Abstract
Purpose :
Alpha-1 antitrypsin (AAT) is a serum anti-protease that prevents overactivity of elastase, collagenase, and various other proteases. AAT is synthesized and secreted by the liver and can be neutralized by the free radicals in cigarette smoke. This depletion of AAT in smokers can result in emphysemas as excessive elastase and collagenase activity can degrade the extracellular matrix of the lung. Coincidently, smoking is the biggest non-genetic risk factor for age-related macular degeneration (AMD). In the advanced stages of AMD retinal-pigmented epithelium (RPE) cells die resulting in geographic atrophy and/or choroidal neovascular pathologies. The RPE is attached on a basal membrane, the Bruch’s membrane (BM), which is rich in elastin and collagen. Smoking could thus contribute to AMD by depletion of AAT and excess degradation of BM components. The primary aim of this study is to understand the role of AAT in the eye, particularly its influence on BM integrity and AMD-like pathologies.
Methods :
We used fundus imaging and fundus fluoresceine angiography (FFA) to monitor AMD-like pathologies over time in AAT deficient mice. Immunohistochemistry and electron microscopy (EM) were used to analyzed BM health and changes in aged mice. Western blotting was used to confirm changes seen by immunohistochemistry.
Results :
The analysis revealed that AAT deficiency disrupts BM integrity resulting in pathologies reminiscent of AMD. Mice develop at a low frequency geographic atrophy (GA) and choroidal neovascularization. Immunohistochemistry revealed a uniform loss of Collagen-IV in the BM with a compensatory increase in Laminin. Interestingly, age-related accumulation of ApoE at the BM was significantly reduced in AAT deficient mice. EM analyses reveled a disintegrated BM that appears often enlarged with loss of a clear collagenous or elastin layer.
Conclusions :
The data suggest that AAT plays an important role in the maintenances of the extracellular matrix of the BM. This suggests that smoking may in part contribute to the increased risk of AMD by depletion of AAT and the subsequent excess activity of extracellular matrix proteases.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.