Lysosomes, autophagosomes and Alzheimer pathology in dementia with Lewy body disease

A failure of protein degradation may underpin Lewy body disease (LBD) where α-synuclein is assimilated into the pathognomic Lewy bodies and Lewy neurites. We investigated histological alterations in lysosomes and autophagosomes in the substantia nigra (SN) and cingulate gyrus (CG) in 34 patients with LBD employing antibodies against phosphorylated α-synuclein and lysosomal (lysosomal associated membrane proteins 1 and 2 (LAMP-1 and LAMP-2), cathepsin D (CTSD)) and autophagosomal (microtubule-associated protein light chain 3α (LC3A)) proteins. Immunostained sections were qualitatively and semi-quantitatively assessed for the appearance, distribution and intensity of staining. Four LBD patients had mutations in GBA1. There was significantly less LAMP-1, LAMP-2 and CTSD immunostaining in neurons of the SN in LBD cases compared to control cases and marginally less LAMP-1 in patients with GBA1 mutations compared to those without. Loss of LAMP-1 and CTSD immunoreactivity correlated with cell loss from the SN. There were no changes in LC3A immunoreactivity in the SN, nor any major changes in the CG, or glial cell activity in the SN and CG, for any of the markers. A proportion of amyloid plaques in both the LBD and control cases was immunoreactive for LAMP-1 and LAMP-2, but not CTSD or LC3A proteins. These immunohisochemical features were seen in glial cells, which were negative for amyloid-β. Alterations in lysosomal structure or function, but not macroautophagy, may underpin the pathogenesis of LBD.