Microglia-specific interleukin-4 delivery by engineered extracellular vesicles restores inner blood-retinal barrier in diabetic retinopathy via GAS6-MERTK pathway.

Maintaining a balanced polarization of microglia is one of the most potential therapeutic approaches for diabetic retinopathy (DR). However, reliable, sustained, effective, and controllable microglial regulation still faces formidable challenges. Here, inspired by the bioavailability and modifiability of extracellular vesicles (EV), we developed an interleukin 4 (IL4)-encapsulated and M1 microglia-targeting EV platform (IL4@CHHSSSARC-EV) for rescuing inner blood-retina barrier (iBRB) deterioration in DR. Delivery of IL4 via IL4@CHHSSSARC-EV enhanced not only the stability of IL4, but also the efficacy of anti-inflammatory phenotype (M2) shift in vitro and in vivo due to their selectivity to pro-inflammatory (M1) microglia. Treatment with IL4@CHHSSSARC-EV significantly ameliorated pathological angiogenesis and iBRB breakdown caused by hypoxia and ischemia in oxygen-induced retinopathy models, and potently minimized leakage, bleeding, lesions, pericyte loss and leukocyte adherence of vascular network in streptozotocin-induced diabetic mice with a high safety profile. Mechanistically, IL4@CHHSSSARC-EV facilitated microglial phagocytic capacity through GAS6-MERTK signaling, thereby engulfing aberrant vessels and disrupting the reciprocal crosstalk between microglia and pathological vasculature. Our study demonstrated that engineering EV as an enduring, efficient and safe implement for manipulating microglia provided a potential strategy for a rebalanced immune profile in DR.