The UPR(ER): Sensor and Coordinator of Organismal Homeostasis.

Life is stressful. Organisms are repeatedly exposed to stressors that disrupt protein homeostasis (proteostasis), resulting in protein misfolding and aggregation. To sense and respond to proteotoxic perturbations, cells have evolved compartment-specific stress responses, such as the unfolded protein response of the endoplasmic reticulum (UPR(ER)). However, UPR(ER) function is impaired with age, which, we propose, creates a permissive environment for protein aggregation, unresolved ER stress, and chronic inflammation. Understanding age-related changes to the UPR(ER) will provide new avenues for therapeutic intervention in metabolic disease, neurodegeneration, and aging.