The tauopathy‐associated PERK variant, PERK‐B, induces maladaptive translation and reveals novel pathogenic mechanisms of PSP

Abstract

AbstractBackgroundA major challenge in the field is identification of molecular mechanisms driving pathological tau accumulation in tauopathies such as progressive supranuclear palsy (PSP). The largest GWAS for PSP identified a protein kinase endoplasmic reticulum kinase haplotype B (PERK‐B) hypomorph as a risk factor for the disease. This variant is less effective at reducing translation as its counterpart, PERK haplotype A (PERK‐A) and promotes the accumulation of pathological hyperphosphorylated tau species. However, the functional differences between PERK‐A and ‐B remain unknown, and this is partly due to the need for chemical induction of ER stress with compounds that provoke pleiotropic effects.MethodTo address these gaps in knowledge and overcome technical issues, we developed novel molecular tools and models to study PERK function. Using CRISPR/Cas9, we generated PERK‐KO HEK cells, transfected them with newly designed PERK plasmids, ER stress sensors, and markers of cap‐dependent translation. We also measured changes in tau accumulation and insolubility because of PERK‐B. In addition, we performed transcriptomic and puromycin proteomics to specifically identify the transcriptome and the nascent proteome resulting from PERK‐B expression.ResultWe established that expression of both PERK variants equally induced ER stress and reduced cap‐dependent translation. In addition, the PERK‐A and ‐B transcriptomes were virtually identical. However, while PERK activity was protective, PERK‐B less effectively cleared tau, leading to accumulation of insoluble pathological hyperphosphorylated tau. SUnSET proteomics revealed four proteins that were only present in the PERK‐B translatome. Given that these proteins had not been previously associated with PSP, we measured their levels in human brains and identified that at least one of them was significantly increased in PSP cases.ConclusionOur data suggest that the PERK‐B variant promotes accumulation of specific proteins associated with PSP. The new link between these proteins and PSP may reveal novel pathogenic mechanisms and could uncover new and effective therapeutic targets. Efforts to establish the role of these proteins in PSP is underway.