The impact of MAEL promoter methylation on human spermatogenesis

Purpose: MAEL null mice can perturb piRNA biogenesis and results in male infertility due to meiotic defects. Furthermore, the observation is concordant with an elevated retrotransposon expression. In this study, we aimed to explore the MAEL epigenetic regulation and transposable elements (TEs) expression in non-obstructive azoospermic (NOA) men with a histopathological diagnosis of hypospermatogenesis (HS).

Materials and Methods: In H358 human cell line, we determined the MAEL transcript levels after endogenous methylation of MAEL promoter region by TDM (target DNA methylation) method. Transposable elements (LINE-1) expressions were checked afterward. In HS with NOA patients, we utilize their testicular tissue under NCKUH IRB regulation. The mRNA transcript levels were determined by quantitative real-time RT-PCR. The methylation levels of MAEL promoter region were investigated by pyrosequencing technology. Moreover, LINE-1 expression were determined afterward. Significance was set at P  < 0.05.

Results: In human cell line, MAEL transcript levels decreased significantly after promoter hypermethylation by TDM method. Nevertheless, LINE-1 transcripts were significantly higher in hypermethylated cells. In human testis, the mRNA transcript levels of MAEL were significantly lower in patients with hypospermatogenesis (P  = 0.004). There are 33 CpGs in our predicted promoter region (−453 to +28, TSS = 1) of the MAEL gene. Total 33 CpGs showed significantly higher % methylation in HS group. LINE-1 transcript levels were significantly higher in HS group (P  = 0.0489).

Conclusion: Our study provides evidence that MAEL participates in the epigenetic regulation of human spermatogenesis. 33 CpG sites in the promoter region are associated with the low expression levels of MAEL. Methylation of MAEL promoter region might contribute to one of the causes of male infertility by interfering piRNA-mediated defense mechanism from transposable elements.