DNA-fragmented sperm ability to bind to the zona pellucida

Abstract

BACKGROUND: A high percentage of the infertile couples are classified as having unexplained infertility. At the same time, male partners may have both normozoospermia and high level of sperm DNA fragmentation. The investigation of the selectivity of the oocyte zona pellucida for spermatozoa with fragmented DNA is an extremely promising direction. The novel data could improve sperm selection methods, which in turn will increase the efficiency of IVF cycles. AIM: The aim of this study was to assess the ability of spermatozoa with fragmented DNA to bind to the zona pellucida. MATERIALS AND METHODS: The material for the study was ejaculate samples from patients with normozoospermia (n = 5) and sperm donors (n = 4), as well as the zona pellucida of immature oocytes (n = 25) from nine patients. Sperm preparation was carried out by centrifugation in a density gradient of silicone particles and the swim-up method. Sperm DNA fragmentation was assessed using the method of fluorescent labeling of single- and double-stranded DNA breaks (TUNEL assay). Manipulations with gametes and the zona pellucida were performed using micromanipulation equipment and a femtosecond laser. RESULTS: Spermatozoa with fragmented DNA can effectively bind to the oocyte zona pellucida. However, among the zona pellucida-bound spermatozoa, the proportion of cells with fragmented DNA was significantly lower than among the unbound ones. The data obtained suggest the key role of the oocyte zona pellucida in the selection of spermatozoa with intact DNA. CONCLUSIONS: Spermatozoa with fragmented DNA retain the ability to bind to the oocyte zona pellucida. The use of the selective binding of spermatozoa with intact DNA to the zona pellucida can serve as a method for selecting gametes for intracytoplasmic injection of spermatozoa into the oocyte. Data on the selective properties of the oocyte zona pellucida can serve to select the optimal strategy in cases of “hidden” male factor, in which men with normozoospermia experience impaired fertility, in particular, due to sperm DNA fragmentation.