Multicatalytic proteinase is associated with characteristic oval structures in cortical Lewy bodies: an immunocytochemical study with light and electron microscopy

Abstract

The ATP-ubiquitin-dependent proteolytic pathway (ubiquitin pathway) is believed to be involved in the formation of various neuronal inclusion bodies including Lewy bodies (LBs), a pathological hallmark of Parkinson disease and diffuse Lewy body disease (DLBD). Since multicatalytic proteinase (MCP) is involved in the ubiquitin pathway, an investigation of whether MCP is involved in neuronal inclusion bodies would provide a clue to the mechanism underlying the formation of neuronal inclusion bodies as well as to the pathogenesis of degenerative neurological disorders. In this study, we investigated detailed immunolocalization of MCP in LBs in DLBD brains using light and electron microscopy. We raised three different monoclonal antibodies against purified human MCP. Each of them recognized different sets of MCP subunits on Western blotting. Immunohistochemically, anti-MCP antibodies recognized all ubiquitin-positive cortical LBs in situ as well as those isolated from frozen DLBD cortices, suggesting that MCP is present in LBs as a whole molecule exhibiting protease activity. In electron microscopy, MCP immunoreactivity (MCP-IR) was exclusively localized on a characteristic oval structure with an approximate diameter of 100 nm. This structure was distributed throughout the LBs and was devoid of ubiquitin immunoreactivity. Treatment of isolated LBs with 2% SDS, but not with 0.5% Triton X-100, removed this structure from LBs in which fibrous materials predominated. Ubiquitin immunoreactivity was also decreased in isolated LBs treated with 2% SDS, suggesting that the fibrous structures in LBs were not ubiquitinated in situ. Thus, it is suggested that LBs are subjected to a proteolytic process in which MCP plays a role via processing of specific components of LBs.