Hyperglycaemia and lipid differentially impair mouse oocyte developmental competence.

Maternal diabetes and obesity are characterised by elevated blood glucose, insulin and lipids, resulting in upregulation of specific fuel-sensing and stress signalling pathways. Previously, we demonstrated that, separately, upregulation of the hexosamine biosynthetic pathway (HBP; under hyperglycaemic conditions) and endoplasmic reticulum (ER) stress (due to hyperlipidaemia) pathways reduce blastocyst development and alter oocyte metabolism. In order to begin to understand how both glucose and lipid metabolic disruptions influence oocyte developmental competence, in the present study we exposed mouse cumulus-oocyte complexes to hyperglycaemia (30 mM) and/or lipid (40 µM) and examined the effects on embryo development. The presence of glucosamine (GlcN; a hyperglycaemic mimetic) or increased lipid during in vitro maturation severely perturbed blastocyst development (P < 0.05). Hyperglycaemia, GlcN and hyperglycaemia + lipid treatments significantly increased HBP activity, increasing total O-linked glycosylation (O-GlcNAcylation) of proteins (P < 0.0001). All treatments also induced ER stress pathways, indicated by the expression of specific ER stress genes. The expression of genes encoding the HBP enzymes glutamine:fructose-6-phosphate amidotransferase 2 (Gfpt2) and O-linked β-N-acetylglucosaminyltransferase (Ogt) was repressed following lipid treatment (P < 0.001). These findings partially implicate the mechanism of O-GlcNAcylation and ER stress as likely contributors to compromised fertility of obese women. This study investigated the influence of high glucose and lipid levels (as seen in obesity) on oocyte health. Both lipid and glucose treatments compromised embryo development and increased the activities of glucose fuel sensing (hexosamine biosynthetic pathway) and lipotoxicity responses (endoplasmic reticulum-stress, ER-stress). However, there were no additive effects when glucose and lipids were combined, and in the case of ER-stress markers, glucose partially recovered the effects of lipotoxicity. [ABSTRACT FROM AUTHOR]