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

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. In vitro maturation (IVM) can provide large numbers of competent oocytes for embryo technology studies as well as for livestock production and human clinical practice 1. It is anticipated that genetically engineered pigs will increasingly be used in biomedical research, because the pigs share many similarities with humans in terms of physiology, metabolism, genome organization, pathology and aging 2,3. However, despite great efforts to make improvements, the developmental competence of IVM porcine oocytes is still low compared with that of their counterparts in vivo and in bovine and mouse 4-6. Further observations indicated that the impaired developmental capacity of IVM oocytes were due mainly to an insufficient cytoplasmic maturation 7. The process of oocyte maturation includes both nuclear and cytoplasmic aspects 8,9. Studies have demonstrated that progression through all the dynamic processes during oocyte maturation requires a large quantity of energy from metabolism of carbohydrates, amino acids and lipids 10,11. Both meiosis resumption 12,13 and the progression of meiosis to metaphase II stage 14,15 are associated with increased glucose metabolism (GM) through one or more pathways. However, although there have been many reports on the effect of GM on oocyte nuclear maturation 16,17 , studies on GM effect on cytoplasmic maturation are limited. In the few studies reporting the GM effect on cytoplasmic maturation, the effect was analyzed together with its effect on nuclear maturation 18-20. Furthermore, in all the previous studies addressing roles of GM and its metabolites on oocyte maturation, intact cumulus-oocyte complexes (COCs) were treated with enzyme inhibitors or stimulators. Because inhibitors/stimula...

PCOS and Role of Cumulus Gene Expression in Assessing Oocytes Quality

“…Xie et al (43) demonstrated that by applying RNA interference silencing of G6PD or GAPDH genes of cumulus cells (genes involved in PPP pathway), lower maturation rates were achieved in denuded oocytes cultured in the medium compared to those of control cumulus cells (43). Similar results were also obtained in another study on the pig oocyte model (44).…”

Supplementing media with NAD⁺ precursors enhances the <i>in vitro</i> maturation of porcine oocytes

“…Additionally, supplementing the embryo culture medium improved the developmental potential of aged mouse oocytes [ 5 ]. Pig oocytes matured in vitro depend more on glucose as an energy substrate while mice utilise pyruvate more readily [ 40 , 41 ], potentially contributing to the variation in effects on oocyte quality. NAD + is consumed by ADP-ribose polymerases, which play an important role in carbohydrate metabolism [ 42 ], however, the function of mitochondrial ADP-ribose polymerases in carbohydrate metabolism remains under scrutiny.…”

Dehydroepiandrosterone Shifts Energy Metabolism to Increase Mitochondrial Biogenesis in Female Fertility with Advancing Age

“…Oocytes require a lot of energy to maintain their cellular constancy and are, therefore, also rich in mitochondria to provide sufficient energy. However, glucose within the oocyte cannot be catabolized directly by glycolysis for energy supply, and the cytoplasmic protrusions of the cumulus cells (CCs) are in direct contact with the oocyte through the zona pellucida, while the end links the oocyte plasma membrane through a slit to provide the oocyte with nutrient metabolites [ 3 ]. Oocytes obtain amino acids, nucleotides, glutathione, and sugar metabolites [ 4 ] through slit links for energy [ 5 ].…”