March 22, 2016 Specialized Subject
Compilation and introduction by Lucy Warner


Just Scratching An Itch
Lucy Warner
March 22, 2016


That horribly annoying condition called chronic itching, usually diagnosed as eczema, is the main focus of these articles. It is considered to be an allergic reaction, and is related to our immunity system. The first selection is by debra-international.org and presents a history of medical studies on the subject, plus the suggestion that there may actually be a specific set of neurons that are involved with itching that are not the cause of pain. The last time I saw anything about itching was in my psych book in college, a course about scientific psychology rather than Freud and his compatriots. It was fascinating. That textbook said that itching is considered to be merely a less intense form of pain, but gave the subject little attention, probably because in 1970 there wasn't much known. Questions like this, or really anything which involves nerves from perception on to animal intelligence explorations, are the type of material dealt with by experimental psychology; from Pavlov’s dog to actual changes in the brain produced by specialized uses the field has grow "like topsy" just like the explosion of new technology. Brain scientists now can actually use the brain to do things like operate a machine. For those applications, go to “Five Incredible—and Real—Mind Control Applications, news.nationalgeographic.com/.../130829-mi...”

The first article that I collected on eczema is from debra-international.org, and discusses theories down through time on itching. It postulates that there may actually be a separate set of nerves which produce itching!! It is known that "itching" does not occur anywhere except the skin. By far the best and most explanatory article however is the one by NIH. I suggest you read it. Then the Wikipedia article on a protein called Thymic stromal lymphopoietin (TSLP) is also very good. One problem in trying to read scientific material is that while most of it is understandable, there are terms that are totally unfamiliar, so I Googled those also, usually putting a summation of what I found after, or embedded within, the article which contained it. The TSLP article states, “It is thought that [by] understanding the mechanism of TSLP production and those potential substances that block the production, one may be able to prevent or treat conditions of asthma and/or eczema.[12]” The final article from ucsf, on the mysterious “Wasabi ion channel,” which enticed me into collecting it also because I hoped that there is actually a drug on the market already to cure eczema and hay fever rather than merely soothing and preventing the symptoms, but alas, it seems not yet. A couple are in the pipeline, however, and hopefully some will soon be on the market.



http://www.debra-international.org/patients/caring-for-someone-with-eb/itching-pruritus.html

Itching (Pruritus)

About 330 years ago, the physician Samuel Hafenreffer said that itching was 'an unpleasant feeling that provokes scratching'. Up to now there has been no better definition. The technical term for it is 'pruritus', from the Latin word 'prurire' meaning burning.

Although itching is a very agonizing [sic] skin sensation, appearing with many skin diseases, only little is known about the mechanisms causing it. The skin contains so-called receptors (this can best be translated by 'perception points') for different sensations like pain, cold, warmth or pressure.

For a long time the parts responsible for the sensation of pain have been thought to be those causing itching, with pain and itching being two varieties of the same sensory perception. But one great difference is that itching can only be triggered in the skin.

In the meantime, latest scientific findings have pointed out that perhaps there are independent nerves for itching, but not all communicating substances and their interplay are known. The phenomenon of the starting of itching has not yet been solved.

Normally itching is answered by scratching or rubbing. This is followed by inflammatory reactions of the skin, which causes the distribution of histamine (a so-called transmitter) and other substances increasing inflammation, and the consisting itching is intensified.



http://www.niams.nih.gov/News_and_Events/Spotlight_on_Research/2014/chronic_itch.asp

June 2014 (historical)

Investigating the Causes of Chronic Itch: New Advances Could Bring Relief

Chronic itch, which occurs in many medical conditions and in response to certain drugs, affects millions of Americans, yet its causes are poorly understood. Now, investigators funded in part by the NIH’s National Institute of Arthritis and Musculoskeletal and Skin Diseases have uncovered previously unknown pathways that trigger chronic itch, painting a clearer picture of the condition and suggesting novel therapeutic strategies.

Itch was once thought to be sensed through the body’s pain pathways, but research over the past few decades has revealed that it uses its own dedicated nerves, molecules and receptors. While itch is ultimately conveyed through nerves to the brain, the most well-understood itch pathway initiates with immune molecules called histamines. Histamines normally serve a protective immune function by helping combat invading pathogens, but they also trigger the itchiness caused by a mosquito bite or a bout of hives by acting on sensory nerves in the skin.

Antihistamines help relieve short-lived itching caused by allergies or insect bites, but they only partially alleviate the chronic itching in diseases like eczema or psoriasis. Part of the problem is that scientists don’t have a clear understanding of the pathways that cause the unrelenting itch in these conditions.

Chronic itch likely stems from many factors, and researchers are following different leads to find them. Three recent studies have examined the possible contributors and will aid the ongoing search for more effective treatments.

Nerve Cells: Itch First Responders

While much of the research on itch has centered on indirect immune triggers like histamines, Diana Bautista, Ph.D., a professor at the University of California, Berkeley, suspected that some molecules could directly act on nerve cells in the skin. Her team focused on a protein produced by damaged skin cells called thymic stromal lymphopoietin (TSLP), which had previously been linked to chronic itch associated with eczema, or atopic dermatitis.

Left: sensory nerve cells sensitive to TSLP. Right: sensory never cells sensitive to capsaicin

In a bundle of sensory nerve cells, only a small number are sensitive to TSLP (left). By comparison, a larger fraction responds to capsaicin (right), the component of chili peppers that produces the burning sensation. Credit: Diana Bautista, Ph.D., University of California, Berkeley.

