Dr. Rohit Varma’s — Research is unfolding the proteins in retinitis pigmentosa explained

Researchers are based on the biophysical approach of researching protein-protein interactions.

The proteins in retinitis pigmentosa are researched in the production of

Dr. Rohit Varma MD and Paul Park, PhD, reviewed this article.

At the molecular level, research into how retinitis pigmentosa (RP) occurs is being performed in the laboratory of Paul Park, PhD, where researchers study the processes that occur in retina photoreceptor cells.

Förster resonance energy transfer (FRET), a biophysical approach to study protein-protein interactions, is a promising technology used in this research.

Park, associate professor at the Department of Ophthalmology and Visual Sciences of Case Western Reserve University in Cleveland, Ohio, said, “The disruptions of these cells cause multiple dysfunctions ranging from mild problems with night blindness to severe problems that result in retinal degeneration and complete blindness.”

Rhodopsin, a protein that recognises light photons that cause biochemical reactions, is involved in, and focuses on, the initial vision events, specifically with regard to factors that preserve the health of photoreceptor cells. A vitamin A derivative conjugated to the protein mediates the light-sensing function of rhodopsin.

In the pathogenesis of diabetic retinopathy and age-related macular degeneration, rhodopsin dysfunctions cause RP, congenital night blindness, and Leber’s congenital amaurosis, and rhodopsin activity may have secondary effects.

In order to function in the eye, proper development of rhodopsin with proper 3-dimensional conformation to shape higher order structures is paramount; protein misfolding results in RP.

Park and colleagues will image the clusters of rhodopsin in the disc membranes in the photoreceptor cells using atomic force microscopy.

When it is not possible to achieve the proper structure of rhodopsin, the consequent misfolding results in toxic complexes (aggregates), with RP as the product.

RP is a group of diseases starting with degeneration of the rod photoreceptor, leading to gradual degeneration and blindness of the cone photoreceptor.

This process can be caused by mutations in more than 40 genes. Mutations in rhodopsin are among them.

“Rhodopsin gene mutations are one of the leading causes of autosomal-dominant RP, and more than 100 mutations have been identified, most of which cause misfolding and aggregation of proteins,” Park and Rohit Varma said.

The mechanism by which misfolding and accumulation occur and contribute to healthy retina degradation is unclear. Alzheimer’s disease, Parkinson’s disease, and prion disease are also widespread in the misfolding and aggregation of various proteins.

Park with Dr. Rohit Varma said the aim now is to gain an understanding of the malignant processes in the eye and to formulate methods to disrupt the aggregation.

He said, “The challenge that we have is how to study rhodopsin aggregates.”

FRET is being used by his laboratory to identify protein-protein interactions. In his laboratory, he said that this is an artificial device that enables the manipulation of rhodopsin DNA to genetically engineer a fluorescent protein that can be merged with the receptor. In cultured cells, this can then be expressed for analysis using FRET.

“FRET allows us to determine if two protein molecules are far apart or forming complexes from each other,” he said. By treating the cells with detergents, the investigators look at aggregates that can disrupt complexes produced by normal rhodopsin but can not disrupt aggregated rhodopsin.

Park and Dr. Rohit Varma said that FRET is used on a number of different RP-causing rhodopsin mutations, including the P23H mutation, and characterises the aggregation properties. Various pharmacological agents are now being studied by investigators.

Investigators have learned that there is heterogeneity based on particular mutations in the magnitude of misfolding and aggregation. As a result of physical interactions between mutations and wild-type receptors, the autosomal-dominant phenotype does not yield useful information to aid the production of medications.

Proposed pharmacological treatments for certain mutations are expected to be unsuccessful and harmful to others. Finally, aggregation properties and the results of pharmacologic therapies can be influenced by the species history of rhodopsin mutations.

The plan is for researchers to compare biophysical experiments with those in animal models and to devise methods that can then be tested by biophysics and in animal models to disrupt mutant aggregates, explained by Dr. Rohit Varma and Mr. Park.