A team of researchers from Brown University discovered that opsin 3, a protein that is closely related to rhodopsin, which enables low-light vision, plays a role in adjusting the pigment amount produced in human skin. This is a determinant of skin color.
Once human beings spend time in the sun with no proper skin protection, the sun’s ultraviolet (UV) radiation prompts the skin to produce more melanin and become darker. The melanin protects the skin against cancer causing effects of radiation. There exist two parts to the solar UV radiation:
- Long wavelength radiation (UVA)
- Short wavelength radiation (UVB)
The skin detects each part in different ways. It has been known for a while how UVB makes humans tan.
However, scientists know little on how the skin detects and how it responds to UVA. Elena Oancea has been studying this question precisely. In 2015, her team unveiled the first clues indicating that melanocytes, which produce melanin, have opsin 3 in abundance. They thought opsin 3 could be the receptor which detects UVA.
Oancea said that they found the purpose of opsin 3 in human melanocytes and learnt the molecular steps allowing opsin 3 achieve this function. She said that opsin 3 modulates the amount of pigment that cells make. Surprisingly, it does this independent of light. Learning more about opsin 3 could be used to treat pigmentation disorders.
The team jumped into experiments using their initial hypothesis that opsin 3 can detect UVA radiation, resulting to calcium ions flooding the melanocytes, triggering production of melanin. Rana Ozdeslik, a research associate, used a genetic engineering tool to greatly minimize the amount of opsin 3 in cultured human melanocytes.
Once Ozdeslik exposed the skin cells without opsin 3 to UV light, they still produced a lot of calcium ions. This means that their initial hypothesis was not correct. According to Ozdeslik, skin cells with no opsin 3 appeare to be much darker. They found out that melanocytes made more pigment in absence of opsin 3.
Lauren Olinski joined the team at this point. Together, they discovered that opsin 3 changed melanocortin-1 receptor activity, a protein which increases synthesis of cyclic adenosine monophosphate (cAMP). cAMP triggers melanin production. Opsin 3 decreases the cAMP levels produced regulating melanin.
The researchers determined that opsin 3 binds retinal. They could not, however, detect opsin 3 absorbing any light wavelength.
The team came to a conclusion that opsin 3 reduces melanin production in skin cells. It does so by decreasing levels of an important molecular signal.
The team is now seeking to learn which other parts of the body opsin 3 is produced and the kind of functions it may have. The findings suggest that opsin 3 could be used for treating pigmentation disorders. Most of the pigmentation disorders do not have available treatment.
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- Brown University. (2019, May 17). How a member of a family of light-sensitive proteins adjusts skin color. ScienceDaily. Retrieved May 19, 2019 from https://www.sciencedaily.com/releases/2019/05/190517161032.htm