Role of protein disulfide isomerase A3 in learning and memory

Abstract

The redox folding through disulfide bond formation constitutes an essential step for protein homeostasis (or proteostasis) of the endoplasmic reticulum (ER). The oxidizing environment of the ER lumen thermodynamically favors disulfide bond formation, but the numerous combinations between cysteine residues in a polypeptide chain can generate non-native disulfide bonds. These non-native bonds lead to abnormal protein conformations that may result in loss of biological function associated to increased protein degradation or cellular toxicity due to accumulation of protein aggregates in the ER. Protein disulfide isomerases (PDIs) comprise a family of oxidoreductases that catalyze disulfide bond formation, isomerization and reduction in the ER lumen. In this manner, these enzymes circumvent the kinetic barrier for formation of native disulfide bonds and repair abnormal protein conformations containing mispaired cysteine residues. Previously, the dysfunction of PDIs had been implicated in the pathogenesis of neurodegenerative diseases. Recently, our research group has discovered a recessive mutation in PDIA3, encoding protein disulfide isomerase A3 (PDIA3), causing severe intellectual disability (ID) in children. The non-synonymous mutation causing ID substitutes a catalytic cysteine residue for tyrosine (p.C57Y), suggesting that loss of PDIA3 enzymatic activity causes cognitive problems. In this manner, we established that alterations of redox folding in the ER can also underlie the etiology of neurodevelopmental disorders. Despite the clear genetic and biochemical evidence associating PDIA3 to nervous system pathologies, its biological role in neural networks remains unknown. The spatiotemporal study of PDIA3 expression and activity in distinct neuronal populations is needed for determining its contribution to neural processes and how its dysfunction entail neuronal vulnerability in pathological conditions, fostering the development of novel therapeutic approaches. In this proposal, we plan to use a systematic and multidisciplinary strategy to unveil PDIA3 function in ER proteostasis of hippocampal neurons and its importance to learning and memory. We will employ genetic manipulation of Pdia3 in mice to study behavior, followed by detailed histopathological and biochemical analysis to determine relevant cellular and molecular alterations underlying possible cognitive phenotypes. In addition, we will use cell culture for the identification of PDIA3 interactors and substrates, whose relevance for learning and memory will be verified through proteomic analysis of the genetic mouse models. (AU)