Abstract
Purpose::
Antibiotics belonging to the aminoglycoside family have been shown to induce translational read-through of premature stop codons in mammalian systems by interfering with the proofreading property of the ribosome. The S334ter rat is a model of Retinitis Pigmentosa caused by a non-sense mutation. S334ter rats express a truncated rhodopsin lacking the last 15 amino acids. The mutant protein exhibits prolonged activation to light. Additionally, loss of presumptive sorting signals causes improper trafficking of the opsin to the OS leading to rod photoreceptor apoptosis. The rate of degeneration in this model phenocopies the progression of the disease in humans. We evaluated a systemic treatment targeting the cellular translation process with the goal of slowing the rate of photoreceptor degeneration induced by the non-sense mutation using the aminoglycoside Gentamicin in the S334ter rat.
Methods::
A subcutaneous injection of 50µg/gm Gentamicin was given daily to S334ter rats from day P5 to P30. In a second study, this was performed from P5 to P60. Control animals were injected with an equal volume of saline. As an additional control, we treated the P23H transgenic rat model of ADRP. The P23H rat carries a mis-sense mutation in the rhodopsin gene, which should not be affected by the translational read-through action of Gentamicin. We assessed the efficiency of treatment by histopathology, ONL morphometry and ERG.
Results::
At P30, retinas of Gentamicin-treated rats display a significant slowing of the degeneration rate, evidenced by greater ONL thickness and ERG a- and b-wave amplitudes in comparison to controls. By P60 there was no morphological or physiological difference between the treated and the control group. P60 is the longest time point we were able to evaluate due to systemic toxicity of the drug.
Conclusions::
We demonstrate that systemic treatment with Gentamicin can slow the rate of photoreceptor cell death in a model of RP caused by a premature stop mutation. These results are proof-of-principle that ribosomal interference has potential as a therapy for RP and other retinal diseases resulting from nonsense mutations. Ongoing in vitro studies are assessing the percentage of read-through generating full-length opsin induced by Gentamicin. Future studies will examine the identity of the amino acid incorporated in place of the premature stop codon and its significance for the function of the restored protein.
Keywords: retina • retinal degenerations: cell biology • photoreceptors