Investigating the effect of glyphosate on brain cells and extracellular vesicles-mediated glia-to-neuron communication

Pesticide exposure is increasingly recognized as a major environmental factor contributing to human disease. Glyphosate (Gly), the principal active compound of the most extensively used herbicide worldwide, has been epidemiologically linked to a higher risk of conditions such as parkinsonism, autism, and Alzheimer’s disease. These epidemiological correlations are supported by experimental evidence demonstrating neurotoxic effects in rodent models, characterized by neuronal damage, synaptic dysfunctions, glutamatergic excitotoxicity, and oxidative stress. Although Gly is known to cross the blood-brain barrier and accumulate within the brain parenchyma, the mechanism by which its neurotoxic effects disseminate across cellular networks remains poorly understood. This thesis investigates both direct and indirect pathways of Gly neurotoxicity. First, we explored the direct effects of acute Gly exposure on primary hippocampal neurons. Even the acceptable daily intake (ADI, 3 μM) of Gly caused rapid impairment of inhibitory synaptic transmission by reducing both GABA release and postsynaptic GABAa receptor availability. Second, we explored astrocytes-mediated effects via extracellular vesicles (EVs). Primary cortical astrocytes exposed for 24 hours with ADI Gly showed a reactive but non-inflammatory phenotype. When applied to primary cortical neurons, ADEVs isolated from Gly-exposed astrocytes (termed Gly-ADEVs) caused a significant reduction in dendritic complexity and synaptic density, unlike control ADEVs (Ctrl-ADEVs). Electrophysiological analyses revealed that Ctrl-ADEVs enhanced neuronal excitability and synaptic strength, whereas Gly-ADEVs abolished these supportive effects by selectively impairing postsynaptic efficacy. Together, these findings reveal that Gly, even at concentrations deemed “safe”, can disrupt neuronal communication through both direct synaptic impairment and indirect astrocyte- 2 mediated mechanisms. By converting a normally trophic glial signal into a non-supportive or neurotoxic one, Gly exposure may compromise neural circuit development and stability. Collectively, this work highlights the vulnerability of neuron–glia signaling to environmental toxicants and identifies ADEVs as novel mediators of synaptic dysfunction with potential implications for neurodevelopmental and neurodegenerative disease risk