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.