Brain activity has an unmistakable signature: neuronal transfer, as brain cells transmit information to each other through triggered release of chemical neurotransmitters that receive long branching dendrites from neighboring cells.
Scientists have found that this microscopic connection is peculiar, but it does not belong only to neurons. Researchers discovered a previously imperceptible similar signaling process outside the nervous system by observing bursts of neuron-like activity in certain skin cells.
The Rockefeller University team observed these interactions between two different types of skin cells: melanocytes, which produce the ultraviolet-absorbing pigment melanin; and keratinocytes, which make up the vast majority of the epidermis, protecting the body from environmental influences, in part through melanin.
“Keratinocytes are known regulators of melanocyte behavior, and a lot of work has been done to understand how keratinocytes affect melanocyte cell proliferation and pigment production and transport in the skin,” the authors write in their new study.
'However, the cell-cell relationship between melanocytes and keratinocytes at the individual cell level is poorly understood.'
In experiments with two types of skin cells, as well as in studies of samples of intact human skin, researchers have brought us closer to understanding how this process actually works, and what is surprising is that it resembles neural communication.
“We've seen keratinocytes wrap around melanocytes, forming tight bonds that remind us of neurons,” says biophysicist Sanford M. Simon.
In a study, the researchers found that chemical signals from keratinocytes trigger signals called calcium transients in the dendrites of melanocytes.
This calcium signaling process, triggered by the production of two secretions of keratinocytes – endothelin and acetylcholine – has also been observed in smaller dendritic vertebral-like structures on melanocytes, which the researchers said can also be seen in intact human skin.
“This type of localized cell-to-cell communication is seen as a hallmark of the nervous system,” the researchers explain.
“Dendritic morphologies are not unique to the nervous system, but it is not known whether non-neuronal dendrites such as melanocytes are capable of compartmentalizing signals received from neighboring cells.”
Coupled with the new discovery of vertebral-like structures protruding from dendrites – which the team say are 'strikingly similar' to neuronal dendritic spines – the results suggest a deeper complexity in skin cell communication that scientists never knew existed.
The results are presented in the Journal of Cell Biology.
Sources: Photo: Belote and Simon, Journal of Cell Biology, 2019
