From background diabetic retinopathy to its proliferative stage. What is the role of gut microbiota in the trajectory of DR? a Mendelian randomization study with mediation analysis.

backgroundGrowing evidence suggests that gut microbiota (GM) plays a role in diabetic retinopathy (DR), but the causal microbial drivers and their stage-dependent roles during DR progression remain poorly characterised. Using genetic causality methods, we aim to depict a longitudinal GM mapping and stage-stratified GM signatures across the DR trajectory, spanning initial background DR (BDR) through non-proliferative form (NPDR), to advanced proliferative stage (PDR).

methodsGWAS data of 207 GM taxa (from phylum to species) were acquired from the Dutch Microbiome Project (N = 7,824), and DR from FinnGen (over 300,000 individuals). A bidirectional two-sample Mendelian Randomization (TSMR) analysis was conducted to elucidate directional causality between GM and DR. Multiple sensitivity evaluations were performed for pleiotropy, heterogeneity, and stability. Additionally, two-step MR and multivariable MR (MVMR) were performed to dissect causal GM-DR relationships using 1400 candidate circulating metabolite level/ratio data from a Canadian cohort (N = 8,299).

resultsWe identified 11 causal GM taxa (1 family, 3 genera, and 7 species) during the progression of DR. Notably, species_Bacteroides_dorei and species_Dorea_longicatena demonstrated pan-stage pathogenicity (BDR and PDR, all OR>1, P

conclusionThis study pioneers causal longitudinal mapping of GM dynamics across DR progression through integrated genetic prediction and metabolomic mediation analyses, delineating stage-specific microbial drivers, pan-stage pathogens, and metabolite mediators that collectively orchestrate DR pathogenesis. The identified GM-metabolite-DR axis establishes an actionable roadmap for targeted microbiome modulation and metabolite-based therapeutic strategies, bridging observational associations to mechanistic intervention opportunities.