Pathological blindness: why exactly do photoreceptors die?

31.05.2022 – 08:00

Swiss National Fund / Fonds national suisse

Bern (ots)

Retinitis pigmentosa, a common eye disease, causes a slow loss of retinal rods and cones. The analysis of certain cells gives an insight into the genesis of this process.

Night blindness and tunnel vision, then a loss of contrasts and colors, ending in the most serious cases with complete blindness: this is the typical evolution of retinitis pigmentosa. This hereditary disease of the retina affects approximately 1 in 3000 people in Switzerland. In these patients, the rods, responsible for black and white vision, begin to deteriorate, followed by the cones that allow color perception.

“We know very well the evolution of degeneration at the advanced stage. On the other hand, the molecular mechanisms at the origin of the disease remain a mystery”, explains Christian Grimm, head of the retinal cell biology laboratory within the University of Zürich. As part of a study funded by the SNSF, his research team carried out analyzes using innovative techniques, which revealed the active genes in the photoreceptors at the very beginning of the degenerative process. The purpose of this study? Find a treatment that prevents retinal degeneration.

To do this, the researchers used mice. Due to a congenital genetic anomaly, they indeed develop retinitis pigmentosa with an evolution identical to that of the human pathology. Nearly 20,000 rods and cones have been isolated from the retinas of mice. The scientists then determined the phase of degeneration of each photoreceptor and which genetic messages had already been read at that time. This method provides information on the type and quantity of proteins produced by the cell. Thanks to comparisons of healthy and diseased photoreceptors, more than 200 proteins – mainly produced in the early stages of the disease – have been identified.

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Is the gene an ally or an enemy?

The scientists noted, in the rods, the particularly frequent reading at the beginning of the degenerative process of a gene called EGR1 which contains the message for the EGR1 protein. This protein is known to control the activity of many other genes. Shortly before the death of the cell, the gene is no longer read in the rods, but in the cones, which in turn die.

The research team therefore assumes that the EGR1 protein plays a considerable role in the degenerative process. “However, we do not know if the protein tries to help the photoreceptors to survive or if it accelerates degeneration”, specifies Christian Grimm. This question is the subject of a follow-up project in which the EGR1 gene is on the one hand deactivated and on the other hand hyperactivated. In the best of cases, the results of this project will constitute a starting point for the development of a new treatment.

Even if in recent years new generation gene therapies have successfully treated hereditary eye diseases, including a certain form of retinitis pigmentosa, the problem remains unresolved. “There are more than 250 mutations responsible for blindness. The development of a gene therapy for each of them would prove to be far too expensive”, explains Christian Grimm. “That’s why we are working to develop a suitable treatment for different forms of blindness.”

Karademir et al.: Single-cell RNA sequencing of the retina in a model of retinitis pigmentosa reveals early responses to degeneration in rods and cones. BMC Biology (2022): https://doi.org/10.1186/s12915-022-01280-9D

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The text of this news and further information are available on the website of the Swiss National Science Foundation.

Contact:

Christian Grimm, Laboratory for Retinal Cell Biology, Department of Ophthalmology, University Hospital Zurich, University of Zurich, Wagistrasse 14, 8952 Schlieren, Tel: +41 43 253 30 01, E-mail: [email protected] .ch

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