Kemal Donlic, Tshering Sherpa, Owen Gerald Canterbury, Kiersten Holguin, Peter C Meighan, Michael D Varnum; Visual dysfunction in a zebrafish FASD model is associated with retinal proteostasis impairment. Invest. Ophthalmol. Vis. Sci. 2021;62(8):3161.
Purpose : Fetal alcohol exposure is associated with a myriad of nervous system impacts. Retinal abnormalities and visual deficits also have been observed in fetal alcohol spectrum disorder (FASD). The purpose of this study was to characterize retinal manifestations of binge-like ethanol (EtOH) exposure in a zebrafish model of FASD and to investigate the role of EtOH-mediated proteostasis impairment for visual dysfunction.
Methods : We exposed zebrafish to 1% EtOH from 5-7 days post fertilization, within a developmental period following early establishment of working cone vision but before maturation of rods. Functional assays were carried out 2- and 3-days post-exposure. We employed a transgenic reporter for ubiquitin-system impairment in cone PRs (gnat2:Ub-G76V-YFP), determining the effect of EtOH on reporter accumulation via immunoblotting. The functional effects of EtOH were assessed by optomotor response (OMR) assays and electroretinogram (ERG) recordings in intact zebrafish larvae.
Results : Exposure to 1% EtOH produced a concentration in larvae of 16±4 mM (SEM, n=5), which returned to baseline levels after one day following washout. OMR performance was significantly impaired at 2 and 3 days post-EtOH exposure, which was evident across different stimulus contrast levels and spatial frequencies. Cone-dependent ERG responses exhibited altered maximum amplitudes, sensitivity, and/or response thresholds for b-waves and isolated a-waves. After 2-days recovery, maximum b and a-wave amplitudes were reduced by 43±10 and 34±23% compared to controls, respectively (p<0.05; n=13-22); response thresholds for b and a waves were increased by 1.0±0.2 and 0.6±0.1 log intensity units, respectively (p<0.05, n=7-12). We also observed accumulation of unstable Ub-G76V-YFP following EtOH exposure in transgenic zebrafish, suggesting ubiquitin-system impairment within cones. Pre-treatment with 0.5 μM Torin1, an mTOR1/2 inhibitor previously shown to enhance both autophagy and proteasomal function (Zhao et al., 2015, PNAS), robustly protected against some damaging effects of EtOH on visual function, as revealed by OMR performance and rescue of multiple ERG parameters.
Conclusions : Together, these results show that binge-like EtOH exposure in immature zebrafish larvae produces visual dysfunction, including effects on cone PR neurons. Part of the damaging effects of EtOH on retinal neurons may involve disruption of proteostasis.
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