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Updated: May 5, 2026
Malachite Green Assay for the Discovery of Heat-Shock Protein 90 Inhibitors
Published on: January 20, 2023
Hsp90 inhibition protects against inherited retinal degeneration
Mònica Aguilà1, Dalila Bevilacqua, Caroline McCulley
1Department of Ocular Biology and Therapeutics.
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.
Insights
Hsp90 inhibition shows promise for treating autosomal dominant retinitis pigmentosa (adRP) by improving visual function and delaying photoreceptor degeneration. However, sustained inhibition may negatively impact vision.
Area of Science:
- Molecular biology
- Neuroscience
- Ophthalmology
Background:
- The molecular chaperone Hsp90 is crucial for client protein maturation, with inhibitors in cancer trials.
- Hsp90 inhibition activates the heat shock response and shows potential for autosomal dominant retinitis pigmentosa (adRP) caused by rhodopsin mutations.
- Rhodopsin mutations, like P23H and R135L, lead to photoreceptor degeneration and vision loss.
Purpose of the Study:
- To investigate the therapeutic potential of Hsp90 inhibition in preclinical models of adRP.
- To elucidate the distinct mechanisms by which Hsp90 inhibition affects different rhodopsin mutations (P23H and R135L).
- To identify Hsp90 client proteins in the retina and assess the long-term effects of Hsp90 inhibition.
Main Methods:
- Utilized a P23H transgenic rat model and cell-based assays.
- Administered Hsp90 inhibitors (HSP990 and 17-AAG) in vivo and in vitro.
- Assessed visual function, photoreceptor degeneration, protein aggregation, protein localization, and expression of heat shock proteins, GRK1, and PDE6.
Main Results:
- A low dose of HSP990 enhanced visual function and delayed degeneration in P23H rats, reducing rhodopsin aggregation.
- Hsp90 inhibition with 17-AAG reduced R135L accumulation and arrestin binding in cells.
- Hsp90 inhibition's effect on P23H was HSF-1 dependent, while on R135L it was HSF-1 independent, mediated by GRK1 maturation.
- In vivo, Hsp90 inhibition restored R135L localization and identified GRK1 and PDE6 as Hsp90 clients.
Conclusions:
- Hsp90 inhibition offers a potential therapeutic strategy for distinct forms of rhodopsin-mediated adRP.
- The mechanisms involve HSF-1 dependent and independent pathways, impacting protein aggregation and maturation.
- Sustained Hsp90 inhibition may have adverse effects on visual function due to reduced GRK1 and PDE6 levels.
