# C9orf72 poly(glycine-alanine) knock-in mice exhibit mild rotarod and proteomic changes consistent with amyotrophic lateral sclerosis/frontotemporal dementia

## TL;DR

Researchers created mice with a genetic mutation linked to ALS and FTD, observing subtle motor and protein changes that may help understand disease mechanisms.

## Contribution

The study introduces a new mouse model expressing polyGA, a protein linked to ALS/FTD, revealing distinct proteomic effects.

## Key findings

- PolyGA knock-in mice show impaired rotarod performance without major neuropathology.
- Proteomic changes in the spinal cord include alterations in known polyGA interactors.
- The polyGA model shows a distinct proteomic response compared to other C9orf72 models.

## Abstract

A GGGGCC repeat expansion in C9orf72 is the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). The repeat expansion is translated into five different dipeptide repeat proteins: poly(glycine-alanine) (polyGA), poly(glycine-proline) (polyGP), poly(glycine-arginine) (polyGR), poly(alanine-proline) (polyAP) and poly(proline-arginine) (polyPR). To investigate the effect of polyGA, which is the most abundant dipeptide repeat protein in patient brains, we used clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR associated nuclease 9 (Cas9) to insert 400 codon-optimized polyGA repeats immediately downstream of the mouse C9orf72 start codon. This generated (GA)400 knock-in mice driven by the endogenous mouse C9orf72 promoter, coupled with heterozygous C9orf72 reduction. PolyGA remains soluble up to 18 months of age and (GA)400 mice develop subtle dysfunction characterized by impaired rotarod performance, without overt neuropathological alterations. Quantitative proteomics revealed polyGA expression caused protein alterations in the spinal cord, including changes in previously identified polyGA interactors. Our findings show that (GA)400 mice are a complementary in vivo model to better understand C9orf72 ALS/FTD pathology and determine the specific role of individual DPRs in disease.

Milioto et al. develop C9orf72 poly(glycine-alanine) (polyGA) knock-in mice to model frontotemporal dementia and amyotrophic lateral sclerosis. Soluble polyGA is generated, which causes impaired rotarod ability and proteomic alterations that overlap with polyGA interactors but not other C9orf72 knock-in mouse model proteome changes, indicating a distinct response to polyGA.

Graphical AbstractFor image description, please refer to the figure legend and surrounding text.