Genetically encoded fluorescent reporters to visualize α-synuclein pathology in live brain

Lewy bodies, a pathological hallmark of Parkinson's disease, are α-synuclein-enriched cytoplasmic inclusions that drive progressive neurodegeneration. A long-standing yet unmet goal has been the visualization of α-synuclein (α-Syn) inclusions in live brain and measurements of their pathological effects on individual neurons. Here, we developed genetically encoded reporters and knock-in mouse lines to achieve this goal. The reporters exhibited a 5-fold increase in fluorescence upon incorporation into α-Syn inclusions. They reliably reflected α-Syn inclusion propagation in the cortex of awake mice. Coupled with Ca²⁺ imaging and whole-cell recording, the reporters enabled measurement of the pathological effects of inclusions on neuronal activity and synaptic function. They could be selectively targeted to specific neuronal subtypes, facilitating measurement of the pathological effects on transcriptomes and metabolomes at the single-cell level. In live-cell imaging, the reporters helped identify inhibitors of α-Syn inclusion formation. Collectively, these genetically encoded reporters support multiple applications to study α-Syn inclusions in live brain.