Abstract
Purpose:
To determine whether the Octodon degus, an animal model of Alzheimer's disease (AD) expresses amyloid and tau proteins indicative of AD in the eye as a function of development.
Methods:
The retina from developing Octodon degus aged less than 6 months (2-6 months-old; n=6) and adults older than 5 years old (n=7) were employed. Eyes were collected immediately post-mortem and immersion fixed in 4% paraformaldehyde in PBS (pH 7.4) for over an hour. Immunocytochemical methods were applied to cross-sections of the retina and retinal whole mounts. Horseradish peroxidase (HRP-DAB) staining was carried out on similar sections. The retina was immunolabeled against the major AD proteins using antibodies against amyloid-beta (APPA4), Aβ peptide (Aβ4G8, Aβ6E10), Aβ oligomers (A11), tau (Tau5A6) and hyper-phosphorylated tau (PHF-tau). The area occupied by the antibody mark in young and old retina was quantified. Congo red staining was used to determine the presence of Aβ plaques.
Results:
AD proteins were predominantly expressed in the ganglion cell layer in the adult but not in the young retina. Tau and hyper-phosphorylated tau were expressed in the central and peripheral retina. Normal amyloid proteins were expressed in both young and old retina while Aβ oligomers were only seen in old animals central retina. Congo red staining revealed no apple-green birefringence.
Conclusions:
There was an age-related expression of AD proteins in O. degus eyes and the existence of common factors in the ocular and brain tissues involved in AD etiology/pathogenesis. This further supports the idea that non-invasive eye tests could be developed for early AD diagnosis and that O. degus is a suitable model for developing and validating diagnostic tests.
Keywords: 688 retina •
413 aging •
636 pathobiology