O-196 Men who fathered embryos with poor pre-implantation development rates exhibit an increased frequency of sperm with high DNA accessibility
Authors: Gill M  E , De Geyter C , Peters A  H F M 
Published: July 2024

Abstract

Study question
Do differing levels of DNA accessibility in sperm affect the ability of embryos generated by ART to undergo pre-implantation development?

Summary answer
Individuals whose sperm generated embryos that failed to efficiently form blastocysts tend to have more sperm with high levels of DNA accessibility.

What is known already
Chromatin is a complex composed of nucleic acids and proteins that serves to condense and regulate the genome in all eukaryotic cells. Sperm chromatin is packaged into a structure with higher density than that found in precursor germ cells or somatic cells. Samples from individuals with decreased normal semen parameters have previously been shown to possess an increased frequency of sperm with aberrant chromatin packaging. However, existing methodologies for measuring sperm chromatin packaging are indirect and non-quantitative.

Study design, size, duration
Prospective cohort study, registered January 2020. We adapted an enzymatic methodology for measuring DNA accessibility known as NicE-view (Nicking Endonuclease-mediated visualization), for use in human sperm. DNA accessibility was quantified in three millions of individual sperm from semen obtained from 60 individuals. Both total sperm and sperm selected for motility via swim-up were analyzed for each participant.

Participants/materials, setting, methods
Participants sought treatment for infertility at Universitätsspital Basel and possessed normospermic levels in conventional semen analysis. Participant partners had normal endocrine parameters and ovulation response to hormonal stimulation. 20 couples obtained pregnancies without the need for ART, while 40 individuals who were treated using ART and divided into two groups differing in pre-implantation development rates: (1) 20 with blastocyst development of &gt; 50% of all zygotes and (2) 20 produced 0-1 blastocyst following embryo culture.

Main results and the role of chance
We quantified DNA accessibility and the presence of single stranded DNA nicks in more than 3 million sperm derived from 117 samples. We found that while DNA nicks were only present in a small fraction of the sperm analyzed, DNA accessibility levels varied dramatically with the data indicating a bimodal distribution. At a single sperm level, DNA accessibility and the presence of single stranded DNA damage both correlated with nuclear size. We found that DNA nicking was more abundant in total sperm samples compared to sperm selected for motility via swim-up preparation. In contrast, sperm with high levels of DNA accessibility were more abundant following swim-up, perhaps resulting from capacitation. We observed that individuals with a history of low blastocyst development were more likely to have high frequencies of sperm harboring DNA nicks and high DNA accessibility. We also measured increased frequencies of sperm with high DNA accessibility to negatively correlate with conventional semen parameter values.

Limitations, reasons for caution
Our study cohort consists of only 60 individuals. Variation is also observed between individuals within each participant category, so further analysis with increased participant numbers is required to strengthen these conclusions.

Wider implications of the findings
Our results suggest measuring DNA accessibility in sperm from normospermic individuals provide additional information about the efficiency of pre-implantation development following ART. Future work examining the sources of increased DNA accessibility in sperm will also be interesting to identify possible treatments for such individuals.

Trial registration number
SNCTP000003654 | NCT04256668