Influence of oocyte-secreted factors and culture duration on the metabolic activity of bovine cumulus cell complexes

Abstract

Intracellular communication between the cumulus cell complex and the oocyte is essential for numerous processes during oocyte maturation. The aim of this study was to determine the interaction between oocyte-secreted factors and the metabolic activity of bovine cumulus cell complexes during in vitro maturation (IVM). Cumulus-oocyte complexes (COCs) were aspirated from ovaries derived from an abattoir and divided into four treatment groups: (i) intact COCs, (ii) oocytectomized complexes (OOX), in which the ooplasm was microsurgically removed, (iii) OOX co-cultured with denuded oocytes (OOX + DO) and (iv) DO. The complexes were cultured individually in IVM media. After 0-4, 10-14 and 20-24 h of culture, the utilization of oxygen, glucose, pyruvate and L-lactate by the complexes was measured. The metabolic activity of the DO was undetectable. There were no significant differences in metabolic measurement among any of the treatment groups, indicating that the metabolism of the cumulus complex is not affected by the presence of the oocyte. When metabolic activity for the complexes was analysed relative to time in culture, there was an approximate twofold increase in the consumption of oxygen, glucose and pyruvate over the 24 h period (P < 0.05), although production of L-lactate remained constant. The relationship between total glucose uptake and L-lactate production indicated that the majority of glucose consumed at the start of culture was being utilized via glycolysis, but by the cessation of the maturation period, there was significant utilization of glucose elsewhere, possibly for the formation of cumulus extracellular matrix. These results indicate that metabolism of COC does not reflect biochemical activity of the oocyte. Nevertheless, the metabolic requirements of the COC increase throughout maturation.

JY-1 , an oocyte-specific gene, regulates granulosa cell function and early embryonic development in cattle

“…The evolution of the above genes in ruminants may be attributed to clear species-specific differences in the trophoblast and the type of placentation mediating maternal-fetal communication (24). Species-specific attributes of oocyte function in general are not well understood, but bovine versus mouse oocytes do differ in their requirement for cumulus cell expansion and ability to promote glucose uptake by such cells (25)(26)(27)(28)(29). Studies in closely related species (e.g., sheep and goats) will be necessary to further determine the specificity in structure and function of the JY-1 gene.…”

The pivotal role of glucose metabolism in determining oocyte developmental competence

“…Glucose consumption by intact cattle COCs and oocytectomised complexes (OOX, surgical removal of the ooplasm, while retaining the cumulus vestment intact) was measured over a 24-h IVM period. Oocyte-secreted factors did not appear to affect the rate of glucose consumption, as cattle COCs, OOX and OOX co-cultured with denuded oocytes all showed similar rates of glucose consumption over a 24-h culture period (Sutton et al 2003a). In contrast, mouse OOX display decreased expression of genes encoding glycolytic enzymes (including PFK, PFKP and lactate dehydrogenase, LDHA) and a tenfold decrease in glycolytic activity compared to intact COCs and OOX co-cultured with denuded oocytes (Sugiura et al 2005).…”

“…We measured the consumption and production of metabolites by cattle COCs, and while there was a significant increase in glucose consumption over a 24-h IVM period, lactate production remained constant (Sutton et al 2003a). Using the assumption that two lactate molecules are produced for one molecule of glucose consumed through the glycolytic pathway, we calculated that the flux of glucose through glycolysis remains constant during maturation (Table 2; Sutton et al 2003a).…”

“…With regard to metabolites, mature bovine COCs consume twofold more glucose, oxygen and pyruvate than immature COCs (Sutton et al 2003a). A long-established tenet of COC energy metabolism is that the oocyte itself has a poor capacity to utilise glucose (Biggers et al 1967), and that the cumulus cells metabolise the bulk of the glucose consumed by the COC to supply metabolic intermediates to the oocyte.…”

Pentose phosphate pathway activity: effect on in vitro maturation and oxidative status of bovine oocytes

“…It has been observed that the uptake of glucose by bovine COCs is mainly directed 59 towards the production of lactate due to a high glycolytic activity, however, it is known that 60 glucose can also be oxidized in the PPP as well (reviewed in Sutton et al 2003). In pigs, a …”