GM-CSF increases glucose uptake and mitochondrial activity and reduces reactive oxygen species levels in mouse cumulus-oocyte complexes during oocyte in vitro maturation

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We have previously reported that the addition of granulocyte macrophage-colony stimulating factor (GM-CSF) during oocyte in vitro maturation (IVM) can increase embryo development in mice. The present study examined glucose uptake, mitochondrial activity, reactive oxygen species (ROS) levels, and the expression of key genes associated with these pathways in cumulus-oocyte complexes (COCs). The addition of 10 ng/ml GM-CSF during IVM increased glucose uptake at 15 min (3.45 vs. 3.48, P < 0.001) compared control. However, at 30 min (3.45 vs. 3.44, P < 0.05) and 60 min (3.45 vs. 3.46, P < 0.01), glucose levels were higher in the control. GM-CSF also increased mitochondrial membrane potential (MMP) in the outer area of COCs compared with the control at the end of IVM (1.92 vs. 2.42, P < 0.01), while no differences were observed in the intermediate and perinuclear areas. GM-CSF reduced MMP across all three regions in denuded oocytes compared with control (outer area 3.64 vs. 3.32, P < 0.05; intermediate 2.05 vs. 1.63, P < 0.01; perinuclear 1.59 vs. 1.28, P < 0.01). GM-CSF reduced ROS levels compared with the control at the end of IVM (6367.7 vs. 3935.8, P < 0.01). ROS levels were also reduced in denuded oocytes in the GM-CSF group with the control group (14870.0 vs. 7117.9, P < 0.001). GM-CSF increased the expression of key genes associated with mitochondrial function and ROS production in COCs at the end of IVM. Together, our findings suggest that GM-CSF increases glucose uptake in the cumulus cells which increases the supply of energy substrates to the oocyte increasing mitochondrial activity while reducing ROS levels.

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