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The Journal of Neuroscience, August 22, 2007, 27(34):9043-9053; doi:10.1523/JNEUROSCI.2245-07.2007

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Neurobiology of Disease
Dark Rearing Rescues P23H Rhodopsin-Induced Retinal Degeneration in a Transgenic Xenopus laevis Model of Retinitis Pigmentosa: A Chromophore-Dependent Mechanism Characterized by Production of N-Terminally Truncated Mutant Rhodopsin

Beatrice M. Tam and Orson L. Moritz

Department of Ophthalmology and Visual Sciences, Centre for Macular Research, University of British Columbia, Vancouver, British Columbia, Canada V5Z 3N9

Correspondence should be addressed to Orson L. Moritz, Department of Ophthalmology and Visual Sciences, University of British Columbia, 2550 Willow Street, Vancouver, British Columbia, Canada V5Z 3N9. Email: olmoritz{at}interchange.ubc.ca

To elucidate the molecular mechanisms underlying the light-sensitive retinal degeneration caused by the rhodopsin mutation P23H, which causes retinitis pigmentosa (RP) in humans, we expressed Xenopus laevis, bovine, human, and murine forms of P23H rhodopsin in transgenic X. laevis rod photoreceptors. All P23H rhodopsins caused aggressive retinal degeneration associated with low expression levels and retention of P23H rhodopsin in the endoplasmic reticulum (ER), suggesting involvement of protein misfolding and ER stress. However, light sensitivity varied dramatically between these RP models, with complete or partial rescue by dark rearing in the case of bovine and human P23H rhodopsin, and no rescue for X. laevis P23H rhodopsin. Rescue by dark rearing required an intact 11-cis-retinal chromophore binding site within the mutant protein and was associated with truncation of the P23H rhodopsin N terminus. This yielded an abundant nontoxic 27 kDa form that escaped the ER and was transported to the rod outer segment. The truncated protein was produced in the greatest quantities in dark-reared retinas expressing bovine P23H rhodopsin and was not observed with X. laevis P23H rhodopsin. These results are consistent with a mechanism involving enhanced protein folding in the presence of 11-cis-retinal chromophore, with ER exit assisted by proteolytic truncation of the N terminus. This study provides a molecular mechanism for light sensitivity observed in other transgenic models of RP and for phenotypic variation among RP patients.

Key words: rhodopsin; ER stress; signal transduction; protein misfolding; photoreceptor; neuronal death

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Received Aug. 28, 2006; revised July 3, 2007; accepted July 5, 2007.

Correspondence should be addressed to Orson L. Moritz, Department of Ophthalmology and Visual Sciences, University of British Columbia, 2550 Willow Street, Vancouver, British Columbia, Canada V5Z 3N9. Email: olmoritz{at}interchange.ubc.ca

This article has been cited by other articles:

				H. F. Mendes and M. E. Cheetham Pharmacological manipulation of gain-of-function and dominant-negative mechanisms in rhodopsin retinitis pigmentosa Hum. Mol. Genet., October 1, 2008; 17(19): 3043 - 3054. [Abstract] [Full Text] [PDF]

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