Functional role of TLR in choroidal neovascularization

Abstract

Purpose: Strong evidence suggests a critical role of inflammation, including the innate immune system, and its dysregulation in the development of sub-retinal choroidal neovascularization (CNV) associated with aged-related macular degeneration. We identified toll-like receptor 2 (TLR2) as one of the molecules involved in the development of CNV, and compared the therapeutic potential of TLR-2 blockage to that of VEGFR2 blockage in experimental models of CNV.

Methods: A novel murine model of spontaneous CNV (sCNV), which is VEGF-dependent and driven by inflammation was used for assessing the effects of intravitreally delivered neutralizing monoclonal antibodies against TNFα, IL1R, TLR2 and VEGFR2. A laser-induced murine CNV (lCNV) model was also used for anti-TLR2 study. TLR2, macrophage and CNV were analysed by immunostaining. CNV number and area evaluated by fluorescein angiography and immunostaining.

Results: Among the neutralizing antibodies tested in an initial pilot experiment, a single intravitreal anti-TLR2 treatment reduced the number of CNV per eye in a sCNV model at day 7 post treatment, although the inhibition was not statistically significant due to the small sample size. In a dose escalation experiment, 2 intravitreal anti-TLR2 treatments 7 days apart significantly reduced both the number and area of sCNV in a dose-dependent manner at day 14, and combination of anti-VEGFR2 and anti-TLR2 treatments did not result in significant additive effects in the different dosages tested. Immunostaining of the lesions showed that the number of F4/80-positive macrophage associated with the sCNV was dramatically reduced by anti-TLR2, whereas anti-VEGFR2 had less obvious effect on sCNV-associated macrophage number. However, intravitreal anti-TLR2 treatment was not effective in suppressing lCNV, suggesting a differential role of TLR2 in this laser damage- and wound healing -driven CNV model.

Conclusions: We have identified TLR2 and its direct functional role in the development of sCNV, and this pathway perhaps is feeding into the VEGF-A pathway because of the lack of additive effect. Furthermore, TLR2 is involved in the recruitment of macrophage to the sCNV, suggesting that it may be an attractive therapeutic target for neovascular AMD via both anti-inflammation and indirect inhibition of the VEGF-A pathway.

Keywords: 453 choroid: neovascularization