Overactivation of Norepinephrine–β2-Adrenergic Receptor Axis Promotes Corneal Neovascularization

PURPOSE. To investigate the role of the sympathetic nervous system in corneal neovascu-larization (CNV) and to identify the downstream pathway involved in this regulation.METHODS. Three types of CNV models were constructed with C57BL/6J mice, including the alkali burn model, suture model, and basic fibroblast growth factor (bFGF) corneal micropocket model. Subconjunctival injection of the sympathetic neurotransmitter nore-pinephrine (NE) was administered in these three models. Control mice received injections of water of the same volume. The corneal CNV was detected using slit-lamp microscopy and immunostaining with CD31, and the results were quantified by ImageJ. The expres-sion of /32-adrenergic receptor (/32-AR) was stained with mouse corneas and human umbilical vein endothelial cells (HUVECs). Furthermore, the anti-CNV effects of /32-AR antagonist ICI-118,551 (ICI) were examined with HUVEC tube formation assay and with a bFGF micropocket model. Additionally, partial /32-AR knockdown mice (Adrb2+/-) were used to establish the bFGF micropocket model, and the corneal CNV size was quantified based on the slit-lamp images and vessel staining. RESULTS. Sympathetic nerves invaded the cornea in the suture CNV model. The NE recep-tor /32-AR was highly expressed in corneal epithelium and blood vessels. The addition of NE significantly promoted corneal angiogenesis, whereas ICI effectively inhibited CNV invasion and HUVEC tube formation. Adrb2 knockdown significantly reduced the cornea area occupied by CNV. CONCLUSIONS. Our study found that sympathetic nerves grow into the cornea in conjunc-tion with newly formed vessels. The addition of the sympathetic neurotransmitter NE and activation of its downstream receptor /32-AR promoted CNV. Targeting /32-AR could potentially be used as an anti-CNV strategy.