Systemic treatment with Gentamicin slows photoreceptor degeneration in the S334ter–4 rat model of Retinitis Pigmentosa.

Abstract

Abstract: : Purpose: The aminoglycosides antibiotics, such as Gentamicin, have been shown to induce translational read–through of premature stop codons in mammalian systems. The S334ter–4 transgenic rat model of autosomal dominant Retinitis Pigmentosa carries a premature stop codon at residue 334. Rats expressing the transgene produce a truncated rhodospin, which lacks the last 15 amino acids of the C–terminal tail, leading to mis–sorting and prolonged activation of the molecule eventually causing photoreceptor death. We tested the ability of Gentamicin to read–through this premature stop codon and improve photoreceptor survival in the S334ter–4 rat model. Methods: S334ter–4 rats were given a daily sub–cutaneous injection of 50µg/gm body weight Gentamicin from post–natal day (PND) 5 to PND30. In a separate experiment, rats were injected with Gentamicin from PND5 to PND15, then osmotic mini–pumps (Alzet) delivering a daily dose of 50µg/gm body weight of Gentamicin were implanted under the animal’s skin. Control animals were injected with an equal volume of saline. Histological analysis to determine ONL thickness and electroretinograms (ERG) (log –2.0, log –0.5 and log 0.5 cd.s/m²) were performed on PND30 rats Results: The superior retina of Gentamicin–treated rats display a significantly larger ONL thickness (30.81µm±0.85, N=11 daily injection; 32.40µm±1.43, N=7 mini–pumps) than control animals (23.58µm ± 1.75, N=5). No significant difference was observed between the 2 Gentamicin–treated groups. Similar results are observed in the inferior part of the retina. Age–matched WT rats display an ONL thickness of 53.79µm±1.34. ERG recordings of animals receiving a daily injection showed a significant improvement in both a– and b–waves at all light levels tested compared to control animals. Interestingly, no significant improvement of the ERG was observed in the animals receiving continuous release of the drug through the mini–pumps. Conclusions: These results show that Gentamicin treatment can decrease the rate of photoreceptor cell death in the S334ter–4 rats and are consistent with previous studies in rd mice showing the potential of aminoglycosides as a systemic therapeutic agent for nonsense mutation–caused disease. Ongoing biochemical analyses will allow us to determine the decrease in truncated rhodopsin synthesis as the result of Gentamicin treatment in this animal model.

Keywords: retinal degenerations: cell biology • neuroprotection • pharmacology