Retinal tau pathology in human glaucomas Neeru Gupta,*†‡§ MD, PhD, FRCSC; Jessica Fong;*†‡ Lee C. Ang,|| MD, FRCSC; Yeni H. Yücel*†‡¶ MD, PhD, FRCPC ABSTRACT • RÉSUMÉ
Background: Tau protein is a microtubule-associated protein critical to neuron structure and integrity. The abnormal hyperphosphorylated tau protein AT8 disrupts microtubules, interferes with axonal transport, and is associated with neuron injury in neurodegenerative diseases such as Alzheimer’s disease. The purpose of this study was to assess the presence of tau protein and abnormal tau protein AT8 in human glaucomas and to determine whether abnormal tau protein plays a role in glaucomatous neural degeneration. Methods: Sections from 11 surgical eye specimens with glaucoma from elevated intraocular pressure causes and 10 age-matched control eye specimens were immunostained for normal tau protein (BT2) and hyperphosphorylated tau protein (AT8). Postmortem specimens with incidental open-angle glaucoma (n = 6) were compared with controls (n = 3). Measurements of immunofluorescence intensity in glaucoma retinas were compared with those in control retinas. Abnormal tau AT8 and parvalbumin, a horizontal cellspecific marker, were studied with double-immunofluorescence techniques to determine colocalization. Results: In surgical glaucoma specimens, normal tau protein was decreased in both the optic nerve and retina compared with age-matched controls. Abnormal tau AT8 was evident within the posterior retina, predominantly at the outer border of the inner nuclear layer in surgical glaucoma specimens, and this was not observed in controls or incidental glaucoma cases. Quantitative immunofluorescence techniques demonstrated significantly increased abnormal tau AT8 in surgical glaucoma specimens compared with controls. Abnormal tau AT8 colocalized with parvalbumin in horizontal cells of the retina. Interpretation: Abnormal tau AT8, a marker of injury in various neurological diseases, is present in human glaucomas with uncontrolled intraocular pressure. The finding of abnormal tau protein in retinal horizontal cells may relate to elevated intraocular pressure and (or) neural degeneration in glaucoma. Tau protein abnormality in glaucoma underscores shared pathways with other neurodegenerative diseases. Contexte : La protéine tau, protéine associée aux microtubules, est cruciale pour la structure et l’intégrité des neurones. La protéine tau hyperphosphorylée AT8 dissocie les microtubules, gène le transport axonal et est associée au traumatisme des neurones dans les maladies neurodégénératives, telle la maladie d’Alzheimer. Cette étude a donc pour objet d’évaluer la présence de protéine tau et de la protéine tau anormale AT8 dans les glaucomes humains et d’établir si la protéine tau anormale joue un rôle dans la dégénérescence neurale glaucomateuse. Méthodes : Des coupes de 11 spécimens oculaires chirurgicaux atteints de glaucome à cause d’une pression intraoculaire élevée et 10 spécimens oculaires d’un même groupe d’âge ont été colorées par voie immunologique pour la protéine tau normale (BT2) et protéine tau hyperphosphorylée (AT8). Coupes oculaires post-mortem ayant un diagnostic de glaucome à angle ouvert incident (n = 6) ont été évaluées comparativement à témoins du même âge (n = 3). On a comparé les degrés d’intensité de l’immunofluorescence des rétines glaucomateuses avec des rétines témoins. On a enfin la protéine tau anormale AT8 et la parvalbumine, marqueur spécifique des cellules horizontales, en utilisant les techniques de double immunofluorescence pour en établir la colocalisation.
From *the Department of Ophthalmology & Vision Sciences, †the Department of Laboratory Medicine & Pathobiology, University of Toronto, Toronto, Ont.; ‡Keenan Research Centre at the Li Ka Shing Knowledge Institute, Toronto, Ont.; §Glaucoma & Nerve Protection Unit, St. Michael’s Hospital, University of Toronto, Toronto, Ont.; ||the Department of Pathology, Neuropathology, University of Western Ontario, London, Ont.; and ¶Ophthalmic Pathology Laboratory, Department of Ophthalmology & Vision Sciences, University of Toronto, Toronto, Ont.
