THE INTERACTION BETWEEN MUTANT PRION PROTEIN AND GLUTAMATE RECEPTORS: A NOVEL MECHANISM FOR NEURONAL DYSFUNCTION IN GENETIC PRION DISEASES

Genetic prion diseases are rare, invariably fatal neurodegenerative disorders linked to mutations in the PRNP gene encoding the prion protein (PrP). PRNP mutations favor the conformational conversion of PrP into a pathogenic, misfolded isoform that accumulates in the central nervous system of affected individuals and kills neurons through an unknown mechanism. Evidence is emerging that neuronal loss in inherited prion diseases is preceded and possibly caused by synaptic dysfunctions. However, the ultimate link between synaptic dysfunction and neurodegeneration is yet to be found. We previously demonstrated that mutant PrP is retained in the endoplasmic reticulum where it interacts with the α2-δ1 subunit of voltage-gated calcium channels. This impairs the correct delivery of the channel complex to the cell surface, impacting synaptic transmission. Nevertheless, this phenomenon alone does not account for neurodegeneration. It has been shown that PrPC engages functional interactions with other proteins that are important for synaptic function, such as glutamate receptors. Here, we aimed to explore whether intracellular retention of mutant PrP affected also the trafficking of glutamate receptors, thereby producing adverse effects on neuronal function and survival. We found that mutant PrP impairs the membrane delivery of specific AMPA and NMDA receptor subunits, resulting in postsynaptic structural alterations and impaired basal glutamatergic transmission and synaptic plasticity. Moreover, retention of the GluA2 subunit of AMPA receptor results in exposure of GluA2-lacking, calcium-permeable AMPA receptors, leading to increased calcium permeability and enhanced sensitivity to excitotoxic cell death. Interestingly, distinct PrP mutations interact differently with glutamate receptors, altering their localization and function in different ways. Our findings identify a new pathological mechanism for genetic prion diseases and may lead to novel therapeutic approaches for such incurable conditions.