JAK2/STAT3 signaling pathway mediates methylmercury toxicity in mouse astrocyte neuronal C8-D1A cell line

Abstract

Methylmercury (MeHg) is an environmental pollutant. Consumption of contaminated fish is the main exposure route in humans, leading to severe neurological disorders. Upon ingestion MeHg reaches the brain and selectively accumulates in astrocytes disrupting glutamate and calcium homeostasis and increasing oxidative stress. Despite extensive research, the molecular mechanisms underlying MeHg neurotoxicity remain incompletely understood. The induction of nuclear factor erythroid 2-related factor 2 (Nrf2) and its role activating antioxidant responses during MeHg-induced oxidative injury have garnered significant attention as a potential therapeutic target against MeHg toxicity. However, recent studies indicate that the Nrf2 signaling pathway alone may not be sufficient to mitigate MeHg-induced damage, suggesting the existence of other protective mechanisms. The signal transducer and activator of transcription 3 (STAT3) plays a crucial role in cell growth and survival. Several studies have also highlighted its involvement in regulating redox homeostasis, thereby preventing oxidative stress through mechanisms that involve modulation of nuclear genes that encode electron transport complexes (ETC) and antioxidant enzymes. These characteristics suggest that STAT3 could serve as a viable mechanism to mitigate MeHg toxicity, either in conjunction with or as an alternative to Nrf2 signaling. Our previous findings demonstrated that MeHg activates the STAT3 signaling pathway in the GT1-7 hypothalamic neuronal cell line, suggesting its potential role in promoting neuroprotection. Here, to elucidate the role of the STAT3 signaling pathway in MeHg neurotoxicity, we pharmacologically inhibited STAT3 using AG490 in the C8D1A astrocytic cell line exposed to 10 µM MeHg. Our data demonstrated that pharmacological inhibition of STAT3 phosphorylation exacerbates MeHg-induced mortality, antioxidant responses, and ROS production, suggesting that STAT3 may contribute to neuroprotection against MeHg exposure in astrocytes.