New alpha- and gamma-synuclein immunopathological lesions in human brain

Introduction: Several neurodegenerative diseases are classified as proteopathies as they are associated with the aggregation of misfolded proteins. Synucleinopathies are a group of neurodegenerative disorders associated with abnormal deposition of synucleins. alpha-Synucleinopathies include Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy. Recently accumulation of another member of the synuclein family-gamma-synuclein in neurodegenerative diseases compelled the introduction of the term gamma- synucleinopathy. The formation of aggregates and deposits of gamma-synuclein is facilitated after its oxidation at methionine 38 (Met(38)). Results: Several types of intracytoplasmic inclusions containing post-translationally modified alpha- and gamma-synucleins are detected. Oxidized Met(38)-gamma-synuclein forms aberrant inclusions in amygdala and substantia nigra. Double staining revealed colocalization of oxidized-gamma-synuclein with alpha-synuclein in the cytoplasm of neurons. Another type of synuclein positive inclusions in the amygdala of dementia with Lewy bodies patients has the appearance of Lewy bodies. These inclusions are immunoreactive when analyzed with antibodies to alpha-synuclein phosphorylated on serine 129, as well as with antibodies to oxidized-y-synuclein. Some of these Lewy bodies have doughnut -like shape with round or elongated shape. The separate immunofluorescent images obtained with individual antibodies specific to oxidized-y-synuclein and phospho-alpha-synuclein clearly shows the colocalization of these synuclein isoforms in substantia nigra inclusions. Phospho-alpha-synuclein is present almost exclusively at the periphery of these structures, whereas oxidized-gamma-syn immunoreactivity is also located in the internal parts forming dot-like pattern of staining. We also identified several types of oxidized-gamma-syn positive astrocytes with different morphology and examined their immunohistochemical phenotypes. Some of them are compact cells with short processes, others have longer processes. Oxidized-gamma-synuclein positive astrocytes may also display mixed morphological and immunocytochemical phenotypes between protoplasmic and fibrous astrocytes. Conclusions: These results reveal new gamma-synuclein positive lesions in human brain. Oxidized-y-synuclein is colocalized with phospho-alpha-synuclein in doughnut --like inclusions. Several types of astrocytes with different morphology are immunopositive for oxidized-gamma-synuclein.