Scientists from the Brown University, Rhode Island, have discovered that skin cells contain a far more sophisticated defence mechanism against UV rays than was previously believed.
Indeed, lead scientists Elena Oancea and Nadine Wicks believe that a photosensitive receptor known as rhodopsin is essentially the same method used by the eye to detect light, giving a far quicker and effective response to UVA rays than previous research had revealed.
Crucially, the scientists believe that this discovery suggests that these skin receptors are providing a greater level of defence against damage to DNA, which can lead to photo-ageing and an increased risk of skin cancer.
Until now, scientists had only proved that melanin production occurs in a matter of days, following exposure to UVB rays, by which time damage to the skin DNA had already begun.
Defence against DNA damage from UV rays happens within a matter of hours
However, the scientists believe that these photosensitive receptors trigger the production of melanin within hours, which is much quicker than was previously thought, and something that may have a bearing on the future development of sun care formulations.
The discovery of the receptors could lead to the development of sun care formulations that take into account the fact that the skin adapts quicker to UV rays.
“As soon as you step out into the sun, your skin knows that it is exposed to UV radiation,” said senior report author Oancea, who is an assistant professor of biology at the department of molecular pharmacology, physiology and biotechnology at Brown University.
“This is a very fast process, faster than anything that was known before. As soon as you step into the sun, you skin knows that it is exposed to UV radiation,” Oancea added.
Melanin production triggered by rhodpsin in melanocytes
The report, which appears in the peer-reviewed journal Current Biology, outlines lab experiments with human melanin-producing skin cells, melanocytes, which contain rhodopsin, and then traced the steps revealing how this substance unleashes calcium ion signals that instigate melanin production using retinal.
Further investigations determined that the cells contained rhodopsin RNA and protein. Under UV exposure, the experiments revealed that reducing rhodopsin levels in the cells led to reduced calcium signalling.
Likewise, when the scientists starved the cells of retinal, they discovered that melanin production also dropped, as well as the fact that it is UVA light, rather UVB light, that stimulates rhodopsin in melanocytes.
Traceable amounts of melanin occur within hours of UV explosure
The results of several experiments led to the conclusion that when UVA light strikes rhodopsin receptors with retinal, calcium signals are triggered in a matter of seconds. Likewise, after an hour, traceable amounts of melanin start to accumulate, albeit in relatively small quantities.
The scientists say that they still have a number of questions to answer, including the discovery of whether or not rhodopsin is working alone or in conjunction with another receptor, as well as the question of whether melanocytes immediately begin to export melanin to other kinds of skin cells, or whether they retain the early supply exclusively.
The authors also concluded their report by emphasising the continued use of comprehensive UV sunscreen products to provide protection from the sun.