Transmission of peripheral blood α-synuclein fibrils exacerbates synucleinopathy and neurodegeneration in Parkinson's disease by endothelial Lag3 endocytosis.

Parkinson's disease (PD) is an age-related neurodegenerative disorder. The pathological feature of PD is abnormal α-synuclein (α-syn) formation and transmission. Recent evidence demonstrates that α-syn preformed fibrils (α-syn PFFs) can be detected in the serum of patients with PD. The peripheral blood α-syn PFF can cross the blood-brain barrier (BBB) and aggravate neuronal damage, but the mechanism remains to be elucidated. We constructed the PD mouse models of different severity: the mild pathology (A53T ONLY) and the severe pathology (A53T + Brain FIB); this was followed by α-syn PFFs intravenous injection. Then, we used endothelium-specific Lag3 knockout mice (Lag3-ECs-CKO) to decrease the blood α-syn PFFs spreading. We observed that intravenous transmission of α-syn PFFs significantly aggravated motor deficits, dopaminergic neuron loss, neuroinflammation, and pathologic α-syn deposition in A53T ONLY, but not in A53T + Brain FIB. Blocking endothelial Lag3 endocytosis by Lag3-ECs-CKO decreased the blood α-syn PFFs spreading and improved the symptoms and pathogenesis of PD mice. Our findings reveal the role of peripheral blood α-syn PFFs transmission in the mild pathology or early-stage PD and the mechanism of endothelial Lag3 endocytosis in the pathology of α-syn transmission. Targeting endothelial Lag3 to prevent α-syn from spreading from the blood to the brain may be a disease-modifying therapy in early-stage PD. This study highlights the transmission mechanism of peripheral blood α-synuclein preformed fibrils (α-syn PFFs) through endothelial Lag3 endocytosis in the mild pathology or early-stage Parkinson's disease (PD). Targeting endothelial Lag3 as a perspective of decreasing peripheral blood α-syn PFFs transmission may be a disease-modifying therapy in early-stage PD.