Effects of glucose metabolism pathways on nuclear and cytoplasmic maturation of pig oocytes

Jing Wen,Guo-Liang Wang,Xiao Han,Hong-Li Xie,Jie Zhang,Jing-He Tan,Shuai Gong,Hong-Jie Yuan

doi:10.1038/s41598-020-59709-6

Jing Wen, Guo-Liang Wang + Show 6 more

Open Access

https://doi.org/10.1038/s41598-020-59709-6

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Abstract

The developmental competence of IVM porcine oocytes is still low compared with that in their in vivo counterparts. Although many studies reported effects of glucose metabolism (GM) on oocyte nuclear maturation, few reported on cytoplasmic maturation. Previous studies could not differentiate whether GM of cumulus cells (CCs) or that of cumulus-denuded oocytes (DOs) supported oocyte maturation. Furthermore, species differences in oocyte GM are largely unknown. Our aim was to address these issues by using enzyme activity inhibitors, RNAi gene silencing and special media that could support nuclear but not cytoplasmic maturation when GM was inhibited. The results showed that GM in CCs promoted pig oocyte maturation by releasing metabolites from both pentose phosphate pathway and glycolysis. Both pyruvate and lactate were transferred into pig DOs by monocarboxylate transporter and pyruvate was further delivered into mitochondria by mitochondrial pyruvate carrier in both pig DOs and CCs. In both pig DOs and CCs, pyruvate and lactate were utilized through mitochondrial electron transport and LDH-catalyzed oxidation to pyruvate, respectively. Pig and mouse DOs differed in their CC dependency for glucose, pyruvate and lactate utilization. While mouse DOs could not, pig DOs could use the lactate-derived pyruvate.

Highlights

The developmental competence of In vitro maturation (IVM) porcine oocytes is still low compared with that in their in vivo counterparts
When cultured with lactate alone, both 1 and 2 mM lactate supported a similar maturation rate of around 60%, while 1 mM lactate produced only 10% blastocysts, 2 mM lactate generated 40% of blastocysts (Fig. 1A). When cultured with both glucose and 1 or 2 mM lactate, blastocyst rates increased to the same level as in oocytes matured with glucose alone, suggesting that lactate did not interfere with metabolism of glucose when used at these concentrations
The results suggested that pig denuded oocytes (DOs) could metabolize pyruvate and lactate to support a certain degree of nuclear maturation; both pyruvate and lactate were transported into the DOs through monocarboxylate transporter (MCT); pyruvate was transferred into mitochondria through MPC in both DOs and cumulus cells (CCs); and while pyruvate was metabolized through electron transport chain (ETC), lactate was utilized via the LDH-catalyzed oxidation to pyruvate to support oocyte maturation in both pig DOs and CCs

Summary

Introduction

The developmental competence of IVM porcine oocytes is still low compared with that in their in vivo counterparts. Because inhibitors/stimulators may have non-specificity and/or toxicity, and culture of COCs cannot differentiate whether GM of cumulus cells (CCs) or that of the cumulus-denuded oocytes (DOs) supports oocyte maturation, the results from previous studies remain to be verified by silencing specific genes in either CCs or DOs. Pig oocytes differ from those of other species in containing a large quantity of endogenous lipid. Effects of GM on cytoplasmic maturation of pig oocytes were studied using special maturation media that could support nuclear maturation but could not support cytoplasmic maturation when GM was inhibited; whether GM in pig CCs or DOs supported oocyte maturation was differentiated by RNAi gene silencing; and the capacity to utilize glucose, pyruvate and lactate was compared between pig and mouse DOs. The results suggested that GM in CCs is essential for oocyte cytoplasmic maturation and that there are significant species differences in energy substrate metabolism between pig and mouse DOs

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