Vitamin D₃ Reshapes Gut Microbiota and Metabolite Profiles in a Rat Model of Inflammation-Induced Myopia

Myopia is increasingly recognized as an inflammatory ocular disease. Vitamin D₃ is a potential modulator of the gut-eye axis, but its role in inflammation-induced myopia remains unclear. This study investigated whether vitamin D₃ supplementation attenuates myopia progression by regulating retinal inflammation, gut microbiota composition, and microbiota-derived metabolites in a TGF-β2-induced myopia model. Three-week-old Brown Norway rats received weekly periocular TGF-β2 injections with or without daily oral vitamin D₃, and myopia development was evaluated on days 1 and 21 by axial length and refractive error. Cecal contents were analyzed for α- and β-diversity and taxonomic differences, and day-21 serum underwent untargeted metabolomic profiling of microbiota-derived metabolites, including bile acids and imidazole derivatives; Spearman correlation linked microbial or metabolic alterations with myopia progression. TGF-β2 induced axial elongation, myopic refractive shifts, and upregulated retinal pro-inflammatory cytokines (p-NFκB, IL-1β, TNF-α), while vitamin D₃ supplementation markedly attenuated myopia progression and retinal inflammation. Cecal α-diversity did not differ among control, vitamin D₃, TGF-β2, and TGF-β2+vitamin D₃ groups, but vitamin D₃ significantly reshaped β-diversity and reduced the Firmicutes/Bacteroidota ratio. Distinct metabolite profiles were observed, with the vitamin D₃ group showing reduced hyodeoxycholic acid and elevated imidazole derivatives (imidazolepropionic and methylimidazoleacetic acids). Vitamin D₃ supplementation attenuated myopia progression by reducing retinal inflammation and concurrently reshaping the gut microbiome and its metabolites compared to the control and myopic groups. These results underscore the potential of vitamin D₃ to modulate the gut-retina axis as a nutritional approach for mitigating myopia development.