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Lab for Retinal Gene Therapy

Our Passion

Genetics and Molecular Diagnostics

In cooperation with human geneticists, we identified disease-associated genes or mutations in IRD patients (Ebermann, School et. al. 2007, Khan, Becirovic et al. 2017, Burkards, Kohl et al. 2018). However, up to 40% of IRD patients studied remain without a confirmed molecular genetic diagnosis. The latter is an important prerequisite to be treated by novel approaches such as gene therapy. One reason for the inadequate diagnostic rate is that despite the use of novel methods, such as massive parallel sequencing, many mutations remain undetected or are difficult to interpret in terms of their pathogenicity. Molecular genetic diagnostics are usually limited to the identification of potential pathogenic variants at the genomic level. Analysis at the transcript level is complicated by the fact that the relevant transcripts are usually not present in cells that can be routinely obtained from patients (e.g. blood cells). We have developed an approach that is suitable to enable the analysis of retinal-specific transcripts in blood cells. In cooperation with national and international ophthalmic clinics, we plan to use this new approach for the diagnosis of IRD patients, which could help filling an important gap in molecular diagnostics.

Pathomechanisms

To elucidate molecular disease mechanisms, we focus on the identification as well as functional characterization of (epi)genetic factors associated with disease development. One of the main focuses is the investigation of the effects of mutations at the transcript level. We have already identified many mutations in various IRD-associated genes (e.g. CDH23, PRPH2, CNGB1, RHO, CLRN1) that cause aberrant splicing and were able to uncover novel genotype-phenotype correlations. At the protein level, we uncovered mutations that affect protein expression, localization, transport and protein-protein interactions. In this context, we have established fluorescence resonance energy transfer (FRET) as a new method to study protein-protein interactions and their biochemical properties such as binding affinities and kinetics in so-called outer segments (i.e. light-detecting compartments of photoreceptor cells) (Becirovic, Ebermann et al. 2008, Becirovic, Nakova et al. 2010, Becirovic, Nguyen et al. 2014, Becirovic, Bohm et al. 2016, Becirovic, Bohm et al.,  2016, Nguyen, Bohm et al. 2016, Bohm, Riedmayr et al. 2017, Riedmayr, Bohm et al. 2020). In the context of epigenetic analyses, we are currently investigating the effects of IRD therapies on the epigenome of treated animals inside and outside the eye. These findings may help to better understand the basis of disease development and to develop tailored therapies for specific forms of IRD. 

 

Development of novel tools for therapy

The development of innovative gene therapy approaches is currently the thematic focus of our research. We are particularly interested in the treatment of most common IRD forms: retinitis pigmentosa, Stargard disease and Usher syndrome. In this context, we use the knowledge gained from molecular diagnostics and the investigation of disease mechanisms to develop tools that can be used to cure IRD that have so far been difficult to treat. These include autosomal dominant forms of retinitis pigmentosa, or diseases caused by mutations in large genes (such as Usher syndrome or Stargardt disease). In our studies in mouse models, we have already provided proof-of-concept for novel therapeutic approaches. These include the use of small molecules, AAV-mediated gene supplementation, and CRISPR/Cas-mediated genome editing (Michalakis, Muhlfriedel et al. 2010, Koch, Sothilingam et al. 2012, Petersen-Jones, Occelli et al.  2018, Bohm, Splith et al. 2020, Panagiotopoulos, Karguth et al. 2020, Riedmayr, Hinrichsmeyer et al. 2022).
With our cooperation partners from different countries we want to evaluate these therapeutic approaches in large animal models for IRD like pigs and dogs. These are much better suited than common rodent models with respect to a) the anatomy of the eye and the disease mechanism dependent on it b) the investigation of effects of different forms and methods of application to deliver the therapeutics into the target cells and c) the analysis of side effects. Therapeutic studies in large animal models would therefore both facilitate the interpretation of the data obtained and accelerate the initiation of clinical trials.