Tweak/Fn14 Pathway is Involved in Retinal Neovascularization

Abstract

Purpose: To test whether TWEAK/Fn14 pathway is required for pathological retinal neovascularization in ischemic retinopathy.

Methods: Oxygen-induced retinopathy (OIR) was produced by maintaining C57BL/6 wild type neonatal mice in 75% oxygen from postnatal day (P)7 to P12 and room air from P12 to P17. Control mice were kept in room air. Retinas were prepared for analysis of mRNA for TWEAK and Fn14 by quantitative PCR. The interaction of TWEAK and Fn14 was blocked by intravitreal injection of a soluble Fn14-Fc decoy receptor (2.5 ug/eye) at P12. At P17, retinal flat mounts were stained with isolectin-B4 for evaluation of retinal neovascularization, and retinal sections were stained with TWEAK and Fn14 antibodies for evaluation of retinal expression of these factors. Quantification of the extent of neovascularization was achieved using NIH Image J loaded with SWIFT_NV macros.

Results: At P12, there was no change in the retinal levels of Fn14 and TWEAK mRNA in the OIR mice compared to control retinas. The level of Fn14 was markedly increased at P13 in the OIR mice and remained high through P17 whereas it showed no change in the control mice from P12 to P17. TWEAK mRNA was increased in the control mice from P12 to P17 but OIR failed to increase it further. In control retinas, the immunoreactivity of both TWEAK and Fn14 was mainly localized in the non-vascular cells in ganglion cell layer and inner nuclear layer. However, in the OIR retina, both TWEAK and Fn14 were predominantly expressed in the neovascular tufts and their expression in non-vascular cells was reduced. Treatment with Fn14-Fc decoy receptor significantly reduced retinal neovascularization.

Conclusions: The TWEAK/Fn14 pathway is upregulated and is critically involved in the initiation and progression of retinal neovascularization during ischemic retinopathy. There is a discernible shift in the expression of TWEAK and Fn14 from the ganglion cell and inner nuclear layers in the normal condition to the endothelial cell membranes in retinal neovascularization.

Keywords: 700 retinal neovascularization • 572 ischemia • 706 retinopathy of prematurity