Proceedings of the National Academy of Sciences of the United States of America · 6 authors, 6 centres
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Using multiple retinitis pigmentosa mouse models, this preclinical study found that cone electroretinogram responses become nearly undetectable in correlation with the near-complete loss of rods, and that suppressing visual chromophore recycling preserves cone function and extends cone survival.
Cone ERG responses became nearly undetectable at a stage correlating with near-complete loss of rods, despite cones still being present and only moderately altered morphologically. Genetic conditions that suppressed visual cycle recycling—Rlbp1 deficiency and the Rpe65 L450M mutation—preserved cone ERG responses, improved cone opsin expression and localization, and extended cone survival. Conversely, misexpression of genes that directly provide cones with chromophore exacerbated cone loss. The authors propose a model in which RP cones are poisoned by excessive free chromophore that reaches a toxic threshold when the last rods die, since rods normally buffer lipophilic retinoids.
