Dysregulation of Wnt signaling in subretinal fibrosis in AMD

7. PROJECT SUMMARY/ABSTRACT Previous studies by others and us have shown that aberrant activation of the canonical Wnt pathway is associated with age-related macular degeneration (AMD) in human patients and in animal models. Furthermore, we have shown that blockade of Wnt signaling partially attenuated retinal inflammation, vascular leakage and neovascularization (NV) in the laser-induced choroidal neovascularization (CNV) model, suggesting that dysregulation of Wnt signaling plays a key role in retinal inflammation, vascular leakage and NV. However, the mechanism for the dysregulation of Wnt signaling in AMD remains elusive. We have previously shown that very low-density lipoprotein receptor (VLDLR) gene knockout (KO) resulted in Wnt signaling over-activation, retinal inflammation, vascular leakage and sub-retinal NV. Our preliminary studies demonstrated that Vldlr KO induced fibrotic factor expression in the RPE. In addition, we showed that VLDLR is expressed predominantly in rod photoreceptors and sheds its soluble N-terminal ectodomain (sVLDLRN) into the inter-photoreceptor matrix (IPM) to modulate Wnt signaling inter-cellularly. sVLDLRN levels in the IPM are reduced in the CNV model and a dry AMD model. Therefore, we hypothesize that the reduced sVLDLRN shedding into the IPM may result in Wnt signaling over-activation in the RPE, leading to retinal inflammation, vascular leakage, sub-retinal NV and fibrosis in AMD. In this project, we will determine if the decreased sVLDLRN shedding from photoreceptors in AMD represents a new pathogenic mechanism for retinal inflammation, vascular leakage, sub-retinal NV, and fibrosis through over-activation of Wnt signaling. Specifically, we will use our newly generated transgenic mice expressing sVLDLRN in rod photoreceptors and secreting sVLDLRN into the IPM to study if over-expression of sVLDLRN in rods will attenuate Wnt signaling over-activation, retinal inflammation, vascular leakage, sub-retinal NV, and fibrosis in AMD models. Furthermore, we will determine if Vldlr KO only in rod photoreceptors is sufficient to induce over-activation of Wnt signaling in the retina and RPE, leading to retinal inflammation, vascular leakage, sub-retinal NV, and fibrosis. We also propose to investigate if sVLDLRN confers an anti-fibrotic effect through inhibition of epithelial-mesenchymal transition induced by Wnt signaling. To explore how sVLDLRN modulates Wnt signaling, we will define the predominant Wnt co-receptor contributing to pathologies in AMD with Lrp5 KO and Lrp6 KO RPE cell lines generated using the CRISPR-Cas9 system. We will also define the Wnt receptor responsible for the interaction with sVLDLRN to inhibit Wnt signaling. This project will establish a new pathogenic mechanism for Wnt signaling dysregulation, retinal inflammation, vascular leakage, CNV, and sub- retinal fibrosis in AMD and identify an intercellular crosstalk between RPE and photoreceptors which modulates Wnt signaling through sVLDLRN shedding. These studies have potential to identify a new therapeutic target for sub-retinal fibrosis in AMD.