Effect of Mare Age on Transcript Abundance of Connexins-37 and -43, Zona Pellucida Proteins, and Sperm Binding.
Authors: Bresnahan Dawn R, Lupole Rebecca E, Stilz Charles R, Carnevale Elaine M
Journal: Journal of equine veterinary science
Summary
# Editorial Summary: Mare Age and Oocyte Quality — Connexin and Zona Pellucida Changes Declining fertility in older mares remains a significant clinical challenge, yet the cellular mechanisms underlying age-related subfertility are incompletely characterised. Bresnahan and colleagues examined transcript abundance of connexins (GJA4 and GJA1)—gap junction proteins critical for communication between cumulus cells and oocytes—alongside zona pellucida glycoproteins (ZP1-4) in follicular cells harvested from young (4–12 years) and aged (>20 years) mares, whilst also assessing sperm binding capacity to oocytes from both age groups. Connexin-43 (GJA1) expression was significantly downregulated in oocytes, corona radiata, and granulosa cells from older mares, with connexin-37 (GJA4) reduced specifically in cumulus cells; zona pellucida protein 1 showed a trend towards decreased expression in corona radiata and cumulus cells of aged animals. Notably, oocytes from older mares demonstrated a tendency towards reduced sperm binding compared with their younger counterparts. These findings suggest that maternal ageing compromises the structural and functional integrity of the oocyte microenvironment through diminished gap junction communication and altered zona pellucida composition, which may directly impair sperm-oocyte interaction and contribute to the well-documented fertility decline in older breeding mares—a consideration worthy of attention when managing breeding programmes and counselling owners regarding mare reproductive prognosis.
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Practical Takeaways
- •Breeding outcomes in mares over 20 years old may be compromised by age-related changes in cellular communication and zona pellucida structure, which could reduce sperm-oocyte interaction
- •Age-related decreases in connexin expression suggest impaired gap junction communication between cumulus and oocyte cells, potentially affecting oocyte maturation and competence
- •Non-cleaved oocytes from failed ICSI procedures can be preserved for up to 2 years and used for research purposes without loss of sperm binding capacity
Key Findings
- •Connexin-43 (GJA1) transcript abundance was decreased in oocytes, corona radiata, and granulosa cells from old mares (>20 years) compared to young mares (4-12 years)
- •Connexin-37 (GJA4) transcript abundance was decreased in cumulus cells from old mares
- •Zona pellucida protein 1 (ZP1) tended to be decreased in corona radiata and cumulus cells from old mares
- •Oocytes from old mares showed a trend toward reduced sperm binding compared to young mares