EPAC1-RAP1 SIGNALING ENHANCES AND RESTORES THE BLOOD-RETINAL BARRIER
Carla Ramos, David Antonetti.
University of Michigan, Ann Arbor, MI.
Abnormalities in retinal vascular permeability are associated with diabetic retinopathy (DR), which is the leading cause of vision loss in working-age adults. Pathological changes in vascular permeability during DR are driven by growth factors such as vascular endothelial growth factor (VEGF) and pro-inflammatory cytokines. We are interested in understanding probarrier mechanisms that block vascular permeability and restore the blood-retinal barrier after VEGF signaling. Activation of Rap1 through the cAMP-dependent guanine nucleotide exchange factor (GEF) EPAC1 was reported to enhance barrier function in human umbilical endothelial cells. However, the role of EPAC1 in the retinal endothelial barrier and the relationship to VEGF-induced permeability is unknown. We hypothesize that EPAC1 activation inhibits VEGF-induced permeability in retinal endothelial cells. Primary bovine retinal endothelial cells (BREC) were used to model the blood-retinal barrier. The cAMP analog 8-pCPT-2-O-Me-cAMP-AM (8CPT) was used to specifically activate EPAC1. Cell monolayer permeability was measured by electrical resistance using the ECIS-Zϴ system or by measuring 70 kDa RITC dextran flux across transwell filters. Pre-treatment of BREC with 8CPT prevented VEGF-induced permeability to dextran and reduced electrical resistance. Importantly, treatment of BREC with VEGF followed by 8CPT treatment reversed VEGF-induced permeability to solute and ion flux. Our results demonstrate that activation of Rap1 in retinal endothelial cells through EPAC1 promotes barrier properties and inhibits VEGF-induced permeability. Importantly, EPAC1-Rap1 activation reversed VEGF-induced permeability. Collectively, our results suggest activation of EPAC1-Rap1 may provide a therapeutic means to restore barrier properties in diseases of increased retinal permeability.