Exogenous Alpha-Synuclein Alters Pre- and Post-Synaptic Activity by Fragmenting Lipid Rafts

• Extracellular αSyn disrupts lipid raft platforms with consequent mislocalization of several pre- and post-synaptic proteins.
• αSyn-driven changes in raft-partitioning of proteins blunt neurotransmission and LTP.
• Cholesterol loading and inhibition of CK2 restore αSyn-induced alterations of the post-synaptic density assembly.Alpha-synuclein (αSyn), a cytosolic protein that can be released from neurons, becomes pathogenic when expressed at high levels, as in Parkinson's disease, due to multiplication of αSyn gene. We show that the mechanism responsible for the defects in synaptic vesicles mobilization and post-synaptic activity induced by extracellular αSyn is the fragmentation of lipid rafts, cholesterol-rich microdomains of the plasma membrane. Moreover restoration of lipid raft platforms and raft-partitioning of surface proteins prevents the alteration of synaptic transmission caused by exposure of neurons to αSyn.

Alpha-synuclein (αSyn) interferes with multiple steps of synaptic activity at pre-and post-synaptic terminals, however the mechanism/s by which αSyn alters neurotransmitter release and synaptic potentiation is unclear. By atomic force microscopy we show that human αSyn, when incubated with reconstituted membrane bilayer, induces lipid rafts' fragmentation. As a consequence, ion channels and receptors are displaced from lipid rafts with consequent changes in their activity. The enhanced calcium entry leads to acute mobilization of synaptic vesicles, and exhaustion of neurotransmission at later stages. At the post-synaptic terminal, an acute increase in glutamatergic transmission, with increased density of PSD-95 puncta, is followed by disruption of the interaction between N-methyl-d-aspartate receptor (NMDAR) and PSD-95 with ensuing decrease of long term potentiation. While cholesterol loading prevents the acute effect of αSyn at the presynapse; inhibition of casein kinase 2, which appears activated by reduction of cholesterol, restores the correct localization and clustering of NMDARs.