Glucose concentration during equine in vitro maturation alters mitochondrial function.

The research explored the influence of glucose concentrations during the in vitro maturation of horse embryos on mitochondrial function and metabolic gene expression.

Objective of the Study

• The study aimed to understand the effects of varying glucose concentrations during in vitro maturation (IVM) on the energy metabolism of equine cumulus-oocyte complexes (COCs), mitochondrial functioning, and gene expression.

Methodology

• Two different base media with physiological (5.6 mM, M199) and supraphysiological (17 mM, DMEM/F-12) glucose concentrations were used for in vitro maturation (IVM).
• Equine COCs were matured in M199-based maturation medium containing either 5.6 or 17 mM glucose, and expression of key genes in oocytes and cumulus cells was evaluated.
• Embryos were fertilized using intracytoplasmic sperm injections (ICSI) and cultured further, after which glucose consumption, lactate, and pyruvate production were measured.
• Additionally, the ATP-coupled respiration, non-mitochondrial respiration, and expression of metabolic enzyme lactate dehydrogenase-A (LDHA) were analyzed.

Findings

• Results showed that glucose consumption and the production of lactate and pyruvate were similar for COCs matured in both 5.6 and 17 mM glucose concentrations.
• The glycolytic index was found to be decreased at 17 mM glucose concentration, indicating high glucose concentration reduces glycolysis.
• COCs cultured in 17 mM glucose revealed decreased ATP-coupled respiration and an increase in non-mitochondrial respiration when compared with COCs in 5.6 mM glucose, demonstrating a negative impact on mitochondrial function due to high glucose concentration.
• The metabolic enzyme LDHA was observed to be downregulated in cumulus cells of oocytes undergoing IVM in 17 mM glucose, suggesting that high glucose can affect gene expression.
• No notable difference was found in maturation or blastocyst rates between the groups.

Conclusion

• The study concludes that high glucose concentration during IVM may alter COC mitochondrial function and gene expression. As such, modifications to glucose levels in IVM protocols could well improve the in vitro embryo production.
• Then again, additional research is needed to understand whether these observed changes in mitochondrial function or gene expression correlate to developmental changes in resultant offspring.