Investigating age-dependent regulation of complement in human eye tissues: implications for Age-related Macular Degeneration

Over half of all cases of blindness in the UK are caused by Age-related Macular Degeneration (AMD), with about 50 million people affected worldwide. AMD is a disease that damages a part of the retina (called the macula) and leads to central vision loss. While there are associations with diet and environmental factors, there is clear evidence that the risk of developing this disease is strongly influenced by our genes. Recent studies revealed that a common variant of one particular gene (known as Complement Factor H or CFH for short) strongly increases the risk of developing AMD. This variant (called the Y402H polymorphism) is present in about 35% of people of European descent and it results in a small, but significant, change in the CFH protein that alters its functional properties. We have recently made an important discovery that the normal and disease-associated forms of CFH (referred to as '402H' and '402Y', respectively) differ in their ability to recognise a particular group of carbohydrate molecules (called GAGs) in the eye. This may influence the localisation of the CFH protein, which is likely to be important to the development of AMD since CFH controls part of our immune system that distinguishes healthy from diseased tissues. If the CFH protein is not present in the correct location (or if there is simply less of it), as we believe is the case for the 402H form of CFH, then the resulting disruption of the immune system would lead to inflammation and tissue damage; i.e. major features of AMD.
Based on our recent (MRC-funded) experiments we have preliminary evidence for age-related changes in the human eye that appear to influence CFH function. We think it likely that normal changes in the eye, which occur during ageing, may be important in the development of AMD, in particular for individuals with an 'at-risk' genetic profile (e.g. those having the 402H form of CFH). Therefore, one aim of this research project is to test this idea by analysing eye tissues from donors of different ages (i.e. ranging from 30 year olds to those over 80), which will be supplied by the Manchester Eye Bank. For example, we will characterise how the structure of GAGs change with age and how this influences the functions of the 402H and 402Y forms of CFH. To our knowledge, this is a unique approach that is not being pursued by other groups, who are mainly focusing on the later stages of AMD, i.e. when tissue damage has already occurred. We have also identified other changes that occur in healthy human eyes that might additionally contribute to the initiation and progression of AMD. We aim to investigate these important new discoveries in further detail to determine whether they might be useful in the design of improved treatments for AMD, which could potentially be targeted early in the disease process. If they do, we are well placed (i.e. with the necessary experience/facilities) to translate our findings from the laboratory to the clinic.
Our own expertise in Manchester, for example in AMD, the CFH protein and carbohydrate chemistry (along with the molecular tools we have developed over the last 8 years), will be supported by a network of scientific collaborators (both in the UK and abroad) providing access to specialised biochemicals and cutting-edge technologies.
Overall these unique and novel studies are likely to lead to a greater understanding of the causes of AMD and may allow the development of new therapeutic strategies for treating this devastating disease.

Dysregulation of the complement system is thought to underlie Age-related Macular Degeneration (AMD), where the Y402H polymorphism in the complement factor H (CFH) gene is a major risk factor for this common form of blindness. Our previous studies have shown that this polymorphism adversely affects the interaction of the disease-associated 402H variant with sulphated glycosaminoglycans (e.g. heparan sulphate (HS) in the human Bruch's membrane), which might result in local chronic inflammation promoting the initiation and progression of tissue damage within the macula. More recently we have obtained preliminary evidence that age-related changes in Bruch's membrane (e.g. in HS composition) may specifically influence the binding of CFH 402H. On this basis, we have hypothesised that normal changes in the macula occurring during ageing contribute to the development of AMD, in particular in individuals carrying the CFH 402H allele. Therefore, the aim of this research is to test this new hypothesis by analysing human eye tissues from donors of different ages (i.e. 30-80+ years); we will characterise how the Bruch's membrane changes with age and how this influences the functions of CFH (in a 402H/402Y allotype-specific manner). This multidisciplinary project will involve immunofluorescent microscopy, HS compositional analysis, mass spectrometry, complement assays, affinity chromatography, microtitre plate-based binding assays and biophysical techniques; here we will utilize the human eye samples we have collected (over the last 3 years), with additional samples to be provided by the Manchester Eye Bank. The project is focused at understanding early changes in the human eye that may be responsible for the initiation/progression of AMD, rather than the later stages, i.e. once tissue damage has occurred. In this regard, our studies have the potential to facilitate the design of improved treatments for AMD, which could potentially be targeted early in the disease process.

The aim of this project is to determine how normal age-related changes in the human eye contribute to the development of Age-related Macular Degeneration (AMD), i.e. in genetically predisposed individuals. Therefore, this work has the potential to have major impacts on the diagnosis, treatment and management of this devastating disease. AMD is the major cause of blindness in the developed world and its incidence is rising due to the demographic of the aging population; it imposes a large socioeconomic burden on the healthcare services (e.g. the NHS), AMD suffers themselves and their carers, both in the UK and throughout the Western world. Given that AMD affects reading, driving etc., this greatly reduces the ability of suffers to contribute to creative and work-related activities. Our research is focused on understanding age-related changes in the human eye that precede AMD and is aimed at facilitating the development of novel therapeutic strategies to slow the progression or indeed prevent the initiation of the disease. This could have direct commercial benefits (e.g. to the UK economy) through drug sales, licensing of IP, spinout companies etc. In addition, our findings could lead to new ways of identifying and treating individuals at risk from AMD (i.e. where preventative therapies and lifestyle changes could enable better management of this condition); currently AMD is not usually diagnosed until after visual changes (blurring/distortion) have occurred. Such changes in policy (e.g. within the NHS) could have a major impact on reducing the socioeconomic burden of AMD. Our public engagement programme (e.g. open days, museum events and press releases) is aimed at increasing the awareness of AMD within the general public, which might also facilitate early diagnosis.