Soluble and membrane-bound isoforms of fractalkine differentially regulate microglia activation and vascular damage in the diabetic retina

Diabetic retinopathy (DR) is the leading cause of blindness worldwide due to neuronal loss, microgliosis, and vascular damage. Inflammation caused by microglia exacerbates retinal damage, resulting in glial and neuronal cell dysfunction. Microglial-neuronal crosstalk mediated by CX3CR1/FKN signaling regulates microglial responses. CX3CR1 polymorphic variants present in 25% of the population decrease FKN binding affinity to CX3CR1, and their role in microglia function in the retina during diabetes is unknown. FKN exists as a membrane-bound (mFKN) adhesion molecule. When cleaved by proteases, the soluble (sFKN) form exerts chemoattractant properties. Previous studies show that disruption of CX3CR1/FKN signaling worsens retinal pathology and can be rescued by administration of recombinant FKN. Mechanisms by which mFKN and sFKN regulate retinal function are still unknown. We hypothesize that during diabetes, the over-expression of sFKN using recombinant adeno-associated viruses (rAAVs) will prevent vascular and neuronal damage, and improve visual function. To test this hypothesis, rAAVs expressing mFKN or sFKN were delivered to FKN-KO mouse retinas. We validated the expression of FKN levels in retinal protein extracts in mice that received rAAVs expressing mFKN or sFKN. Our findings revealed that rAAV-sFKN minimizes microglial activation, reduces fibrinogen deposition, and rescues neuronal loss, compared to rAAV-mFKN. rAAV-sFKN retinas of diabetic and non-diabetic mice improved visual function in a two-choice visual discrimination task. FKN appears to be neuroprotective, serving as an alternative therapeutic approach to minimize retinal pathology and improve visual function. Supported by NIH/NEI RO1 EY029913