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March 20, 2016

Penn Vet blindness study shows how eye cells regenerate before they die

In at least three canine diseases, photoreceptor cells proliferate before blindness takes hold

The causes of inherited blindness are so staggeringly complex that scientists have identified over 300 genes related to retinal degeneration in humans. However, new research on dogs conducted by the Penn School of Veterinary Medicine has uncovered a key fact that could help scientists better understand and eventually treat early-onset blindness.

The surprising finding is that before photoreceptor cells in the eyes die and blindness takes hold, there is actually a period of regeneration, reports Penn News.

Photoreceptor cells, better known as rods and cones, capture light and turn it into a neural signal. Normally, cell division in dogs' eyes stops within two weeks of birth.

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However, scientists have observed cell proliferation in the eyes several weeks beyond that in three canine diseases.

There is a brief period of "balance" as some cells die and others divide into more cells. Eventually, however, "the balance between death and division tips, and the retina degenerates," said professor Gustavo Aguirre to Penn News. 

Penn scientists first observed this phenomenon in 2011, when they examined puppies with early retinal degeneration (ERD) and found that rods in their eyes had a period of proliferation before cell death caused blindness.

In their latest study, the scientists looked at two more diseases that cause early-onset blindness in dogs: X-linked progressive retinal atrophy (XLPRA) and rod cone dysplasia (RCD). Unlike ERD, these two diseases are quite "similar and comparable" to equivalent conditions in humans, the study noted.

Interestingly, there appeared to be two distinct groups of rod cells, one that thrived and the other that died.

"There are distinct subsets of [photoreceptor] cells: one that is dying, while the other is dividing," the study said.

It is unclear whether these proliferating cells play a "primary" or a "bystander" role as the eye degenerates. Scientists hope that further investigation into this phenomenon will allow them to shine a light into the progression of blindness. 

Read the full story here.

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