mTOR inhibition mitigates molecular and biochemical alterations of vigabatrin-induced visual field toxicity in mice

Publication date: Available online 3 October 2016
Source:Pediatric Neurology
Author(s): Kara R. Vogel, Garrett R. Ainslie, Michelle A. Schmidt, Jonathan P. Wisor, K. Michael Gibson
PurposeGamma-vinyl-GABA (vigabatrin, VGB) is an antiepileptic drug and irreversible GABA transaminase inhibitor associated with visual field impairment which limits its clinical utility. Here, we sought to relate altered visual evoked potentials associated with VGB intake to transcriptional changes in the mTOR pathway and GABA receptors to expose further mechanisms of VGB-induced visual field loss.MethodsVGB was administered to mice via osmotic pump for two weeks to elevate GABA. VEP was examined, eye samples were collected and gene expression was measured by qRT-PCR. Similarly, human retinal pigment epithelial cells (ARPE19) were exposed to VGB and treated with mTOR inhibitors for mTOR pathway analysis, and to assess alterations in organelle accumulation by microscopy.ResultsDysregulated expression of transcripts in the mTOR pathway, GABAA/B receptors, metabotropic glutamate (Glu) receptors 1/6 and GABA/glutamate transporters in the eye was found in association with VEP changes during VGB administration. Rrag genes were found to be upregulated in both mouse eye and ARPE19 cells. Immunoblot of whole eye revealed >3-fold upregulation of a 200kDa band when immunoblotted for RRAGD. Microscopy of ARPE19 cells revealed selective reversal of VGB-induced organelle accumulation by autophagy inducing drugs, notably Torin 2 . Changes in mTOR pathway gene expression, including Rrag genes, were corrected by Torin 2 in ARPE19 cells.ConclusionsOur studies, indicating GABA-associated augmentation of RRAG/mTOR signaling, support further preclinical evaluation of mTOR inhibitors as a therapeutic strategy to potentially mitigate VGB-induced ocular toxicity.



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