Correspondence to: Neeru Gupta, MD, Glaucoma & Nerve Protection Unit, St. Michael’s Hospital, University of Toronto, 30 Bond Street, Cardinal Carter Wing, Suite 8-072, Toronto, ON M5B 1W8;
[email protected] This article has been peer-reviewed. Cet article a été évalué par les pairs. Can J Ophthalmol 2008;43:53–60 doi:10.3129/i07-185
Presented at the annual meeting of the American Academy of Ophthalmology in New Orleans, La., November 2007 Originally received Mar. 23, 2007. Revised July 24, 2007 Accepted for publication Aug. 15, 2007 Published online Jan. 21, 2008 CAN J OPHTHALMOL—VOL. 43, NO. 1, 2008
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Retinal tau pathology in human glaucomas—Gupta et al. Résultats : Chez les spécimens chirurgicaux de glaucome, la protéine tau normale avait baissé dans le nerf optique et la rétine comparativement aux témoins du même âge. La protéine tau anormale AT8 s’est avérée évidente dans la partie postérieure de la rétine et prédominante dans la couche nucléaire interne des spécimens glaucomateux chirurgicaux, alors qu’on n’en a pas observé chez les groupes témoins ni les spécimens oculaires post-mortem. Les techniques quantitatives d’immunofluorescence ont démontré que la protéine tau anormale AT8 avait augmenté façon substantielle par rapport aux groupes témoins. La protéine tau anormale AT8 était colocalisée avec la parvalbumine dans les cellules horizontales de la rétine. Interprétation : La protéine tau anormale AT8, marqueur de lésions dans diverses maladies neurologiques, est présente dans le glaucome humain à cause d’une pression intraoculaire non maîtrisée. La présence de la protéine tau anormale dans les cellules horizontales de la rétine peut être reliée a une forte pression intraoculaire et (ou) à une dégénérescence neurale avancée dans le glaucome. L’anormalité de la protéine tau dans le glaucome met en évidence le partage de voies avec d’autres maladies dégénératives.
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laucoma is a leading cause of irreversible blindness, with elevated intraocular pressure (IOP) as a major risk factor. Elevated IOP may lead to retinal ganglion cell (RGC) death, characteristic optic nerve head changes, and central visual pathway degeneration.1–8 Blocked axon transport following IOP elevation may contribute to neural injury by deprivation of essential nutrient and growth factor supplies.9,10 Tau protein is a microtubule-associated protein associated with axon transport in healthy nerve cells. The abnormal phosphorylation of tau may disrupt microtubules, interfere with axon transport mechanisms,11 and be toxic to neurons.12 Abnormal tau protein is a hallmark of a number of neurodegenerative diseases collectively known as tauopathies and these include Alzheimer’s disease, supranuclear palsy, corticobasal degeneration, Pick’s disease, argyrophilic grain disease, and frontotemporal dementia and parkinsonism linked to chromosome 17 with tau mutations, among others.13,14 Abnormal tau AT8 with the phospho-epitope at serine 202 is well characterized, and AT8 antibody is used routinely to stage human neurodegenerative diseases in neuropathology.15–18 It is not known whether abnormal tau protein AT8 plays a role in glaucomatous neural degeneration. Using immunocytochemical and quantitative methodologies, this study investigates normal tau protein and abnormal tau AT8 in the human retina in glaucomas with uncontrolled IOP, and incidental primary open-angle glaucoma, compared with age-matched controls. METHODS Specimens and processing
Following institutional research ethics board approval, normal and glaucoma human eye specimens were obtained from the Eye Bank of Canada, Ontario Division, and the Ophthalmic Pathology Laboratory, University of Toronto. Inclusion criteria for surgical glaucoma specimens were a history of glaucoma necessitating enucleation for uncontrolled IOP and histopathological demonstration of optic nerve head excavation, a patho-
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logical hallmark of glaucomatous damage. Incidental glaucoma cases were based on a history of glaucoma at the time of death. Exclusion criteria included chronic central nervous system disorder, diabetes, and intraocular tumor. Eleven glaucoma surgical eye specimens enucleated because of uncontrolled IOP from different subjects and 10 control eyes from different age-matched control subjects were studied (Table 1). The mean ages of surgical glaucoma patients and control patients were 42.7 (SD 20.0) years and 49.3 (SD 20.6) years, respectively. To assess whether these changes were related to uncontrolled IOP, 6 incidental open-angle glaucoma specimens and 3 age-matched control eyes were also studied, with mean ages of 77 (SD 5.55) years and 74 (SD 14.45) years, respectively (Table 2). The specimens were fixed in 10% neutral-buffered formalin, processed routinely, embedded in paraffin, and sectioned with a rotatory microtome at 7 μm. Sections were deparaffinized in Histoclear II (National Diagnostics, Atlanta, Ga.) and rehydrated in a Table 1—Details of surgical glaucoma and control eyes Sex
Eye
Pathological diagnosis/ cause of death
Time to fixation* (h)
19 19 24 29 37 38 49 52 57 66 80
M M M M M M M M M M M
OD OS OD OS OS OD OS OD OS OD OD
Angle closure Juvenile glaucoma Juvenile glaucoma Angle closure Angle closure Angle closure Angle closure Angle closure Angle recession Primary open-angle glaucoma Angle closure
