Abstract
Synucleinopathies, including Parkinson’s disease (PD), Lewy body dementia (LBD), Alzheimer’s disease with amygdala restricted Lewy bodies (AD/ALB), and multiple system atrophy (MSA) comprise a spectrum of neurodegenerative disorders characterized by the presence of distinct pathological α-synuclein (αSyn) inclusions. Experimental and pathological studies support the notion that αSyn aggregates contribute to cellular demise and dysfunction with disease progression associated with a prion-like spread of αSyn aggregates via conformational templating. The initiating event(s) and factors that contribute to diverse forms of synucleinopathies remain poorly understood. A major post-translational modification of αSyn associated with pathological inclusions is a diverse array of specific truncations within the carboxy terminal region. While these modifications have been shown experimentally to induce and promote αSyn aggregation, little is known about their disease-, region- and cell type specific distribution. To this end, we generated a series of monoclonal antibodies specific to neo-epitopes in αSyn truncated after residues 103, 115, 119, 122, 125, and 129. Immunocytochemical investigations using these new tools revealed striking differences in the αSyn truncation pattern between different synucleinopathies, brain regions and specific cellular populations. In LBD, neuronal inclusions in the substantia nigra and amygdala were positive for αSyn cleaved after residues 103, 119, 122, and 125, but not 115. In contrast, in the same patients' brain αSyn cleaved at residue 115, as well as 103, 119 and 122 were abundant in the dorsal motor nucleus of the vagus. In patients with AD/ALB, these modifications were only weakly or not detected in amygdala αSyn inclusions. αSyn truncated at residues 103, 115, 119, and 125 was readily present in MSA glial cytoplasmic inclusions, but 122 cleaved αSyn was only weakly or not present. Conversely, MSA neuronal pathology in the pontine nuclei was strongly reactive to the αSyn x-122 neo-epitope but did not display any reactivity for αSyn 103 cleavage. These studies demonstrate significant disease-, region- and cell type specific differences in carboxy terminal αSyn processing associated with pathological inclusions that likely contributes to their distinct strain-like prion properties and promotes the diversity displayed in the degrees of these insidious diseases.
Highlights
Parkinson’s disease (PD), Lewy body dementia (LBD) and multiple system atrophy (MSA) are characterized by the progressive accumulation of brain intracytoplasmic inclusions comprised of the protein α-synuclein and are collectively termed α-synucleinopathies [11, 21,22,23, 66]
The positive antibodies were screened by Enzyme‐linked immunosorbent assay (ELISA) using plates coated with recombinant full-length human αSyn, compared to recombinant human αSyn proteins corresponding to the respective carboxy truncation of each antibody, selecting for antibodies against neo-epitopes that would only be present in the truncated proteins and not full-length proteins
It is clear that the presence of preformed fibrillar αSyn seeds can kick-start this process and that different types of seeds have different potencies that can be propagated with altered properties akin to prion-like strains [8, 27, 64]. αSyn carboxy terminal truncation that can result from varied but specific biological activities is a predominant post-translational modification associated with the formation of αSyn pathological inclusions and this type of modification can dramatically promote the aggregation of αSyn, as the highly negatively charged carboxy terminal region inhibits this process when intact
Summary
Parkinson’s disease (PD), Lewy body dementia (LBD) and multiple system atrophy (MSA) are characterized by the progressive accumulation of brain intracytoplasmic inclusions comprised of the protein α-synuclein (αSyn) and are collectively termed α-synucleinopathies [11, 21,22,23, 66]. Previous studies with carboxy truncated specific antibodies have shown that αSyn cleaved after residue 119 is detected in MSA glial cytoplasmic inclusions (GCIs) and Lewy pathology in PD, LBD and incidental Lewy body (LB) disease [1, 38, 50], while reactivity to αSyn cleaved at residues 103 and 122 was detected in Lewy pathology [14, 69] These previous pathological assessments of human tissue were performed with rabbit antibodies to short peptides corresponding to carboxy truncated forms of αSyn at residues 103, 119 and 122 [1, 14, 38, 50, 69] and some of these antibodies were proprietarily generated by Elan Pharmaceuticals (South San Francisco, CA, USA) [1, 50] and are not currently available
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