Exosomal FOXL1 from bone marrow mesenchymal stem cells activates the METTL3/ATXN2L pathway to ameliorate high glucose-induced human retinal microvascular endothelial cell injury.

BACKGROUND: Bone marrow mesenchymal stem cells (BMSCs) and their secreted exosomes have been shown to possess therapeutic potential in various diseases, including diabetic retinopathy (DR). Retinal microvascular endothelial cell (RMEC) injury is a key factor in DR, and understanding the underlying molecular mechanisms is crucial for the treatment of DR. The study investigated the role of MSC-derived exosomes in RMEC injury and the underlying mechanism. METHODS: Human retinal microvascular endothelial cells (HRMECs) were exposed to high glucose (HG) to establish an in vitro DR model. Exosomes were isolated from BMSCs using differential centrifugation and co-incubated with HRMECs for functional studies. mRNA expression of ataxin 2 like (ATXN2L), methyltransferase-like 3 (METTL3), and forkhead box L1 (FOXL1) was assessed by quantitative real-time polymerase chain reaction. Protein expression was evaluated by western blotting. Cell viability was measured with a cell counting kit-8 assay, and pro-inflammatory cytokines (TNF-α, IL-1β, and IL-6) were analyzed by enzyme-linked immunosorbent assays. Apoptosis was analyzed through flow cytometry. MDA levels, GSH-Px activity, and ROS levels were determined by colorimetric methods and fluorescence microscopy, respectively. The association of METTL3 with ATXN2L and FOXL1 was investigated using a dual-luciferase reporter assay and RNA immunoprecipitation assay. RESULTS: HG treatment increased the secretion of pro-inflammatory factors, apoptosis rate, and oxidative stress in HRMECs. BMSC-derived exosomes inhibited inflammation, apoptosis and oxidative stress in HRMECs by transferring FOXL1 into HRMECs. FOXL1 functioned as an RNA-binding protein of METTL3, which stabilized ATXN2L mRNA expression through m6A methylation in HRMECs. ATXN2L expression was reduced in DR patients' serum and HG-treated HRMECs. Overexpression of ATXN2L mitigated the high glucose-induced inflammation, apoptosis, and oxidative stress in HRMECs. CONCLUSION: Exosomal FOXL1 from BMSCs stabilized METTL3 to increase ATXN2L expression, thus offering a protective effect against high glucose-induced injury in HRMECs. This finding holds clinical significance for the development of targeted therapies for DR.