Everolimus suppresses glucose transporter 3 membrane trafficking to improve therapeutic efficacy of umbilical cord blood-derived mesenchymal stem cell transplantation in diabetic retinopathy

Diabetic retinopathy (DR) is a microvascular and retinal neurologic disorder that occurs in patients with long-term diabetes. Umbilical cord blood-derived mesenchymal stem cell (UCB-MSC) therapy has emerged as a promising treatment because of its regenerative potential; however, its effectiveness is limited under hyperglycemic conditions, which results in the overproduction of mitochondrial reactive oxygen species (mtROS), leading to cellular senescence. In this study, we examined the potential of everolimus, a mammalian target of rapamycin (mTOR) inhibitor, to enhance the efficacy of MSCs in a high glucose environment, which is typical of DR. Increased glucose levels enhanced glucose uptake, primarily through glucose transporter 3 (GLUT3) overexpression, which resulted in the excess generation of mtROS and ultimately induced cell death. Everolimus inhibited intracellular glucose levels and mtROS production, and increased the survival of MSCs under high glucose conditions. Everolimus also inhibited mTORC1, which resulted in reduced actin stabilization and decreased membrane translocation of GLUT3. This effect was associated with the down-regulation of cofilin phosphorylation, a key factor in actin dynamics, which further suppressed high glucose-induced glucose influx and mtROS generation. Furthermore, the results of the streptozotocin (STZ)-induced DR rat model indicated that the groups receiving a subconjunctival injection of GLUT3 knockdown or everolimus-pretreated UCB-MSCs in STZ rats showed improved retinal function compared with the untreated DR groups. Taken together, the results suggest that everolimus enhances the viability and function of UCB-MSCs under hyperglycemic conditions by modulating glucose homeostasis and reducing oxidative stress. This represents a novel therapeutic strategy for the treatment of DR.