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Hikmet Basmak, Huseyin Gursoy, Ayse Idil Cakmak, Nilgun Yildirim, Nese Tuncel, Nilufer Erkasap, Mete Ozkurt; The expression of vaoactive intestinal peptide receptors and ZENK protein in form-deprivation myopia. Invest. Ophthalmol. Vis. Sci. 2013;54(15):5184.
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© ARVO (1962-2015); The Authors (2016-present)
Many candidate molecules, including vasoactive intestinal peptide (VIP), have been proposed to be involved in the myopia patho-physiology. Our aim was to investigate the expression of mRNA of VIP receptors and ZENK protein on the retina and choroid of form-deprived myopic chick eyes and the effects of intravitreal VIP injection on these receptors and protein.
Three groups of eight white Leghorn chicks were included. They wore a unilateral translucent hemispherical plastic diffuser to induce myopia in their right eyes. Group 1 was the control group that received nothing. The intravitreal injections of 10 μl of saline and 10 μl of VIP (0.5 ng/μl) were applied in group 2 and 3 respectively every 24 hours for seven days. On the first and eight day of experiment the refraction was assessed with retinoscopy. On the eight day of the experiment the chicks were sacrificed. The mRNA levels of VIP1 and VIP2 receptors and ZENK protein on the retina and choroid of the right eyes, in relation to the housekeeping gene, glyceraldehyde 3-phosphate dehydrogenase (GAPDH), was determined using real time PCR (RT-PCR) with Taqman prob. Total RNA was extracted from retinal tissue by the RNA stabilization reagent and quantified by measuring the absorbance at 260 nm. RT-PCR was performed by monitoring in real time the increase in the amount of Taqman prob using Rotor-Gene 6000 RT-PCR. RT-PCR data were collected using the Rotor-Gene 6000 detection system. Cycle threshold (CT) values were determined by automated threshold analysis.
The mean final refraction (D) detected in the right eyes was -13.5±2.7, -9.9±3.6 and -1.8±2.8 in group 1, 2 and 3 respectively. The final myopia obtained was significantly lower in VIP injected eyes (p<0.05). mRNA levels for VIP1 receptors were undetectable. The mean delta-delta CT for VIP2 receptors was 1.11±0.16, 1.37±0.20 and 0.36±0.08 in group 1, 2 and 3, respectively (p=0.013 for group 1 vs 3 and p=0.002 for group 2 vs 3). The mean delta-delta CT for ZENK protein was 2.48±1.58, 3.64±0.65 and undetectable in group 1, 2 and 3, respectively (p=0.059 for group 1 vs 3 and p<0.001 for group 2 vs 3).
Prevention of experimental myopia by exogenous VIP seems to be mediated by down-regulating the expression of VIP2 receptors and ZENK protein, indicating that it may be a promising agent for the treatment of myopia.
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