Gene therapy targeting CFH and lipoprotein dynamics in AMD - Gene therapy targeting CFH and lipoprotein dynamics in AMD ABSTRACT Age-related macular degeneration (AMD) is the most common cause of irreversible blindness among the elderly in industrialized countries, and there are no treatments for the majority of patients. Early hallmarks of AMD are the formation of lipid- and protein-rich, extracellular sub-retinal pigmented epithelium (RPE) drusen and basal laminar deposits that contain many constituents that are attributable to the activation of the complement cascade and lipid metabolism. Complement and lipoprotein pathway genes have also been independently associated with AMD through genetic risk association and epidemiological studies. Efforts to understand contributions of lipid metabolism/trafficking and complement dysregulation to AMD pathogenesis have been limited by the lack of age-dependent in vivo models that recapitulate these features of the disease. The aim of the proposed studies is to leverage data derived from novel animal models of AMD that we have developed. These models integrate advanced age, complement dysregulation and lipid/cholesterol perturbation, all known contributors to human AMD risk. Specifically, we generated mouse models based on the most replicated genetic risk variant associated with AMD risk, the tyrosine (Y) to histidine (H) substitution at amino acid position 402 (Y402H) of human complement factor H (CFH), the soluble regulator of the alternative complement pathway. Only mice expressing the human H402 AMD risk variant (CFH-H/H) develop an AMD phenotype compared to mice expressing the normal human Y402 CFH variant. Significantly, the AMD phenotype correlates with lipoprotein level changes in blood and in the RPE/Bruch’s membrane (BrM)/choroid complex. Thus, we are the first to observe a functional consequence of the Y402H polymorphism in vivo, which promotes an AMD-like pathology and affects lipoprotein levels in aged mice. Our analysis of ApoA-I containing lipoproteins isolated from BrM and plasma of elderly human donors found that these tissues have very different protein compositions. The most striking difference is the significantly higher concentration of ApoB and ApoE in BrM, which are known to bind to glycosaminoglycans (GAGs) and could promote lipoprotein deposition onto BrM GAGs; likely initiating downstream effects that contribute to RPE dysfunction/death. Based on these observations and other studies we hypothesize that aberrant RPE-derived high-density lipoprotein (HDL)-like secretion contributes to AMD development and is modulated by CFH. The goals of the proposed studies are to use our novel animal models of AMD and human RPE to test the extent to which AAV-gene therapies augmenting normal CFH and/or enhancing local HDL clearance are viable strategies for treating AMD. Outcomes from these studies will mechanistically determine the interaction of two risk factors, CFH and lipoproteins in AMD and provide preclinical evidence for these factors as therapeutic targets for AMD.
