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      Hsp90 inhibition protects against inherited retinal degeneration

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          Abstract

          The molecular chaperone Hsp90 is important for the functional maturation of many client proteins, and inhibitors are in clinical trials for multiple indications in cancer. Hsp90 inhibition activates the heat shock response and can improve viability in a cell model of the P23H misfolding mutation in rhodopsin that causes autosomal dominant retinitis pigmentosa (adRP). Here, we show that a single low dose of the Hsp90 inhibitor HSP990 enhanced visual function and delayed photoreceptor degeneration in a P23H transgenic rat model. This was associated with the induction of heat shock protein expression and reduced rhodopsin aggregation. We then investigated the effect of Hsp90 inhibition on a different type of rod opsin mutant, R135L, which is hyperphosphorylated, binds arrestin and disrupts vesicular traffic. Hsp90 inhibition with 17-AAG reduced the intracellular accumulation of R135L and abolished arrestin binding in cells. Hsf-1 −/− cells revealed that the effect of 17-AAG on P23H aggregation was dependent on HSF-1, whereas the effect on R135L was HSF-1 independent. Instead, the effect on R135L was mediated by a requirement of Hsp90 for rhodopsin kinase (GRK1) maturation and function. Importantly, Hsp90 inhibition restored R135L rod opsin localization to wild-type (WT) phenotype in vivo in rat retina. Prolonged Hsp90 inhibition with HSP990 in vivo led to a posttranslational reduction in GRK1 and phosphodiesterase (PDE6) protein levels, identifying them as Hsp90 clients. These data suggest that Hsp90 represents a potential therapeutic target for different types of rhodopsin adRP through distinct mechanisms, but also indicate that sustained Hsp90 inhibition might adversely affect visual function.

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          Most cited references36

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          Repression of heat shock transcription factor HSF1 activation by HSP90 (HSP90 complex) that forms a stress-sensitive complex with HSF1.

          Heat shock and other proteotoxic stresses cause accumulation of nonnative proteins that trigger activation of heat shock protein (Hsp) genes. A chaperone/Hsp functioning as repressor of heat shock transcription factor (HSF) could make activation of hsp genes dependent on protein unfolding. In a novel in vitro system, in which human HSF1 can be activated by nonnative protein, heat, and geldanamycin, addition of Hsp90 inhibits activation. Reduction of the level of Hsp90 but not of Hsp/c70, Hop, Hip, p23, CyP40, or Hsp40 dramatically activates HSF1. In vivo, geldanamycin activates HSF1 under conditions in which it is an Hsp90-specific reagent. Hsp90-containing HSF1 complex is present in the unstressed cell and dissociates during stress. We conclude that Hsp90, by itself and/or associated with multichaperone complexes, is a major repressor of HSF1.
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            Experimental validation of novel and conventional approaches to quantitative real-time PCR data analysis.

            Real-time PCR is being used increasingly as the method of choice for mRNA quantification, allowing rapid analysis of gene expression from low quantities of starting template. Despite a wide range of approaches, the same principles underlie all data analysis, with standard approaches broadly classified as either absolute or relative. In this study we use a variety of absolute and relative approaches of data analysis to investigate nocturnal c-fos expression in wild-type and retinally degenerate mice. In addition, we apply a simple algorithm to calculate the amplification efficiency of every sample from its amplification profile. We confirm that nocturnal c-fos expression in the rodent eye originates from the photoreceptor layer, with around a 5-fold reduction in nocturnal c-fos expression in mice lacking rods and cones. Furthermore, we illustrate that differences in the results obtained from absolute and relative approaches are underpinned by differences in the calculated PCR efficiency. By calculating the amplification efficiency from the samples under analysis, comparable results may be obtained without the need for standard curves. We have automated this method to provide a means of streamlining the real-time PCR process, enabling analysis of experimental samples based upon their own reaction kinetics rather than those of artificial standards.
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              Mechanisms of cell death in rhodopsin retinitis pigmentosa: implications for therapy.

              Retinitis pigmentosa (RP) is a group of retinal degenerative diseases that are characterised primarily by the loss of rod photoreceptor cells. Mutations in rhodopsin are the most common cause of autosomal-dominant RP (ADRP). Here, we propose a new classification for rhodopsin mutations based on their biochemical and cellular properties. Several different potential gain-of-function mechanisms for rhodopsin ADRP are described and discussed. Possible dominant-negative mechanisms, which affect the processing, translocation or degradation of wild-type rhodopsin, are also considered. Understanding the molecular and cellular consequences of rod-opsin mutations and the underlying disease mechanisms in ADRP are essential to develop future therapies for this class of retinal dystrophies.
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                Author and article information

                Journal
                Hum Mol Genet
                Hum. Mol. Genet
                hmg
                hmg
                Human Molecular Genetics
                Oxford University Press
                0964-6906
                1460-2083
                15 April 2014
                2 December 2013
                2 December 2013
                : 23
                : 8
                : 2164-2175
                Affiliations
                [1 ]Department of Ocular Biology and Therapeutics,
                [2 ]Department of Genetics, UCL Institute of Ophthalmology , 11–43 Bath Street, London EC1V 9EL, UK
                [3 ]Centre de Biotecnologia Molecular, Departament d'Enginyeria Química, Universitat Politècnica de Catalunya , Rambla Sant Nebridi 22, 08222 Terrassa, Catalonia, Spain
                Author notes
                [* ]To whom correspondence should be addressed at: UCL Institute of Ophthalmology, 11–43 Bath Street, London EC1V 9EL, UK. Tel: +44 2076086944; Fax: +44 2076086892; Email: michael.cheetham@ 123456ucl.ac.uk
                [†]

                Present address: University Eye Hospital Freiburg, Freiburg , Germany.

                Article
                ddt613
                10.1093/hmg/ddt613
                3959821
                24301679
                d88663c9-ad43-46fd-96f3-4f8a2f10441b
                © The Author 2013. Published by Oxford University Press.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/3.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 18 September 2013
                : 22 November 2013
                : 28 November 2013
                Categories
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                Genetics
                Genetics

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