Transcription factor Foxp1 is essential for the induction of choroidal neovascularization

The exudative form of age-related macular degeneration (AMD) is characterized by abnormal blood vessel growth, which is stimulated by vascular endothelial growth factor (VEGF) released from retinal pigment epithelium (RPE). The angiogenic behaviors of vascular endothelial cells in vitro depend on forkhead box protein P1 (Foxp1), a transcription repressor widely expressed in human and murine tissues during development. In this study, we aimed to determine whether loss of Foxp1 affects laser-induced choroidal neovascularization (CNV) in mouse.

Eye-selective deletion of Foxp1 was obtained by crossing Foxp1^flox/flox with Six3-Cre mice. Laser photocoagulation was delivered to six- to eight-week-old mice to induce CNV. The expression of Foxp1 and Cre was determined by immunofluorescence in cryostat sections of the eyes. Fundus fluorescein angiography (FFA), optical coherence tomography (OCT), and B4 isolectin staining were applied to analyze the leakage, bulge height, and area of CNV lesions, respectively. RPE-choroid tissues were isolated for the determination of VEGF and pigment epithelium derived factor (PEDF) by Western blotting.

Foxp1 was expressed in retinal ganglion cells, RPE, and the choroidal endothelial cells. Laser photocoagulation increased the number of Foxp1⁺-endothelial cells and induced CNV. Six3-Cre reduced Foxp1 expression in RPE but not the endothelium, leading to a lower level of VEGF in the RPE-choroid. Foxp1 knockout inhibited pathological angiogenesis and vascular leakage of the laser-induced CNV lesions.

Foxp1 regulates the expression of VEGF in the RPE, and inhibition of Foxp1 could potentially be a novel strategy for the prevention and therapy of neovascularization related to AMD.