H3K4me2 accompanies chromatin immaturity in human spermatozoa: an epigenetic marker for sperm quality assessment.

ABSTRACT

Chromatin remodeling, including histone post-translational modifications, during spermatogenesis can affect sperm quality and fertility, and epigenetic marks may therefore be useful for clinical evaluations of sperm. Together with histone hyperacetylation, the dimethylation of histone H3 on lysine K4 (H3K4me2) is also required during protamination. Accordingly, we evaluated the utilization of this epigenetic mark for the identification of sperm with decrease quality and immature chromatin. In this study, 99 semen samples, including 22 normozoospermic (N), 63 asthenozoospermic (A), and 14 oligoasthenozoospermic (OA) samples, were comprehensively analyzed with respect to H3K4me2 levels, DNA damage (DNA fragmentation index, DFI), and sperm immaturity (high DNA stainability, %HDS), as determined by a sperm chromatin structure assay using flow cytometry. We detected a significant relationship between H3K4me2 and %HDS (r = 0.47; p < 0.001). Furthermore, we observed negative correlations between H3K4me2 and sperm concentration, motility, and mitochondrial activity (p < 0.05). The increase in immaturity as semen quality decreased (N > A > OA) indicates the importance of chromatin immaturity and histone code deviations in sperm evaluations. Using various approaches, our study elucidated H3K4me2 as a molecular marker of sperm quality with potential use in reproductive medicine.Abbreviations A asthenozoospermic; AO acridine orange; ART assisted reproductive therapy; BWW Biggers-Whitten Whittingham; DAPI 4',6' -diamidino-2-phenylindole; DFI DNA fragmentation index; H3K4me2 dimethylation of lysine K4 on histones H3; HDS high DNA stainability; HRP horseradish peroxidase; MACS magnetic-activated cell sorting; N normospermic; NGS normal goat serum; OA oligoasthenozoospermic; PTM post-translational modification; SCSA sperm chromatin structure assay; SUTI sperm ubiquitin tag assay; TBS-T TBS with 0.5% Tween-20.