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A. Dibas, H. Oku, M. Fukuhara, T. Kurimoto, T. Ikeda, T. Yorio; Abnormalities in Ubiquitin Proteasomal System Following Optic Nerve Crush. Invest. Ophthalmol. Vis. Sci. 2010;51(13):984.
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© ARVO (1962-2015); The Authors (2016-present)
The glaucomas represent a heterogeneous group of diseases that result in a progressive optic neuropathy characterized by functional and structural impairment of ocular tissues. The hallmark of glaucoma is the demyelination and degeneration of the optic nerve and death of retinal ganglion cells leading eventually to irreversible blindness. Axonal degeneration is likely to involve the ubiquitin-proteasome system (UPS). UPS activity is altered in many neurodegenerative diseases such as Alzheimer’s & Parkinson’s diseases but remain uncharacterized in retinal injuries following optic nerve crush. This study was designed to analyze changes in the expression of different subunits of UPS following optic nerve crush.
The optic nerve of the right eye of Wistar rats was crushed. Retinal Ganglion Cells were retrogradely labeled by applying fluoroGold onto the left superior colliculus one week prior to crushing. Retinal injuries were induced by optic nerve crush in rat eyes. Changes in ubiquitin-activating enzyme E1 (rate limiting enzyme in the ubiquitination process), X-subunit (chymotrypsin-like), Y-subunit (caspase-like), and Z-subunit (trypsin-like), S1 (plays a role in holding the lid and base of the 19S regulatory complex), S6’ (recognize polyubiquitinated substrates), PGP9.5 (ubiquitin hydrolase), Bcl-XL, and glial fibrillary acidic protein (GFAP) expression were also followed in cytosolic retinal extracts using western blotting. Assay of the proteasomal activity was followed by western blotting using antibodies against ubiquitin.
The mean number of RGCs labeled retrogradely from superior colliculus was 2090 ± 85/mm2 in rats without any treatment, which decreased to 1091 ± 78 (52%) and 497 ± 87/mm2 (24%) on day 7 and 14, respectively. Y-subunit (caspase-like proteolytic activity) and PGP9.5 ubiquitin hydrolase decreased at all three time points. E1, X-subunit (chymotrypsin-like proteolytic activity), and Z-subunit (trypsin-like proteolytic activity) decreased significantly at only 2 days. By contrast, ubiquitination increased at 2 days while decreased at 7 and 14 days. In addition, while GFAP (a marker of astrogliosis) increased at 2, 7 and 14 days, Bcl-XL (anti-apoptotic) decreased as determined by western blotting. No significant changes in S1 or S6’ were detected.
Abnormalities in the UPS may lead to optic nerve axonal damage and provide new insight and aid in the development of new neuroprotective therapeutics targets for glaucoma.
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