Aggregation promoting C-terminal truncation of α-synuclein is a normal cellular process and is enhanced by the familial Parkinson's disease-linked mutations

Abstract

␣-synucleinopathy ͉ mass spectrometry ͉ proteolysis ͉ Lewy body P arkinson's disease (PD) is a common progressive neurodegenerative disease characterized by the loss of dopaminergic neurons of substantia nigra and the presence of the fibrillar cytoplasmic aggregates of ␣-synuclein (␣-Syn) in multiple brain regions (1, 2). Mutations in the ␣-Syn gene (3-7) and the abnormal aggregation of ␣-Syn are implicated in the pathogenesis of PD, and other related diseases are classified as ␣-synucleinopathies (1, 8-10). ␣-Syn is a highly conserved protein of 140 amino acids that is predominantly expressed in neurons, particularly in presynaptic terminals (11), and may have a role in synaptic plasticity and modulation of dopaminergic neurotransmission (11).Although the bulk of previous studies focused on the aggregation and the biology of the full-length ␣-Syn (␣-SynFL) (12, 13), the conspicuous presence of lower molecular mass ␣-Syn species in ␣-Syn aggregates (14, 15), and the enhanced in vitro fibril assembly of recombinant C-terminally truncated ␣-Syn (16, 17) suggests that the low-molecular mass ␣-Syn species may be of pathogenic significance. However, because postpathogenic and͞or postmortem processes could potentially generate a variety of ␣-Syn species, the significance of low-molecular mass ␣-Syn species to the development of ␣-synucleinopathy is uncertain.Herein, we demonstrate that C-terminally truncated lowmolecular mass ␣-Syn species (␣-Syn⌬C) with aggregationpromoting properties are normally generated in vivo. The expression of familial PD (FPD)-linked mutant human (Hu) ␣-Syn is associated with the higher cellular accumulation of ␣-Syn⌬C. Moreover, human cases with ␣-Syn lesions show preferential accumulation of ␣-Syn⌬C in aggregates and higher relative levels of soluble ␣-Syn⌬C. Our findings show that ␣-Syn⌬Cs are not an artifact of postpathologic processes and are likely to participate in the disease-linked aggregation of ␣-Syn. Materials and MethodsAdditional details are provided in Supporting Materials and Methods, which is published as supporting information on the PNAS web site.

Identification of a helical intermediate in trifluoroethanol-induced alpha-synuclein aggregation

“…We show that αS is likely to aggregate via such an intermediate in the presence of TFE, suggesting that membrane-induced αS aggregation may also involve the formation of a helical intermediate. Furthermore, TFE-induced fibrils are β-sheet rich and resemble previously reported aggregates formed by C terminally truncated αS (11), as well as structures induced by detergent and lipid interactions (12,13), which may be linked to PD initiation and progression (14)(15)(16)(17).…”

Role of Matrix Metalloproteinase 3-mediated α-Synuclein Cleavage in Dopaminergic Cell Death

“…The ability of ␣-synuclein to aggregate and form fibrillar deposits has been shown to play a central role in its pathology. The facts that the presence of C-terminally truncated ␣-synuclein in LB of sporadic PD and LB dementia (9,10), the existence of various lengths of the truncated forms of ␣-synuclein in brain (10,11), and the formation of C-terminally truncated ␣-synuclein in A53T transgenic mice that show motor symptoms (12) implicate the probable involvement of endopeptidases in cleaving ␣-synuclein in brains. In addition, about 15% of ␣-synuclein in LB are truncated forms, and incomplete degradation of ␣-synuclein produced highly amyloidogenic fragments (9,13).…”

Caspase-1 clipping causes complications for α-synuclein

“…There is also mounting evidence that PD-linked missense mutations can enhance the production of C-terminally truncated αSyn species and such truncation of αSyn may also occur in healthy brains (7). The increased brain levels of these fragments observed in PD and dementia with Lewy bodies (DLB) (7,8) and the vulnerability of dopaminergic neurons in αSyn transgenic (tg) rodents to enhanced C-terminal truncation [e.g., due to overexpression (9) or PD-relevant toxins (8)] all argue for a critical threshold of truncated αSyn.…”

“…The increased brain levels of these fragments observed in PD and dementia with Lewy bodies (DLB) (7,8) and the vulnerability of dopaminergic neurons in αSyn transgenic (tg) rodents to enhanced C-terminal truncation [e.g., due to overexpression (9) or PD-relevant toxins (8)] all argue for a critical threshold of truncated αSyn. Notably, such truncated species can accelerate the aggregation of the full-length αSyn protein in vitro (10) and in vivo (11), and thus may contribute to or even initiate the aggregation process.…”

“…Notably, such truncated species can accelerate the aggregation of the full-length αSyn protein in vitro (10) and in vivo (11), and thus may contribute to or even initiate the aggregation process. Numerous laboratories have identified truncated αSyn species in LBs of PD and DLB (7,12) as well as in the oligodendroglial inclusions (GCIs) of multiple system atrophy (MSA) Fig. 1.…”