Alpha-synuclein aggregates trigger anti-viral immune pathways and RNA editing in human astrocytes

Parkinson’s disease is a neurodegenerative disease characterised by a proteinopathy with marked astrogliosis. To investigate how a proteinopathy may induce a reactive astrocyte state, and the consequence of reactive astrocytic states on neurons, we generated hiPSC-derived astrocytes, neurons and co-cultures and exposed them to small soluble alpha-synuclein aggregates. Oligomeric alpha-synuclein triggered an inflammatory state associated with TLR activation, viral responses and cytokine secretion. This reactive state resulted in loss of neurosupportive functions, and the induction of neuronal toxicity. Notably, interferon response pathways were activated leading to upregulation, and isoform switching of the RNA deaminase enzyme, ADAR1. ADAR1 mediates A-to-I RNA editing, and increases in RNA editing were observed in inflammatory pathways in cells, as well as in post-mortem human PD brain. Aberrant, or dysregulated, ADAR1 responses and RNA editing may lead to sustained inflammatory reactive states in astrocytes triggered by alpha-synuclein aggregation, and this may drive the neuroinflammatory cascade in Parkinson’s.