Thesis title: New approaches to study human excitotoxicity-related neuronal pathologies.
Excitotoxicity is a complex process generated by the excess of glutamate and other excitatory neurotransmitters and their impaired reuptake. The excessive binding of glutamate to its receptors, in particular to the NMDA (N-Methyl-D-Aspartate) receptor class, causes an overwhelming influx of Ca2+, starting a cascade that leads to mitochondrial impairment, reactive oxygen species (ROS) overproduction, caspase activation and, ultimately, neuronal function impairment and cell death. Excitotoxicity has been linked to several neuropathologies and neurodegenerative diseases, such as Alzheimer’s and Parkinson’s diseases, Amyotrophic Lateral Sclerosis (ALS), and epilepsies. To date, there are few approved treatments for these conditions, and most of them block the channel activity (memantine, used for Alzheimer’s disease) or glutamate release (riluzole, used to treat ALS), leading to severe adverse effects.
Here, we tested and used a new two-fluorophores technique to record the Ca2+ and Na2+ influxes of Ca2+ permeable cation channels, which can be used to quantify their Ca2+ permeability and to rapidly screen molecules able to reduce it, like the NMDA receptor negative allosteric modulator EU1794-4. This modulator reduced the Ca2+ permeability of the human NMDA receptor in both a heterologous expression model (Hek 293T cells) and human induced Pluripotent Stem cells (iPSC)-derived spinal motoneurons, that natively express the receptor. We also characterized the functional activity of these iPSC-derived spinal motoneurons during maturation and used them to obtain data on ALS impairment. In WT motoneurons and motoneurons with a FUS P525L mutation (common in familial ALS), we measured cell membrane capacitance and resting potential, and recorded action potentials, synaptic activity, and the response to various neurotransmitters (GABA, glycine, glutamate and acetylcholine), observing neuronal maturation during the four time points (DiV 14, 21, 28, 35). Furthermore, FUS-mutated motoneurons’ maturation is slowed, while action potential, synaptic activity and neurotransmitters response are severely impaired.