The Influence Of Rhodopsin Chromophore Binding On Protein Biosynthesis Examined In Vivo

Abstract

Over 100 mutations in the rhodopsin gene are associated with retinitis pigmentosa (RP) and other retinal disorders. A subset of mutations found in the N-terminus of rhodopsin cause sector RP in which the lower retina is preferentially affected, suggesting that in these cases retinal degeneration (RD) is influenced by light exposure. One such example, P23H, is the most prevalent RP-causing rhodopsin mutation in North America. Recently we have developed X. laevis (frog) models of RP based on human and bovine P23H rhodopsin which demonstrate light sensitivity. In these models, dark rearing either partially or completely rescues RD. We have shown that the rescuing effect of dark rearing is associated with chromophore binding, since blocking binding also prevents rescue. Light exposure is associated with decreased expression of P23H rhodopsin and decreased transport of P23H rhodopsin to the rod outer segment, suggesting a defect in export of the mutant protein from the ER. In order to define the role of chromophore binding in the rescue of P23H-induced RD, we have performed an extensive characterization of light sensitivity in these models. We raised transgenic F1 tadpoles in varying intensities, durations and wavelengths of light and determined the influence of these factors on RD. Our results suggest that the rescuing effects of dark rearing are not mediated by increased chromophore availablility, but rather by increased stability of rhodopsin in the secretory pathway. Our results have significant implications for the design of molecular chaperone therapies for RP.