alpha-Synucleinopathies are neurodegenerative disorders that range pathologically from the demise of select groups of nuclei to pervasive degeneration throughout the neuraxis. Although mounting evidence suggests that alpha-synuclein lesions lead to neurodegeneration, this remains controversial. To explore this issue, we generated transgenic mice expressing wild-type and A53T human alpha-synuclein in CNS neurons. Mice expressing mutant, but not wild-type, alpha-synuclein developed a severe and complex motor impairment leading to paralysis and death. These animals developed age-dependent intracytoplasmic neuronal alpha-synuclein inclusions paralleling disease onset, and the alpha-synuclein inclusions recapitulated features of human counterparts. Moreover, immunoelectron microscopy revealed that the alpha-synuclein inclusions contained 10-16 nm wide fibrils similar to human pathological inclusions. These mice demonstrate that A53T alpha-synuclein leads to the formation of toxic filamentous alpha-synuclein neuronal inclusions that cause neurodegeneration.

Aggregated alpha-synuclein proteins form brain lesions that are hallmarks of neurodegenerative synucleinopathies, and oxidative stress has been implicated in the pathogenesis of some of these disorders. Using antibodies to specific nitrated tyrosine residues in alpha-synuclein, we demonstrate extensive and widespread accumulations of nitrated alpha-synuclein in the signature inclusions of Parkinson's disease, dementia with Lewy bodies, the Lewy body variant of Alzheimer's disease, and multiple system atrophy brains. We also show that nitrated alpha-synuclein is present in the major filamentous building blocks of these inclusions, as well as in the insoluble fractions of affected brain regions of synucleinopathies. The selective and specific nitration of alpha-synuclein in these disorders provides evidence to directly link oxidative and nitrative damage to the onset and progression of neurodegenerative synucleinopathies.

Neuronal and oligodendrocytic aggregates of fibrillar ␣-synuclein define several diseases of the nervous system. It is likely that these inclusions impair vital metabolic processes and compromise vialibity of affected cells. Here, we report that a 12-amino acid stretch ( 71 VT-GVTAVAQKTV 82 ) in the middle of the hydrophobic domain of human ␣-synuclein is necessary and sufficient for its fibrillization based on the following observations: 1) human ␤-synuclein is highly homologous to ␣-synuclein but lacks these 12 residues, and it does not assemble into filaments in vitro; 2) the rate of ␣-synuclein polymerization in vitro decreases after the introduction of a single charged amino acid within these 12 residues, and a deletion within this region abrogates assembly; 3) this stretch of 12 amino acids appears to form the core of ␣-synuclein filaments, because it is resistant to proteolytic digestion in ␣-synuclein filaments; and 4) synthetic peptides corresponding to this 12-amino acid stretch self-polymerize to form filaments, and these peptides promote fibrillization of full-length human ␣-synuclein in vitro. Thus, we have identified key sequence elements necessary for the assembly of human ␣-synuclein into filaments, and these elements may be exploited as targets for the design of drugs that inhibit ␣-synuclein fibrillization and might arrest disease progression.

Alpha-synuclein (alpha-syn) and tau polymerize into amyloid fibrils and form intraneuronal filamentous inclusions characteristic of neurodegenerative diseases. We demonstrate that alpha-syn induces fibrillization of tau and that coincubation of tau and alpha-syn synergistically promotes fibrillization of both proteins. The in vivo relevance of these findings is grounded in the co-occurrence of alpha-syn and tau filamentous amyloid inclusions in humans, in single transgenic mice that express A53T human alpha-syn in neurons, and in oligodendrocytes of bigenic mice that express wild-type human alpha-syn plus P301L mutant tau. This suggests that interactions between alpha-syn and tau can promote their fibrillization and drive the formation of pathological inclusions in human neurodegenerative diseases.