Altered retinal neovascularization in TNF receptor-deficient mice

Purpose: Tumor necrosis factor alpha (TNF-alpha) has been shown to play an integral role in inflammation, apoptosis, and angiogenesis. We induced retinopathy in tumor necrosis factor receptor-deficient mice (TNFR-) in order to examine the role TNF-a plays in the pathogenesis of retinopathy of prematurity. Methods: On postnatal day (P)7, TNFR- knockout mice and their congenic controls, B6129JF1 (B6129) mice, were exposed to 75% oxygen for up to 5 days and then allowed to recover in room air. Retinopathy was qualitatively assessed by examining fluorescein (FITC) angiography. Furthermore, retinal vascular changes were quantified by immunolabeling retinal vessels in cross sections with an anti-type IV collagen antibody. Disease pathology was quantified by counting preretinal neovascular nuclei. TUNEL analysis was performed to determine if TNFR-mice exhibited a reduced number of apoptotic cells after oxygen-induced retinopathy. Results: FITC-perfused retinas qualitatively demonstrated similar degrees of vascular development and vaso-obliteration on P12 in the room air and hyperoxia-exposed TNFR- and B6129 mice. On P17, the hyperoxia-exposed TNFR- and B6129 mice qualitatively appeared to develop a similar degree of retinal neovascularization. However, FITC-perfused retinal flat mounts on P21 suggested that the hyperoxia-exposed TNFR- mice had a prolonged neovascular response compared to the hyperoxia-exposed B6129 mice. Type IV collagen staining revealed delayed development of the deep intraretinal vessels in the TNFR- room control mice and hyperoxia-exposed TNFR- mice, as compared with B6129 controls. On P17, the average number of preretinal nuclei was similar between the hyperoxia-exposed TNFR-mice and B6129 mice. However, on P21, the neovascularization in the B6129 mice had regressed (3.9 +/- 0.57, preretinal nuclei), whereas neovascularization in the TNFR-mice remained prominent (25.6 +/- 6.3, preretinal nuclei). On P21, the B6129 mice exhibited increased apoptosis in preretinal vascular tufts as compared with TNFR-mice. Conclusions: TNFR-mice had both an altered development of the intraretinal vessels and altered angiogenic response after hyperoxia. Therefore, absence of the TNF-alpha pathway appears to disrupt the local microenvironment promoting angiogenesis in the deep retinal vascular network, as well as altering tuft regression by modifying endothelial cell apoptosis.