A study conducted at The Scripps Research Institute (TSRI) shows that nerve cells and blood vessels in the eye constantly “talk” to each other to maintain healthy blood flow and prevent disease. “It turns out these neurons produce a chemical critical for the survival of blood vessels and the survival and function of photoreceptors–the most important cells for maintaining sight,” said TSRI Professor Martin Friedlander, senior author of the study.
For such a small organ, the eye is extremely complex. Light enters through the pupil and passes through four layers in the retina before reaching the light-sensitive photoreceptors. “The retina has a very sophisticated architecture,” said Friedlander. “If you have a little extra fluid, some swelling or a few dead cells, light isn’t going to come through correctly and vision can be impaired.”
The second, intermediate layer of the retinal blood vessels seems to activate during periods of low oxygen and acts as a “reserve” of blood vessels in the retina. When blood flow and oxygen levels are low, a transcription factor called hypoxia-inducible factor (HIF) triggers the production vascular endothelial growth factor (VEGF). VEGF then prompts new blood vessel growth, bringing more oxygen to the area.
Unfortunately, these new blood vessels can leak blood and other fluids and obscure vision. This is the case with age-related macular degeneration—a “wet” version of which causes vision loss in the center of the eye—and diabetic retinopathy—in which some people with diabetes develop blurry or patchy vision.
In this study, the team focused on neurons called amacrine cells and horizontal cells, which have a known role in “preprocessing”—or adjusting—electrical signals transmitted to the brain from the photoreceptors after they have been stimulated by light photons. These cells first caught the researchers’ attention because they appear to wrap themselves around the blood vessels (all together called the vasculature) of the intermediate layer.
“We wondered if these neurons were actually altering the way the vasculature forms and behaves,” said TSRI Research Associate Peter Westenskow, co-first author of the paper.
Since the retina is a direct extension of the brain, scientists can now easily visualize how neurons, blood vessels and other neurological players work together. Further, their study not only has implications for treating vision loss, but also brain diseases such as Alzheimer’s, Parkinson’s and even amyotrophic lateral sclerosis (ALS).
“For example, patients with Alzheimer’s get protein deposits in the brain, and we can see similar deposits in the backs of the eyes of patients who have macular degeneration,” said Friedlander. “If we can better understand what leads to accumulations of these abnormal proteins in the eye, that will hopefully also give us insight into how the brain works.”
The study published in The Journal of Clinical Investigation, has implications for treating diseases such as diabetic retinopathy and age-related macular degeneration—the leading causes of vision loss in adults. Since the eye is often a good model for understanding the workings of the brain, the findings also provide clues to major neurological diseases such as Alzheimer’s.
More details on this study and the press release can be accessed here.