The gene behind orange-red hair seen in a section of people may also provide some health advantages by protecting the cells that produce the pigment, a new study suggests.
The protein building-block molecule cysteine is essential for the body to make proteins, but its levels must be kept low within cells, below the threshold of toxicity.
An excessive accumulation of cystine within cells has been recognised as the cause of a form of cell death.
Meanwhile, the orange-red pigment found in human red hair and in some bird feathers – called pheomelanin – is made using cysteine.
For a long time, the pigment has presented an evolutionary puzzle, with previous research linking it to a higher risk of skin cancer even without UV radiation exposure.
It has remained unclear why traits that encourage pheomelanin production, such as orange hair, have persisted over time.
Researchers have now found that producing this pigment may actually protect health by drawing down excess cysteine in cells, preventing the molecules from causing any damage.
“These findings represent the first experimental demonstration of a physiological role for pheomelanin,” they explain in the study published in the journal PNAS Nexus.
The latest research was possible thanks to a recent discovery of a molecule, ML349, that could block pheomelanin synthesis in the body.
In the study, scientists assessed 65 adult zebra finches, whose orange beaks contain pheomelanin.
The 65 birds were divided into a treatment group and a control group.
In the treatment group, male zebra finches were given dietary cysteine along with ML349, a drug that blocks pheomelanin synthesis.
Male birds that received both cysteine and ML349 showed more serious cell damage than males that received cysteine alone.
Scientists found that pheomelanin production seemed to help cells keep cysteine levels in balance.
Female birds given cysteine alone also tended to show more cell-level damage than controls.
The findings suggest pheomelanin production in the body helps maintain cysteine balance by converting excess cysteine into an inert pigment that doesn’t damage cells.
“These results demonstrate that pheomelanin synthesis avoids cellular damage by excreting excess cysteine to inert keratinous structures such as feathers,” scientists wrote.
This protective role, according to researchers, could be why pheomelanin-promoting genetic traits remain in populations, even though there are associated melanoma risks.
“These findings prove a role of pheomelanin in cysteine homeostasis, opening a better understanding of melanoma risk through environmental factors affecting cysteine availability,” scientists wrote.
