Pentose phosphate pathway inhibition during in vitro maturation substantially affects the metabolism of bovine COCs and blastocysts

Glucose metabolism is widely examined in terms of its effect on oocytes and embryos quality. There are two main pathways of glucose metabolism - glycolysis and pentose phosphate pathway (PPP). The glycolytic pathway allows for energy production in the form of ATP and metabolites such as pyruvate and lactate, whereas PPP activity generates NADPH as well as ribose 5-phosphate, a precursor for the synthesis of nucleotides. The aim of the present experiment was the selective inhibition of either glycolysis or PPP during in vitro maturation of bovine cumulus-oocyte complexes (COCs) to demonstrate, how it affects COCs and further embryos with regard to selected lipidomic and metabolomic aspects. Inhibitors of glycolysis (IO) or PPP (DHEA) were applied during IVM, and the control group was matured under standard conditions. A set of COCs from each group was fertilized and obtained embryos were cultured to the blastocyst stage. ATP level was measured in oocytes, relative mRNA level of selected genes involved in energy metabolism was measured in cumulus cells (CC; real time PCR), lipid droplets parameters were evaluated in oocytes and CC whereas metabolome and lipidome (mass spectrometry) were evaluated in oocytes, CC and blastocysts as well. The experiment shows that glycolysis inhibition during IVM affects mainly CC with no effect in oocytes. It allows to maintain the good developmental potential of oocytes and no negative effect of blastocysts quality and quantity is observed. In contrary, PPP inhibition negatively affects metabolic and lipidomic parameters of both oocyte and CC, which further decreases blastocyst rate and quality. It is therefore concluded that PPP is the most crucial pathway of glucose metabolism for COC developmental potential.