Valproic Acid Induces Post-Translational Redox Modifications in Mouse Embryos That Are Prevented via Prior Nrf2 Activation.

Valproic acid (VPA) is a human developmental toxicant that causes neural tube defects and neurobehavioral deficits. Recent work has implicated VPA-induced oxidative stress in cell models of neurodifferentiation, where oxidative post-translational modifications (PTMs) in undifferentiated cells, primarily protein sulfenylation (Pr-SOH), were unique compared to differentiated neurons, primarily protein S-glutathionylation (Pr-SSG). Many of these effects could be mitigated by pretreatments with an Nrf2 inducer. However, it is unclear how early-stage mouse embryos (gestational day 8.5) respond to VPA treatments. Using whole embryo culture, mouse embryos were treated with VPA. A time course assessment of glutathione/glutathione disulfide redox potentials was performed via HPLC throughout 24 h of culture. At 6 h of VPA treatment, embryos were collected for the assessment of protein redox states and specific protein PTMs via various blotting techniques. Also, at 6 h of treatment, the localization of specific PTMs was determined via whole mount staining. Some embryos were pretreated with an Nrf2 inducer. Our data demonstrated that VPA caused a sharp oxidation of redox potentials, which were the greatest between 2 and 6 h, but reverted to control levels by 24 h. Preemptive Nrf2 activation prevented VPA-induced oxidation. Redox blotting showed that VPA caused oxidation of the proteome but this could be reversed by D3T pretreatment. More specifically, Pr-SOH levels increased but Pr-SSG levels were unchanged. Increased Pr-SOH could also be reversed with prior Nrf2 activation. We conclude that embryos at these early stages of development are highly sensitive to VPA and respond more like undifferentiated cells, promoting a more pro-oxidizing outcome for proteins, increasing Pr-SOH formation vs. Pr-SSG. These findings may support specific windows of development where embryos are more susceptible to VPA-induced oxidative injury. Further understanding of redox control and regulation at these susceptible states may serve to develop preventative strategies to reduce poor developmental outcomes after exposures.