Cytosolic β-amyloid deposition and supranuclear cataracts in lenses from people with Alzheimerʹs disease

Background Pathological hallmarks of Alzheimerʹs disease include cerebral β-amyloid (Aβ) deposition, amyloid accumulation, and neuritic plaque formation. We aimed to investigate the hypothesis that molecular pathological findings associated with Alzheimerʹs disease overlap in the lens and brain. Methods We obtained postmortem specimens of eyes and brain from nine individuals with Alzheimerʹs disease and eight controls without the disorder, and samples of primary aqueous humour from three people without the disorder who were undergoing cataract surgery. Dissected lenses were analysed by slit-lamp stereophotomicroscopy, western blot, tryptic-digest/mass spectrometry electrospray ionisation, and anti-Aβ surface-enhanced laser desorption ionisation (SELDI) mass spectrometry, immunohistochem-istry, and immunogold electron microscopy. Aqueous humour was analysed by anti-Aβ SELDI mass spectrometry. We did binding and aggregation studies to investigate Aβ-lens protein interactions. Findings We identified Aβ1–40 and Aβ1–42 in lenses from people with and without Alzheimerʹs disease at concentrations comparable with brain, and Aβ1–40 in primary aqueous humour at concentrations comparable with cerebrospinal fluid. Aβ accumulated in lenses from individuals with Alzheimerʹs disease as electron-dense deposits located exclusively in the cytoplasm of supranuclear/deep cortical lens fibre cells (n=4). We consistently saw equatorial supranuclear cataracts in lenses from people with Alzheimerʹs disease (n=9) but not in controls (n=8). These supranuclear cataracts colocalised with enhanced Aβ immunoreactivity and birefringent Congo Red staining. Synthetic Aβ bound βB-crystallin, an abundant cytosolic lens protein. Aβ promoted lens protein aggregation that showed protofibrils, birefringent Congo Red staining, and Aβ/αB-crystallin coimmunoreactivity. Interpretation Aβ is present in the cytosol of lens fibre cells of people with Alzheimerʹs disease. Lens Aβ might promote regionally-specific lens protein aggregation, extracerebral amyloid formation, and supranuclear cataracts.