Melatonin as an Alleviator in Decabromodiphenyl Ether-Induced Aberrant Hippocampal Neurogenesis and Synaptogenesis: The Role of Wnt7a.

Developmental exposure to polybrominated diphenyl ethers (PBDEs), which are commonly used as flame retardants, results in irreversible cognitive impairments. Postnatal hippocampal neurogenesis, which occurs in the subgranular zone (SGZ) of the dentate gyrus, is critical for neuronal circuits and plasticity. Wnt7a-Frizzled5 (FZD5) is essential for both neurogenesis and synapse formation; moreover, Wnt signaling participates in PBDE neurotoxicity and also contributes to the neuroprotective effects of melatonin. Therefore, we investigated the impacts of perinatal decabromodiphenyl ether (BDE-209) exposure on hippocampal neurogenesis and synaptogenesis in juvenile rats through BrdU injection and Golgi staining, as well as the alleviation of melatonin pretreatment. Additionally, we identified the structural basis of Wnt7a and two compounds via molecular docking. The hippocampal neural progenitor pool (Sox2+BrdU+ and Sox2+GFAP+cells), immature neurons (DCX+) differentiated from neuroblasts, and the survival of mature neurons (NeuN+) in the dentate gyrus were inhibited. Moreover, in BDE-209-exposed offspring rats, it was observed that dendritic branching and spine density were reduced, alongside the long-lasting suppression of the Wnt7a-FZD5/β-catenin pathway and targeted genes (Prox1, Neurod1, Neurogin2, Dlg4, and Netrin1) expression. Melatonin alleviated BDE-209-disrupted memory, along with hippocampal neurogenesis and dendritogenesis, for which the restoration of Wnt7a-FZD5 signaling may be beneficial. This study suggested that melatonin could represent a potential intervention for the cognitive deficits induced by PBDEs.