Increased Subretinal Fibrosis Secondary To Choroidal Neovascularization In Aged Mice Due To High Levels of Circulating Fibrocytes

Abstract

Purpose : Old age is the primary risk factor for age-related macular degeneration (AMD). More than half of neovascular AMD (nAMD) patients develop macular fibrosis even after intravitreal injection of VEGF inhibitors. This study aimed to understand the impact of age on subretinal fibrosis secondary to nAMD.

Methods : Young (2.5 months; n=17, 12 male, 5 female) and old (15 months; n=14, 10 male, 4 female) C57BL/6J mice were used in the study. To induce subretinal fibrosis, first, laser-induced choroidal neovascularization (CNV) was conducted, 10 days later, a second laser was applied to each CNV to induce haemorrhage or leakage. Animals were sacrificed one month after the second laser treatment. Eyes were collected for immunohistochemistry and RPE/choroid flatmount investigations. Peripheral blood and bone marrow samples were collected for flow cytometry of fibrocytes using antibodies against CD45, collagen 1, and CXCR4. Bone marrow cells were treated with TGFb and the expression of collagen 1 and fibronectin was examined by real-time RT-PCR.

Results : Confocal microscopy of RPE/choroid flatmounts showed that the size of subretinal collagen 1⁺ fibrotic lesion was significantly larger in aged mice compared with that in young mice. The two-stage laser treatment significantly increased the population of CD45⁺Collagen1⁺ cells in the bone marrow and blood in both young and aged mice. The population of blood CD45⁺collagen1⁺fibrocytes and CD45⁺CXCR4⁺ cells was significantly higher in aged mice compared to that in young mice. The population of bone marrow CD45⁺collagen1⁺ cells and CD45⁺CXCR4⁺cells was comparable between young and aged mice. However, upon TGFb stimulation bone marrow cells from aged mice expressed significantly higher levels of collagen 1 than the cells from young mice.

Conclusions : Aging promotes subretinal fibrosis partially due to high levels of circulating fibrocytes.

This is a 2020 ARVO Annual Meeting abstract.