Abstract for laypersons

For modeling Usher Syndrome (USH), we have modified the genome of a pig to carry a sequence that cause congenital deafness, vestibular dysfunction and vision loss in human patients. The latter is severely affecting patients, because there is no treatment for this component of the disease, leading to physical impairment, social isolation and psychological burden. In previous studies, we showed that disrupting the function of the causative USH1C gene in the pig resulted in the same picture that is observed in USH1 patients, proving its relevance as a model of the disease. While research is ongoing on the assessment of distinct therapeutic strategies, the focus of this project is on elaborating molecular and cellular consequences of the genetic defect in USH1C. This is important for understanding basic mechanisms of the disease, which might lead to novel treatment approaches as well as for estimating the curative window of opportunity, i.e. the period of time within which a therapy has a reconstituting effect. We will specifically execute this by investigating gene therapy for USH1C, which builds on the well-established strategy to overcome the loss of genetic function by viral vectors. In this approach, the missing genetic information is encapsulated in virus particles and shuttled into the cells of the retina where it will produce the lacking USH1C gene product, harmonin. Finally, we will also provide experimental animals for collaboration projects within SPP2127 and will improve the interpretation of vision in pigs by comparing clinically relevant examination tools such as electroretinography with behavioral parameters and molecular signatures.

Abstract for scientists

In an established pig model for Usher Syndrome (USH) (Grotz et al. 2022, EMBO Mol Med, doi:10.15252/emmm.202114817), we have partially humanized the porcine USH1C gene to carry the human disease-relevant R31X nonsense mutation. Stimulated by our previous studies that have documented the characteristic combination of congenital deafness, vestibular dysfunction and vision loss, we here aim at clarifying the retinal component of USH1C at more molecular detail. In particular, the recently identified abundance of the USH1C protein product, harmonin, in Mueller Glia cells (MGC) raised the question for their relevance in disease progression in addition to established deformation of photoreceptor cells (PRC). This is of outstanding relevance for the required cell-type specificity of future therapeutic approaches as well as for the identification of potentially new treatment strategies. Characterizing disease progression by combined examination with clinically relevant tools such as electroretinography (ERG), behavioral tests and molecular signatures over time is also important for estimating the therapeutic window of opportunity and for optimizing the definition of primary endpoints in future pre-clinical treatment approaches. In our project, we will make use of this approach in a classical gene addition therapy, using AAV9 vectors, which showed transduction of both, PRC and MGC, in preliminary experiments. Overall, we expect not only insight about the general improvement of AAV-based gene therapy in USH, but also information about the spatial range of treatment, the reconstitution of harmonin abundance in distinct cell types and potential immunological side effects. In collaboration, we will also support partners within SPP2127 by providing experimental animals for their respective research programs.