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Lauren N. Correa, Ying Li, Zhengying Wang, Pingping Chen, Yiwen Li, Byron L. Lam, Rong Wen; Inhibition of Protein Glycosylation by Tunicamycin Induces Shortening and Disorganization of Rod Outer Segments and Photoreceptor Degeneration in Mouse. Invest. Ophthalmol. Vis. Sci. 2012;53(14):6550.
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We have recently identified the K42E mutation in DHDDS (dehydrodolichol diphosphate synthase) as the cause of retinitis pigmentosa (RP) phenotype in a single family with non-syndromic recessive RP. Three-dimensional atomic models of human DHDDS suggest a loss of function mechanism by the K42E mutation in effectively binding the substrate farnesyl pyrophosphate phosphate. Thus, the mutation may lead to a dolichol deficiency, which in turn leads to protein glycosylation deficiency. In the present work, we studied changes in photoreceptors over time when protein glycosylation was inhibited in mouse eyes by intravitreal tunicamycin (TM) of different doses.
TM was dissolved in DMSO and then diluted with PBS to final concentrations of 5, 10, and 25 µg/µl. Adult Balb/c mice were injected intravitreally with 10, 20, or 50 µg (in 2 µl) of TM. Eyes were collected 1, 2, or 4 weeks after injection. Semi-thin plastic sections were cut to display the entire retina along the vertical meridian and the morphology of photoreceptors was examined by light microscopy.
No significant changes in photoreceptors was detectable in the 10-µg group 1-2 wk after TM injection, but shortening and disorganization of rod outer segments were noticed in some eyes 4 wk after TM treatment. In both the 20- and 50-µg groups, rod outer segments (ROS) started to shorten and became disorganized 1 wk after TM injection. Complete loss of ROS is evident in the superior retina 2 wk after TM injection in both groups, accompanied by loss of photoreceptors. By 4 wk after TM treatment, significant loss of photoreceptors occurred in the superior retina in both the 20- and 50-µg groups. No significant changes were detected in the rest of the retina.
Intravitreal TM induces dose- and time-dependent changes in photoreceptors, including shortening and disorganization of ROS and photoreceptor death. These results indicate that photoreceptors are vulnerable to glycosylation deficiency. TM-induced photoreceptor degeneration can be used in combination with genetic models to study retinal degeneration in congenital disorders of glycosylation, as well as in DHDDS mutation associated retinal degeneration.
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