Microvascular abnormalities and angiogenesis in NF1 mice

Abstract

Purpose : Ocular manifestations are common in the phacomatosis neurofibromatosis type 1 (NF1). Recently, microvascular abnormalities of the retina and choroid have been described in persons with NF1 with high frequency. Given the hyper-pigmentation common to NF1 and presence of melanin in the posterior eye, we hypothesized that excess melanin may underlie the predisposition for microvascular abnormalities in the eyes of NF1 patients.

Methods : Nf1 heterozygous (Nf1+/-) and littermate WT mice (9-13 weeks) underwent a battery of tests to evaluate visual function including scotopic and photopic electroretinogram (ERG), optical coherence tomography (SD-OCT), intraocular pressure (IOP), and fluoresceine angiography (FA). Choroidal neovascularization was induced in Nf1+/- and WT mice using a diode laser(N=4) (240mJ duration 70 ms) with 4 lesions per eye within a 2-disc diameter from the optic disc. Retinal thickness and CNV area (longest length x width) was measured (SD-OCT) five days after laser injury. Density of melanin in the choroid, iris, and ciliary body in Nf1+/- and WT mice was analyzed using immunohistology and flow cytometry.

Results : Nf1+/- mice demonstrated significantly increased scotopic and photopic response to B wave in all luminance (P < 0.05), but no difference in total retinal thickness except for the outer segment when compared with WT mice (61.7 ± 0.9 mm vs. 60.4 ± 1.2 mm, P <0.01). Similar, no difference in IOP or vessel density by fluoresceine angiography was identified. In response to laser injury, choroidal neovascularization was more pronounced in Nf1+/- mice when compared with WT mice (0.025 ± 0.01 mm2 vs. 0.011 ± 0.03 mm2, P <0.0001). Immunohistochemical staining of the choroid, iris, and ciliary body demonstrated significant increased melanin deposition in Nf1+/- mice when compared with WT mice. Confirmation of melanosome density in the retina pigmented epithelium or choroid by flow cytometry and responses following exposure to ultraviolet light are in progress.

Conclusions : Our findings are consistent with our hypothesis that increase melanin deposition and or melanocytic activity, as seen in NF1, may impart sensitivity to retinal neovascularization and phototransduction.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.