α-Synuclein Preformed Fibrils Bind to β-Neurexins and Impair β-Neurexin-Mediated Presynaptic Organization

Abstract

Synucleinopathies form a group of neurodegenerative diseases defined by the misfolding and aggregation of α-synuclein (α-syn). Abnormal accumulation and spreading of α-syn aggregates lead to synapse dysfunction and neuronal cell death. Yet, little is known about the synaptic mechanisms underlying the α-syn pathology. Here we identified β-isoforms of neurexins (β-NRXs) as presynaptic organizing proteins that interact with α-syn preformed fibrils (α-syn PFFs), toxic α-syn aggregates, but not α-syn monomers. Our cell surface protein binding assays and surface plasmon resonance assays reveal that α-syn PFFs bind directly to β-NRXs through their N-terminal histidine-rich domain (HRD) at the nanomolar range (KD: ~500 nM monomer equivalent). Furthermore, our artificial synapse formation assays show that α-syn PFFs diminish excitatory and inhibitory presynaptic organization induced by a specific isoform of neuroligin 1 that binds only β-NRXs, but not α-isoforms of neurexins. Thus, our data suggest that α-syn PFFs interact with β-NRXs to inhibit β-NRX-mediated presynaptic organization, providing novel molecular insight into how α-syn PFFs induce synaptic pathology in synucleinopathies such as Parkinson’s disease and dementia with Lewy bodies.

α-Synuclein propagation leads to synaptic abnormalities in the cortex through microglial synapse phagocytosis.

“…Microglial engulfment may not be the sole cause of synapse degeneration during α-synuclein propagation. Other studies have suggested that PFF also impacts the formation and molecular organization of presynaptic terminals by inhibiting βneurexin [34] or by decreasing the levels of soluble α-synuclein [35]. However, it is worth noting that the latter studies examined the direct effects of PFFs on neurons in culture, whereas our study assessed the effects of α-synuclein propagation throughout a neural network in an intact-tissue environment.…”

The immune checkpoint receptor LAG3: Structure, function, and target for cancer immunotherapy

“…This interaction was reported to initiate α-synuclein PFF endocytosis, transmission, and neuronal cell toxicity ( 16 ). However, this study did not rule out possible contributions by other α-synuclein PFF binding partners, for example, neurexin 1β ( 63 ). In addition, a more recent study found no evidence of LAG3 expression in neurons or of a role for LAG3 in modulating α-synucleinopathies ( 64 ).…”

A dual hit of α-synuclein internalization and immune challenge leads to the formation and maintenance of Lewy body-like inclusions in human dopaminergic neurons

“…Purification of α-syn was described previously by Feller et al 103 . In brief, the pGEX-6P-1 plasmid (University of Dundee MRC Protein Phosphorylation and Ubiquitination Unit, DU30005) cloned with full-length human wild-type α-syn was transformed to BL-21(DE3) E.coli.…”

“…Then PFF was sonicated at least 40 cycles of 30-sec on/30-sec off using a Bioruptor ® Pico sonication unit (Diogenode, B01020001). Samples (∼20 μL) were reserved for PFF quality control by thioflavin T assay, dynamic light scattering (using Zetasizer Nano S, Malvern, DLS assay) and TEM imaging as described 103 .…”

“…Characterized PFF were conjugated with 10 nm gold beads (CytoDiagnostics, CGN5K- 10-2), immediately before experimental use, as described by Bayati et al 105 .…”