U of T researcher focuses on preventing vision loss in patients with rare genetic disorder

An image of a larval zebrafish retina
Vincent Tropepe, a professor in U of T's department of cell and systems biology, is studying the retinas of larval zebrafish, pictured, as part of his research into vision loss associated with Usher Syndrome (photo by Jeff Stulberg)

Usher syndrome, a genetic condition that results in hearing and vision loss in childhood, affects about four out of every 100,000 Canadians and accounts for over 50 per cent of the Deafblind community.

Now, with new funding from Fighting Blindness Canada (FBC), Vincent Tropepe, professor and chair of the department of cell and systems biology in the Faculty of Arts & Science, will try to identify what, exactly, causes the retinal degeneration that results in Usher syndrome blindness.

“I’m honoured to have FBC’s support in pursuing this research project,” says Tropepe, a specialist in the production of nerve cells and their role in sensory processing.

Tropepe’s lab will conduct research on zebrafish, a small freshwater species native to South Asia. Zebrafish contain genetic clues to the way retinal degeneration happens in humans since they possess a gene that can be mutated to mimic a gene found in 20 per cent of Usher patients.

The gene mutation in the zebrafish leads to degeneration in the outer segment of the retina – the region that captures light and facilitates vision. The result is a progressive loss of photoreceptors.

Tropepe’s lab will focus on a particular protein associated with the mutated gene that is also thought to be crucial to the photoreceptors’ larger support system. If researchers can find defects in this protein and the structure it is part of, they may be able to reveal new mechanisms that maintain the stability and functionality of the photoreceptors.

Professor Vincent Tropepe is the chair of the department of cell and systems biology in the Faculty of Arts & Science (photo by Diana Tyszko)

Such a result would be a breakthrough for gene therapy since it could prevent retinal degeneration and resulting vision loss in Usher syndrome patients. Moreover, Tropepe can use existing research into Usher-related deafness to help uncover the mechanisms that lead to blindness.

“The way that photoreceptors need this protein to support their structure is analogous to the ways in which appendages called cilia support the sensory cells of the inner ear,” says Tropepe.

“When this protein is absent or defective, the inner ear cells malfunction and the result is hearing loss. At the moment, it’s a complete mystery how this protein’s degradation or absence affects vision loss, but we speculate it’s similar to what happens in hearing loss. Our research will help identify the components of this protein and how it supports the structure and function of photoreceptors responsible for vision.

“If we can stabilize the larger structure when that particular protein is defective in patients with Usher syndrome, it could form the basis for a novel drug discovery.”

Tropepe’s lab comprises members of all levels, from graduate students to postdoctoral researchers. He says the funding will “support graduate student research and recruitment, as well as allowing me to maintain a very exciting international collaboration on this and related topics.”

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