Astrocytes contribute to toll-like receptor 2-mediated neurodegeneration and alpha-synuclein pathology in a human midbrain Parkinson's model

BackgroundParkinson's disease (PD) is characterised by degeneration of ventral midbrain dopaminergic (DA) neurons and abnormal deposition of alpha-synuclein (alpha-syn) in neurons. Activation of the innate immune pathogen recognition receptor toll-like receptor 2 (TLR2) is associated with exacerbation of alpha-syn pathology. TLR2 is increased on neurons in the PD brain, and its activation results in the accumulation and propagation of alpha-syn through autophagy inhibition in neurons. In addition to the aggregation and propagation of pathological alpha-syn, dysfunction of astrocytes may contribute to DA neuronal death and subsequent clinical progression of PD. However, the role of astrocytes in TLR2-mediated PD pathology is less explored but important to address, given that TLR2 is a potential therapeutic target for PD.MethodsInduced pluripotent stem cells from three controls and three PD patients were differentiated into a midbrain model comprised of neurons (including DA neurons) and astrocytes. Cells were treated with or without the TLR2 agonist Pam3CSK4, and alpha-syn pathology was seeded using pre-formed fibrils. Confocal imaging was used to assess lysosomal function and alpha-syn pathology in the different cell types, as well as DA neuron health and astrocyte activation.ResultsTLR2 activation acutely impaired the autophagy lysosomal pathway, and potentiated alpha-syn pathology seeded by pre-formed fibrils in PD neurons and astrocytes, leading to degeneration and loss of DA neurons. The astrocytes displayed impaired chaperone-mediated autophagy reducing their ability to clear accumulated alpha-syn, and increases of A1 neurotoxic phenotypic proteins SerpinG1, complement C3, PSMB8 and GBP2. Moreover, the phenotypic changes in astrocytes correlated with a specific loss of DA neurons.ConclusionsTaken together, these results support a role for astrocyte dysfunction in alpha-syn accumulation and DA neuronal loss following TLR2 activation in PD.