Motor dysfunction and neurodegeneration in a C9orf72 mouse line expressing poly-PR

Zongbing Hao,Rui Wang,Zhouteng Tao,Hongyang Sun,Zhixiong Zhang,Liu Liu,Haigang Ren,Zixuan Lin,Jiawei Zhou,Guanghui Wang,Chenchen Mu

doi:10.1038/s41467-019-10956-w

Abstract

A GGGGCC hexanucleotide repeat expansion in intron 1 of chromosome 9 open reading frame 72 (C9ORF72) gene is the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia. Repeat-associated non-ATG translation of dipeptide repeat proteins (DPRs) contributes to the neuropathological features of c9FTD/ALS. Among the five DPRs, arginine-rich poly-PR are reported to be the most toxic. Here, we generate a transgenic mouse line that expresses poly-PR (GFP-PR28) specifically in neurons. GFP-PR28 homozygous mice show decreased survival time, while the heterozygous mice show motor imbalance, decreased brain weight, loss of Purkinje cells and lower motor neurons, and inflammation in the cerebellum and spinal cord. Transcriptional analysis shows that in the cerebellum, GFP-PR28 heterozygous mice show differential expression of genes related to synaptic transmission. Our findings show that GFP-PR28 transgenic mice partly model neuropathological features of c9FTD/ALS, and show a role for poly-PR in neurodegeneration.

Highlights

A GGGGCC hexanucleotide repeat expansion in intron 1 of chromosome 9 open reading frame 72 (C9ORF72) gene is the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia
As the expression of GFP-PR28 was localized in Purkinje cells of the cerebellum, and GFP-PR28 transgenic mice showed obvious motor imbalance, we evaluated the numbers of Purkinje cell in the cerebellum
As motor behavior defects can be attributed to the loss of upper and lower motor neurons, we evaluated the number of motor neurons in the motor cortex and lumbar spinal cord at 2, 6, and 12 months of age

Summary

Introduction

A GGGGCC hexanucleotide repeat expansion in intron 1 of chromosome 9 open reading frame 72 (C9ORF72) gene is the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia. The BAC transgenic mouse lines display RNA foci and dipeptide-repeat protein (DPR) inclusions of c9FTD/ALS, either with or without a phenotype or neurodegeneration that may be associated with expression level, age, and repeat length in animals[12,18,19,20]. Several groups have generated C9ORF72 BAC transgenic mice, which suggest that gain of function may be a primary cause of c9FTD/ALS12,18–20. Expression of DPRs in primary cultured neurons and flies, especially poly-PR and poly-GR, is toxic to neurons[23] It remains unclear whether the poly-PR is sufficient to induce neurodegeneration and behavioral changes in mice. Our results show that GFP-PR28 homozygous mice decrease survival, while GFP-PR28 heterozygous mice develop DPR inclusions and show atrophy of the cerebral cortex and loss of Purkinje cells in the cerebellum and motor neurons in the spinal cord. Gene Ontology (GO) analyses after RNA sequencing suggest a dysregulation of synaptic transmissionrelated genes and activation of inflammation in the GFP-PR28 heterozygous mice

Methods

Results

Conclusion