'MacuSIM': A microfluidic, in vitro model of the outer retina as an experimental platform for macular disease and therapeutic trials.

Lead Research Organisation: University of Southampton
Department Name: Clinical and Experimental Sciences

Abstract

Age-related Macular Degeneration (AMD) is a common blinding condition that results in the gradual loss of central vision. This is often associated with difficulties in performing simple daily activities such as reading, driving and recognising faces and is a particular concern for the elderly who are at a greater risk of developing the disease. In fact, one in three people will exhibit some form of AMD by the age of 70. AMD currently affects around 600,000 people in the UK alone and costs the economy £1.6 billion annually. This is predicted to increase as our population ages, where outpatient appointments have risen by 30% over the past 4 years and approximately 200 new AMD cases are reported daily. Although treatments exist for some forms of AMD, these are only applicable to 50% of cases and remain ineffective long-term. Thus, there is no cure for AMD at present, which is largely due to our limited understanding of how the disease develops. This constantly remains under investigation by scientists in order to develop new treatments.

A number of animals are used by AMD researchers to investigate the underlying causes of disease and in the development of new drugs. Of these, rodents are the most commonly used species which have provided important insights into detrimental changes associated with AMD. However, the structure of the rodent eye is markedly different to that of humans and therefore they have been questioned as a relevant model for the study of AMD. In fact, rodents do not have a macula, the specialised part of the eye affected in AMD. Monkeys (non-human primates) offer the closest similarity to the human eye but come with considerable ethical concerns and must be aged for long periods in order to exhibit disease symptoms. There has therefore been a longstanding requirement for a system that is capable of modelling the full disease spectrum of AMD, but that also exhibits fast turnaround times as well as economic viability.

One method of avoiding this difficulty is using cells cultured in a dish, which scientists have used effectively to make discoveries. However, whilst current cell culture models have allowed researchers to investigate individual components of the outer retina and how these are affected in AMD, none have succeeded in modelling the complex relationships and how they may collectively lead to disease. Similarly, no current system models the blood supply to the human retina and how it differs within the macula, the specific region of the eye affected.

In this proposal, we aim to validate and demonstrate the applicability of MacuSIM to AMD research, a novel cell culture model of the outer retina developed by the applicants that is capable of recapitulating the key cell types affected in AMD as well as their reliance on the retinal blood supply. This allows the region of the eye most susceptible to AMD to be investigated outside of animal models for the first time, thus reducing their requirement in AMD research. We will employ cutting edge techniques at the forefront of engineering and physics to manufacture this transformative model and will validate the system for use with various biological applications. Our experiments will then involve demonstrating its relevance to AMD research and benefits over existing methods, to promote its uptake within both the academic and pharmaceutical sectors. Here, we will model increased environmental stresses to the macula and test the ability of compounds to alleviate disease symptoms.

Through this research we hope to provide a more economic and high throughput model that will lead to the faster development of treatments for AMD patients and reduce associated costs to the NHS. In fact, this work will also benefit research into other eye diseases including Best disease, Stargardt disease and retinitis pigmentosa, highlighting the far reaching impacts and benefits of MacuSIM to society.

Technical Summary

Age-related Macular Degeneration (AMD) is the leading cause of irreversible sight loss in the developed world, accounting for 50% of registered blindness. The disease affects a central region of the retina, termed the macula, and is characterised by atrophy of the Retinal Pigment Epithelium (RPE) and/or choroidal neovascularisation. Disease management currently involves treatment with anti-VEGF inhibitors, although these are only applicable to 50% of cases and remain ineffective long-term. This is due an incomplete understanding of disease aetiology which requires further investigation to devise new treatments. Animal models, including rodents and non-human primates, are employed in AMD research to elucidate factors driving disease onset. However, whilst informative these either lack an anatomical macula (rodents), and/or entail extensive ethics. Associated time frames and costs are also unfavourable compared to in vitro models, which boast additional scientific benefits.

The proposed work aims to reduce and replace the number of animals used in AMD research through the development of MacuSIM, a microfluidic in vitro model that mimics key features of the human macula including the vasculature and environmental stresses specific to macula RPE. We will exploit cutting edge technologies, such as 3D printing and high-precision laser machining to manufacture MacuSIM. Established methods will then be used to validate use for RPE (iPSC-RPE, ARPE-19) and choroidal endothelial (RF/6A) cell culture including immunofluorescence, molecular biology techniques, electron microscopy, ELISA and cell viability assays. This novel approach has the potential to transform research into maculopathies and act as an invaluable drug discovery tool in both academia and industry. Thus, ongoing experiments will demonstrate its benefits over existing methods, where we will recapitulate the oxidative macula environment and test the ability of compounds to alleviate associated pathology.

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