Posts tagged photoreceptor cells
Articles and news from the latest research reports.
The eyes have it: Scientists reveal how organic mercury can interfere with vision
More than one billion people worldwide rely on fish as an important source of animal protein, states the United Nations Food and Agriculture Organization. And while fish provide slightly over 7 per cent of animal protein in North America, in Asia they represent about 23 per cent of consumption.
Humans consume low levels of methylmercury by eating fish and seafood. Methylmercury compounds specifically target the central nervous system, and among the many effects of their exposure are visual disturbances, which were previously thought to be solely due to methylmercury-induced damage to the brain visual cortex. However, after combining powerful synchrotron X-rays and methylmercury-poisoned zebrafish larvae, scientists have found that methylmercury may also directly affect vision by accumulating in the retinal photoreceptors, i.e. the cells that respond to light in our eyes.
(Image: A cross section of a zebrafish eye shows the localization of mercury in the outer segments of photoreceptor cells.)
Dr. Gosia Korbas, BioXAS staff scientist at the Canadian Light Source (CLS), says the results of this experiment show quite clearly that methylmercury localizes in the part of the photoreceptor cell called the outer segment, where the visual pigments that absorb light reside.
“There are many reports of people affected by methylmercury claiming a constricted field of vision or abnormal colour vision,” said Korbas. “Now we know that one of the reasons for their symptoms may be that methylmercury directly targets photoreceptors in the retina.”
Korbas and the team of researchers from the University of Saskatchewan including Profs. Graham George, Patrick Krone and Ingrid Pickering conducted their experiments using three X-ray fluorescence imaging beamlines (2-ID-D, 2-ID-E and 20-ID-B) at the Advanced Photon Source, Argonne National Laboratory near Chicago, US, as well as the scanning X-ray transmission beamline (STXM) at the Canadian Light Source in Saskatoon, Canada.
After exposing zebrafish larvae to methylmercury chloride in water, the team was able to obtain high-resolution maps of elemental distributions, and pinpoint the localization of mercury in the outer segments of photoreceptor cells in both the retina and pineal gland of zebrafish specimens. The results of the research were published in ACS Chemical Biology under the title “Methylmercury Targets Photoreceptor Outer Segments”.
Korbas said zebrafish are an excellent model for investigating the mechanisms of heavy metal toxicity in developing vertebrates. One of the reasons for that is their high degree of correlation with mammals. Recent studies have demonstrated that about 70 per cent of protein-coding human genes have their counterparts in zebrafish, and 84 per cent of genes linked to human diseases can be found in zebrafish.
“Researchers are studying the potential effects of low level chronic exposure to methylmercury, which is of global concern due to methylmercury presence in fish, but the message that I want to get across is that such exposures may negatively affect vision. Our study clearly shows that we need more research into the direct effects of methylmercury on the eye,” Korbas concluded.
(Source: lightsource.ca)
Research finds protein that prevents light-induced retinal degeneration
Research led by Minghao Jin, PhD, Assistant Professor of Ophthalmology and Neuroscience at the LSU Health Sciences Center New Orleans Neuroscience Center of Excellence, has found a protein that protects retinal photoreceptor cells from degeneration caused by light damage. This protein may provide a new therapeutic target for both an inherited retinal degenerative disease and age-related macular degeneration. The paper is published in the February 13, 2013 issue of the Journal of Neuroscience.
The visual cycle is essential for regenerating visual pigments that sense light for vision. However, abnormal visual cycles promote formation of toxic byproducts that contribute to the development of age-related macular degeneration (AMD), the leading cause of vision loss in elderly people that affects an estimated 2 million Americans. The mechanisms that regulate the visual cycle have been unclear. Identification and characterization of regulators of the visual cycle enzymes are critical for understanding these mechanisms.
RPE65 is a key enzyme involved in the visual cycle. RPE65 mutations have been linked to early onset vision loss, retinal degeneration, and blinding eye diseases. Despite such importance, the mechanisms that regulate the function of RPE65 are unknown. To identify and characterize previously unknown inhibitors of RPE65, the scientists tested five candidate proteins. Using gene screening, the LSUHSC research team discovered that one of them – fatty acid transport protein 4 (FATP4) – is a negative regulator; it inhibits RPE65.
"We found that FATP4 protects retinal photoreceptor cells from experimentally-induced retinal degeneration," notes Nicolas Bazan, MD, PhD, Boyd Professor, Ernest C. and Yvette C. Villere Endowed Chair of Retinal Degeneration, and Director of the LSU Health Sciences Center New Orleans Neuroscience Center of Excellence, who is a co-author of the paper.
Recently, mutations in the human FATP4 gene have been identified in patients with a certain recessive disorder which also features one of the toxic byproducts associated with abnormal visual cycles. This byproduct, called A2E accumulates in retinal pigment epithelial cells with age, prompting a call for further investigation to determine whether FATP4 mutations cause age-related vision impairment and retinal degeneration.
"These findings suggest that FATP4 may be a therapeutic target for the inherited retinal degenerative disease caused by RPE65 mutations and AMD," concludes Dr. Jin.
(Image: Eyeland Design Network)