Effects of Oral Metformin on Choroidal Neovascularization, RPE/Choroidal Transcriptome, and Gut Microbiota

Abstract

Purpose : Emerging studies indicate that metformin plays a protective role in the development of age-related macular degeneration (AMD). While the mechanism remains unclear, the gut microbiome has been implicated in this process. Using a murine model, we assessed metformin-induced changes on choroidal neovascularization (CNV), retinal pigment epithelium (RPE)/choroid transcriptome, and gut microbiota.

Methods : Adult male, wild-type C57Bl/6J mice were treated via daily oral gavage of either metformin 300mg/kg or vehicle control for 1 week prior to laser induction and maintained until sacrifice 1 week post-laser. CNV lesion size and macrophage/microglial infiltration were visualized by isolectin-IB4 and Iba1 immunostaining. 16S rRNA Illumina sequencing was performed on fecal DNA at 3 time points: beginning of treatment, after 1 week, and after 2 weeks. Differential abundances were explored with edgeR. High-throughput RNA-seq of the RPE/choroid was performed on mice treated with metformin 1 week prior to laser induction. Enrichment analysis was performed with Limma and Lynx.

Results : Metformin treatment 1 week prior to laser induction suppressed CNV lesion size by 2.1 fold (p<0.01) and decreased Iba1+ macrophage/microglial infiltration around the lesion (p<0.005). 2-week metformin treatment increased the Bacteroidetes/Firmicutes ratio, with a significant increase in genera Bifidobacterium and Akkermansia. Metagenomic analysis showed an enrichment in lipid metabolism and downregulation in amino acid metabolism. Network analysis revealed an association between genera Clostridia, decreased with metformin treatment, and increased CNV size. 145 differentially expressed genes were identified in the metformin-treated group (p<0.05) with a downregulation in pro-angiogenic genes TIE1, PGF, and GATA2. Pearson’s correlation revealed a negative association between hub genus Akkermansia and angiogenesis genes CCL11 and RSPO3.

Conclusions : We demonstrate that oral metformin inhibits CNV and macrophage/microglial response while altering angiogenesis- and AMD-related chorioretinal transcription pathways. Importantly, network analysis strongly suggests these changes are driven in part by modulation of the gut microbiota. Together, these findings shed new insight into a potential therapeutic strategy for AMD, driven by metformin’s protective effects on the gut-retina axis.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.