Glucose concentration during equine in vitro maturation alters mitochondrial function

Area of Science:

• Animal Science
• Reproductive Biology
• Biochemistry

Background:

• In vitro embryo production in horses is growing, but protocols require optimization.
• Common in vitro maturation (IVM) media use differing glucose concentrations (5.6 mM vs. 17 mM).
• High glucose effects on equine oocytes are unknown, unlike in other mammals.

Purpose of the Study:

• To investigate the impact of physiological (5.6 mM) versus supraphysiological (17 mM) glucose concentrations during equine IVM on oocyte energy metabolism and gene expression.
• To compare mitochondrial function and key metabolic gene expression in equine oocytes and cumulus cells matured under different glucose conditions.

Main Methods:

• Equine cumulus-oocyte complexes (COCs) were matured in M199 with either 5.6 mM or 17 mM glucose.
• Spent media analyzed for glucose consumption, lactate, and pyruvate.
• Mitochondrial function assessed via respirometry.
• Expression of lactate dehydrogenase-A (LDHA) analyzed in cumulus cells.

Main Results:

• No significant differences in COC glucose consumption, lactate, or pyruvate production between groups.
• A decreased glycolytic index observed at 17 mM glucose.
• IVM in 17 mM glucose led to reduced ATP-coupled respiration and increased non-mitochondrial respiration.
• LDHA was downregulated in cumulus cells matured with 17 mM glucose.
• Maturation and blastocyst rates remained unaffected by glucose concentration.

Conclusions:

• Supraphysiological glucose (17 mM) during equine IVM alters COC mitochondrial function and LDHA gene expression.
• These metabolic changes occur without affecting maturation or blastocyst rates.
• Further investigation is required to determine the long-term developmental consequences for offspring.