AAV Delivery of CFH Constructs for Complement Regulation in the Murine Eye

Age-related macular degeneration (AMD), a major cause of irreversible vision loss in elderly populations, has been associated genetically with the complement system, and especially with complement factor H (CFH). However, it remains unknown how CFH affects risk of developing AMD. Humans additionally express a truncated splice variant of CFH, Factor H-like 1 (FHL-1). The retinal pigmented epithelium (RPE) is separated from circulation by Bruch’s membrane (BrM), and it has been reported that CFH is unable to diffuse through BrM, while FHL-1 can. Therefore, it is uncertain whether FHL-1 is responsible for most complement regulation in BrM and on RPE cells, or if local production of CFH is more important. We examined this question in Cfh-/- animals through the use of AAVs, allowing expression of both FHL-1 or truncated versions of CFH retaining the C-terminal end of protein, 18tCFH and 12tCFH, from either local sources following subretinal injection or from systemic sources following tail vein injection. While all constructs showed regulation of the complement system using Western blots in circulation, only 18tCFH, the most complete of the constructs, showed definitive regulation of the complement system following subretinal injection. Additionally, there was more evidence of complement regulation following expression locally in the eye, as opposed to circulation. These results suggest that the C-terminus of the protein is essential for complement regulation in the eye, and that local delivery of the protein is the better delivery route. These findings are important for the design of future gene therapies for complement regulation in AMD patients.