity of SSCs from the different age groups by transplantation. Aged rats had numerically fewer SSCs than young rats (<50%; not significant) despite the lack of testicular atrophy, and 21-mo-old rats show a significant reduction in colony length, suggesting that the quality of SSCs also deteriorates. To evaluate any molecular changes occurring in the early cells of spermatogenesis with age, we isolated an SSC-enriched population of CD9-positive (CD9(+)) cells using fluorescence-activated cell sorting (confirmed by transplantation studies) and extracted RNA for microarray analysis. In the aged CD9(+) cells, 60 transcripts were upregulated and more than 500 downregulated compared to the young cells. An altered expression was found for transcripts involved in mitosis and in DNA damage response. These results suggest molecular alterations in the SSC-enriched population of aged CD9(+) cells, implying that reproductive aging originates in the undifferentiated cells of spermatogenesis.
父亲年龄的增加与生殖功能的下降之间存在很强的相关性。睾丸老化与睾丸萎缩、DNA 损伤增加和新突变有关。目前尚不清楚这些问题是源自精原干细胞（SSC），还是随着年龄较大的生殖细胞通过精子发生而积累的异常，或者两者兼而有之。我们假设，随着维持生殖细胞群体的 SSC 持续分裂，这些细胞会随着时间的推移发生变化。为了验证这一点，我们利用仅在生殖细胞中表达 GFP 的年轻（4 月龄）和年老（18 月龄和 21 月龄）转基因大鼠。我们首先通过移植检查了来自不同年龄组的 SSC 的数量和活性。尽管没有睾丸萎缩，但老年大鼠的 SSC 数量明显少于年轻大鼠（<50%；无统计学意义），21 月龄大鼠的菌落长度明显缩短，这表明 SSC 的质量也在恶化。为了评估随着年龄的增长，精子发生早期细胞中发生的任何分子变化，我们使用荧光激活细胞分选（通过移植研究证实）分离了富含 SSC 的 CD9 阳性（CD9(+))细胞群，并提取 RNA 进行微阵列分析。与年轻细胞相比，年老的 CD9(+)细胞中 60 个转录本上调，超过 500 个转录本下调。发现涉及有丝分裂和 DNA 损伤反应的转录本的表达发生改变。这些结果表明，年老的 CD9(+)细胞富含 SSC 的群体中存在分子改变，这意味着生殖衰老起源于精子发生的未分化细胞。
