Histopathological and Biochemical Characterization of a Knockin Mouse Line Expressing Mutant Pdia3 Associated to Intellectual Disability

• Grant number: 24/00316-2
• Support Opportunities: Scholarships in Brazil - Master
• Start date: March 01, 2024
• End date: February 28, 2026
• Field of knowledge: Biological Sciences - Biology
• Principal Investigator: Danilo Bilches Medinas
• Grantee: Rodolfo da Silva Pereira
• Host Institution: Instituto de Química (IQ). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated research grant: 21/06287-6 - Role of protein disulfide isomerase A3 in learning and memory, AP.JP

Abstract

Intellectual disability (ID) encompasses a broad range of conditions with reduced cognitive capacity and adaptive behaviors. The genetic heterogeneity of these conditions poses a challenge for understanding pathogenic mechanisms and designing therapeutic interventions. Given this complex genetic landscape, functional studies of mutant genes are paramount for unveiling molecular networks associated to abnormal development and malfunctioning of the nervous system. Recently, we have discovered a recessive mutation in PDIA3, the gene encoding protein disulfide isomerase A3 (PDIA3), causing severe ID. PDIA3 is an enzyme belonging to the protein disulfide isomerases (PDIs) family, which comprise approximately 20 oxidoreductases localized in the endoplasmic reticulum (ER) that catalyze redox folding of membrane and secreted proteins. This process involves the formation and isomerization of disulfide bonds in the ER, where PDIA3 acts on glycosylated proteins interacting with the lectin-like chaperones calnexin (CNX) and calreticulin (CRT). The non-synonymous mutation in PDIA3 causing ID substitutes a catalytic cysteine residue for tyrosine (p.C57Y), suggesting that loss of PDIA3 enzymatic activity leads to cognitive problems. Alteration of PDIs activity can perturb protein homeostasis (proteostasis) in the ER, leading to accumulation of misfolded and aggregated proteins in the organelle, a condition referred to as ER stress that is associated to several neurological disorders. The ER is a key organelle contributing to neuronal morphogenesis and synaptic transmission. The elucidation of molecular and cellular alterations resulting from PDIA3C57Y expression in different regions of the nervous system can uncover pathogenic mechanisms in ID. Thus, we have generated a mutant Pdia3 knockin (KI) mouse line to recapitulate the neurodevelopmental condition of humans in a tractable experimental model. In this dissertation, we aim to investigate histopathological and biochemical features possibly related to ID in mutant Pdia3 KI mice. We hypothesize that expression of mutant PDIA3 perturbs the redox folding and quality control of proteins in the ER resulting in disruption of neural circuits. Thus, we will perform systematic histological examination of hippocampus and brain cortex to determine whether expression of PDIA3C57Y leads to morphological abnormalities in neurons, alterations in synaptic content, and ER stress responses associated to pathological conditions. In addition, we will conduct unbiased proteomic analysis of protein aggregates and synaptosomes fraction of brain tissue for determination of molecular signatures resulting from PDIA3C57Y expression. Using this experimental strategy, we will generate critical knowledge about the pathogenic mechanisms linking altered ER proteostasis to the etiology of ID.