Enhanced phosphorylation of PERK in primary cultured neurons as an autonomous neuronal response to prion infection

Abstract

Conversion of cellular prion protein (PrP C ) into the pathogenic isoform of prion protein (PrP Sc ) in neurons is one of the key pathophysiological events in prion diseases. However, the molecular mechanism of neurodegeneration in prion diseases has yet to be fully elucidated because of a lack of suitable experimental models for analyzing neuron-autonomous responses to prion infection. In the present study, we used neuron-enriched primary cultures of cortical and thalamic mouse neurons to analyze autonomous neuronal responses to prion infection. PrP Sc levels in neurons increased over the time after prion infection; however, no obvious neuronal losses or neurite alterations were observed. Interestingly, a finer analysis of individual neurons co-stained with PrP Sc and phosphorylated protein kinase RNA-activated-like endoplasmic reticulum (ER) kinase (p-PERK), the early cellular response of the PERK-eukaryotic initiation factor 2 (eIF2α) pathway, demonstrated a positive correlation between the number of PrP Sc granular stains and p-PERK granular stains, in cortical neurons at 21 dpi. Although the phosphorylation of PERK was enhanced in prion-infected cortical neurons, there was no sign of subsequent translational repression of synaptic protein synthesis or activations of downstream unfolded protein response (UPR) in the PERK-eIF2α pathway. These results suggest that PrP Sc production in neurons induces ER stress in a neuron-autonomous manner; however, it does not fully activate UPR in prion-infected neurons. Our findings provide insights into the autonomous neuronal responses to prion propagation and the involvement of neuron-non-autonomous factor(s) in the mechanisms of neurodegeneration in prion diseases.

Neuron Scale Modeling of Prion Production with the Unfolded Protein Response

“…Other studies, investigating the role of UPR upon neurodegeneration in prion diseases, indicate that a high concentration of PrP Sc triggers ER stress. This activates the UPR and results in a transient global shutdown of protein synthesis [27,26,43,38,33]. The latter studies, which will constitute the basis of our biological assumptions, lead us to suggest that UPR indirectly downregulates PrP Sc : by preventing global protein translation, UPR activation shuts down the production of PrP c which ultimately hampers the production of PrP Sc .…”

“…In the context of prion-diseases, knowledge becomes clearer as some studies performed on mice highlight links between PrP Sc aggregates, ER stress and UPR mechanism [19,45,27,26,43,38,33]. For instance, some works seem to indicate that UPR downregulates PrP Sc through secreted chaperones acting over the extracellular proteostasis [15,16].…”

“…Here, we propose a mathematical modeling that describes PrP c and PrP Sc concentrations at the neuron scale and incorporates the role of UPR through an induced shutdown of global protein synthesis. Based on recent studies [27,26,43,38,33], we model the effect UPR with a negative feedback mechanism reflecting a global translation attenuation. To do so, we suppose that a high concentration of misfolded PrP Sc around neurons triggers ER stress and UPR activation.…”

Bioinorganic Modulators of Ferroptosis: A Review of Recent Findings

“…Also, both these alterations, attenuated by PERK inhibitor GSK2656157 as well as by overexpression of Mfn-2 plasmid, were shown to repress As-caused ferritin upregulation and to abolish As-induced GPX4 downregulation, leading to the inhibition of As-induced ferroptosis in pulmonary epithelial cells. These results point to MAMs as a potential mediator of the ferroptotic cell death that underlies pulmonary function decline caused by exposure to arsenic [ 147 , 148 , 149 ].…”

The Cellular Prion Protein—ROCK Connection: Contribution to Neuronal Homeostasis and Neurodegenerative Diseases

“…Only a few reports describe translational repression within a prion-infectious context induced by the Unfolded Protein Response (UPR) that occurs in the endoplasmic reticulum (ER) (Roffé et al, 2010 ; Moreno et al, 2013 ; Tanaka et al, 2020 ). The proteostress that exerts in the ER of prion-infected neurons provokes the activation by phosphorylation of the kinase PERK (PKR-like ER protein kinase) in the ER membrane, which in turn promotes the hyperphosphorylation of the translation factor eIF2α (eukaryotic initiation factor 2).…”