Covalent crosslinking of neurofilament proteins by oxidized catechols as a potential mechanism of Lewy body formation.

Brainstem Lewy bodies (LB) are neuronal inclusions that are closely related to Parkinson's disease (PD). The filamentous component of LB from patients with PD contains biochemically altered neurofilaments (NF). Herein we have tested the hypothesis that the oxidized products of catechols may covalently crosslink NF. Neurofilaments were incubated in the presence of oxidized L-dopa, dopamine, or dopac and then analyzed by SDS-PAGE and protein staining or immunoblotting with monoclonal antibodies specific for neurofilament subunit proteins. Oxidized catechols yielded the same pattern of NF protein crosslinking as known covalent crosslinking agents. Coincubation of NF and catechols with N alpha-acetyl-L-lysine (NAL) produced strong reactivity on immunoblots probed with a polyclonal antiserum specific for NAL crosslinked to protein (antiserum 1400/3). Crosslinking of NAL to model proteins by oxidized dopac was followed by antibody capture assays using antiserum 1400/3. Increasing immunoreactivity was observed for 0.01 to 1.0 mM dopac and was augmented by Cu2+, Fe2+, Fe3+, Mn2+, or Mn3+ up to 0.1 mM. These results show that the products of catechol oxidation can covalently crosslink neurofilaments, that the crosslinking mechanism can involve lysine, and that copper, iron, and manganese ions can accelerate catechol-mediated protein crosslinking.