C9orf72 hexanucleotide repeat expansions impair microglial response in ALS.

Area of Science:

• Neuroscience
• Genetics
• Immunology

Background:

• Microglia and neuroinflammation are implicated in amyotrophic lateral sclerosis (ALS).
• The specific molecular mechanisms driving ALS pathogenesis, particularly in different genetic forms, remain unclear.
• C9orf72 mutations are a common cause of inherited ALS.

Purpose of the Study:

• To investigate the distinct molecular and cellular responses of microglia in sporadic ALS (sALS) versus C9orf72-linked ALS (C9-ALS).
• To elucidate the role of C9orf72 hexanucleotide repeat expansion (HRE) in microglial function and response.
• To identify potential therapeutic targets by understanding subtype-specific cellular alterations in ALS.

Main Methods:

• Single-nuclei RNA sequencing of spinal cord and motor cortex from sALS and C9-ALS patients.
• Human microglia xenograft models to assess C9orf72 mutation effects on microglial activation.
• Induced pluripotent stem cell (iPSC)-derived microglia to confirm endolysosomal pathway alterations.
• Analysis of astrocyte responses and ligand-receptor interactions in microglia and astrocytes.

Main Results:

• C9orf72 is highly expressed in microglia, and its HRE leads to haploinsufficiency.
• sALS microglia adopt disease-associated states, whereas C9-ALS microglia display a blunted response with endolysosomal pathway dysregulation.
• C9orf72 mutations reduce microglial activation in xenograft and iPSC models.
• C9orf72 HRE astrocytes also show diminished responses, with identified dysregulated ligand-receptor pairs in both cell types.

Conclusions:

• Distinct cellular substrates underlie sporadic and C9orf72-linked ALS.
• C9orf72 deficiency impairs microglial and astrocyte responses, contributing to ALS pathogenesis.
• Findings have significant implications for patient stratification and personalized treatment approaches in ALS.