p114RhoGEF signalling in retinal disease

Inherited retinal dystrophies are diverse group of diseases that lead to progressive vision loss. They affect the retina at the back of the eye. The retina is the tissue that senses light and transmits signals to the brain enabling one to see.

The condition can manifest itself from birth or can develop later in life. The disease is passed on within families due to mutations in specific genes that encode molecules important for vision. Mutations are alterations in the information in a gene. Therefore, mutations can affect how encoded molecules function.

Inherited retinal dystrophies are still very difficult to treat because mutations in many different genes can cause the disease. For many of these genes, we know very little how the encoded molecules function and why mutations disrupt such functions. Developing effective treatment for such diseases requires such knowledge.

This proposal focuses on a molecule called p114RhoGEF. Mutations in the gene encoding p114RhoGEF lead to inherited retinal dystrophy in adults. p114RhoGEF is part of a large molecular complex that makes specific cells in the retina to adhere to each other. This adhesion complex is called outer limiting membrane. The cells forming the outer limiting membrane include photoreceptors, which are the cells that sense light and stimulate nerve cells to transmit signals to the brain.

Adhesive complexes such as the outer limiting membrane have two main biological roles. They function as a glue that sticks neighbouring cells together, and they are regulatory hubs that signal to the cell to guide its behaviour and function. This signalling role also helps cells to deal with stressful conditions, such as those experienced by the retina in daily life over many decades.

Our pilot studies indicate that disrupting p114RhoGEF in the cells that form the outer limiting membrane in mice induces retinal dystrophy. We have also established alternative models of cells in culture that enable us to study the molecular processes that are deregulated in cells lacking functional p114RhoGEF. This includes cells donated by a patient carrying disease-causing mutations in p114RhoGEF that enable us to grow retina-like structures in plastic dishes.

In our proposed study, we aim to determine how the absence of functional p114RhoGEF leads to retinal disease and to identify the underlying molecular mechanisms.

We expect to identify new molecular and cellular processes responsible for retinal degeneration in patients carrying mutations in p114RhoGEF. Such processes can then be targeted for the development of future therapies. p114RhoGEF is part of an adhesive complex in the retina that includes other molecules that can be mutated in inherited retinal dystrophies. Therefore, such therapies might be useful for different types of genes mutated in retinal disease. We also expect to identify the main cell types affected by mutations in p114RhoGEF. Such knowledge will be important for the possible development of gene replacement approaches (gene therapy).

Inherited retinal dystrophies are a group of progressive blinding diseases caused by mutations in different genes. For many such genes, no effective treatments are available. This proposal focuses on ARHGEF18/p114RhoGEF. Biallelic mutations in the p114RhoGEF gene lead to adult-onset retinal degeneration. Here, we ask how p114RhoGEF malfunction leads to retinal degeneration with the aim to identify affected cell types and underlying molecular mechanisms that can be targeted for future therapeutic approaches.

We have developed cell-type specific knockout mouse models and novel in vitro systems to address this question. Pilot studies indicate that p114RhoGEF is important for retinal outer limiting membrane integrity and that its malfunction triggers pathologically relevant subcellular signalling mechanisms that regulate gene expression. We hypothesize that p114RhoGEF regulates retinal structure and function by maintaining cell-cell adhesion and adhesion-regulated signalling mechanisms at the outer limiting membrane and, thereby, prevents retinal tissue damage and vision dysfunction.

We propose to use newly developed mouse models and in vitro systems based on cultured retinal cell lines and retinal organoids generated from patient-derived induced pluripotent stem cells to determine the molecular mechanisms underlying retinal degeneration induced by p114RhoGEF dysfunction.

We expect to establish a new paradigm of how cell-cell adhesion at the retina's outer limiting membrane is regulated by p114RhoGEF-driven RhoA signalling, and how such mechanisms might be targeted in the future for the development of therapies for retinal dystrophies caused by mutations in the p114RhoGEF gene or, possibly, other genes encoding components of the outer limiting membrane.