Wnt/β-Catenin Signaling Pathway Is Strongly Implicated in Cadmium-Induced Developmental Neurotoxicity and Neuroinflammation: Clues from Zebrafish Neurobehavior and In Vivo Neuroimaging

Cadmium (Cd) is a toxic heavy metal and worldwide environmental pollutant which seriously threatens human health and ecosystems. It is easy to be adsorbed and deposited in organisms, exerting adverse effects on various organs including the brain. In a very recent study, making full use of a zebrafish model in both high-throughput behavioral tracking and live neuroimaging, we explored the potential developmental neurotoxicity of Cd(2+) at environmentally relevant levels and identified multiple connections between Cd(2+) exposure and neurodevelopmental disorders as well as microglia-mediated neuroinflammation, whereas the underlying neurotoxic mechanisms remained unclear. The canonical Wnt/β-catenin signaling pathway plays crucial roles in many biological processes including neurodevelopment, cell survival, and cell cycle regulation, as well as microglial activation, thereby potentially presenting one of the key targets of Cd(2+) neurotoxicity. Therefore, in this follow-up study, we investigated the implication of the Wnt/β-catenin signaling pathway in Cd(2+)-induced developmental disorders and neuroinflammation and revealed that environmental Cd(2+) exposure significantly affected the expression of key factors in the zebrafish Wnt/β-catenin signaling pathway. In addition, pharmacological intervention of this pathway via TWS119, which can increase the protein level of β-catenin and act as a classical activator of the Wnt signaling pathway, could significantly repress the Cd(2+)-induced cell cycle arrest and apoptosis, thereby attenuating the inhibitory effects of Cd(2+) on the early development, behavior, and activity, as well as neurodevelopment of zebrafish larvae to a certain degree. Furthermore, activation and proliferation of microglia, as well as the altered expression profiles of genes associated with neuroimmune homeostasis triggered by Cd(2+) exposure could also be significantly alleviated by the activation of the Wnt/β-catenin signaling pathway. Thus, this study provided novel insights into the cellular and molecular mechanisms of Cd(2+) toxicity on the vertebrate central nervous system (CNS), which might be helpful in developing pharmacotherapies to mitigate the neurological disorders resulting from exposure to Cd(2+) and many other environmental heavy metals.