Professor Alan Wright FRCP FRSE FMedSci: Medical and Developmental Genetics
Retinal Degeneration Programme
Summary
The aims of this programme are to identify and characterise genes involved in both simple and complex forms of human retinal degeneration, to understand disease mechanisms and to work towards effective therapies. We are pursuing three general approaches. Firstly, we are analysing the functions of two genes, which we previously identified, that each cause monogenic forms of retinal degeneration (RPGR, RPGRIP1). The products of these two genes interact and both localise to spindle poles in dividing cells and to basal bodies and ciliary axonemes in ciliated cells, including photoreceptors.
Figure 2 In 2003, we identified the cause of late-onset retinal macular degeneration, a genetic model of age-related macular degeneration (AMD), as a mutation in the C1QTNF5 gene10. The gene product is a short-chain collagen which is co-expressed with the Membrane Frizzled Related Protein (MFRP) in retinal pigment epithelium and interacts with MFRP at the plasma membrane9-10. Other interacting proteins or glycosaminoglycans have recently been identified which are currently being analysed and provide clues as to the function of C1QTNF5 and its role in macular degeneration. The sub-retinal pigment epithelium deposits and choroidal neovascularisation seen in L-ORMD are strikingly similar to those seen in AMD so that we hope that understanding C1QTNF5 disease will help to elucidate the more common and complex disorder, AMD. In parallel with this we have been analysing genome-wide association studies in AMD in close collaboration with clinicians in Edinburgh, Cambridge and London. This led to the identification of variants in the complement component 3 (C3) gene as a susceptibility factor in AMD12. Other potential risk loci are currently being followed up.
Another area that has been an increasing focus of our research is the identification of cell death mechanisms and pathways in photoreceptor degenerations1-2. We have proposed that oxidative stress at the level of mitochondria is a key factor regulating the rate of degeneration (Figure 3). We are currently measuring oxidative stress within mitochondria in a variety of genetic disorders and physiological states using redox-sensitive enzyme and antioxidant assays. We have also been trying to modify rates of cell death using mitochondrially targeted drugs.
Figure 3 Rates of inherited neurodegeneration in the retina and brain of different species are inversely proportional to life span and mitochondrial reactive oxygen species formation1.
Lab Members
Current lab members involved in this work are:
- Brian Tulloch BSc (MRC core funding)
- Chloe Stanton BSc (PhD student, MRC studentship)
- Retinal Degeneration Programme
(this page) - Retinal Degeneration Programme Publications
We have a developed a conditional mouse model for RPGR loss-of-function mutations and use both in vivo and in vitro methods to analyse the protein functions and to detect other protein interactions. Secondly, we are developing methods for evaluating and modifying mitochondrial oxidative stress in neurodegenerative disorders in general and retinal degeneration in particular. We have both experimental and theoretical evidence that intra-mitochondrial oxidative stress is a key factor in determining rates of degeneration.
The final approach is to investigate genetic influences in the genetically complex disorder age-related macular degeneration (AMD), the commonest cause of blindness in the western world, firstly using a human model of this disorder, called late-onset retinal macular degeneration (L-ORMD), which is an autosomal dominant trait caused by mutation in the C1QTNF5 gene, encoding a short-chain collagen. We have made mouse knock-out and knock-in models of C1QTNF5 disease, the latter containing the common Ser163Arg mutation. We have also been studying C1QTNF5 protein interactions, using a variety of methods and have identified some interesting interacting partners. In parallel with this, we have been collaborating with clinicians in Edinburgh, Cambridge and London to perform and analyse -wide association scans in Scottish and English AMD case-control series with a total of >1200 cases and a similar number of unaffected controls.
Purpose
- To identify and characterise genes and their products that are responsible for both simple monogenic and genetically complex human retinal degenerative disorders.
- To identify disease mechanisms common to retinal and other neurodegenerative disorders.
- To help develop effective therapies for these disorders.
Approach, Progress Future Work
For many years we have been involved in the mapping, identification or characterisation of monogenic disorders associated with human retinal degenerations, including RPGR, RPGRIP1, TULP1, BBS4, NR2E3 and C1QTNF5 (Figure 1). We continue to examine the functions of RPGR, RPGRIP1 and C1QTNF5 proteins in health and disease. We use a variety of methods to study gene function, principally in cellular or animal models of these blinding disorders, together with immunohistochemical and biochemical analyses, RNA interference and protein interaction studies. In order to characterise protein interactions, we use yeast two-hybrid analysis, affinity chromatography, plate binding assays, surface plasmon resonance and tandem affinity purification methods. Using such methods, we showed that RPGR interacts with RPGRIP1 and localises both to cell nuclei and to spindle poles, basal bodies and cilia5,6 (Figure 2). RPGR also interacts with the multifunctional chaperone nucleophosmin5 and co-immunoprecipitates with a variety of centrosomal or microtubular transport proteins, suggesting a role in the polarised trafficking of proteins to the photoreceptor outer segments7. We are now looking at the effects of RNAi knockdown and post-translational modification on the functions of RPGR and RPGRIP1 in a ciliated cell model.
