The primary goals of this project are to investigate the transfer of extracellular microRNAs (miRNA) between retinal pigment epithelium (RPE) and microglia as a means of intercellular communication and to evaluate the use of engineered RPE-derived extracellular vesicles (EVs) as an interventional strategy to mitigate retinal inflammation and injury. MicroRNAs are small RNA molecules that regulate gene expression by reducing the stability of target messenger RNAs (mRNAs) and/or inhibiting mRNA translation into proteins. Cells release miRNAs into EVs, including exosomes, which can be delivered to recipient cells to modify their functions. The RPE and microglia are two important types of supporting cells in the neural retina that control the inflammation and immune responses. In our published and preliminary studies, we found that retinal microglia can uptake RPE-derived EVs; and their miRNA levels and signaling pathways can be influenced by these EVs and their miRNA contents. The most abundant miRNA in RPE EVs is miR-204, which targets Tgfbr2 gene in microglia and regulates lipid metabolism. RPE-derived EVs can improve microglial function in miR-204 knockout mice. The current application aims to further investigate whether RPE EVs can rejuvenate the aging retinal microglia, and to use computational modeling to define a dynamic and condition-specific regulatory relationships between miRNAs and mRNAs in microglia. Additionally, experiments will be performed to examine whether EVs produced by human iPSC-RPE cells can be engineered for enhanced protective functions. The results of these studies will provide insights into how EVs and their associated miRNAs mediate signal transduction between two distinct cell types in the outer retina. The findings could also guide future applications of EV-based delivery of miRNA mimics or related compounds to modulate microglia function and alleviate the progression of age- related retinal diseases.