Anatomical and Transcriptional Alterations in the Mouse Choroid Induced by All- Trans Retinoic Acid

Purpose: Choroidal all-trans retinoic acid (atRA) has been proposed as a regulator of scleral remodeling during myopia development; however, its choroidal effects and underlying mechanisms remain poorly understood. Here, we aimed to characterize choroidal changes using an established atRA-induced myopia mouse model. Methods: Male C57BL/6J mice received peribulbar injections of atRA, atRA combined with BMS493 (a pan-retinoic acid receptor [RAR] inverse agonist), BMS493, or vehicle every 3 days for 2 weeks. Refraction, axial length, vitreous chamber depth, choroidal thickness (ChT), and choroidal blood perfusion (ChBP) were measured at baseline and endpoint. Choroidal RNA sequencing was performed, and selected genes were validated by real-time quantitative PCR and western blot. Early ocular and molecular assessments were performed following the first atRA injection. Results: BMS493 significantly attenuated atRA-induced myopia in mice. The atRA treatment markedly reduced ChT and ChBP, both of which were notably restored by BMS493. BMS493 alone induced no detectable changes. Gene Ontology analysis revealed significant enrichment of extracellular matrix (ECM)-related terms in both the atRA versus vehicle and the atRA+BMS493 versus atRA comparisons. Gene set enrichment analysis showed downregulation of ECM gene sets by atRA and their upregulation by BMS493. Bone morphogenetic protein 2 (Bmp2) and Bmp7, two myopia-associated ECM genes, were validated at transcriptional and protein levels, showing regulation consistent with sequencing findings. Early downregulation of choroidal Bmp2/7 occurred without detectable axial elongation or choroidal structural changes. Conclusions: In mice, atRA induces axial myopia, accompanied by decreased ChT and ChBP. Mechanistically, its choroidal effects are RAR dependent and are associated with ECM modulation.