Role of a alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor on methylmercury-induced calcium dysregulation on motor neurons

Methylmercury (MeHg) is a persistent environmental neurotoxicant to which humans are exposed mainly through the consumption of fish. MeHg leads to neuronal cell death in acute or chronic exposure and its mechanism of toxicity is not yet understood. Due to its high prevalence in the environment and its mechanism of toxicity MeHg has been considered a possible contributor to the development of Amyotrophic Lateral Sclerosis (ALS). Alterations in glutamate reuptake and Ca2+ regulation in ALS and after MeHg exposures have been well documented. Most importantly, MeHg-induced alterations in intracellular Ca2+ ([Ca2+]i) in motor neurons lead to early onset ALS-like phenotype in the superoxide dismutase 1 (SOD1-G93A) mouse, a mouse model genetically susceptible to ALS. One of the ion channels that contribute to the alterations in [Ca2+]i observed in ALS and after MeHg exposure is the ionotropic glutamate receptor α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA). My research has focused on characterizing the effects of MeHg on motor neurons in vitro. I used two cell lines: a mouse motor neuron hybrid cell line NSC34 and an induced pluripotent stem cell derived-motor neuron (hiPSC-MN) cell line of human origin. I investigated MeHg toxicity in these cell types and on AMPA receptors in order to understand the role these ion channels play in the observed alterations in [Ca2+]i. Results from the studies in this dissertation demonstrate that MeHg exposure in vivo or in vitro lead to alterations in the AMPA receptor and the RNA editing enzyme ADAR2 gene expression. Also, that hiPSC-MNs are more susceptible than NSC34 cells to MeHg toxicity observed as an earlier concentration dependent cell death. I also identified that MeHg induces a bi-phasic increase in [Ca2+]i in hiPSC-MNs and Ca2+ permeable AMPA receptors are mediating those increases. Taken together these results suggest a potential role of the AMPA receptors in MeHg-induced toxicity in MNs. These findings contribute to the understanding of MeHg-induced toxicity in motor neurons and provide a platform for ongoing studies in our lab which are focused on identifying the underlying mechanisms by which MeHg is contributing to the accelerated onset of ALS-like phenotype.