UC San Diego

Tauopathies, such as Alzheimer’s Disease (AD) and Progressive Supranuclear Palsy (PSP), are characterized by the central nervous system accumulation of misfolded tau protein. Endoplasmic reticulum (ER) stress and Unfolded Protein Response (UPR) may be cellular mechanisms that cause tauopathies. As one of three major branches of UPR, PERK was identified as a genetic risk factor for AD and PSP in several GWAS studies. Upon activation, PERK attenuates protein translation to restore ER homeostasis but prolonged PERK activation can induce apoptosis. Here, we studied the role of PERK in tau aggregation in human AD and PSP brain tissues and in a cell culture model. We prepared protein lysates from the hippocampus region of advanced AD patient brains (Braak 6) and normal brains (Braak 1). We found more tau aggregated protein in Braak 6 brains in comparison to Braak 1 brains by immunoblotting. We also found a statistically significant increase of phosphorylated PERK in Braak 1 brains in comparison to Braak 6 brains in AD patients. This finding suggests that PERK activity is inversely proportional to insoluble misfolded tau aggregation. We did not find any correlation between PERK-haplotype and PERK functional in AD brains. We also prepared protein lysates from 3 different anatomic regions from PSP patient brains (midbrain, frontal cortex, and occipital cortex). The PSP results were highly variable due to technical problems, and we did not identify any reproducible correlations between tau levels and phosphorylated PERK levels.We further studied how PERK and tau interact utilizing HEK293 cells stably expressing TauRD-YFP (Biosensor cells) developed by Marc Diamond’s group as a cellular model of tau protein aggregation. We activated or inhibited PERK activity in TauRD biosensor cells by treating them with pharmacochemical small molecule modulators (GSK2656157, GSK2606414, salubrinal, ISRIB). We monitored tau aggregation by the formation of YFP fluorescent puncta in the cells. We found an inverse association between PERK pathway activation and tau aggregation. In summary, our brain and cell culture findings implicate PERK as a regulator of tau protein accumulation. PERK pathway activation may have high therapeutic potential for tauopathy treatment.