Louie K, Minor A, Ng R, Poon K, Chow V, Ma S
Department of Obstetrics and Gynaecology, University of British Columbia, Vancouver, BC, Canada.
Andrology. 2016 Sep;4(5):825-31. doi: 10.1111/andr.12240. Epub 2016 Jul 1.
Altered DNA methylation has been previously identified in the spermatozoa of infertile men; however, the origins of these errors are poorly understood. DNA methylation is an epigenetic modification which is thought to play a fundamental role in male germline development. DNA methylation reactions rely on the cellular availability of methyl donors, which are primarily products of folate metabolism, where a key enzyme is methylenetetrahydrofolate reductase (MTHFR). The MTHFR C677T single nucleotide polymorphism (SNP) reduces enzyme activity and may potentially alter DNA methylation processes during germline development. The objective of this study was to determine whether altered DNA methylation in spermatozoa is associated with the MTHFR C677T SNP. DNA methylation was evaluated at the H19, IG-GTL2, and MEST imprinted differentially methylated regions in the spermatozoa of 53 men - 44 oligozoospermic men and nine fertile men with normal sperm parameters via bisulfite sequencing of sperm clones. The 44 infertile men were stratified by severity of oligozoospermia - three normal (>15 million spermatozoa/mL), eight moderate (5-15 million spermatozoa/mL), 23 severe (1-5 million spermatozoa/mL), and 10 very severe (<1 million spermatozoa/mL). MTHFR C677T SNP genotyping was conducted in a subset of 44 peripheral blood samples via restriction fragment length polymorphism. A total of three men - severe oligozoospermic and CT genotype - were found to be altered, which is defined as having ≥50% of their clones altered, where an altered clone was in turn defined as ≥50% of CpGs with incorrect DNA methylation patterns. The incidence of three altered men within the CT subgroup, however, was not significantly higher than the incidence in the CC subgroup. Taken together, altered DNA methylation in spermatozoa was not significantly associated with the MTHFR C677T SNP; however, there was a trend for higher incidence of alterations among severe oligozoospermic infertile men with CT genotypes.
先前已在不育男性的精子中发现DNA甲基化改变；然而，这些错误的起源却知之甚少。DNA甲基化是一种表观遗传修饰，被认为在雄性生殖系发育中起重要作用。DNA甲基化反应依赖于甲基供体的细胞可用性，甲基供体主要是叶酸代谢的产物，其中关键酶是亚甲基四氢叶酸还原酶（MTHFR）。MTHFR C677T单核苷酸多态性（SNP）会降低酶活性，并可能在生殖系发育过程中改变DNA甲基化过程。本研究的目的是确定精子中DNA甲基化改变是否与MTHFR C677T SNP相关。通过精子克隆的亚硫酸氢盐测序，对53名男性（44名少精子症男性和9名精子参数正常的可育男性）精子中的H19、IG-GTL2和MEST印记差异甲基化区域的DNA甲基化进行了评估。44名不育男性按少精子症严重程度分层：3名正常（>1500万精子/mL）、8名中度（500-1500万精子/mL）、23名重度（100-500万精子/mL）和10名极重度（<100万精子/mL）。通过限制性片段长度多态性对44份外周血样本的一个子集进行了MTHFR C677T SNP基因分型。共发现3名男性（重度少精子症且为CT基因型）发生改变，改变定义为其克隆中有≥50%发生改变，其中改变克隆又定义为具有不正确DNA甲基化模式的CpG中有≥50%。然而，CT亚组中3名改变男性的发生率并不显著高于CC亚组。综上所述，精子中DNA甲基化改变与MTHFR C677T SNP无显著相关性；然而，CT基因型的重度少精子症不育男性中改变的发生率有升高趋势。
