The mechanisms of itchy skin differ in furry and furry skin

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These sections of the hind legs of the mouse allow Georgia Tech researchers to visualize the nerves in the skin. Credit: Christopher Moore, Georgia Tech

Chronic itchy skin leads more people to the dermatologist than any other condition. In fact, the latest scientific literature finds that 7% of adults in the United States and between 10 and 20% of people in developed countries suffer from dermatitis, an inflammatory condition of the common skin that causes itching.

“Itching is a major clinical problem, often caused by medical conditions underlying the skin, liver, or kidney. Due to our limited understanding of the mechanisms of itching, we do not have for most patients, ”said Liang Han, an assistant professor in the School of Biological Sciences at the Georgia Institute of Technology, who is also a researcher at the Parker H. Petit Institute for Bioengineering and Bioscience.

Until recently, neuroscientists considered the mechanisms of itchy skin to be the same. But Han and his research team recently discovered differences in itching in non-hairy versus hairy skin areas, opening up new areas for research.

His research, published April 13 in the journal PNAS (Proceedings of the National Academy of Sciences), could open new more effective treatments for patients suffering from persistent itching.

The origins of itching are more than deep skin

According to the researchers, there are two different types of nervous system stimuli that trigger the itching sensation through the skin’s sensory nerves: chemical and mechanical. In their study, Han and his team identified a specific population of neurons that controls itching in “glabrous” skin: the smoothest, hardest skin found on the soles of the hands and feet.

Itching in these areas poses a greater difficulty for patients and is surprisingly common. In the United States, it is estimated that there are 200,000 cases a year of dyshidrosis, a skin condition that causes the formation of itchy blisters only on the palm and plants. Another chronic skin condition, palmoplantar pustulosis (a type of psoriasis that causes inflamed, scaly skin and intense itching on palms and soles), affects up to 1.6 million people in the U.S. each year.

“Actually, this is one of the most debilitating places (to bite),” said Haley R. Steele, first author, a graduate student at the School of Biological Sciences. “If you have itchy hands, it’s hard to grasp things, and if it’s your feet, it can be hard to walk. If it’s itchy in your arm, you can still write. You’ll be distracted, but you’ll agree. hands and feet, it’s harder to do everyday things. ”

Itching vision: the mechanisms of itchy skin differ in hairy and furry skin

The sensory nerves of the glabrous skin (non-hairy skin of the plantar hind leg of the mouse) are marked by red fluorescence. Credit: Christopher Moore, Georgia Tech

Ability to block, activate itchy neurons in laboratory mice

Because many biological mechanisms underlying itching, such as receptors and nerve pathways, are similar in mice and humans, most studies of itching are based on the mouse test. Georgia Tech researchers, who used mice in their lab, were able to activate or block them. .

The research shows, for the first time, “the actual neurons that send itching are different populations. The neurons that are in the hairy skin that does not detect itching in glabrous skin are one population and another detects itching in glabrous skin.” .

Why has an explanation so far eluded science? “I think one of the reasons is because most people in the field assumed it was the same mechanism that controls sensation. Technically it’s a challenge. It’s harder than working with hairy hair,” Han said.

To overcome this technical hurdle, the team used a new research procedure, or trial, based on human contact allergic dermatitis, Steele said.

The above method would have been to inject itchy chemicals into the skin of the mice, but most of the skin of a mouse is covered with hair. The team had to focus on the glabrous, smooth skin of mice and hands. The use of genetically modified mice also helped identify the appropriate sensory neurons responsible for glabrous skin itching.

“We activated a specific set of itch-causing neurons and saw that the biting behavior was reshaped,” Steele said, referring to how mice usually treat itchy skin.

A set of study mice was given a chemical to specifically kill an entire line of neurons. Focusing on three previously known neuron mechanisms related to the itchy sensation found in hairy skin, they found that two of the neurons, MrgprA3 + and MrgprD +, did not play an important role in non-itchy skin. hairy, but the third neuron, MrgprC11 +, yes. Removing it reduced the acute and chronic itching on the test plants and palms .

Itching vision: the mechanisms of itchy skin differ in hairy and furry skin

Georgia Tech researchers Liang Han (left) and Haley Steele (right) have discovered differences in itching on hairy and non-hairy skin that could lead to more effective treatments for patients with persistent itching. Credit: Christopher Moore, Georgia Tech

Potential to drive new treatments for chronic itching

Han’s team hopes the research will lead to treatments that deactivate itch-causing neurons, perhaps blocking them in human skin.

“To date, most treatments for itchy skin do not discriminate hair and glabrous hair, except for the potential medication potential due to the increase in skin thickness in glabrous skin,” he noted. Ron Feldman, Assistant Professor in the Department of Dermatology at Emory University School of Medicine. Georgia Tech’s findings “provide a reason to develop therapies aimed at chronic itching of the hands and feet that, if left untreated, can greatly affect the patient’s quality of life,” he concluded.

What will happen next for Han and his team? “We would like to investigate how these neurons transmit information to the spinal cord and brain,” said Han, who also wants to investigate the mechanisms of chronic itchy diseases that mainly affect glabrous skin, such as cholestatic itching, or itching due to reduction or blockage. biliary flow often seen in diseases of the liver and biliary system.

“I joined this lab because I love working with Liang Han,” added Steele, who selected Glabre research for his doctorate “because it was the most technically challenging and had the greatest potential to be really interesting and meaningful to the field.”


Rubbing the skin activates the neural pathway that relieves itching


More information:
Haley R. Steele and others, MrgprC11 + sensory neurons mediate the itching of glabrous skin, Proceedings of the National Academy of Sciences (2021). DOI: 10.1073 / pnas.2022874118

Citation: Itching Information: The mechanisms of itchy skin differ between hairy and furry skin (2021, May 21) Retrieved May 22, 2021 at https://medicalxpress.com/news/2021-05 -insight-skin-mechanisms-differ-hairless.html

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