The D826V point mutation in IREB2 causes early-onset neurodegeneration in mice

Abstract

The iron regulatory protein IREB2 (Iron Responsive Element Binding Protein 2) plays a crucial role in maintaining cellular iron homeostasis through the posttranscriptional regulation of genes involved in iron metabolism. Mutations in the IREB2 gene have been linked to NDCAMA (OMIM#618451), a rare genetic neurological disorder characterized by early-onset neurodegeneration, choreoathetoid movements, and microcytic anemia. However, the absence of an IREB2-mutated animal model has left the underlying pathogenic mechanisms poorly understood. To investigate this, we establish a CRISPR-Cas9-mediated Ireb2D826V/D826V mouse model, which carries the c.2477A>T (p.D826V) pathogenic variant in IREB2 identified in a Chinese pedigree with NDCAMA. Behavioral studies, including the Morris water maze (MWM), open field test (OFT), and Y-maze, reveal significant neurobehavioral deficits, such as impaired spatial learning and memory and reduced motor activity, in Ireb2D826V/D826V mice. Furthermore, we observe increased microglial activation and decreased dendritic spine density in the hippocampus, along with impaired long-term potentiation (LTP) and elevated paired-pulse facilitation (PPF), indicating synaptic dysfunction. Mechanistically, Ireb2D826V/D826V mice present reduced Ireb2 protein levels, dysregulated iron metabolism, and an altered expression profile associated with neurological function. This study elucidates the molecular mechanisms underlying NDCAMA and establishes Ireb2D826V/D826V mice as a model for iron metabolism-driven neurodegeneration. This finding links the instability of IREB2 to synaptic failure and neuroinflammation, highlighting potential therapeutic implications for neurodegenerative diseases.

1. Introduction

Iron homeostasis is critically regulated by IREB2, an RNA-binding protein that coordinates cellular iron uptake and storage through its interaction with iron-responsive elements (IREs) in target mRNAs, including the transferrin receptor (TFRC) and the heavy and light ferritin chains (FTH1 and FTL) [1–3]. Dysregulated iron metabolism has increasingly been implicated in neurodegenerative diseases, such as Alzheimer’s disease (AD), Parkinson’s disease (PD), amyotrophic lateral sclerosis (ALS), and Huntington’s disease (HD) [4–10]. Notably, mutations in IREB2 are associated with NDCAMA (OMIM#618451), an autosomal recessive disorder characterized by severe psychomotor developmental abnormalities, abnormal movements, and functional iron deficiency [11–13]. Despite this association, the molecular pathways linking IREB2 dysfunction to neuronal degeneration remain undefined.

We previously identified a novel IREB2 c.2477A>T (p.D826V) variant in a patient with NDCAMA, which is predicted to destabilize IREB2 through increased proteasomal degradation [14]. To elucidate its pathogenic role, we engineered Ireb2D826V/D826V mice via CRISPR-Cas9 technology. Given the vulnerability of the hippocampus to neurodegenerative processes [15–17], we prioritized investigations in this region. Neurodegenerative pathogenesis often involves synaptic dysfunction and neuroinflammation [18,19]. Microglial activation, a hallmark of central nervous system (CNS) injury, exacerbates synaptic loss through proinflammatory signaling [20,21], whereas the dysregulation of iron directly impairs neuronal plasticity [22].

In this study, we integrate behavioral, electrophysiological, and transcriptomic approaches to elucidate how destabilization of IREB2 disrupts iron homeostasis, the synaptic architecture, and immune responses. Our findings connect defects in iron metabolism to neurodegenerative pathways, providing mechanistic insights into NDCAMA and broader neurodegenerative contexts.