Neurobehavioral deficits of mice expressing a low level of G127V mutant frataxin

Daniel Fil; Robbie L Conley; Aamir R Zuberi; Cathleen M Lutz; Terry Gemelli; Marek Napierala; Jill S Napierala

doi:10.1016/j.nbd.2023.105996

Neurobehavioral deficits of mice expressing a low level of G127V mutant frataxin

Neurobiol Dis. 2023 Feb:177:105996. doi: 10.1016/j.nbd.2023.105996. Epub 2023 Jan 10.

Authors

Daniel Fil¹, Robbie L Conley¹, Aamir R Zuberi², Cathleen M Lutz³, Terry Gemelli⁴, Marek Napierala¹, Jill S Napierala⁵

Affiliations

¹ Department of Biochemistry and Molecular Genetics, University of Alabama at Birmingham, Birmingham, AL 35294, USA.
² Technology Evaluation and Development, JAX Center for Precision Genetics, Rare Disease Translational Center, The Jackson Laboratory, Bar Harbor, ME 04609, USA.
³ The Rare and Orphan Disease Center, JAX Center for Precision Genetics, Rare Disease Translational Center, The Jackson Laboratory, Bar Harbor, ME 04609, USA.
⁴ Department of Neurology, Peter O'Donnell Jr. Brain Institute, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
⁵ Department of Biochemistry and Molecular Genetics, University of Alabama at Birmingham, Birmingham, AL 35294, USA. Electronic address: Jill.Napierala@UTSouthwestern.edu.

Abstract

Friedreich's ataxia (FRDA) is a neurodegenerative disease caused by reduced expression of the mitochondrial protein frataxin (FXN). Most FRDA patients are homozygous for large expansions of GAA repeats in intron 1 of FXN, while some are compound heterozygotes with an expanded GAA tract in one allele and a missense or nonsense mutation in the other. A missense mutation, changing a glycine to valine at position 130 (G130V), is prevalent among the clinical variants. We and others have demonstrated that levels of mature FXN protein in FRDA G130V samples are reduced below those detected in samples harboring homozygous repeat expansions. Little is known regarding expression and function of endogenous FXN-G130V protein due to lack of reagents and models that can distinguish the mutant FXN protein from the wild-type FXN produced from the GAA-expanded allele. We aimed to determine the effect of the G130V (murine G127V) mutation on Fxn expression and to define its multi-system impact in vivo. We used CRISPR/Cas9 to introduce the G127V missense mutation in the Fxn coding sequence and generated homozygous mice (Fxn^G127V/G127V). We also introduced the G127V mutation into a GAA repeat expansion FRDA mouse model (Fxn^GAA230/KO; KIKO) to generate a compound heterozygous strain (Fxn^G127V/GAA230). We performed neurobehavioral tests on cohorts of WT and Fxn mutant animals at three-month intervals for one year, and collected tissue samples to analyze molecular changes during that time. The endogenous Fxn G127V protein is detected at much lower levels in all tissues analyzed from Fxn^G127V/G127V mice compared to age and sex-matched WT mice without differences in Fxn transcript levels. Fxn^G127V/G127V mice are significantly smaller than WT counterparts, but perform similarly in most neurobehavioral tasks. RNA sequencing analysis revealed reduced expression of genes in oxidative phosphorylation and protein synthesis, underscoring the metabolic consequences in our mouse model expressing extremely low levels of Fxn. Results of these studies provide insight into the unique pathogenic mechanism of the FXN G130V mechanism and the tolerable limit of Fxn/FXN expression in vivo.

Keywords: Frataxin; Friedreich's ataxia; Mitochondria; Point mutation.

Publication types

Research Support, N.I.H., Extramural
Research Support, Non-U.S. Gov't

MeSH terms

Animals
Disease Models, Animal
Frataxin
Friedreich Ataxia* / metabolism
Iron-Binding Proteins / genetics
Iron-Binding Proteins / metabolism
Mice
Neurodegenerative Diseases* / genetics
Protein Biosynthesis
Trinucleotide Repeat Expansion

Substances

Iron-Binding Proteins

Abstract

Publication types

MeSH terms

Substances

Grants and funding