A high glucose concentration during early stages of in vitro equine embryo development alters expression of genes involved in glucose metabolism.
Authors: Sánchez-Calabuig María J, Fernández-González Raúl, Hamdi Meriem, Smits Katrien, López-Cardona Angela P, Serres Consuelo, Macías-García Beatriz, Gutiérrez-Adán Alfonso
Journal: Equine veterinary journal
Summary
Equine embryos demonstrate an unusual capacity to tolerate elevated glucose concentrations in vitro, yet the consequences of culturing them under these hyperglycaemic conditions remain poorly characterised. Researchers cultured ICSI-produced equine embryos in three different glucose regimens across sequential culture periods (Days 0–4 and 4–9): 5–10 mmol/L, 5–17 mmol/L, and 10–17 mmol/L, analysing gene expression patterns related to glucose metabolism, mitochondrial function, and embryo viability in 270 embryos, alongside in vivo-produced controls. Whilst cleavage and blastocyst rates showed no significant differences between groups, the 10–17 mmol/L protocol produced markedly altered expression profiles, with upregulation of the apoptotic marker BAX/BCL2 and key glycolytic enzymes (PFKP, LDHA) alongside increased COX2 expression; conversely, maintaining 5 mmol/L glucose during early development (both 5–10 and 5–17 groups) suppressed this metabolic over-activation. For embryo transfer practitioners, these findings suggest that reducing glucose concentration during the first four days of culture may protect against unnecessary glycolytic stress and apoptotic signalling, though definitive improvements in post-transfer developmental competence remain to be demonstrated through field studies. Current culture protocols should be reconsidered in light of these molecular markers, particularly given that apparent morphological success may mask detrimental metabolic programming with consequences for pregnancy rates and foetal development.
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Practical Takeaways
- •Current commercial equine embryo culture media using high glucose concentrations (17.5 mmol/L) may be suboptimal; consider protocols starting with 5 mmol/L glucose for the first 4 days
- •Gene expression changes suggesting increased cellular stress and apoptosis under high glucose warrant further investigation to determine whether this affects embryo survival after transfer
- •Embryo developmental competence cannot be accurately predicted from cleavage and blastocyst rates alone; transfer outcomes are needed to validate whether lower glucose protocols improve practical breeding success
Key Findings
- •High glucose concentration (10-17 mmol/L) during early equine embryo culture upregulated genes associated with apoptosis (BAX/BCL2) and glycolytic metabolism (PFKP, LDHA, COX2)
- •Low glucose concentration (5 mmol/L) during initial culture stage (Days 0-4) produced gene expression patterns similar to each other and distinct from continuous high glucose conditions
- •No significant differences in cleavage or blastocyst rates were observed among different glucose treatment groups, suggesting quality differences are subtle and require gene expression analysis to detect
- •5 mmol/L glucose during early culture stages appears preferable to reduce over-activation of embryonic glycolytic pathways compared to 10-17 mmol/L conditions