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

A missense mutation, changing a glycine to valine at position 130 (G130V) in frataxin, is prevalent among the clinical variants in FRDA. 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. This group aimed to determine the effect of the G130V (murine G127V) mutation on Fxn expression and to define its multi-system impact in vivo. CRISPR/Cas9 was used to introduce the G127V missense mutation in the Fxn coding sequence and homozygous mice (FxnG127V/G127V) were generated. The G127V mutation was also introduced into a GAA repeat expansion FRDA mouse model (FxnGAA230/KO; KIKO) to generate a compound heterozygous strain (FxnG127V/GAA230). The investigators 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 FxnG127V/G127V mice compared to age and sex-matched WT mice without differences in Fxn transcript levels. FxnG127V/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.

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