ABSTRACT: Genetic variants that hinder post-translational protein modifications by UFM1, UFMylation, cause encephalopathies. UFMylation regulates endoplasmic reticulum (ER) homeostasis, but how UFMylation-deficiencies cause selective neurological defects is unknown. Using Ufm1 knock-out mice, we investigated two types of UFMylation pathologies, UFM1 loss and expression of a pathogenic UFM1-R81C variant. We found that UFM1-deficiency confounds neuron development and synapse function. Mechanistically, UFM1 loss is associated with induction of ER stress, activation of the PERK-UPR pathway, and reduced protein translation. These defects are rescued by wild-type UFM1, but only partially by UFM1-R81C. UFM1-deficient and UFM1-R81Cexpressing neurons display distinct responses to ER stress, indicating that UFM1-R81C is not merely a loss-of-function variant. Exploring therapeutic options, we show that the PERK-UPR inhibitor Trazodone restores protein translation solely in UFM1-R81C-expressing neurons, and increases synapse number. Our study unveils a pivotal role for UFMylation in neuronal development, provides a molecular understanding of the signaling mechanisms altered in UFM1- associated encephalopathies, and offers important insights into potential treatments for these Genetic variants that hinder post-translational protein modifications by UFM1, UFMylation, cause encephalopathies. UFMylation regulates endoplasmic reticulum (ER) homeostasis, but how UFMylation-deficiencies cause selective neurological defects is unknown. Using Ufm1 knock-out mice, we investigated two types of UFMylation pathologies, UFM1 loss and expression of a pathogenic UFM1-R81C variant. We found that UFM1-deficiency confounds neuron development and synapse function. Mechanistically, UFM1 loss is associated with induction of ER stress, activation of the PERK-UPR pathway, and reduced protein translation. These defects are rescued by wild-type UFM1, but only partially by UFM1-R81C. UFM1-deficient and UFM1-R81C-expressing neurons display distinct responses to ER stress, indicating that UFM1-R81C is not merely a loss-of-function variant. Exploring therapeutic options, we show that the PERK-UPR inhibitor Trazodone restores protein translation solely in UFM1-R81C-expressing neurons, initiating an increase in synapse number. Our study unveils a pivotal role for UFMylation in neuronal development and provides a molecular understanding of the signaling mechanisms altered in UFM1-associated encephalopathies, offering valuable insights into potential treatments for these disorders.
