LRP1 is a neuronal receptor for α-synuclein uptake and spread

Abstract

Background The aggregation and spread of α-synuclein (α-Syn) protein and related neuronal toxicity are the key pathological features of Parkinson’s disease (PD) and Lewy body dementia (LBD). Studies have shown that pathological species of α-Syn and tau can spread in a prion-like manner between neurons, although these two proteins have distinct pathological roles and contribute to different neurodegenerative diseases. It is reported that the low-density lipoprotein receptor-related protein 1 (LRP1) regulates the spread of tau proteins; however, the molecular regulatory mechanisms of α-Syn uptake and spread, and whether it is also regulated by LRP1, remain poorly understood. Methods We established LRP1 knockout (LRP1-KO) human induced pluripotent stem cells (iPSCs) isogenic lines using a CRISPR/Cas9 strategy and generated iPSC-derived neurons (iPSNs) to test the role of LRP1 in α-Syn uptake. We treated the iPSNs with fluorescently labeled α-Syn protein and measured the internalization of α-Syn using flow cytometry. Three forms of α-Syn species were tested: monomers, oligomers, and pre-formed fibrils (PFFs). To examine whether the lysine residues of α-Syn are involved in LRP1-mediated uptake, we capped the amines of lysines on α-Syn with sulfo-NHS acetate and then measured the internalization. We also tested whether the N-terminus of α-Syn is critical for LRP1-mediated internalization. Lastly, we investigated the role of Lrp1 in regulating α-Syn spread with a neuronal Lrp1 conditional knockout (Lrp1-nKO) mouse model. We generated adeno-associated viruses (AAVs) that allowed for distinguishing the α-Syn expression versus spread and injected them into the hippocampus of six-month-old Lrp1-nKO mice and the littermate wild type (WT) controls. The spread of α-Syn was evaluated three months after the injection. Results We found that the uptake of both monomeric and oligomeric α-Syn was significantly reduced in iPSNs with LRP1-KO compared with the WT controls. The uptake of α-Syn PFFs was also inhibited in LRP1-KO iPSNs, albeit to a much lesser extent compared to α-Syn monomers and oligomers. The blocking of lysine residues on α-Syn effectively decreased the uptake of α-Syn in iPSNs and the N-terminus of α-Syn was critical for LRP1-mediated α-Syn uptake. Finally, in the Lrp1-nKO mice, the spread of α-Syn was significantly reduced compared with the WT littermates. Conclusions We identified LRP1 as a key regulator of α-Syn neuronal uptake, as well as an important mediator of α-Syn spread in the brain. This study provides new knowledge on the physiological and pathological role of LRP1 in α-Syn trafficking and pathology, offering insight for the treatment of synucleinopathies.

Synucleins: New Data on Misfolding, Aggregation and Role in Diseases

“…Recent studies indicated an essential role of low-density lipoprotein receptor-related protein 1 (LRP1) in α-synuclein spreading between cells [ 54 ]. LPR1 is a highly expressed central nervous system protein receptor involved in intracellular signaling and endocytosis.…”

“…It is located predominantly in the plasma membrane. Chen et al [ 54 ], using LRP1 knockout (LRP1-KO) induced pluripotent stem cells (iPSCs), demonstrated that LRP1 is a vital regulator of α-synuclein neuronal uptake and mediator of its spread in the brain. LRP1 binds to the N-terminus of α-synuclein through lysine residues, being a key regulator for the endocytosis of both monomeric and oligomeric forms of α-synuclein.…”

Molecular and Cellular Interactions in Pathogenesis of Sporadic Parkinson Disease

“…αSyn fibrils can spread from cell to cell, contributing to pathogenicity [ 140 , 141 ]. LRP1 was recently shown to be a key regulator of αSyn neuronal uptake, as well as an important mediator of αSyn spread in the brain [ 17 ]; previously it was mainly known to regulate the spread of tau proteins [ 142 ]. At the same time, the expression of LRP1 is lowered in the brain endothelial cells of PD patients, breaking the maintenance of the BBB [ 143 ].…”

“…This is facilitated by the expression of inflammatory cytokines that disrupt the blood–brain barrier (BBB) [ 16 ]. Other factors than inflammatory cytokines, e.g., cell membrane receptors, such as low-density lipoprotein receptor-related protein 1 (LRP1), lymphocyte activation gene 3 (LAG3) and amyloid precursor-like protein 1 (APLP1) are involved in cell-to-cell transmission [ 17 , 18 ].…”

LRP1: a novel receptor for the transmission of pathological α-Synuclein

“…The authors then established a murine model that discriminates between neurons transduced with the adeno-associated virus expressing human α-syn and neurons that receive human α-syn through spreading. Using this novel model, they demonstrated that the deletion of LRP1 in the neurons suppresses the transmission of human α-syn in mice [ 8 ].…”