Functional and ultrastructural features of DNA-fragmented human sperm

The functional significance of deoxyribonucleic acid (DNA) fragmentation in ejaculated human sperm is unclear. In this study the extent of DNA strand breakage in swim-up selected spermatozoa was evaluated by terminal deoxynuc leotidyl transferase-mediated fluorescein-dUTP nick end labeling (TUNEL)-co upled flow cytometry and correlated with several functional and morphologic al sperm parameters. The extent of DNA fragmentation (mean = 11.07% +/- 8.0 0%, range = 0.79%-42.64%, n = 140) was positively related to abnormal morph ology and associated with defects of the sperm tail. A negative correlation was found between DNA breakage and progressive motility. When a stepwise m ultiple linear regression model was used to analyze the relationship betwee n DNA fragmentation and the aforementioned parameters, only motility result s were included in the model. The presence of spermatozoa showing submicros copic characteristics resembling those of somatic apoptosis has been report ed in human ejaculate. To verify whether sperm DNA fragmentation was associ ated with the presence of such apoptotic-like cells, we performed electron microscopy and TUNEL-coupled flow cytometry in a limited number of sperm sa mples (n = 24). Although we did not observe any significant relationship be tween DNA breakage and the characteristics that are suggestive of apoptosis , an association was found with several ultrastructural features, indicatin g an impaired motility. Hence, we conclude that in ejaculated sperm, DNA fr agmentation does not correspond to the apoptosis-like phenomenon and that i t is associated with defects of motility.