Cumulus cell DNA fragmentation as non-invasive biomarker of equine oocyte quality in in vitro embryo production.

Overview

• This study explored whether DNA fragmentation in cumulus cells can serve as a non-invasive biomarker to predict the quality of horse oocytes used in in vitro embryo production.
• The researchers assessed the relationship between cumulus cell DNA fragmentation and embryo development outcomes, finding that higher DNA fragmentation was linked to lower blastocyst formation rates.

Background and Rationale

• In vitro embryo production (IVP) efficiency is limited by the lack of practical, non-invasive markers to evaluate oocyte quality before fertilization.
• Cumulus cells surround the oocyte and their DNA fragmentation index (CC-DFI) has been proposed as a biomarker of oocyte health in humans, but evidence in animals, particularly horses, is scarce.
• Identifying reliable biomarkers would improve oocyte selection, potentially enhancing embryo production outcomes and animal breeding programs.

Objectives

• Investigate the association between cumulus cell DNA fragmentation index (CC-DFI) and oocyte developmental outcomes during in vitro maturation (IVM) and intracytoplasmic sperm injection (ICSI) in horses.
• Examine the relationship between CC-DFI and mare-related factors, seasonal effects (notably the autumnal transition period), cumulus cell viability, and cumulus expansion.

Methods

• Ovum pick-up was used to retrieve cumulus-oocyte complexes (COCs) from mares.
• COCs underwent in vitro maturation (IVM) and were later denuded to separate cumulus cells.
• CC-DFI was assessed immediately after denudation for each mare using a chromatin dispersion assay across 54 ICSI sessions.
• Cumulus cell viability was evaluated via membrane integrity tests.
• Cumulus expansion was quantified by measuring changes in the total COC area.
• Only mature oocytes post-IVM were selected for ICSI fertilization and subsequent in vitro culture.

Results

• No significant association between CC-DFI and oocyte maturation rate or cleavage rate after fertilization was found.
• Blastocyst rates and blastocyst yield were significantly negatively correlated with CC-DFI, indicating that increased DNA fragmentation in cumulus cells corresponds with reduced ability of oocytes to develop into blastocysts.
• Blastocyst yield at day 7 was also negatively associated with CC-DFI; however, no correlation was found when looking specifically at grade 1 (high-quality) blastocysts.
• There were no significant associations between CC-DFI and mare-related factors (such as age or reproductive history), the autumnal transition period, cumulus cell viability, or cumulus expansion.

Conclusions and Implications

• The study supports the potential role of CC-DFI as a predictive biomarker for oocyte developmental competence in equine ICSI, particularly in relation to the ability of the oocyte to form blastocysts.
• Using CC-DFI could improve oocyte selection methods, thereby enhancing the efficiency of embryo production in horse breeding programs involving assisted reproduction.
• However, the study emphasizes the need for further validation before CC-DFI can be implemented routinely in clinical settings or reproductive technologies.