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Jingyu Yao, Yaoyan Qiu, Lin Jia, Kecia Feathers, Debra A Thompson, David N Zacks; Protective effect of shifting protein degradation from autophagy to proteasome on retinal degeneration in P23H mice. Invest. Ophthalmol. Vis. Sci. 2019;60(9):4208.
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© ARVO (1962-2015); The Authors (2016-present)
The P23H variant of rhodopsin represents the most common causes of autosomal dominant retinitis pigmentosa (adRP) in the United States. Misfolding of P23H rhodopsin results in ER stress and persistently imbalanced activation of autophagy relative to proteasome (i.e., an increased A:P ratio), which in turn promotes photoreceptor (PR) cell death. The purpose of this study is to examine the effects of pharmacologically shifting protein degradation from autophagy to the proteasome on retinal degeneration in the P23H mouse, either by facilitating folding of P23H rhodopsin using 4-phenylbutyric acid (4-PBA), or by increasing proteasome activity using rolipram.
P23H mice of both sexes were given daily intraperitoneal injections of 4-PBA or rolipram for up to 12 weeks, beginning on postnatal day 14. Age matched control groups were injected daily with vehicle only. Retinal structure and function were evaluated by immunohistochemistry (IHC), optical coherence tomography (OCT) and optometry at different age points. Levels of autophagy and ER stress were measured by western blot and quantitative PCR. Proteasome activity was measured by chymotrypsin-like activity assay. The effects of rolipram were also examined in vitro in HEK cells expressing wild type or P23H rhodopsin.
P23H mice treated with 4-PBA or rolipram exhibited decreased rates of photoreceptor degeneration, with preserved PR morphology and visual function. Treatment with either 4-PBA or rolipram resulted in decreased autophagy and increased proteasome activity, thus lowering the A:P ratio and decreasing activation of cell death pathways. Reduced autophagy activation and improved proteasome activities were also observed in rolipram treated HEK cells expressing P23H rhodopsin.
Our results suggest that shifting protein degradation from autophagy to the proteasome reduces the imbalanced A:P ratio and is protective in both in vivo and in vitro models of P23H-rhodopsin adRP. Our observations provide a potential therapeutic approach and a unique useful measure of cell stress for evaluating the efficacy of therapies in adRP and, potentially, other diseases of proteotoxicity.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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