Introduction: Extracellular vesicles (EV) are membrane-enclosed delivery vehicles, that function in cellular communication through the selective transfer of molecular cargo including microRNA (miRNA) between cells. Since cell-to-cell communication is critical for tissue survival, dysregulation in EV communication is linked to the development of inflammatory and neurodegenerative diseases including in the retina. We therefore aimed to investigate the role of EV-miRNA transfer in mediating retinal homeostatic regulation and in disease development.
Methods: Retinal EV were isolated from mouse retinas using ultracentrifugation and were characterised using nanotracking analysis. Small RNA-seq was performed on retinal EV. To investigate the role of EV or EV-miRNA on retinal homestasis, EV from healthy mouse retinas or EV-abundant microRNA were supplemented into the degenerating retina via intravitreal injection. Electroretinography and optical coherence tomography were used to measure retinal function and morphology respectively following EV/miRNA administration, while TUNEL and IBA-1+ immunohistochemistry was conducted on retinal cryosections to determine levels of cell death and inflammation.
Results: EV were found to alter in their concentration, size and molecular contents in degeneration compared to healthy controls. The top ten EV-miRNA were found to make up ~67% of the total retinal miRNA concentration, and along with upregulated differentially expressed EV proteins were identified to control inflammatory and cell survival pathways known to be heavily involved in retinal degenerations. Compared to controls, mice injected with retinal EV had significantly higher retinal function, reduced inflammation and decreased photoreceptor cell death. Further, intravitreal administration of key EV miRNA protected the retina against photo-oxidative damage-induced retinal degeneration, ameliorating inflammation and cell death, and preserving retinal function.
Conclusions: Taken together, our data suggests that a loss of EV-miRNA bioavailability is correlated to progressive retinal degeneration, while supplementation of healthy retinal EV or highly abundant EV-miRNA can restore homeostatic communication pathways and slow the progression of retinal degeneration.