Single-nucleus brain transcriptomics reveals microglia dysfunction in multiple system atrophy

Area of Science:

• Neuroscience
• Immunology
• Genomics

Background:

• Multiple system atrophy (MSA) is a rare neurodegenerative disease with a severe course, sharing features with Parkinson's disease (PD).
• Understanding the distinct cellular pathophysiology of MSA is crucial for developing targeted therapies.

Purpose of the Study:

• To investigate the distinct cellular and molecular differences between MSA and PD using single-nucleus RNA sequencing.
• To identify the roles of glial subtypes and immune responses in the pathophysiology of MSA.

Main Methods:

• Single-nucleus RNA sequencing was performed on postmortem striatal brain tissue from 7 MSA patients, 12 PD patients, and 10 non-neurological controls.
• Comparative analysis of glial (astroglia, microglia, oligodendroglia) and neuronal cell populations and their transcriptomic profiles.
• In vitro assays using induced pluripotent stem cell (iPSC)-derived microglia exposed to patient cerebrospinal fluid (CSF).

Main Results:

• Significant differences in astroglia and microglia subtypes were observed between MSA and PD brains.
• PD brains exhibited proinflammatory microglia and homeostatic astrocytes, whereas MSA brains showed reactive astrocytes and non-activated microglia.
• Transcriptomic analysis indicated compromised oligodendrocyte signaling in MSA and signs of immune tolerance or exhaustion in microglia.
• iPSC-derived microglia showed reduced phagocytic activity when exposed to MSA patient CSF, suggesting impaired immune function.

Conclusions:

• The study highlights distinct glial cell compositions and immune responses in MSA compared to PD.
• Dysfunctional immune responses, including reactive astrocytes and exhausted microglia, may contribute to the more severe neurodegeneration in MSA.
• Impaired microglial phagocytic activity in MSA suggests a novel mechanism contributing to disease progression.