The study uses multi-omics, biochemical assays, and PFF mouse models to identify tripeptidyl peptidase II (TPPII) as the primary serine endopeptidase that maintains lysosomal function and promotes clearance of α-synuclein seeds, with TPPII overexpression reducing aggregation and propagation in vivo.

By linking a specific, druggable protease to lysosomal degradation of α-synuclein seeds and demonstrating in vivo neuroprotective effects, the work highlights TPPII as a translationally relevant target for therapies (e.g., gene delivery or small-molecule activators) to slow or prevent Parkinson's…

Parkinson's disease is neuropathologically characterized by the progressive loss of dopaminergic neurons and the pathological accumulation of α-synuclein. While these hallmarks are well established, the molecular drivers of this irreversible neurodegenerative process are not fully understood. Through an integrated multi-omics approach combining nascent protein mass spectrometry and bulk RNA sequencing of cellular and transgenic Parkinson's disease mouse models, we revealed suppressed serine endopeptidase activity during the early pathogenic stages of the disease. Subsequent functional analyses identified tripeptidyl peptidase II as the principal enzyme mediating serine endopeptidase activity, as demonstrated through a series of biochemical assays. Mechanistic investigations showed that tripeptidyl peptidase II deficiency impairs lysosomal function, prolongs the clearance of α-synuclein fibrillar seeds, and disrupts synaptic homeostasis in hippocampal neurons. Importantly, overexpression of tripeptidyl peptidase II effectively attenuated pathological α-synuclein aggregation and prevented the cell-to-cell propagation of α-synuclein pathology in wild-type mice injected with α-synuclein preformed fibrils. Our findings establish tripeptidyl peptidase II as a critical regulator of lysosome-mediated amyloidogenic seed degradation and reveal its neuroprotective role against α-synuclein-associated synucleinopathies.