Induced long-term potentiation improves synaptic stability and restores network function in ALS motor neurons

Abstract

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease causing progressive dysfunction and degeneration of upper and lower motor neurons. An increasing body of evidence has identified synaptic alterations in patients and experimental models of ALS. Importantly, these have been associated with functional impairments in motor neuron networks, suggesting that synaptic impairments are early events in the disease cascade resulting in functional compensatory reconfigurations. The synapse may therefore represent a disease-modifying target to delay disease progression. In this study, we aimed to stabilize synapses and modify structural connectivity to restore network balance in ALS patient-derived motor neuron networks. To this end, we blocked the potassium channels using tetraethylammonium (TEA) which has been shown to induce chemical long-term potentiation (cLTP). The unperturbed ALS patient-derived motor neuron networks developed clear signs of subtle network dysfunction, including increased firing rate and bursting, and accompanying structural abnormalities. These features were partially restored by temporarily blocking the potassium channels. Specifically, the TEA-treated ALS networks were characterized by a reduction in aberrant branching and stabilization of dendritic spines, alongside a temporary reduction in firing rate and bursting. Furthermore, protein expression assays revealed restoration of dysregulated molecular pathways, including protein synthesis and metabolic pathways, and upregulation of pathways involved in synapse organization in the TEA-treated ALS networks. Collectively, these findings improve our understanding of the association between synaptic impairments and functional alterations in ALS, and demonstrate the relevance of modulating synaptic plasticity to promote network balance.