INRAE, BREED, Université Paris-Saclay, UVSQ, 78350, Jouy-en-Josas, France.
Ecole Nationale Vétérinaire d'Alfort, BREED, 94700, Maisons-Alfort, France.
Clin Epigenetics. 2022 Apr 27;14(1):54. doi: 10.1186/s13148-022-01275-x.
Conflicting results regarding alterations to sperm DNA methylation in cases of spermatogenesis defects, male infertility and poor developmental outcomes have been reported in humans. Bulls used for artificial insemination represent a relevant model in this field, as the broad dissemination of bull semen considerably alleviates confounding factors and enables the precise assessment of male fertility. This study was therefore designed to assess the potential for sperm DNA methylation to predict bull fertility.
A unique collection of 100 sperm samples was constituted by pooling 2-5 ejaculates per bull from 100 Montbéliarde bulls of comparable ages, assessed as fertile (n = 57) or subfertile (n = 43) based on non-return rates 56 days after insemination. The DNA methylation profiles of these samples were obtained using reduced representation bisulfite sequencing. After excluding putative sequence polymorphisms, 490 fertility-related differentially methylated cytosines (DMCs) were identified, most of which were hypermethylated in subfertile bulls. Interestingly, 46 genes targeted by DMCs are involved in embryonic and fetal development, sperm function and maturation, or have been related to fertility in genome-wide association studies; five of these were further analyzed by pyrosequencing. In order to evaluate the prognostic value of fertility-related DMCs, the sperm samples were split between training (n = 67) and testing (n = 33) sets. Using a Random Forest approach, a predictive model was built from the methylation values obtained on the training set. The predictive accuracy of this model was 72% on the testing set and 72% on individual ejaculates collected from an independent cohort of 20 bulls.
This study, conducted on the largest set of bull sperm samples so far examined in epigenetic analyses, demonstrated that the sperm methylome is a valuable source of male fertility biomarkers. The next challenge is to combine these results with other data on the same sperm samples in order to improve the quality of the model and better understand the interplay between DNA methylation and other molecular features in the regulation of fertility. This research may have potential applications in human medicine, where infertility affects the interaction between a male and a female, thus making it difficult to isolate the male factor.
在精子发生缺陷、男性不育和不良发育结局的情况下，有关精子 DNA 甲基化改变的结果相互矛盾。在这一领域，用于人工授精的公牛代表了一个相关的模型，因为公牛精液的广泛传播极大地减轻了混杂因素，并能够精确评估男性生育能力。因此，本研究旨在评估精子 DNA 甲基化预测公牛生育能力的潜力。
从 100 头年龄相近的蒙贝利亚尔公牛中，每头公牛汇集 2-5 次射精，组成了一个独特的 100 个精子样本集，根据 56 天后的返情率，将这些样本评估为可育（n=57）或亚不育（n=43）。使用简化代表性亚硫酸氢盐测序获得这些样本的 DNA 甲基化图谱。在排除潜在的序列多态性后，鉴定出 490 个与生育力相关的差异甲基化胞嘧啶（DMC），其中大多数在亚不育公牛中呈高甲基化状态。有趣的是，46 个被 DMC 靶向的基因参与胚胎和胎儿发育、精子功能和成熟，或在全基因组关联研究中与生育力有关；其中 5 个进一步通过焦磷酸测序进行了分析。为了评估与生育力相关的 DMC 的预后价值，将精子样本分为训练集（n=67）和测试集（n=33）。使用随机森林方法，从训练集的甲基化值构建预测模型。该模型在测试集上的预测准确率为 72%，在来自 20 头公牛的独立队列中收集的单个射精样本上的预测准确率为 72%。
本研究在迄今进行的最大的公牛精子样本组的表观遗传学分析中表明，精子甲基组是男性生育力生物标志物的有价值来源。下一个挑战是将这些结果与同一精子样本的其他数据结合起来，以提高模型的质量，并更好地理解 DNA 甲基化与调节生育力的其他分子特征之间的相互作用。这项研究可能在人类医学中有应用，在那里，不育症影响男性和女性之间的相互作用，从而难以分离男性因素。
