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April 08, 2013


Skin 'Sees' UV Light, Starts Producing Pigment



In a new study, biologists report that melanocyte skin cells detect ultraviolet light using a photosensitive receptor previously thought to exist only in the eye. This eye-like ability of skin to sense light triggers the production of melanin within hours, more quickly than previously thought, in an apparent rush to protect against damage to DNA.


For most people, tanning seems a simple proposition. A naturally light-skinned person lies in the sun for hours and ends up as bronzed as a Jersey Shore star. To scientists, the reaction of skin to ultraviolet light is more mysterious. A new study demonstrates that skin detects UVA radiation using a light-sensitive receptor previously found only in the eye and that this starts melanin production within a couple of hours. Until now, scientists only knew that melanin production occurred days after UVB radiation had already begun damaging DNA.


light-sensitive receptor 光感受性受容体

"As soon as you step out into the sun, your skin knows that it is exposed to UV radiation," said senior author Elena Oancea, assistant professor of biology in the Department of Molecular Pharmacology, Physiology, and Biotechnology at Brown University. "This is a very fast process, faster than anything that was known before."

"あなたが太陽を浴びるとすぐに、皮膚はUV照射に暴露されていることを知ります。"とブラン大学、分子薬理学・生理学・バイオテクノロジー学科、生物学准教授、第一著者のElena Oancea,は述べた。"これは、以前に知られていたより何よりも極めて高速なプロセスです。"

Scientists believe that melanin protects the DNA in skin cells against damage from UVB rays by absorbing the incoming radiation. It isn't perfect, which is why people must use sun block. But the new study in the journal Current Biology shows that the body mounts its defense much sooner, well before it becomes apparent in the form of a tan.


incoming radiation 入射


In lab experiments with human melanin-producing skin cells called melanocytes, Oancea, graduate student Nadine Wicks, and their team discovered that the cells contain rhodopsin, a photosensitive receptor used by the eye to detect light. Moreover, they traced the steps of how rhodopsin unleashes calcium ion signals that instigate melanin production.

メラノサイトと呼ばれるヒトメラニン産生皮膚細胞のラボ実験では、Oancea, 大学院生Nadine Wicks,および彼らのチームは、メラノサイト細胞が光を検出する眼で使用される感光性受容体、ロドプシンを含有していることを発見した。さらに、彼らはロドプシンがメラニン産生を扇動するカルシウムイオン信号を如何に放出するかの手順を追跡した。


ロドプシン (Rhodopsin)、別名視紅(しこう)は脊椎動物の光受容器細胞に存在する色素である。網膜において光受容器細胞の形成と光の認識の初期段階をつかさどる。Gタンパク結合受容体ファミリーに属し光に敏感であり、夜間視力はこの物質のおかげで成り立つ。光を浴びると即座に退色し、その回復にヒトの場合は約30分かかる。

Eyes on the skin


In the team's first experiment, the scientists were looking to see whether UV light instigated a calcium signaling response. They found nothing. But guessing that the skin might sense light like the eyes do, they added retinal, a co-factor of opsin receptors including rhodopsin.
"When we did that, we saw an immediate and massive calcium response," said Wicks, the study's lead author.


calcium signaling response カルシウム信号応答
retinal:レチナール (βカロチン誘導体の視物質アルデヒド体)

Further investigations found that the cells contained rhodopsin RNA and protein. Under UV light, when the scientists reduced rhodopsin levels in the cells, calcium signaling was reduced. Later, when they starved cells of retinal, they found that melanin production dropped. The authors also determined that long-wavelength UVA light, rather than short-wavelength UVB light, is what stimulates rhodopsin in melanocytes.


Calcium Signaling:カルシウムシグナリング

During several experiments they were able to trace the following process: When UVA light strikes rhodopsin receptors with retinal, calcium signals are triggered within a few seconds. After an hour, measurable amounts of melanin accumulate, although in relatively small quantities compared to the production that will occur within 24 hours.


As much as they learned, Oancea and Wicks still have some questions. One is whether rhodopsin is acting alone or in concert with another yet undiscovered receptor. Another question is whether melanocytes immediately begin exporting melanin to other kinds of skin cells for protection or whether they keep the early supply for themselves.

彼らが学んだと同じくらい、Oancea とWicksはまだ幾つかの疑問があります。一つはロドプシンが、単独で、または別のまだ発見されていない受容体との共同で作用するのかどうかです。別の疑問はメラノサイトがすぐに守るために他の種類の皮膚細胞にメラニンを輸送するのかどうか、またはそれらが彼ら自身のために早期供給を続けているかどうかです。

Just because scientists are learning more about how the skin responds to and protects itself against UV radiation, Oancea said, that's no reason for people to change what they do to protect themselves.


"This doesn't say, 'Don't use sunscreen'," Oancea said.


In addition to Oancea and Wicks, other authors were Jason Chan, Julia Najera, and Jonathan Ciriello.

OanceaとWicksに加えて、他の著者はJason Chan, Julia Najera, およびJonathan Ciriello.であった

Brown University, the National Institutes of Health, and the Natural Sciences and Engineering Research Council of Canada supported the research.





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