Amyloid precursor protein processing and retinal pathology in mouse models of Alzheimer’s disease
Retinal ganglion cell loss is considered to be a cause of visual impairment in Alzheimer`s patients. Alterations in amyloid precursor protein (APP) processing and amyloid-β (Aβ) accumulation, key molecules associated with Alzheimer`s disease pathogenesis, may therefore contribute to retinal damage. We therefore investigated retinal APP processing and eye morphology in Alzheimer`s transgenic mouse models.
Eyes and brain samples of 2- to 18-month-old transgenic mice expressing human APP with the double Swedish mutation (APPswe) (APP K595N/M596L)(Tg2576) were compared with eyes and brain tissue from wild-type background C57BL6xSJL controls. In addition, 6- to 12-month-old double transgenic mice over-expressing human APPswe and mutant presenilin 1 with exon 9 deletion (APPswe/PS1-dE9) were compared with background controls of C57BL6xC3H strain. Tissue samples were fixed in formalin for immunohistochemistry, and dissected retinal and cerebellar extracts were frozen for Western blotting and enzyme-linked immunosorbent assay (ELISA). Monoclonal antibodies 1E8 and WO2 were used for immunohistochemical detection of APP and Aβ, whereas Aβ 42/40 levels were assayed by ELISA. APP and processed fragments were detected biochemically by Western blotting with domain-specific antibodies, using antibody WO2 (Aβ) and rabbit antibody 369 to the C-terminal domain of APP.
Immunocytochemistry revealed strong cytoplasmic expression of APP and possibly Aβ in retinal ganglion cells and inner nuclear layer cells, and in lens and corneal epithelia for APP transgenic mice. Retinas from the APP transgenic mouse strains contained 18 to 70 kDa APP proteolytic products that were not detected in the cerebellum. We found a higher proportion of APP α-secretase generated C-terminal fragments in transgenic retinal tissues than β-secretase-generated C-terminal fragments. Very low level Aβ was detected in transgenic retinas by ELISA; retinal Aβ 42 was 75 times less than for transgenic brain. Aβ was not detected in mouse retina by Western blotting in our study, indicating much less generation of Aβ in retina than brain tissue.
Alzheimer’s mouse model retinas present with different APP proteolytic products and have a significantly lower production of amyloidogenic Aβ than found in brain.
KeywordsAlzheimer’s mouse model Amyloid precursor protein Retina Amyloid beta peptide
We thank Karen Hsiao Ashe for the Tg2576 mice, Laura Leone for assistance with histology, and Katrina Laughton for ELISA assays. We thank the Bethlehem Griffiths Research Foundation, Victoria and the Australian National Health and Medical Research Council for funding support.
- 14.Goldstein LE, Muffat JA, Cherny RA, Moir RD, Ericsson MH, Huang X, Mavros C, Coccia JA, Faget KY, Fitch KA, Masters CL, Tanzi RE, Chylack LT Jr, Bush AI (2003) Cytosolic beta-amyloid deposition and supranuclear cataracts in lenses from people with Alzheimer’s disease. Lancet 361:1258–1265. doi: 10.1016/S0140-6736(03)12981-9 PubMedCrossRefGoogle Scholar
- 19.Ning A, Cui JZ, To E, Hsiao Ashe K, Matsubara JA (2008) Amyloid beta deposits lead to retinal degeneration in a mouse model of alzheimer disease. Invest Ophthalmol Vis SciGoogle Scholar
- 20.Shimazawa M, Inokuchi Y, Okuno T, Nakajima Y, Sakaguchi G, Kato A, Oku H, Sugiyama T, Kudo T, Ikeda T, Takeda M, Hara H (2008) Reduced retinal function in amyloid precursor protein-over-expressing transgenic mice via attenuating glutamate-N-methyl-d-aspartate receptor signaling. J Neurochem 107:279–290. doi: 10.1111/j.1471-4159.2008.05606.x PubMedCrossRefGoogle Scholar
- 23.Ida N, Hartmann T, Pantel J, Schroder J, Zerfass R, Forstl H, Sandbrink R, Masters CL, Beyreuther K (1996) Analysis of heterogeneous A4 peptides in human cerebrospinal fluid and blood by a newly developed sensitive Western blot assay. J Biol Chem 271:22908–22914. doi: 10.1074/jbc.271.37.22908 PubMedCrossRefGoogle Scholar
- 24.Buxbaum JD, Gandy SE, Cicchetti P, Ehrlich ME, Czernik AJ, Fracasso RP, Ramabhadran TV, Unterbeck AJ, Greengard P (1990) Processing of Alzheimer beta/A4 amyloid precursor protein: modulation by agents that regulate protein phosphorylation. Proc Natl Acad Sci USA 87:6003–6006. doi: 10.1073/pnas.87.15.6003 PubMedCrossRefGoogle Scholar
- 25.Culvenor JG, Henry A, Hartmann T, Evin G, Galatis D, Friedhuber A, Jayasena UL, Underwood JR, Beyreuther K, Masters CL, Cappai R (1998) Subcellular localization of the Alzheimer’s disease amyloid precursor protein and derived polypeptides expressed in a recombinant yeast system. Amyloid 5:79–89PubMedGoogle Scholar
- 26.Fodero-Tavoletti MT, Smith DP, McLean CA, Adlard PA, Barnham KJ, Foster LE, Leone L, Perez K, Cortes M, Culvenor JG, Li QX, Laughton KM, Rowe CC, Masters CL, Cappai R, Villemagne VL (2007) In vitro characterization of Pittsburgh compound-B binding to Lewy bodies. J Neurosci 27:10365–10371. doi: 10.1523/JNEUROSCI.0630-07.2007 PubMedCrossRefGoogle Scholar
- 28.Vassar R, Bennett BD, Babu-Khan S, Kahn S, Mendiaz EA, Denis P, Teplow DB, Ross S, Amarante P, Loeloff R, Luo Y, Fisher S, Fuller J, Edenson S, Lile J, Jarosinski MA, Biere AL, Curran E, Burgess T, Louis JC, Collins F, Treanor J, Rogers G, Citron M (1999) Beta-secretase cleavage of Alzheimer’s amyloid precursor protein by the transmembrane aspartic protease BACE. Science 286:735–741. doi: 10.1126/science.286.5440.735 PubMedCrossRefGoogle Scholar