Increased O-Linked N-Acetylglucosamine Modification of NF-ΚB and Augmented Cytokine Production in the Placentas from Hyperglycemic Rats

Abstract

Inflammation as a result of NF-κB activation may result from the classical (canonical) pathway, with disconnection of the IκB inhibitor and subsequent nuclear translocation or, alternatively, by post-translational modifications of modulatory proteins or NF-κB subunits (non-canonical pathway). We hypothesized that hyperglycemia-induced increased glycosylation with O-linked N-acetylglucosamine (O-GlcNAc) of NF-κB in placental tissue leads to augmented production of pro-inflammatory cytokines, culminating in placental dysfunction and fetal restriction growth. Single injections of streptozotocin (40 mg/kg) or vehicle were used to induce hyperglycemia or normoglycemia, respectively, in female Wistar rats. After 3 days, rats were mated and pregnancy confirmed. Placental tissue was collected at 21 days of pregnancy. Placental expression of p65 subunit was similar between groups. However, nuclear translocation of p65 subunit, showing greater activation of NF-κB, was increased in the hyperglycemic group. Reduced expression of IκB and increased expression of phosphorylated IκB were observed in the placenta from hyperglycemic rats, demonstrating increased classical NF-κB activation. Augmented modification of O-GlcNAc-modified proteins was found in the placenta from hyperglycemic rats and p65 subunit was a key O-GlcNAc target, as demonstrated by immunoprecipitation. Tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6) expressions were increased in the placenta from hyperglycemic rats. Furthermore, placental weight was increased, whereas fetal weight was decreased under hyperglycemic conditions. TNF-α and IL-6 demonstrated positive correlations with placental weight and negative correlations with fetal weight and placental efficiency. Therefore, under hyperglycemic conditions, a modulatory role of O-GlcNAc in NF-κB activity was demonstrated in the placenta, contributing to fetal and placental dysfunction due to inflammatory cytokine exacerbation.

O-GlcNAc Modification During Pregnancy: Focus on Placental Environment

“…Augmented O- GlcNAc levels in the placenta during hyperglycemia coincided with augmented placental levels of interleukin (IL)-6 and tumor necrosis factor alpha (TNF-α). Interestingly, both cytokines positively correlated with placental weight, and negatively correlated with fetal weight and placental efficiency in hyperglycemic conditions ( Dela Justina et al, 2017 ). Reduced embryo implantation and impaired blastocyst development was observed in an experimental mouse model of diabetes.…”

“…Under hyperglycemic conditions, O- GlcNAc modifications also occur in nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), found in rat placental tissue ( Dela Justina et al, 2017 ). This represents non-canonical activation of NF-κB, also described in other cells ( Yang et al, 2008 ), in which augmented levels of O- GlcNAc bind to NF-κB, favoring its translocation to the nucleus, augmenting production of pro - inflammatory cytokines ( Dela Justina et al, 2017 ).…”

Altered Glycosylation Contributes to Placental Dysfunction Upon Early Disruption of the NK Cell-DC Dynamics

“…This finding correlates with the reduced fetal vascular density in the labyrinth upon NK depletion and with the inflammatory status due to the increased NK cell density in the mesometrial lymphoid aggregate of pregnancy (13). Interestingly, changes in the glycosylation status predominantly affecting the placental labyrinth and junctional zone have been reported in a rat model of hyperglycemic placental dysfunction (46,47); suggesting that glycovariations in these layers induced by adverse maternal environments may have direct impact on placental function.…”

Working Hypothesis for Glucose Metabolism and SARS-CoV-2 Replication: Interplay Between the Hexosamine Pathway and Interferon RF5 Triggering Hyperinflammation. Role of BCG Vaccine?

“…Nuclear factor-kB (NF-kB) and IKK are associated with metabolic disorders (24), also playing important roles in inflammatory and immune responses (25). O-GlcNAcylation regulates direct modification of transcription factors such as NF-kB (26,27). Cells use the HBP and OGT to potentiate gene expression through NF-kB as a glucose-responsive transcription factor in response to TNFα (28) (Figure 1).…”