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When the Rods & Cones Need Fixing

Posted by Ilena Di Toro | Posted on June 21, 2022

The rods and cones in the retina do a lot work when it comes to vision. Rods are sensitive to changes in light and dark, as well as shape in movement. Cones are sensitive to one of three colors, red, green and blue, and can detect fine details.

If the rods and cones aren’t working properly, can anything be done to “fix” them? Wouldn’t you know it, research is taking place in this area to learn more about the rods and cones.

Stem Cell Model of Albinism
Researchers at the National Eye Institute developed the first patient-derived stem cell model to study eye conditions related to oculocutaneous albinism. Pigment in the eye, specifically the retinal pigment epithelium, aids vision by preventing light from being scattered. Persons with oculocutaneous albinism don’t have pigment in the retinal pigment epithelium and they have an underdeveloped fovea, which is the part of the retina that is important for central vision.

Animal studies of albinism were limited because they lack a fovea. Creating a human stem cell model that mimics oculocutaneous albinism is an important advance in both understanding albinism and testing therapies to treat it. To create the model, scientists reprogrammed skin cells from persons without oculocutaneous albinism and those with the two most common types of oculocutaneous albinism, known as OCA1A and OCA2, into pluripotent stem cells. These cells were then differentiated to retinal pigment epithelium cells. The retinal pigment epithelium cells from the oculocutaneous albinism patients were the same as the retinal pigment epithelium cell from those without oculocutaneous albinism but they had greatly reduced pigmentation.

Researchers plan to use this model to see how the lack of pigmentation affects the physiology and function of the retinal pigment epithelium. The theory is if fovea development is depended on retinal pigment epithelium pigmentation and pigmentation can be improved in those with oculocutaneous albinism, then vision defects could be at the very least partially resolved. Currently, scientists are looking into how to use this model for screening of potential therapies for oculocutaneous albinism.

Mutations in the Rods
What is going on in the molecular level that is leading to blindness? Scientists at University of California, Irvine, in association with Max-Planck Institute of Biochemistry, in Germany studied this and what they found gave them insights into how the retina is compromised by diseases, such as retinitis pigmentosa.

Researchers studied mouse rod outer segments to learn more about the pathologies of certain gene mutations. Their finding show that the gene mutation would prevent disks within the rod cells from forming, which disrupts the structural integrity of the rod outer segments, and compromises the function of the retina, leading to blindness.

The research team used cryo-electron tomography and a new sample preparation method to get high resolution images of the rod outer segments. As a result, they were able to see the disc structures and assess the connectors between disks. Now that they have seen the disc structures, new therapeutic approaches to treating and possibly curing blindness can be developed.

Stem cell models and learning about the molecular structure of rods are shedding light into the whys of oculocutaneous albinism and retinitis pigmentosa. The information the researchers acquired will lead to therapies that will improve outcomes for people with these conditions.


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