Neuronal Semaphorin 3A Forms a Barrier Preventing Retinal Revascularization in Ischemic Proliferative Retinopathies

Abstract

Purpose: : The energy requirement of neurons triggers retinal neovascularization. Paradoxically, normal revascularization is impeded in ischemic retinopathies, where blood vessels grow towards the vitreous body instead of ischemic regions of the retina. In light of the anatomic coupling between neurons and vessels, shared guidance mechanisms have been inferred. Here we explore the pathological contribution of neuronal derived Sema3A (a classic neuronal repulsion cue) in mediating cardinal features of proliferative retinopathies.

Methods: : The expression of Sema3A and their receptor Neuropilin-1 was assessed by Western blot, immnunohistochemistry and laser micro-dissection (LCM) with quantitative real time PCR. The extent of retinal neovascularization (NV) following Sema3A knockdown in retinal ganglion cells (RGCs) (silenced by intra-vitreal injection of lentivirus-containing shRNA) was determined in a mouse model of oxygen-induced retinopathy (OIR; 75% O2 from P7-P12). Repulsion of vessels by Sema3A was confirmed ex vivo using endothelial cells and aortic ring sprouting assays.

Results: : Following OIR, ischemic RGCs in the avascular zone produce Sema3A, while their receptor Neuropilin-1 is predominantly expressed on neo-vascular tufts. Silencing Sema3A during OIR greatly increased tip cell formation and promoted physiologic revascularization of the ischemic retina (by more then 50%). Moreover it curtailed pathological pre-retinal neovessel formation (by ~50%). In line, neo-vessels persistently avoided Sema3A rich zones in a 3D model of vascular sprouting.

Conclusions: : Neuronal-derived Sema3A forms an important chemical barrier that impedes normal revascularization and contributes to pre-retinal growth in OIR. Approaches to foster normal retinal revascularization while countering pathological neovascularization independently of VEGF are highly desirable for patients afflicted with ischemic proliferative retinopathies.

Keywords: retinal neovascularization • ganglion cells • retinopathy of prematurity