Form deprivation (FD) and exogenous all-trans retinoic acid (atRA) result in similar myopigenesis and scleral phenotypes in mice

Abstract

Purpose : Visual stimuli influence myopic axial elongation via a retina-to-sclera signaling cascade, ultimately triggering scleral remodeling and influencing biomechanics; however, it is still unclear which signaling molecules relay myopigenic cues across the posterior eye wall. Here, we show that ocular outcomes between mice exposed to FD and those treated with oral atRA are highly comparable, suggesting a role for atRA in myopigenic retinoscleral signaling.

Methods : Male C57 Bl/6J mice (4 wks of age) were subjected to unilateral FD (n=15), leaving the contralateral eye untreated (Contra; n=15). Additional mice received daily delivery of icing sugar pellets (Ctrl, 2.5 g/kg, n=11) or sugar+atRA (RA, 25 mg atRA/kg, n=17) via a voluntary feeding paradigm. Refractive error (RE) was measured prior to and at the conclusion of treatment (FD: 3 wks, RA: 2 wks). After sacrifice, sclerae were isolated and used to quantify either tensile stiffness (unconfined compression and biphasic modeling; Brown et al., J Royal Soc Int, 2020) or glycosaminoglycan (GAG) and DNA content (dimethylmethylene blue and picogreen assays).

Results : Contra and Ctrl eyes were not significantly different on any outcome measure, and all animals had comparable RE at baseline. Both FD and oral atRA caused relative myopia to develop vs. controls (FD: -4.3D, p<0.001; RA: -5.6D, p<0.001). The changes in RE were accompanied by significantly decreased scleral tensile stiffness (34% and 32% lower in the FD and RA groups vs controls, respectively, FD: p<0.001, RA: p<0.001). Neither the degree of myopia (p=0.29) nor decrease in stiffness (p=0.92) differed between atRA vs. FD. Neither scleral GAG nor DNA content significantly differed between any group.

Conclusions : FD, a myopigenic visual cue, and oral atRA both induce myopia and comparably alter scleral properties in mice. The unchanged scleral DNA content suggests oral atRA is not influencing biomechanics via altered cellular proliferation; thus, the decreased stiffness may be due to scleral remodeling. GAGs were hypothesized as a biomechanically relevant remodeling target that may overlap between the two treatments; however, GAG content of the entire sclera was not measurably affected by either treatment. Work is ongoing to better characterize scleral GAGs via immunohistochemistry and to measure atRA concentrations in FD-treated eyes.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.