Elsevier

The Lancet

Volume 361, Issue 9365, 12 April 2003, Pages 1258-1265
The Lancet

Mechanisms of Disease
Cytosolic β-amyloid deposition and supranuclear cataracts in lenses from people with Alzheimer's disease

https://doi.org/10.1016/S0140-6736(03)12981-9Get rights and content

Summary

Background

Pathological hallmarks of Alzheimer's 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 Alzheimer's disease overlap in the lens and brain.

Methods

We obtained postmortem specimens of eyes and brain from nine individuals with Alzheimer's 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 Alzheimer's 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 Alzheimer's 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 Alzheimer's 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 Alzheimer's disease. Lens Aβ might promote regionally-specific lens protein aggregation, extracerebral amyloid formation, and supranuclear cataracts.

Introduction

Pathogenesis of Alzheimer's disease is characterised by age-dependent cerebral deposition of β-amyloid (Aβ) peptides, which are 39–43 aminoacid residues long and are generated by endoproteolytic cleavage of the β-amyloid precursor protein (β-APP). The Aβ1–42 isoform is enriched in neocortical deposits,1 is overproduced in people with familial Alzheimer's disease,2 and contributes to disease-associated oxidative stress, protein aggregation, and neurotoxic effects.3

The human lens is also vulnerable to age-dependent degenerative changes and shows progressive deposition of insoluble protein and extensive oxidative damage.4, 5 Early-onset cataracts and Alzheimer's disease are typical comorbid disorders in adults with Down's syndrome6 and in those with familial Danish dementia,7 an Alzheimer's disease variant with cerebral Aβ amyloidosis. Evidence shows that Aβ is expressed in rodent and monkey lens.8 Conversely, αB-crystallin—an abundant cytosolic lens protein and small heat-shock protein with molecular chaperone properties9—is expressed in brain of individuals with Alzheimer's disease.10 Moreover, Aβ interacts with αB-crystallin in vitro11, 12 and in Aβ-expressing transgenic Caenorhabditis elegans.13

Despite speculation8, 14, 15 about the possibility of overlapping Alzheimer's disease-associated molecular pathological findings in the lens and brain of people with this disorder, to our knowledge, no study to date has investigated this hypothesis in man. Thus, we aimed to investigate this hypothesis.

Section snippets

Samples

The study adhered to hospital regulations, national laws, and the Declaration of Helsinki. Procurement of tissue specimens for this study was approved by institutional review boards at the Massachusetts General Hospital and the Massachusetts Eye and Ear Infirmary, Boston, MA, USA. We obtained informed consent for research use of the brain and both eyes from next-of-kin relatives. Lenses were dissected from intact globes obtained through collaborative arrangement with the Massachusetts

Results

We first identified and characterised β-APP and Aβ in the adult human lens (Figure 1, Figure 2, Figure 3). We detected full-length β-APP (110 kD and 130 kD) by affinity purification and western blot with monoclonal antibody 6E10, an antibody that detects the Aβ region of β-APP (figure 1). We also detected full-length β-APP in the B3 human lens epithelial cell line and primary human lens epithelial cells by western blot with antibodies against the C-terminal (A8717) and N-terminal (22C11)

Discussion

We have identified Aβ1–42 and Aβ1–40 in the human lens and Aβ1–40 in human primary aqueous humour. Our findings show that concentrations of Aβ1–42 and Aβ1–40 in the human lens, and Aβ1–40 in primary human aqueous humour, are comparable with those in aged human cerebral cortex and cerebrospinal fluid, respectively.24 We also noted increased deposition of electron-dense Aβ-immunoreactive aggregates within lens fibre-cell cytoplasm in the supranuclear subregion of lenses from people with

GLOSSARY

electrospray ionisation mass spectrometry
Analytical technique for the study of large molecules, especially proteins and peptides. The technique derives detailed information about molecular weights and structures from very small sample quantities. Electrospray ionisation refers to the methods by which the molecule under analysis is charged, or ionised. In this technique, charged droplets are generated by spraying the sample solution under a strong electric field. Ionisation occurs by protonation

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      Specimens were negatively stained with uranyl acetate in 2% methyl cellulose (Sigma Aldrich) and examined on a JEOL 1200EX transmission electron microscope (Electron Microscope Facility, Harvard Medical School). All analyses included specificity controls in which identically processed specimens were incubated with immunodepleted detection antibody prepared by pre-absorption with synthetic human Aβ peptide (Keck Laboratory, Yale University, New Haven, CT) as previously described (Goldstein et al., 2003). Lenses (n = 4) were dissected from 10-week-old Tg2576 transgenic (Tg+) mice and age-matched non-transgenic (Tg–) littermate control mice (n = 4).

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