Identifying the mechanism of beta2-adrenergic receptor dependent choroidal neovascularization

Neovascular age-related macular degeneration (nAMD) is the leading cause of blindness in the developed world. Vascular endothelial growth factor (VEGF) is a key factor in nAMD pathogenesis, and intravitreal anti-VEGF therapy is the first line treatment. Despite these advances, patients must undergo a significant treatment burden consisting of frequent injections, introducing the risk of endophthalmitis1. Furthermore, VEGF is necessary for other physiological functions, and its complete blockade has both ocular2 and systemic3,4 consequences. Despite these advances, some patients are resistant to anti-VEGF treatment. Recent studies have implicated the complement cascade5, inflammatory cell recruitment6,7, and inflammatory cytokines8 as other key components contributing to nAMD progression. Interleukin-6 (IL-6) is a pro-inflammatory cytokine, and serum IL-6 levels correlate with disease progression9. Additionally, aqueous IL-6 levels are associated with disease activity10. In the mouse laser-induced choroidal neovascularization (CNV) model, IL-6 increases after laser treatment, and IL-6 blockade reduces CNV area8. Thus, inhibition of inflammatory signaling is a potential alternative treatment for patients resistant to anti-VEGF therapy. It was serendipitously discovered that the -adrenergic receptor (AR) blocker propranolol regresses severe hemangioma of infancy11 by reducing VEGF expression12. In addition, 2-AR antagonism inhibits retinal neovascularization in the oxygen-induced ischemic retinopathy (OIR) mouse model by reducing VEGF levels13,14. Based on these data, we hypothesized that -AR antagonism inhibits CNV and tested this hypothesis in the laser-induced mouse CNV model. We found that systemic -AR antagonism and local 2-AR inhibition (Fig 1A) reduce CNV area and IL-6 expression in vivo 15,16. Additionally, we demonstrated that 2-AR agonism stimulates VEGF and IL-6 expression, while 2-AR antagonism inhibits VEGF and IL-6 expression, in isolated primary mouse choroidal endothelial cells (ChEC), microglia (resident macrophages in retina), and retinal pigment epithelial (RPE) cells. Finally, we showed that 2-AR agonism induces VEGF and IL6 mRNA expression in human fetal RPE cells. Based on these data, we hypothesize that -AR signaling is pro-inflammatory, enhancing VEGF expression, and promoting nAMD. Here we propose to determine which cell types regulate 2-AR-driven VEGF and IL-6 expression in vivo and elucidate the signaling pathways downstream of the 2-AR in each relevant cell type.