Lactate inhibits glucose‐induced zigzag motility and enhances linear motility in bull spermatozoa by suppressing glycolysis

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BACKGROUND: Energy metabolism and substrate balance are critical determinants of sperm motility and fertility. Linear motility is necessary for sperm forward movement, whereas hyperactivated motility is a prerequisite for fertilization. The preference of metabolic pathways depends on substrate availability which controls sperm motility. However, there are differences in substrate composition in seminal plasma, vagina, uterus and oviducts. OBJECTIVES: This study aims to clarify how the spermatozoa maintains its metabolic homeostasis and functions in the presence of glucose and lactate either alone or in combinations. MATERIALS AND METHODS: Fresh bull spermatozoa was incubated with modified human tubal fluid (mHTF) medium containing either no-energy, glucose, lactate, or a combination of glucose and lactate. Sperm motility, kinematics, adenosine triphosphate (ATP) production, mitochondrial membrane potential, glucose incorporation, glycolysis, oxidative phosphorylation (OXPHOS), and acrosome reaction were systematically assessed. RESULTS: Glucose resulted in zigzag motility and lactate induced linear motility. Glucose-derived zigzag motility was suppressed by lactate with increasing lactate concentration in a dose-dependent manner. The addition of lactate with glucose showed higher mitochondrial membrane potential, higher oxygen consumption rate (OCR), and lower extracellular acidification rate (ECAR). Lactate suppressed glucose incorporation in midpiece and tail regions, reduced glycolysis, and shifted sperm metabolism toward OXPHOS which resulted in linear motility and maintained acrosome integrity. DISCUSSION: Lactate played a metabolic and regulatory role in bull sperm metabolism. As a metabolic role, it oxidized through OXPHOS and maintained linear motility. The metabolic changes by lactate suppressed glucose-induced acrosome reactions and maintained linear motility, which might be beneficial for sperm transportation toward the fertilization site of the female reproductive tract and results in successful fertilization. CONCLUSION: This is a novel finding that explores the regulatory role of lactate over glucose metabolism in bull sperm functionality. Optimum balancing of glucose and lactate maintains the motility and functionality of bull spermatozoa. These outcomes might have substantial implications for the enhancement of sperm preservation techniques, sperm handling, and fertility outcomes.

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