Immunohistochemical localization of apoptosome-related proteins in Lewy bodies in Parkinson׳s disease and dementia with Lewy bodies

• Cytochrome c immunoreactivity was mainly localized to the core of Lewy bodies.
• Apaf-1 and caspase-9 were mainly immunoexpressed in the halo of Lewy bodies.
• Activated caspase-9 immunoreactivity accumulated in brainstem-type Lewy bodies.
• CD68-immunopositive microglia contained activated caspase-9 immunoreactivity.
• Cortical Lewy bodies were also immunoreactive for apoptosome-related proteins.

Apoptotic stimuli induce the release of cytochrome c from the mitochondria to the cytosol, and this released cytochrome c promotes the formation of the apoptosome, which contains cytochrome c, Apaf-1 and caspase-9, resulting in the activation of caspase-9 and the promotion of apoptotic cell death. To investigate the role of the apoptosome in patients with Parkinson׳s disease (PD), we performed immunohistochemical studies on apoptosome-related proteins in formalin-fixed, paraffin-embedded sections from 8 normal subjects, 10 patients with PD and 5 patients with dementia with Lewy bodies (DLB). Furthermore, we performed double-labeling immunohistochemistry for cleaved caspase-9 and CD68 in some sections from 8 normal subjects and 10 patients with PD. In the substantia nigra and locus ceruleus from both control and PD cases, the somata and processes of melanin-containing neurons were immunostained for cytochrome c, Apaf-1 and caspase-9. In the same areas from the PD cases, brainstem-type Lewy bodies were also immunoreactive for cytochrome c, Apaf-1 and caspase-9, and cleaved caspase-9 immunoreactivity was detected in brainstem-type Lewy bodies and CD68-immunopositive microglia. In addition to brainstem-type Lewy bodies, cortical Lewy bodies were also immunoreactive for these apoptosome-related proteins in the frontal and temporal cortices from the DLB cases. Our results suggest that apoptosome formation accompanied by caspase-9 activation may occur in the substantia nigra and locus ceruleus in brains affected by PD, and that a mitochondria-dependent apoptotic pathway may be partially associated with the pathogenesis of PD.