Mechanisms contributing to the reduced developmental competence of glucosamine-exposed mouse oocytes.

Glucosamine (GlcN) is a widely used hyperglycaemia mimetic because of its ability to upregulate the 'energy-sensing' hexosamine biosynthesis pathway in a dose-dependent manner. A previous study demonstrated that addition of GlcN (2.5-5 mM) during IVM of cattle and pig cumulus-oocyte complexes (COC) inhibited development following fertilisation and early cleavage. In the present study, we demonstrate that the addition of 2.5 mM GlcN during IVM of mouse COCs similarly inhibits embryo development, with the degree of inhibition dependent upon the availability of glucose in the maturation medium. Furthermore, we determined that the effect of GlcN is likely mediated by the cumulus cell vestment, because we failed to observe inhibitory effects of GlcN following maturation of denuded (and therefore already developmentally compromised) oocytes. As with cattle oocytes, inhibition of O-linked glycosylation of unknown proteins within mouse cumulus cells significantly reversed the effects of GlcN. Finally, we also provide preliminary evidence that GlcN may inhibit the pentose phosphate metabolic pathway within the oocyte, an effect possibly mediated by cumulus cells in intact COCs. Collectively, our results demonstrate that GlcN inhibits the developmental competence of IVM mouse oocytes and suggest that this occurs via cumulus cell-mediated mechanisms. Therefore, the in vitro addition of GlcN is a useful experimental tool to determine the mechanisms of hyperglycaemic responses within COCs.