Priority Research Centre in Reproductive Science, Discipline of Biological Sciences, School of Environmental and Life Sciences, University of Newcastle, Callaghan, NSW 2308, Australia.
J Cell Sci. 2013 Mar 15;126(Pt 6):1488-97. doi: 10.1242/jcs.121657. Epub 2013 Feb 1.
DNA repair has long been considered impossible in human spermatozoa due to the high level of DNA compaction observed in these cells. However, detailed examination of the base excision repair pathway in human spermatozoa has revealed the presence of an enzyme critical to this pathway, 8-oxoguanine DNA glycosylase 1 (OGG1). This glycosylase was associated with the sperm nucleus and mitochondria and could actively excise 8-hydroxy-2'-deoxyguanosine (8OHdG), releasing this adduct into the extracellular space. This activity was significantly reduced in the presence of cadmium (II), a recognized inhibitor of OGG1, in a time- and dose-dependent manner (P<0.001). Remarkably, spermatozoa do not possess the downstream components of the base excision repair pathway, apurinic endonuclease 1 (APE1) and X-ray repair complementing defective repair in Chinese hamster cells 1 (XRCC1). The absence of these proteins was particularly significant, as APE1 is required to create a 3'-hydroxyl (3'-OH) terminus at the apurinic site created by OGG1, which would be recognized by the terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) assay. As a result, TUNEL was unable to detect oxidatively induced DNA damage in spermatozoa following exposure to hydrogen peroxide. In the same cells, intracellular and extracellular 8OHdG could be clearly detected in a manner that was highly correlated with the outcome of the sperm chromatin structure assay (SCSA). However, incubation of these cells for 48 hours revealed a time-dependent increase in TUNEL positivity, suggesting the perimortem activation of a nuclease. These results emphasize the limited capacity of mature spermatozoa to mount a DNA repair response to oxidative stress, and highlight the importance of such mechanisms in the oocyte in order to protect the embryo from paternally mediated genetic damage.
长久以来，由于在人类精子中观察到高水平的 DNA 压缩，人们一直认为精子中的 DNA 修复是不可能的。然而，对人类精子中碱基切除修复途径的详细检查揭示了一种对该途径至关重要的酶的存在，即 8-氧鸟嘌呤 DNA 糖基化酶 1（OGG1）。这种糖基化酶与精子核和线粒体有关，并能主动切除 8-羟基-2'-脱氧鸟苷（8OHdG），将这种加合物释放到细胞外空间。在镉（II）存在的情况下，这种活性显著降低，镉（II）是 OGG1 的一种公认抑制剂，呈时间和剂量依赖性（P<0.001）。值得注意的是，精子不具有碱基切除修复途径的下游成分，即无嘌呤内切酶 1（APE1）和 X 射线修复互补缺陷修复在中国仓鼠细胞 1（XRCC1）。这些蛋白质的缺失尤其重要，因为 APE1 是 OGG1 在由其产生的无嘌呤位点上创建 3'-羟基（3'-OH）末端所必需的，该末端将被末端脱氧核苷酸转移酶 dUTP 缺口末端标记（TUNEL）检测法识别。因此，TUNEL 无法检测到在过氧化氢暴露后精子中氧化诱导的 DNA 损伤。在相同的细胞中，可以以与精子染色质结构检测（SCSA）结果高度相关的方式清楚地检测到细胞内和细胞外的 8OHdG。然而，孵育这些细胞 48 小时后，TUNEL 阳性率呈时间依赖性增加，表明一种核酸酶的即时激活。这些结果强调了成熟精子对氧化应激产生 DNA 修复反应的能力有限，并强调了这种机制在卵母细胞中的重要性，以保护胚胎免受来自父系的遗传损伤。
