Environmental Pollutant PBDE‐209 Regulates NO/cGMP Signaling through Activating NMDA Receptors In Neuronal Cells

Decabromodiphenyl ether (PBDE‐209) is a persistent and important environmental pollutant that was once incorporated into many domestic products as a fire retardant. Once PBDE‐209 was thought to be safe. This is because it accumulated only at 500nM or lower concentrations in the human body and was rapidly metabolized. However, recent epidemiological studies showed that perinatal exposure to the compound causes neurodevelopmental abnormalities, such as delayed cognitive behavior development. Moreover, PBDE‐209 has been found to be toxic to cultured neurons, significantly impairing neuronal differentiation. However, the molecular mechanisms through which PBDE‐209 causes these untoward effects in neurons are unclear. Nitric oxide (NO) and cGMP signaling play an important role in regulating neuronal maturation and abnormalities in this pathway have been linked to neuronal dysfunction and cell death. Accordingly, we tested whether relevant levels of PBDE‐209 disrupts nitric oxide (NO) and cGMP signaling in HT‐22 cells, a model neuronal cell line. We measured NO production and cGMP levels in these cells due to exposure to 100nM, 200nM, and 400nM PBDE‐209 in culture media. Whereas 100nM PBDE‐209 did not alter the levels of these mediators, we found that 200nM and 400nM PBDE‐209 increased NO production and that 400nM PBDE209 increased cGMP levels. After pretreatment with L‐nitro‐arginine methylester (L‐NAME), a nitric oxide synthase (NOS) inhibitor, NO production and cGMP levels were decreased in the PBDE‐209 exposed cells. This result suggested that NOS mediates the effects of PBDE‐209 on NO/cGMP signaling. Next, we tested the role of N‐methyl‐D‐aspartate (NMDA) receptors on PBDE‐209's regulation of NO/cGMP using MK‐801, a NMDA receptor inhibitor. We determined that PBDE‐209 increases NO production, cGMP levels, and neuronal nitric oxide synthase (nNOS) isoform expression through the activity of the NMDA receptor. Moreover, this NMDA receptor‐mediated effect of PBDE‐209 was observed to regulate cGMP levels through inhibiting the expression of phosphodiesterase (PDE) 5, which hydrolyzes cGMP, and PDE2, which is highly abundant in the hippocampus and metabolizes cAMP in addition to cGMP. Under certain conditions, cGMP mediates apoptosis in neuronal cells. Therefor, we measured the effect of PBDE‐209 on the Bcl‐2/Bax ratio, which was indicative of apoptosis induction, using immunoblotting. We found that PBDE‐209‐stimulated NMDA receptor activity increases the Bcl‐2/Bax ratio in the neuronal cell line. Our studies implicate the NMDA‐NO/cGMP pathway in pathogenic mechanisms through which PBDE‐209 induces neurotoxicity. Support or Funding Information A Chinese National Nature Science Grant (Youth Project: 81402652) supported these research studies.