α-Synuclein and Its A30P Mutant Affect Actin Cytoskeletal Structure and Dynamics

Abstract

The function of ␣-synuclein, a soluble protein abundant in the brain and concentrated at presynaptic terminals, is still undefined. Yet, ␣-synuclein overexpression and the expression of its A30P mutant are associated with familial Parkinson's disease. Working in cell-free conditions, in two cell lines as well as in primary neurons we demonstrate that ␣-synuclein and its A30P mutant have different effects on actin polymerization. Wild-type ␣-synuclein binds actin, slows down its polymerization and accelerates its depolymerization, probably by monomer sequestration; A30P mutant ␣-synuclein increases the rate of actin polymerization and disrupts the cytoskeleton during reassembly of actin filaments. Consequently, in cells expressing mutant ␣-synuclein, cytoskeleton-dependent processes, such as cell migration, are inhibited, while exo-and endocytic traffic is altered. In hippocampal neurons from mice carrying a deletion of the ␣-synuclein gene, electroporation of wild-type ␣-synuclein increases actin instability during remodeling, with growth of lamellipodia-like structures and apparent cell enlargement, whereas A30P ␣-synuclein induces discrete actin-rich foci during cytoskeleton reassembly. In conclusion, ␣-synuclein appears to play a major role in actin cytoskeletal dynamics and various aspects of microfilament function. Actin cytoskeletal disruption induced by the A30P mutant might alter various cellular processes and thereby play a role in the pathogenesis of neurodegeneration.

GRP78 clustering at the cell surface of neurons transduces the action of exogenous alpha-synuclein

“…27 We previously demonstrated that actin is a target for intracellular Syn, and that wt and A30P-mutated Syn differentially modulate actin dynamics. 13 Here, we provide evidences that the extracellular accumulation of either wt or A30P Syn correlates with an unbalance of actin turnover, resulting in microfilament stabilization. Extracellular Syns, delivered either as purified monomeric proteins in unfolded conformation or with the medium of overexpressing neurons, induced the formation of large lamellipodia-like actin protrusions along the neurites and at their tips.…”

“…We previously demonstrated that Syn can physiologically control actin turnover, activity that is altered in the Syn A30P mutant. 13 As Syn is released from neurons, we wondered whether high levels of extracellular Syn could affect actin dynamics in a similar way. The morphology of the actin cytoskeleton was monitored in young hippocampal neurons after incubation for 1 h with 1 mM purified human recombinant wt or A30P Syn.…”

“…Constructs encoding the human full-length wt or A30P Syn inserted in the pET21d plasmid were a kind gift from Dr. Brett Lauring (Columbia University, New York, NY, USA). Purification was performed as in, 13 followed by gel filtration in Superdex 75 10/300 column (GE Healthcare Life Sciences, Uppsala, Sweden). Denaturing of Syns was achieved by boiling the proteins for 5 min at 100 1C.…”

“…The influence of Syn on the microtubule-based cytoskeleton has been characterized in vitro. 12 Recently, 13 Syn has been shown to depolymerize actin cytoskeleton, a master regulator of synaptic function, 14 raising the possibility that the effects of Syn on synaptic vesicle dynamics are mediated by its interaction with actin.…”

Mechanisms Implicated in Parkinson Disease from Genetic Perspective

“…Through the animal experiments was shown that α-synuclein participates in the trafficking of synaptic vesicles and in the regulation of the exocytic [31] and fusion processes [32]. One of its roles in synaptic activity is performed by interaction with actin in order to regulate the synaptic vesicle mobilization [33] demonstrated by inhibition of actin polymerization and cytoskeletal disruption caused by the mutant α-synuclein [34]. α-synuclein is involved in the SNARE-complex assembly with possible implications during aging [35].…”