Htra1 Transgenic Mice Manifest Polypoidal Choroidal Vasculopathy Phenotypes Identified In Human Genetic Association Studies

Abstract

Purpose: : Age-related macular degeneration (AMD) is the leading cause of irreversible blindness in the elderly. Wet AMD can be categrized by typical choroidal neovascularization (CNV) and polypoidal choroidal vasculopathy (PCV). The etiology and pathogenesis of CNV and PCV are not well understood. Genome-wide association studies have linked a multifunctional serine protease, HTRA1, to AMD. However, the precise role of HTRA1 in AMD remains unknown. To clarify the role of HTRA1 in AMD pathogenesis, we generated a mouse line (hHTRA1+) overexpressing human HTRA1 in mouse RPE.

Methods: : The expression of human HTRA1 in hHTRA1+ mice was determined by real-time RT-PCR, western blotting and immunohistochemistry. The phenotypes of hHTRA1+ mice were examined by fluorescein angiography (FA), indocyanine green angiography (ICGA), fundus imaging, spectral-domain optical coherence tomography (SD-OCT), histology and electron microscopy (EM). The VEGF level was analyzed by western blotting and immunohistochemistry.

Results: : Human HTRA1 was specifically expressed in the RPE of hHTRA1+ mice. On ICGA, hHTRA1+ mice exhibited cardinal features of PCV: polypoidal lesions resembling grape clusters and a network of branching abnormal vessels. In late phase FA, senescent hHTRA1+ mice showed speckled hyperfluorescence with poorly demarcated leakage, resembling occult CNV. SD-OCT showed that the lesions were located beneath the RPE. Histology staining revealed serous exudation and abnormally dilated, thin-walled blood vessels in the choroid. These features are similar to histopathologic findings on surgically excised human PCV specimens. EM analysis showed that the tunica media and elastic laminae of choroidal arteries were severely degenerated or completely lacking. Both the RPE and photoreceptors showed atrophic changes. Another prominent feature of the hHTRA1+ mice was that the integrity of the Bruch’s membrane was severely compromised as occurred in human CNV patients. Moreover, increased HTRA1 leads to the upregulation of VEGF in the RPE and choroid.

Conclusions: : Our results demonstrate that increased HTRA1 is sufficient to cause PCV, and is a significant risk factor for CNV.

Keywords: age-related macular degeneration • choroid • retinal pigment epithelium