Genetic risk of AMD at both the CFH and ARMS2/HTRA1 loci is associated with increased protease expression and activity in human Bruch’s membrane/inner choroid.

Abstract

Purpose : To investigate the mechanisms underpinning genetic risk of AMD at the major CFH (Chr1) and ARMS2/HTRA1 (Chr10) loci.

Methods : Macular punch biopsies from genotyped and phenotyped human donor eye tissue were analysed, with the macular biopsy from one eye being used for histological/immunohistochemistry analysis and from the contralateral eye being used for proteomics. The eye tissue analysed did not have clinical features of AMD, apart from one subgroup which had drusen (> 63 µm). Based upon genotyping four groups were compared, each of which was homozygous for: no risk at Chr1 or 10 (n=8); risk at Chr10, no risk at Chr1 (n=8); risk at Chr1, no risk at Chr10 (n=8); risk at Chr1, no risk at Chr10 with drusen (n=6). For the proteomic study Bruch’s membrane with the choroid largely scraped away (Bruch’s membrane/inner choroid) was isolated from the macular biopsies and its cellular content minimised by extensive washing with PBS then distilled water. The Bruch’s membrane/inner choroid was homogenised by ultrasonication and following extraction proteins were subjected to iTRAQ proteomics analysis; a Baysian statistical approach was used to analyse the data.

Results : The proteomics analysis revealed that Bruch’s membrane/inner choroid from donors who had risk at Chr1 or Chr10 both contained significantly increased levels of proteases compared to tissue from donors who had no genetic risk at these loci. The most striking changes in both the Chr1 and Chr10 risk tissue were increased levels of mast cell-derived proteases including tryptase, chymase and mast cell carboxypeptidase A3. Histological/immunohistochemical analyses demonstrated that this increased protease activity was associated with mast cell infiltration and extracellular matrix destruction.

Conclusions : The choroid from eyes with genetic risk of AMD at both Chr1 and Chr10 contains infiltrating mast cells that secrete proteases, suggesting a common mechanism between Chr1 and Chr10 risk. The resultant proteolytic activity is associated with destruction of extracellular matrix and may have an important role in AMD initiation and progrogression.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.