Patterns of protein nitration in dementia with Lewy bodies and striatonigral degeneration

Abstract.

The synucleinopathies are a group of neurodegenerative disorders characterized by the presence of α-synuclein inclusions in neurons (Lewy body diseases, LBD) or glial cells (multiple system atrophies, MSA). Recently, nitration of α-synuclein has been reported as the possible modification that induces its aggregation and deposition in these disorders. In this study we investigated the distribution and relationships of α-synuclein inclusions and 3-nitrotyrosine (3-NT), a marker of protein nitration through oxidative mechanisms, in brains diagnosed with LBD or MSA and control brains using double immunohistochemical techniques. In LBD cases, 3-NT colocalized with α-synuclein immunoreactivity in classic and cortical Lewy bodies and in dystrophic neurites in substantia nigra. However, most pale bodies and diffuse deposits in substantia nigra and Lewy neurites in hippocampus lack 3-NT immunoreactivity. A majority of cases showed diffuse cytoplasmic 3-NT staining in pyramidal cells of the CA2–3 regions of the hippocampus that was independent of α-synuclein deposits. All MSA cases showed 3-NT immunoreactivity in glial inclusions. 3-NT neuronal staining was restricted to pontine nuclei with three cases showing nuclear and one case cytoplasmic staining. There was no colocalization of 3-NT nuclear immunoreactivity with α-synuclein-immunopositive nuclear inclusions in pontine neurons. These data show that protein nitration in LBD and MSA cases has a widespread distribution and is not only associated with the α-synuclein deposits. The presence of α-synuclein-positive deposits lacking 3-NT immunoreactivity suggests that nitration is not a prerequisite for α-synuclein deposition.