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A. Marcha Penha, M. P. Feldkaemper; Insulin, Insulin Receptor, IGF-1 and IGF-1 Receptor mRNA Expression in the Chicken Eye After Positive and Negative Lens Treatment. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3851.
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Previous studies have shown that insulin injections, in chickens, have a powerful myopigenic effect and can influence the mRNA levels of some genes, normally linked to myopia development, like the transcription factor ZENK. As the targets of insulin in the eye are not well defined, this study measured mRNA expression levels of insulin, insulin receptor (IR), insulin-like growth factor-1 (IGF-1) and IGF-1 receptor (IGF-1R), in the fundal layers of the eye, in control animals and after imposed myopic and hyperopic defocus.
Chicks were either treated binocularly with plus or minus spectacle lenses or with no lenses for 4 or 24 hours (n=6 per group) Chicks were sacrificed and the fundal layers carefully dissected. Semi-quantitative real-time PCR was used to quantify mRNA levels in the retina, retinal pigment epithelium (RPE), choroid and sclera, using beta-actin as a house-keeping gene.
In untreated control animals, IR and IGF-1R mRNA levels were highest in the retina and cartilagineous sclera followed by the RPE. Very low levels of IR and IGF-1R were measured in the choroid and fibrous sclera. IGF-1 mRNA expression was highest in the retina followed by the RPE. Insulin mRNA was detected in the retina but in very low concentrations. Lens treatment did not significantly influence gene expression levels in the retina. In the RPE we found a trend (p=0.06) in minus lens treated chicks of a down-regulation in the IR mRNA levels compared to the plus lens and control group. After 24 hours of treatment, the choroid showed an opposite effect; mRNA levels were significantly higher in the minus lens treated group, compared to the plus but not control values (-7D vs. +7D: ANOVA, p = 0.01).
Since insulin and IGF-1 receptors are highly expressed in the retina and cartilagineous sclera, these tissues are most probably a target for insulin and IGF-1. Negative lens treatment increased IR mRNA expression in the choroid and decreased IR mRNA levels in the RPE. The time course of these changes will be studied now in more detail.
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