MULTICATALYTIC PROTEINASE IS ASSOCIATED WITH CHARACTERISTIC OVAL STRUCTURES IN CORTICAL LEWY BODIES - AN IMMUNOCYTOCHEMICAL STUDY WITH LIGHT AND ELECTRON-MICROSCOPY

The ATP-ubiquitin-dependent proteolytic pathway (ubiquitin pathway) is believed to be involved in the formation of various neuronal inclusio n bodies including Lewy bodies (LBs), a pathological hallmark of Parki nson disease and diffuse Lewy body disease (DLBD). Since multicatalyti c proteinase (MCP) is involved in the ubiquitin pathway, an investigat ion of whether MCP is involved in neuronal inclusion bodies would prov ide a clue to the mechanism underlying the formation of neuronal inclu sion bodies as well as to the pathogenesis of degenerative neurologica l disorders. In this study, we investigated detailed immunolocalizatio n of MCP in LBs in DLBD brains using light and electron microscopy. We raised three different monoclonal antibodies against purified human M CP. Each of them recognized different sets of MCP subunits on Western blotting. Immunohistochemically, anti-MCP antibodies recognized all ub iquitin-positive cortical LBs in situ as well as those isolated from f rozen DLBD cortices, suggesting that MCP is present in LBs as a whole molecule exhibiting protease activity. In electron microscopy, MCP imm unoreactivity (MCP-IR) was exclusively localized on a characteristic o val structure with an approximate diameter of 100 nm. This structure w as distributed throughout the LBs and was devoid of ubiquitin immunore activity. Treatment of isolated LBs with 2% SDS, but not with 0.5% Tri ton X-100, removed this structure from LBs in which fibrous materials predominated. Ubiquitin immunoreactivity was also decreased in isolate d LBs treated with 2% SDS, suggesting that the fibrous structures in L Bs were not ubiquitinated in situ. Thus, it is suggested that LBs are subjected to a proteolytic process in which MCP plays a role via proce ssing of specific components of LBs.