Earlier studies had shown that TSLP, when injected into the skin of laboratory mice, caused them to scratch. It was generally assumed that the itch occurred through activation of mast cells, a type of immune cell that produces histamines. But Dr. Bautista’s team discovered that TSLP brought about the scratching behavior even in mice lacking these cells, suggesting that another mechanism was at work.

Further experiments uncovered a molecular receptor for TSLP on certain skin nerve cells, and showed that the protein acts directly on these cells to transmit itch signals.

While TSLP is also thought to promote itch through immune molecules, Dr. Bautista’s work suggests that the nervous system itself could play a larger role than expected in directly promoting the sensation. If TSLP is the primary trigger, as Dr. Bautista suspects, then blocking the molecule’s activity could stop the inflammation and chronic itch that characterize eczema.

"Only a small minority of neurons in the skin respond to TSLP,” said Dr. Bautista. “If we could find a way to specifically target theses neurons without affecting other sensory pathways like pain and touch, we could have the beginnings of a new treatment for chronic itch that would not impact these other critically important functions."

Itching by Borrowing From Pain

Another study led by Zhou-Feng Chen, Ph.D., director of the Center for the Study of Itch at Washington University in St. Louis, also focuses on nerve cell involvement in chronic itch. His team was interested in a protein called BRAF, which is known to help convey pain signals from sensory nerves in the skin to the brain.

Activated BRAF (in red) in sensory nerve cells
Activated BRAF (represented in red), when introduced into sensory nerve cells in mouse skin, triggers the itch sensation. Credit: Zhou-Feng Chen, Ph.D., Washington University in St. Louis.

To gain a better understanding of BRAF’s function, the researchers introduced a continually active version of the molecule into sensory neurons in mice. They expected the mice to show signs of pain, but to their surprise, instead the mice scratched incessantly.

Additional experiments revealed that the cells containing activated BRAF produced elevated levels of a key itch-inducing signaling protein called gastrin-releasing peptide (GRP).

Moreover, the team also noticed that the activated BRAF-containing cells triggered GRP production in many more neighboring, pain-sensing cells. Dr. Chen suspects that the recruitment of these pain-sensing neurons intensifies the itch sensation and could explain why chronic itch is so uncomfortable.

The researchers also showed that tamping down BRAF activity or GRP signaling reduced the scratching behavior in the mice, suggesting that blocking the BRAF pathway could be an effective strategy for developing novel anti-itch therapies.

"Using BRAF, we have created a mouse with chronic itch that appears similar to the incessant itching that people experience in diseases like eczema and allergic contact dermatitis," said Dr. Chen. "Scientists can now use this mouse model to further explore the biochemical mechanisms that underlie itch, and use it to test experimental drugs."

Itch-Inducing Bacteria

An unusual characteristic of people with eczema is the prevalence of Staphylococcus aureus bacteria on their skin—90 percent of patients harbor the microbe. Gabriel Núñez, M.D., a professor at the University of Michigan Health System, wondered what role, if any, the bacteria played in the disease.

To investigate the possibility that Staphylococcus aureus produces a protein that contributes to the skin inflammation and itching in people with eczema, Núñez’s team began by collecting all the proteins secreted by the bacterium. The researchers then bathed laboratory-grown mast cells in a cocktail of these proteins to see if the cells would release their itch-provoking histamines. They focused on mast cells because previous research had indicated that these cells played a key role in eczema.

The results clearly showed that Staphylococcus aureus stimulates mast cells—they quickly discharged their histamines in response to the bacterial protein mixture.

Next, they identified the specific bacterial protein found in Staphylococcus aureus responsible for the effect, a molecule called delta toxin. When they infected mice with normal Staphylococcus aureus, the mice’s skin became inflamed, but when they used a strain that had been engineered to lack delta toxin, their skin remained largely healthy. Applying delta toxin to the mice’s skin caused eczema-like symptoms, further implicating the protein in the disease.

Activated BRAF (in red) in sensory nerve cells
Mast cells harbor dozens of histamine-laden granules (left) but when stimulated by delta toxin (right) the granules are expelled into the cell’s surroundings. Credit: Gabriel Núñez, M.D., University of Michigan Health System.

Delta toxin’s exact function is not known, but previous research suggests that it may kill competing bacteria in the skin.

"Staphylococcus aureus probably doesn’t make delta toxin to cause disease in people," said Dr. Núñez. "What we know about the protein suggests that the inflammation it causes in human skin could simply be collateral damage in a battle among microbes for a specific niche in the host’s body."

In future work, Dr. Núñez plans to search for ways to curb the effects of delta toxin, for example, by identifying its receptor on mast cells, then testing various approaches to blocking it. He also plans to examine eczema patients to see if delta toxin plays a similar role in people.

The research reported in this article was supported in part by NIH’s National Institute of Arthritis and Musculoskeletal and Skin Diseases [grant numbers R01AR059385 (Bautista), R01AR056318 (Chen) and R01AR059688 (Núñez)].

Kirstie Saltsman, Ph.D

# # #

The epithelial cell-derived atopic dermatitis cytokine TSLP activates neurons to induce itch. Wilson SR, Thé L, Batia LM, Beattie K, Katibah GE, McClain SP, Pellegrino M, Estandian DM, Bautista DM. Cell. 2013 Oct 10;155(2):285-95. doi: 10.1016/j.cell.2013.08.057. Epub 2013 Oct 3. PMID: 24094650

Chronic itch development in sensory neurons requires BRAF signaling pathways. Zhao ZQ, Huo FQ, Jeffry J, Hampton L, Demehri S, