Exploring the UPR pathway effects in synaptic activity of cortical neurons, under the context of prion disease

Introduction: Cellular prion protein (PrPC) can misfold into its pathogenic form (PrPSc), leading to transmissible spongiform encephalopathies (TSEs). This process induces endoplasmic reticulum (ER) stress and activates the Unfolded Protein Response (UPR), a pathway with three branches aimed at restoring proteostasis. One branch involves PERK-mediated phosphorylation of eIF2α, which reduces global protein translation. UPR inhibition has been shown to decrease neurotoxicity without affecting PrPSc levels, while UPR activation reduces PrPC levels, potentially limiting PrPSc formation. Despite the relevance of UPR in prion pathology, its effect over excitatory and inhibitory synaptic activity either in normal or prion infected conditions, remains unexplored. Objective: This study evaluated the effects of UPR activation on postsynaptic excitatory and inhibitory activity in non-infected cortical neurons.

Methodology: Cortical neurons from E15 mice cultivated in vitro for 12 days were treated with increasing concentrations of tunicamycin (1 to 2 ug/ml) to activate the UPR system. The impact of tunicamycin on spontaneous postsynaptic activity was evaluated by whole-cell electrophysiological recordings. In addition, PrP and phosphorylated eIF2α-P levels were evaluated by Western blot and immunofluorescence analysis.

Results and discussion: Ours experimental data showed that tunicamycin (2ug) induced the phosphorylation of eIF2α. Electrophysiological recordings revealed changes in the mean amplitude as well as in the frequency of inhibitory postsynaptic currents. These findings indicate that UPR activation enhances inhibitory synaptic transmission in cortical neurons and suggest a potential modulatory role of UPR in prion-related synaptic dysfunction. Founding: Fondecyt 1251488