A new study in mice concludes that light-sensitive proteins on fat cells can detect sunlight. It also finds that too little natural light can alter how fat cells behave and may increase the risk of metabolic syndrome.
Throughout the evolution of life on Earth, much has changed. One notable constant, however, is the light from our sun. We cannot overstate our reliance on this huge ball of plasma 93 million miles away.
Because life in all its forms evolved under the glow of our nearest star, animals have evolved to utilize its emissions. Most obviously, the eyes contain photoreceptors that detect light and share the information with the brain, which then generates an image of a person’s surroundings.
The light from the sun also trains us into a roughly 24 hour circadian sleep–wake cycle. Virtually every land animal on Earth uses the sun to maintain their daily rhythms.
A new study that now appears in the journal Cell Reports describes a new way that sunlight might influence the lives of mammals.
Light beyond the eyes
Animals can detect light using proteins called opsins. Two of the most well-known in humans are melanopsin and neuropsin, which are expressed in some retinal cells.
In other animals, light-detecting compounds are present outside of the visual system. For example, frogs can detect light through cells in their skin called chromatophores.
Until quite recently, scientists believed that mammals only detected light through their eyes. However, several studies have now overturned this notion.
For instance, one study from 2019 found that neuropsin in the skin of rats can detect light and help them maintain their circadian rhythms. Still, evidence of so-called extraocular photoreception in mammals is scarce.
For the first time, a new study has investigated whether or not certain proteins on fat cells that lie beneath the skin might also detect light.
Senior study author Richard Lang, Ph.D. — from Cincinnati Children’s Hospital Medical Center in Ohio — explains, “This idea of light penetration into deep tissue is very new, even to many of my scientific colleagues. But we and others have been finding opsins located in a variety of tissue types. This is still just the beginning of this work.”