Widespread loss of the silencing epigenetic mark H3K9me3 in astrocytes and neurons along with hippocampal-dependent cognitive impairment in C9orf72 BAC transgenic mice

Nur Jury,Marcia Manterola,Fabiola Rojas,Miguel V Guerra,Brigitte Van Zundert,Ivan Diaz,Cristian Arredondo,Pablo Martinez,Adriana Rojas,Andrea Herrera-Soto,Paula Cubillos,Martín Montecino,Sebastian Abarzua,Estibaliz Ampuero,Lorena Varela-Nallar

doi:10.1186/s13148-020-0816-9

Abstract

BackgroundHexanucleotide repeat expansions of the G4C2 motif in a non-coding region of the C9ORF72 gene are the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Tissues from C9ALS/FTD patients and from mouse models of ALS show RNA foci, dipeptide-repeat proteins, and notably, widespread alterations in the transcriptome. Epigenetic processes regulate gene expression without changing DNA sequences and therefore could account for the altered transcriptome profiles in C9ALS/FTD; here, we explore whether the critical repressive marks H3K9me2 and H3K9me3 are altered in a recently developed C9ALS/FTD BAC mouse model (C9BAC).ResultsChromocenters that constitute pericentric constitutive heterochromatin were visualized as DAPI- or Nucblue-dense foci in nuclei. Cultured C9BAC astrocytes exhibited a reduced staining signal for H3K9me3 (but not for H3K9me2) at chromocenters that was accompanied by a marked decline in the global nuclear level of this mark. Similar depletion of H3K9me3 at chromocenters was detected in astrocytes and neurons of the spinal cord, motor cortex, and hippocampus of C9BAC mice. The alterations of H3K9me3 in the hippocampus of C9BAC mice led us to identify previously undetected neuronal loss in CA1, CA3, and dentate gyrus, as well as hippocampal-dependent cognitive deficits.ConclusionsOur data indicate that a loss of the repressive mark H3K9me3 in astrocytes and neurons in the central nervous system of C9BAC mice represents a signature during neurodegeneration and memory deficit of C9ALS/FTD.

Highlights

Hexanucleotide repeat expansions of the G4C2 motif in a non-coding region of the C9ORF72 gene are the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD)
Reduced levels of nuclear H3K9me3 in primary spinal cord astrocytes from C9ALS/FTD bacterial artificial chromosomes (BACs) mouse model (C9BAC) mice To explore the role of mono, di, and tri-methylation marks of histone H3 (H3K9me1/me2/me3) and histone modifications in the C9orf72 pathology, we first assessed the subnuclear distribution of these marks in primary cultures of spinal cord astrocytes derived from the recently engineered C9BAC mice [13]
We focused on astrocytes as multiple studies have shown that these glial cells and astrocyte-derived conditioned media (ACM) from cultured mouse and human fALS and sALS astrocytes induce non-cell autonomous toxicity towards motoneurons by releasing soluble neurotoxic factor(s) [33,34,35,36,37]

Summary

Introduction

Hexanucleotide repeat expansions of the G4C2 motif in a non-coding region of the C9ORF72 gene are the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Tissues from C9ALS/FTD patients and from mouse models of ALS show RNA foci, dipeptide-repeat proteins, and notably, widespread alterations in the transcriptome. Analyses of postmortem brain tissues of C9ALS/FTD patients, as well as of patientderived cultured cells, have led to proposed mechanisms whereby C9ORF72 repeat expansions cause the diseases; these include loss of C9ORF72 function (i.e., haploinsufficiency) and gain-of-toxicity from repeat-containing RNAs and aberrant dipeptide-repeat (DPR) proteins, through repeat-associated non-AUG-dependent (RAN) translation [4, 5, 9, 10]. We investigated whether epigenetic processes are aberrant in C9BAC mice that can account for changes in the expression profile reported in C9ALS/FTD

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Conclusion