Age-Dependent Changes In Heparan Sulfate In Human Bruch’s Membrane: Implications For Age-Related Macular Degeneration

Abstract

Purpose: Heparan sulfate (HS) plays an important role in retinal homeostasis. It may be implicated in age-related macular degeneration (AMD), as it is the major binding partner for complement factor H (CFH) in human macular Bruch’s membrane. The aim of this study was to investigate potential changes with age in the quantity and composition of HS in the human retina.

Methods: Postmortem human ocular tissue was obtained from consenting eye donors without known retinal disease (n=4 pairs of younger globes, age 26-35 years; n=6 pairs of older globes, age 71-88 years). Retinal tissue was dissected, and HS was extracted and partially purified by anion exchange chromatography. Following heparinase digestion, HS disaccharides were labeled with AMAC and quantified according to sulfation pattern by HPLC alongside reference standards. Separately, HS was detected by immunohistochemistry in frozen human macular tissue sections (n=6 from younger globes, age 18-34 years; n=5 from older globes, age 79-89 years).

Results: The quantity of HS in Bruch’s membrane was 44% lower in older donors (p<0.04). The disaccharide composition was similar between age groups; the proportions of N-sulfated, 6-O-sulfated and 2-O-sulfated disaccharides were 26%, 13% and 9%, respectively. The quantity of HS in neurosensory retina, by contrast, was 19% higher in older donors. Again, the disaccharide composition was similar between age groups; the proportions of sulfated disaccharides were 33%, 17% and 13%, respectively. Immunohistochemistry indicated that the quantity of HS in macular Bruch’s membrane was around 50% lower in older donors.

Conclusions: The quantity of HS decreases with age in human Bruch’s membrane, while its disaccharide/sulfation composition remains unchanged. The presence of fewer highly sulfated disaccharides in older Bruch’s membrane means that fewer binding sites are available for the 402H variant of CFH. This may contribute to AMD pathogenesis through reduced CFH binding and increased complement activation.

Keywords: 412 age-related macular degeneration • 661 proteoglycans/glycosaminoglycans • 555 immunomodulation/immunoregulation