A novel small molecule chaperone of rod opsin and its potential therapy for retinal degeneration

Abstract

Rhodopsin homeostasis is tightly coupled to rod photoreceptor cell survival and vision. Mutations resulting in the misfolding of rhodopsin can lead to autosomal dominant retinitis pigmentosa (adRP), a progressive retinal degeneration that currently is untreatable. Using a cell-based high-throughput screen (HTS) to identify small molecules that can stabilize the P23H-opsin mutant, which causes most cases of adRP, we identified a novel pharmacological chaperone of rod photoreceptor opsin, YC-001. As a non-retinoid molecule, YC-001 demonstrates micromolar potency and efficacy greater than 9-cis-retinal with lower cytotoxicity. YC-001 binds to bovine rod opsin with an EC50 similar to 9-cis-retinal. The chaperone activity of YC-001 is evidenced by its ability to rescue the transport of multiple rod opsin mutants in mammalian cells. YC-001 is also an inverse agonist that non-competitively antagonizes rod opsin signaling. Significantly, a single dose of YC-001 protects Abca4−/−Rdh8−/− mice from bright light-induced retinal degeneration, suggesting its broad therapeutic potential.

Retinal photoreceptor damage produced in guinea pigs by tunicamycin

“…14 Moreover, rhodopsin homeostasis is closely linked to POS morphology, and any reduction in rhodopsin biosynthesis leads to a shortened POS. 15 Thus, in the present study, impairment of rhodopsin biosynthesis by tunicamycin resulted in retraction of abbreviated rods away from the RPE and a marked reduction in rhodopsin immunoexpression in these damaged rods.…”

The Retinoid and Non-Retinoid Ligands of the Rod Visual G Protein-Coupled Receptor

“…Despite the natural ligand 11-cis-retinal, this hydrophobic cavity also fits other retinoid analogs [16][17][18]. Moreover, the non-retinoid ligands consisting of aromatic rings can accommodate the retinal-binding pocket and interact with the surrounding residues via van-der-Waals and π-π stacking interactions [19,20]. The interaction profiles of rod opsin with YC-001 (Table 1), a recently identified small molecule chaperone that improves membrane targeting of retinitis pigmentosa (RP)-linked P23H opsin mutant, and flavonoids (Table 1) emerged from our in silico analyses are shown in Figure 3A and B, respectively.…”

“…The advantageous effect of the 11-cis-retinal chromophore, 9-cis-retinal isochromophore as well as non-isomerisable 11-cis-7-ring-membered-retinal has been reported for several partially misfolded adRP mutants, including P23H, the most prevalent RP-causing mutation found in patients in the United States [42][43][44][45]. These retinoids added to the cultured cells expressing opsin mutants early during biogenesis result in the improved folding and their significantly higher levels in the plasma membrane [19]. Consequently, binding of retinoid rescues cells from the toxic effects of misfolded protein, its accumulation, and aggregation in the ER.…”

“…Thus, identification of non-retinoid small molecules that would improve the stability of partially misfolded opsin mutants is an ongoing effort of multiple research laboratories. A novel small molecule chaperone of rhodopsin, YC-001 with agonist-like binding and non-competitive antagonist activities towards rod opsin, was recently identified using high-throughput screening (HTS) [19]. YC-001 does not form a Schiff base with opsin apo-protein.…”

“…Developing new small molecules advantageous for the specific adRP-linked rhodopsin mutants is at the forefront of current research [19,47,51]. However, caution is necessary as such synthetic drugs, despite their distinct positive effects, may cause toxicity and undesired side effects.…”