Overexpression of HtrA1 and exposure to mainstream cigarette smoke leads to choroidal neovascularization and subretinal deposits in aged mice

We determined the function of ARMS2 and HtrA1 in the choroid and retina using transgenic (Tg) mice and evaluated the effects of mainstream cigarette smoke on these mice. The chicken actin promoter (CAG) was used to drive mouse HtrA1, human ARMS2, and ARMS2 (A69S) expression in the entire body of a mouse for one year. Fundus observations were performed with a Spectralis HRA+ optical coherence tomograph (OCT). Eyes were sectioned, stained with hematoxylin and eosin (H&E), and analyzed with immunohistochemistry. Mice were exposed to cigarette smoke for 30 min/d, 5 d/wk for 12 weeks using a mainstream smoking chamber (INH06-CIGR02A, MIPS). After 12 weeks, fundus observations and pathological analyses were performed. Approximately 18.2% of 12-month-old HtrA1 Tg mice exhibited choroidal neovascularization (CNV) by OCT and positive immunostaining with anti-CD31 and anti-fibronectin antibodies. Furthermore, elastic van Gieson (EVG) staining showed Bruch's membrane damage in HtrA1 Tg mice. No retinal changes were observed in ARMS2 and ARMS2 (A69S) Tg mice. A total of 12 weeks of exposure to mainstream cigarette smoke led to CNV rates of 7.7% for wild type (Wt) mice and 20% for HtrA1 Tg mice, but had no effect on ARMS2 Tg mice. In addition, abnormal deposits were observed between photoreceptor cells and the RPE in an HtrA1 Tg mouse exposed to mainstream cigarette smoke. The HtrA1 overexpression and mainstream cigarette smoke can independently lead to CNV. The HtrA1 gene is a strong risk factor for wet AMD, but not all of the HtrA1 Tg mice developed CNV, suggesting that CNV development depends on multiple risk factors.