Placental and embryonic growth restriction in mice lacking the transcription factor Nrf2

Objectives: The nuclear factor-erythroid 2-related factor 2 (Nrf2) is a potent activator that regulates the expression of antioxidants and detoxication enzymes. Recent discussion about a link between Nrf2 and vascular angiogenic balance in preeclampsia has focussed on the downstream target protein, heme oxygenase-1 (HO-1). The effect Nrf2 on placental development has not been yet discussed. In particular, we evaluated the placental and fetal growth, the feto-placental phenotype and oxidative stress status in Nrf2 knockout (Nrf2^-/^-) mice at different stages of pregnancy.

Methods: Placentae from Nrf2^-/^- and wild type Nrf2⁺/⁺ were collected on days 13.5, 15.5 and 18.5 post coitum. We performed Periodeic Acid Schiff staining on paraffin-embedded samples. The total volume of every genotype placenta was estimated using the Cavalieri estimator of volume. The expression of the lipid peroxidation marker 4-hydroxy-2-nonenal (4-HNE) and HO-1-antibodies were analysed by immunohistochemical methods and RT-PCR.

Results: At 18.5 days post coitum the fetal weight in Nrf2^-/^-- was reduced (0.8391 ± 0.01569) versus Nrf2⁺/⁺ (0.9715 ± 0.01897) indicating a decrease in placental efficiency. The volume of the placenta and the labyrinth area was estimated via Cavalieri estimator and there was a significant reduction in both total and labyrinth-volume in case of Nrf2 deletion.

The Nrf2^-/^- -labyrinth cells showed increased levels of the lipid peroxidation product 4-hydroxynonenal (4-HNE) and a significant decrease in HO-1, an important endogenous antioxidant enzyme and a key regulator of trophoblast invasion and placental function.

Conclusion: These data point out the necessity of a functional Nrf2 for the fetal and placental development. Nrf2 signalling may interact with the differentiation of the trophoblast lineage, and may influence the intrauterine development. Nrf2 knockout mice could be a novel model for late-onset IUGR.