The Role of Fractalkine-mediated Neuroprotection in the Diabetic Retina

Diabetic retinopathy (DR) is a leading cause of blindness worldwide due to hallmarks that include neuronal loss, microgliosis, and vasculature damage. Evidence suggests neurodegeneration and neuronal loss precedes vascular dysfunction in early diabetes. Inflammation caused by microglia exacerbates retinal pathology. Microglia, the resident immune cells of the central nervous system (CNS), become activated due to hyperglycemia and are believed to contribute to the development of DR. The microglia-neuronal crosstalk mediated by CX3CR1 and fractalkine (CX3CL1; FKN) signaling provides a neuroprotective environment in several neurological diseases. FKN is a protein expressed on neuronal membranes (mFKN) and undergoes constitutive cleavage to release a soluble domain (sFKN), while the C-terminal fragment (ctFKN), localized in the intracellular face of the cell membrane can translocate to the nucleus of neurons, inducing cell survival. The role by which mFKN, sFKN, and ctFKN regulate retinal function are still unknown. This dissertation is sought to investigate the microglia-neuronal signaling axis (CX3CR1/FKN) in regulating microglial physiology in the diabetic retina and highlighted the contributions of mFKN and sFKN on microglia-mediated inflammation using recombinant adeno-associated viruses (rAAVs), address the contribution of full-length FKN and ctFKN to retinal inflammation in our models of diabetes. Here, we show that prophylactic administration of sFKN, but not mFKN, prevented vascular and neuronal damage, and improved visual acuity in FKN knockout (FKN-KO) mice at onset and early stages of DR. Additionally, therapeutic delivery of sFKN at onset stages DR reversed vascular dysfunction; minimized vascular tortuosity and fibrin(ogen) deposition, enhanced gap- and tight-junction integrity, and visual acuity during early stages of DR. Lastly, we found that FKN is an essential molecule, by which the ctFKN undergoes nuclear localization during diabetes, suggesting to enhance neuronal cell survival and maintenance. Altogether, these data indicate that FKN signaling serve as an alternative pathway to implement translational and therapeutic approaches to minimize retinal pathology and improve neuronal function.