The transcription factor Nrf2 and the placental inflammatory response; potential implication in the pathogenesis of IUGR

Introduction and Objectives:

Oxidative stress is known to play a huge role in the normal development of the placenta as well as in the pathophysiology of complications such as intrauterine growth restriction (IUGR). The transcription factor Nrf2 displayed a major function in its ability to show resistance against oxidative stress. Finding obtained from studies with Nrf2 knockout mice showed a susceptibility of the mice to a board range of chemical toxicity and disease conditions associated with oxidative pathology mainly IUGR. However, the influence of Nrf2 deficiency on fetal growth has not been well described. The main objective of this study was therefore, to examine the effect of Nrf2-deletion on fetal and placental development in the knockout mouse model.

Materials and methods:

Nrf2 heterozygote mice were paired to conditionally induce gene deletion in the coming embryos. Placentas from Nrf2 knockout (Nrf2-KO) and Nrf2 wild type fetuses (Nrf2-WT) were collected on embryonic days 13.5, 15.5 and 18.5 post coitum. One fixed half was processed into paraffin wax, exhaustively sectioned and then stained with Periodic Acid Schiff (PAS). The total volume of each placenta was estimated using the Cavalieri estimator of volume. The other half was used for molecular biology analyses. Expression of the pro-inflammatory cytokines IL-6, IL-1, TNF-α and the anti-inflammatory enzyme Heme oxygenase-1 were analyzed by ELISA. Immunostaining was performed to analyze the nuclear accumulation of the transcription factor NFKB, which is required for maximal transcription of many cytokines.

Results:

The Nrf2-deficient fetuses presented reduced weight when compared to the wild type ones. In addition, the placental volume of Nrf2 deleted fetuses was reduced significantly (Nrf2-WT121 ± 4 vs. Nrf2-KO 92 ± 5 mm³). Placentas from preterm Nrf2-deleted fetuses showed increased levels of the pro-inflammatory cytokines (IL-6 and TNF-α), and decreased expression of HO-1. The nuclear accumulation of the transcription factor NFKB was higher in Nrf2-KO placentas.

Conclusion:

Our results show that the impairment in Nrf2 signaling leads to a significant reduction in the fetal weight as well as placental weight. The absence of Nrf2 leads to intensified NFKB activity, which is in turn leads to increased cytokine production. These findings suggest that intrauterine inflammation may be a cause for the IUGR in this model, and that the modulation of Nrf2 in response to NFKB activation portrays a protective mechanism against placental inflammation.