Rational design of structure-based vaccines targeting misfolded alpha-synuclein conformers of Parkinson's disease and related disorders

Abstract

BackgroundSynucleinopathies, including Parkinsons disease, multiple system atrophy, and dementia with Lewy bodies, are neurodegenerative disorders caused by the accumulation of misfolded alpha-synuclein protein. Developing effective vaccines against synucleinopathies has been challenging due to the difficulty of stimulating an immune-specific response against alpha-synuclein, conferring neuroprotection without causing harmful autoimmune reactions, and selectively targeting only pathological forms of alpha-synuclein. Previous attempts using linear peptides and epitopes without control of the antigen structure for immunization failed in clinical trials. The immune system was unable to distinguish between the native alpha-synuclein and its amyloid form. ResultsThe prion domain of the fungal HET-s protein was selected as a scaffold to introduce select epitopes from the surface of alpha-synuclein fibrils. Four vaccine candidates were generated by introducing specific amino acid substitutions onto the surface of the scaffold protein in regions that showed structural similarity to alpha-synuclein fibril structures. Each vaccine candidate had unique amino acid substitutions that imitated a specific epitope from alpha-synuclein amyloid fibrils. The approach successfully mimicked the stacking of the parallel in-register beta-sheet structure seen in alpha-synuclein fibrils as the vaccine candidates were found to be structurally stable and self-assembling into the desired conformations. All vaccine candidates induced substantial levels of IgG antibodies that recognized pathological alpha-synuclein fibrils derived from a synucleinopathy mouse model. Furthermore, the resulting anti-sera recognized pathological alpha-synuclein aggregates in brain lysates from patients who died from dementia with Lewy bodies, multiple system atrophy, or Parkinsons disease, but did not recognize linear alpha-synuclein peptides. Each vaccine candidate induced a unique pattern of reactivity toward alpha-synuclein aggregates contained in distinct disease pathologies. ConclusionsThis new approach, based on the rational design of vaccines using the secondary and tertiary structure of alpha-synuclein amyloid fibrils and strict control over the exposed antigen structure used for immunization, as well as the ability to mimic aggregated alpha-synuclein, provides a promising avenue towards developing effective vaccines against alpha-synuclein fibrils, which may be crucial for the prevention and treatment of synucleinopathies.