MSC-derived small extracellular vesicles attenuate diabetic retinopathy through miR-29a-3p regulated microglia M1-like polarization

Diabetic retinopathy (DR), considered as a neurovascular disorder, significantly causes permanent vision loss and blindness worldwide among working-age adults. The inflammation caused by M1-like microglia is involved in DR. Mesenchymal stem cell (MSC)-derived small extracellular vesicles (sEVs) is an attractive candidate for inflammation modulation. However, the regulatory effect of sEVs secreted by MSCs on M1 differentiation of microglia in diabetic retinopathy has not been thoroughly investigated. In this study, intravitreal injection of sEVs reduced retinal inflammation, mitigated vascular leakage, and suppressed M1-like microglia via the HMGB1/TLR4 signaling pathway. Based on MSC-sEVs miRNA sequencing, bioinformatics prediction, and dual-luciferase reporter assay, miR-29a-3p was identified as a key effector in the modulation of M1-like microglia through the down-regulation of HMGB1. The silencing of miR-29a-3p in MSC-sEVs negated their therapeutic efficacy in STZ-induced diabetic rats and human microglial cells (HMC3) treated with advanced glycation end products (AGEs). Silencing miR-29a-3p in MSC-sEVs reversed the therapeutic effects of MSC-sEVs on STZ-induced rats and advanced glycation end products (AGEs)-treated HMC3. Additionally, overexpression of miR-29a-3p could suppress M1-like microglia, which could be effectively reversed by overexpressing HMGB1. Overall, this study demonstrated that MSC-sEVs carrying miR-29a-3p attenuate retinal injury in diabetic rats by reducing M1 microglia polarization through the targeting of HMGB1, thereby reducing inflammation and protecting the blood-retinal barrier (BRB). MSC-sEVs and miRNAs may be explored as promising therapeutic targets for DR.