Mesenchymal stem cell exosomes as nanotherapeutics for dry age-related macular degeneration

Oxidative stress-induced retinal pigment epithelial (RPE) cell damage is a major factor in the pathogenesis of dry age-related macular degeneration (AMD). Although the therapeutic effect of mesenchymal stem cell (MSC) exosomes on dry AMD has been preliminarily discussed, the underlying mechanism has yet to be reported. Here, we demonstrate that MSC exosomes, acting as a nanodrug, can effectively reduce the incidence of dry AMD by regulating Nrf2/Keap1 signaling pathway. In the in vitro study, MSC exosomes relieved the damage of ARPE-19 cells, suppressed the activity of lactate dehydrogenase (LDH), decreased the level of reactive oxygen species (ROS) and upregulated the activity of superoxide dismutase (SOD). In the in vivo study, MSC exosomes were administered via intravitreal injection. MSC exosomes effectively protected RPE layer, photoreceptor outer segment/inner segment (OS/IS) layer and outer nuclear layer (ONL) from NaIO₃-induced damage. Western blotting results showed that the ratio of Bcl-2/Bax was increased after pre-administration of MSC exosomes in both in vitro and in vivo studies. Moreover, MSC exosomes were found to upregulate the expressions of Nrf2, P-Nrf2, Keap1 and HO-1, while the antioxidant effect of MSC exosomes was blocked by ML385 (a Nrf2 inhibitor). Besides, immunofluorescence results showed that MSC exosomes upregulated the expression of P-Nrf2 in the nucleus compared to the oxidant group. These results indicate that MSC exosomes protect RPE cells from oxidative damage by regulating Nrf2/Kepa1 signaling pathway. In conclusion, MSC exosomes are promising nanotherapeutics for the treatment of dry AMD.