January 22, 2013
Researchers Identify Key Player In Skin Response To UVA Light
April Flowers for redOrbit.com - Your Universe Online
A group of researchers from Brown University have demonstrated that certain skin cells use a light-sensitive receptor found outside of the eye to detect ultraviolet light and quickly begin producing melanin to prevent DNA damage. The same team, in a new study published in Proceedings of the National Academy of Sciences, has identified a key player in that biomolecular chain of events that could become a pharmacological target for improving this protective response.
The team, led by Professor Elena Oancea, assistant professor of medical science in the Department of Molecular Pharmacology, Physiology, and Biotechnology, had discovered that human melanocyte skin cells rely on an ion channel called TRPA1 to allow a deluge of calcium ions into the cells when they are exposed to UVA light. This response results in an abundance of calcium ions, which signals the cell to begin melanin production. Melanin is the pigment responsible for the tanning process in humans.
The team performed several experiments to show that TRPA1, known from a number of other appearances elsewhere in the body, is an essential step on the skin's response to UVA light.
This finding strengthens the previous evidence of a parallel between the skin's response to UVA light and the eye's method of light detection.
"It´s exciting because it confirms this phototransduction pathway is similar to those found in the eye. It consists of a light-sensitive receptor, molecular signaling cascade, and an ion channel," Oancea said. "The involvement of an ion channel makes this pathway a lot more like other phototransduction pathways."
TRPA1 has been shown to help detect pungent but benign chemicals in other parts of the body, such as those in intensely flavorful foods. According to the study, TRPA1's chemical sensitivity offers the intriguing possibility that it could become a target for experiments meant to boost melanin production.
"TRPA1 ion channels are involved in the detection of pungent chemicals such as cinnamaldehyde, wasabi, and mustard oil, and we've now found it's important for this melanin response," Nicholas Bellono said. "There is a possibility that we can pharmacologically alter pigmentation through regulation of this ion channel."
The team stresses, however, that people engaged in activities in the sun should always take widely recommended precautions to protect their skin. Such precautions include using high-SPF commercial sunscreens or wearing protective hats and clothing.
From the team's prior research, Bellono knew he was looking for some kind of molecular pathway that would start with a light sensitive receptor and trigger an elevated level of calcium ions in the melanocytes. They even suspected that a TRP ion channel would be involved as TRPs are involved in phototransduction in other places in the body that lead to an increase in intracellular calcium.
The molecular identity of the UVA-activated channel in melanocytes was not apparent, however, as there are many types of TRP channels. After many experiments, the researchers hit upon TRPA1 and amassed a large amount of evidence to confirm its vital role.
One experiment, for example, treated melanocytes with "antagonist" chemicals that are known to block TRPA1 activity. These cells were then exposed to UVA light, and the resulting electrical response was measured. Those cells treated with the antagonists had an 80-90 percent reduction in electrical current compared to the untreated cells. A similar technique - blocking TRPA1 activity — was used to show that the ion channel contributes greatly to the presence of calcium ions after exposure to UVA light. The team found that melanocytes produced little to no melanin after UVA light exposure when TRPA1 is blocked.
The researchers did not test to see whether adding TRPA1 stimulating substances could increase melanin production.