Oral Treatment Targeting the Unfolded Protein Response Prevents Neurodegeneration and Clinical Disease in Prion-Infected Mice

Pharmacological inhibition of PERK, the key kinase of the unfolded protein response that mediates translational shutdown, restores protein synthesis in prion-infected mice, thus preventing neurodegeneration and clinical disease. Perking Up Prion Disease Therapy There are no effective treatments for neurodegenerative disorders such as Alzheimer’s disease (AD), Parkinson’s disease (PD), and prion disease. These diseases share common features, including the accumulation of misfolded disease-specific proteins in the brain, leading to neuronal loss, which is ultimately fatal. In addition, the brains of patients with these neurodegenerative diseases show overactivation of a cellular defense pathway for dealing with misfolded proteins called the unfolded protein response (UPR). The UPR deals with the misfolded protein load in a number of ways including transiently switching off translation. Moreno et al. now report that the buildup of misfolded prion protein in mice with prion disease causes sustained overactivation of this pathway. This results in long-term translational inhibition, causing a critical decline in key proteins needed for neuronal survival. The authors used a newly described specific inhibitor of a key UPR kinase mediating translational shutdown to test if pharmacological inhibition would be neuroprotective. The compound prevented neurodegeneration and the emergence of clinical disease in prion-infected mice, whereas untreated animals all succumbed to disease. These data suggest that the UPR may represent a new therapeutic target for drug development to treat prion disease and possibly other neurodegenerative diseases as well. During prion disease, an increase in misfolded prion protein (PrP) generated by prion replication leads to sustained overactivation of the branch of the unfolded protein response (UPR) that controls the initiation of protein synthesis. This results in persistent repression of translation, resulting in the loss of critical proteins that leads to synaptic failure and neuronal death. We have previously reported that localized genetic manipulation of this pathway rescues shutdown of translation and prevents neurodegeneration in a mouse model of prion disease, suggesting that pharmacological inhibition of this pathway might be of therapeutic benefit. We show that oral treatment with a specific inhibitor of the kinase PERK (protein kinase RNA–like endoplasmic reticulum kinase), a key mediator of this UPR pathway, prevented UPR-mediated translational repression and abrogated development of clinical prion disease in mice, with neuroprotection observed throughout the mouse brain. This was the case for animals treated both at the preclinical stage and also later in disease when behavioral signs had emerged. Critically, the compound acts downstream and independently of the primary pathogenic process of prion replication and is effective despite continuing accumulation of misfolded PrP. These data suggest that PERK, and other members of this pathway, may be new therapeutic targets for developing drugs against prion disease or other neurodegenerative diseases where the UPR has been implicated.