α‐synuclein assemblies sequester neuronal α3‐Na⁺/K⁺‐ATPase and impair Na⁺ gradient

Abstract

Extracellular a-synuclein (a-syn) assemblies can be up-taken by neurons; however, their interaction with the plasma membrane and proteins has not been studied specifically. Here we demonstrate that a-syn assemblies form clusters within the plasma membrane of neurons. Using a proteomic-based approach, we identify the a3-subunit of Na + /K + -ATPase (NKA) as a cell surface partner of a-syn assemblies. The interaction strength depended on the state of a-syn, fibrils being the strongest, oligomers weak, and monomers none. Mutations within the neuron-specific a3-subunit are linked to rapid-onset dystonia Parkinsonism (RDP) and alternating hemiplegia of childhood (AHC). We show that freely diffusing a3-NKA are trapped within a-syn clusters resulting in a3-NKA redistribution and formation of larger nanoclusters. This creates regions within the plasma membrane with reduced local densities of a3-NKA, thereby decreasing the efficiency of Na + extrusion following stimulus. Thus, interactions of a3-NKA with extracellular a-syn assemblies reduce its pumping activity as its mutations in RDP/AHC.

Pathological α-synuclein transmission initiated by binding lymphocyte-activation gene 3

“…A recent study also identified neurexin 1α and 2α as α-syn fibril binding partners (32). The Toll-like receptor 2 (TLR2) on microglia was shown to be involved in the activation of microglia due to exposure to oligomeric α-syn from conditioned neuronal media (38).…”

“…The Toll-like receptor 2 (TLR2) on microglia was shown to be involved in the activation of microglia due to exposure to oligomeric α-syn from conditioned neuronal media (38). Heparan sulfate proteoglycans (HSPGs) can mediate α-syn aggregate uptake and seeding via micropinocytosis (39) and the Α3-subnit of the Na + /K + -ATPase (α3-NKA) binds to α-syn fibrils and oligomers (32). Whether these alternative α-syn binding partners contribute to α-syn transmission and pathogenesis and how they might interact with LAG3 requires further study.…”

“…Since deletion of the LAG3 ICD domain may reduce α-syn PFF toxicity, signaling through the ICD of LAG3 may contribute to α-syn PFF toxicity. Furthermore, since calcium might be involved in α-synuclein-induced neurotoxicity (13, 28–32), calcium influx was monitored in response to α-syn PFF. Perfusion of α-syn PFF (500 nM) onto WT cortical neurons led to a gradual increase in intracellular calcium levels (fig.…”

“…Co-localization of internalized α-syn-biotin PFF and Rab5 was assessed by confocal microscopy, scale bar, 10 µm. ( D ) Quantification of panel C, cell number (13–32) from n = 4. One-way ANOVA with Tukey’s correction.…”

Selective neuronal vulnerability in Parkinson disease

“…Similarly, proteins extracted from human brains with LP (which would contain α-syn fibrils and other LP proteins) and injected into the striatum of monkeys can retrogradely propagate 28 . Recent work has identified surface proteins (such as lymphocyte activation gene 3 protein and neurexins) that specifically interact with α-syn fibrils and are necessary for spreading 29,30 . In spite of the methodological and biological issues surrounding these studies (such as dose dependence and cellular specificity 31–33 ), they do demonstrate that extracellular α-syn fibrils can be taken up and retrogradely (and possibly anterogradely) transported, and can induce LP-like pathology.…”