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Priyamvada M Pitale, Alex S McKeown, Timothy W Kraft; Role of Interphotoreceptor binding protein (IRBP) and Insulin-like Growth Factor-1 (IGF-1) in enhancing sensitivity of rod photoreceptors in isolated mouse retina. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):991.
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© ARVO (1962-2015); The Authors (2016-present)
In a recent study of rod adaptation, our lab described the phenomenon of adaptive potentiation (AP), during which the rod phototransduction cascade is hypersensitive following periods of light exposure. We proposed a model where the rod sensitivity was modulated extracellularly by light-dependent activation of the IGF-1 receptor. Thus in the experiments presented here, we explored the role of retinoids and the proteins of the interphotoreceptor matrix (IPM) in signaling AP. In IPM, IRBP transports all-trans retinol (ROL) to the retinal pigment epithelium (RPE), this process is important for photoreceptor function and cell survival. We show that IRBP and IGF binding protein-3 (IGFBP3) are still present in the IPM following RPE removal.
Isolated retina ERG was used to study changes in the rod light response during application of chromophores and growth factors. For protein analysis, retinas were isolated using an identical dissection technique and RPE was left adherent to the retina in control eyes. Immunohistochemistry performed to identify IRBP and IGFBP3 in isolated retinas and control eyes. Protein levels were quantified using Western blot. All mice (2-4 months old) used in these experiments were on the C57B/6J background.
Application of low concentrations of ROL during isolated tissue ERG increased light response amplitudes and decreased the magnitude of AP. Application of high levels of ROL and all-trans retinal decreased response amplitudes. IGF-1 application (0.1 ng/mL) had similar effects to ROL. IHC indicated that both IRBP and IGFBP3 are present in the isolated retina, suggesting that they may function in AP signaling despite detachment of the RPE. Western blot analysis revealed IRBP and IGFBP-3 in the isolated retina samples, supporting our immunofluorosence results. Upon quantification, we found reduced amounts of both IRBP and IGFBP-3 in isolated retinal tissue compared to RPE attached whole retina, suggesting some protein loss following dissection
Our quantification and immunofluorosence results of IRBP and IGFBP-3 show that IPM integrity is preserved in isolated retina preparations in absence of RPE. Given the presence of the IPM proteins in the isolated retinas, there is a potential for IRBP and IGFBPs to signal chromophore bleaching and AP in isolated photoreceptors
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