Ranjay Chakraborty

ON pathway mutations increase susceptibility to form-deprivation myopia.

The ON pathway mutation in nob mice is associated with altered refractive development, and an increased susceptibility to form-deprivation (FD) myopia. In this study, we used mGluR6-/- mice, another ON pathway mutant, to determine whether the nob phenotype was due to the Nyx mutation or abnormal ON pathway transmission. Refractive development under a normal visual environment for mGluR6-/- and age-matched wild-type (WT) mice was measured every 2 weeks from 4 to 16 weeks of age. The response to monocular FD from 4 weeks of age was measured weekly in a separate cohort of mice. Refraction and ocular biometry were obtained using a photorefractor and optical coherence tomography. Retinas were harvested at 16 weeks, and analyzed for dopamine (DA) and DOPAC using high-performance liquid chromatography. Under normal conditions, mGluR6-/- mice were significantly more myopic than their WT controls (refraction at 12 weeks; WT: 9.40 ± 0.16 D, mGluR6-/-: 6.91 ± 0.38 D). Similar to nob mice, two weeks of FD resulted in a significant myopic shift of -5.57 ± 0.72 D in mGluR6-/- mice compared to -1.66 ± 0.19 D in WT animals. No significant axial length changes were observed with either normal or FD visual conditions. At 16 weeks, mGluR6-/- retinas showed significantly lower DOPAC levels (111.2 ± 33.0 pg/mg) compared to their WT counterparts (197.5 ± 11.2 pg/mg). Retinal DA levels were similar between the different genotypes. Our results indicate that reduced retinal DA metabolism/turnover may be associated with increased susceptibility to myopia in mice with ON pathway defect mutations.

Altered Refractive Development in Mice With Reduced Levels of Retinal Dopamine

Purpose The neuromodulator dopamine (DA) has been implicated in the prevention of excessive ocular elongation and myopia in various animal models. This study used retina-specific DA knockout mice to investigate the role of retinal DA in refractive development and susceptibility to experimental myopia. Methods Measurements of refractive error, corneal curvature, and ocular biometrics were obtained as a function of age for both untreated and form-deprived (FD) groups of retina-specific tyrosine hydroxylase knockout (rTHKO) and control (Ctrl) mice. Retinas from each group were analyzed by HPLC for levels of DA and its primary metabolite (DOPAC). Results Under normal visual conditions, rTHKO mice showed significantly myopic refractions (F(1,188) = 7.602, P < 0.001) and steeper corneas (main effect of genotype F(1,180) = 5.1, P < 0.01) at 4 and 6 weeks of age compared with Ctrl mice. Retina-specific THKO mice also had thinner corneas (main effect of genotype F(1,181) = 37.17, P < 0.001), thinner retinas (F(6,181) = 6.07, P < 0.001), and shorter axial lengths (F(6,181) = 3.78, P < 0.01) than Ctrl mice. Retina-specific THKO retinas contained less than 15% of DA and DOPAC compared with Ctrl retinas, and the remaining DA had a significantly higher turnover, as indicated by DOPAC/DA ratios (Students t-test, P < 0.05). Retina-specific THKO mice showed similar, yet more variable, responses to 6 weeks of FD compared with Ctrl mice. Conclusions Diminished retinal DA induced spontaneous myopia in mice raised under laboratory conditions without form deprivation. The relative myopic shift in rTHKO mice may be explained by steeper corneas, an unexpected finding. The chronic loss of DA did not significantly alter the FD myopia response in rTHKO mice.

Molecular and Biochemical Aspects of the Retina on Refraction.

Mutant mouse models with specific visual pathway defects offer an advantage to comprehensively investigate the role of specific pathways/neurons involved in refractive development. In this review, we will focus on recent studies using mouse models that have provided insight into retinal pathways and neurotransmitters controlling refractive development. Specifically, we will examine the contributions of rod and cone photoreceptors and the ON and OFF retinal pathways to visually driven eye growth with emphasis on dopaminergic mechanisms.

Genome-wide scleral micro-and messenger-RNA regulation during myopia development in the mouse

Purpose MicroRNA (miRNAs) have been previously implicated in scleral remodeling in normal eye growth. They have the potential to be therapeutic targets for prevention/retardation of exaggerated eye growth in myopia by modulating scleral matrix remodeling. To explore this potential, genome-wide miRNA and messenger RNA (mRNA) scleral profiles in myopic and control eyes from mice were studied. Methods C57BL/6J mice (n = 7; P28) reared under a 12L:12D cycle were form-deprived (FD) unilaterally for 2 weeks. Refractive error and axial length changes were measured using photorefraction and 1310-nm spectral-domain optical coherence tomography, respectively. Scleral RNA samples from FD and fellow control eyes were processed for microarray assay. Statistical analyses were performed using National Institute of Aging array analysis tool; group comparisons were made using ANOVA, and gene ontologies were identified using software available on the Web. Findings were confirmed using quantitative PCR in a separate group of mice (n = 7). Results Form-deprived eyes showed myopic shifts in refractive error (−2.02 ± 0.47 D; P < 0.01). Comparison of the scleral RNA profiles of test eyes with those of control eyes revealed 54 differentially expressed miRNAs and 261 mRNAs fold-change >1.25 (maximum fold change = 1.63 and 2.7 for miRNAs and mRNAs, respectively) (P < 0.05; minimum, P = 0.0001). Significant ontologies showing gene over-representation (P < 0.05) included intermediate filament organization, scaffold protein binding, detection of stimuli, calcium ion, G protein, and phototransduction. Significant differential expression of Let-7a and miR-16-2, and Smok4a, Prph2, and Gnat1 were confirmed. Conclusions Scleral mi- and mRNAs showed differential expression linked to myopia, supporting the involvement of miRNAs in eye growth regulation. The observed general trend of relatively small fold-changes suggests a tightly controlled, regulatory mechanism for scleral gene expression.