Mapping O-linked glycosylation in the rat hypothalamus in pregnancy and lactation

Many maternal adaptations occur during pregnancy to support the metabolic demands of the developing fetus and to prepare for the continued metabolic demands of lactation. Among these maternal adaptations are changes in the hypothalamic areas that regulate energy homeostasis: the paraventricular nucleus (PVN), ventromedial hypothalamic nucleus (VMH) and arcuate nucleus (ARC). The adaptive changes in the PVN, VMH, and ARC are believed to be driven by reduced responsiveness to the satiety hormone, leptin, during pregnancy. However, increased maternal metabolism is supported by elevated circulating glucose levels in pregnancy, and glucose itself can alter cell function by O-linked N-acetylglucosamine (O-GlcNAc) post-translational modification of proteins (O-GlcNAcylation). Therefore, we hypothesized that O-GlcNAcylation would be increased within the hypothalamic brain areas that are involved in the maternal adaptations to the increased metabolic demands of pregnancy: the ARC, VMH, and PVN. We completed immunohistochemistry and western blotting for O-GlcNAc in the ARC, VMH, and PVN from non-pregnant, late-pregnant, and lactating rats. Unexpectedly, we found that the number of O-GlcNAc-expressing cells and the levels of O-GlcNAc protein expression were similar within each area in non-pregnant, late-pregnant, and lactating rats. However, western blot analysis showed that the specific proteins that were O-GlcNAcylated appeared to be different between the reproductive states within each area. Further work will be required to identify the specific proteins that are differentially O-GlcNAcylated in each of the areas during pregnancy and lactation to determine whether this might contribute to the maternal adaptations required to cope with the metabolic demands of pregnancy and lactation.