Histone methylation and acetylation in ejaculated human sperm: effects of swim-up and smoking

Abstract

Objective: To assess global methylation and acetylation level before and after swim-up in ejaculated human sperm.

Design: Prospective experimental study.

Setting: University-based hospital.

Patient(s): Semen samples were obtained from 50 healthy volunteers (single sample per person) between December 2012 and May 2014.

Intervention(s): The semen samples were processed by the swim-up method.

Main outcome measure(s): Sperm motility, strict morphology, DNA fragmentation index (DFI) by TUNEL, abnormal chromatin structure by toluidine blue staining, immunostaining of 8-hydroxy-2'-deoxyguanosine (8-OHdG) as an oxidative stress marker, immunostaining of 5-methyl-cytosine (5-mC) as a measurement of methylation level and immunostaining of six acetylation markers (H3K9ac, H3K14ac, H4K5ac, H4K8ac, H4K12ac, and H4K16ac) before and after swim-up.

Result(s): After swim-up, motility and the percentage of normal form was significantly elevated. In the swim-up fraction, DFI and the percentage of abnormal chromatin structure were significantly lower and 8-OHdG levels were significantly higher. The 5-mC levels were significantly lower in the swim-up fraction, whereas no changes were observed in the positivity of six acetylation markers. Elevated percentage of normal form and decreased DFI and 5-mC levels were observed only in nonsmokers; 8-OHdG level was significantly higher in the swim-up fraction only from smokers. After swim-up, 5-mC levels were positively correlated with DFI.

Conclusion(s): This is the first study demonstrating decreased methylation and unchanged acetylation patterns in human sperm after swim-up preparation.

Keywords: Spermatozoa; epigenomics; histone; methylation; smoking.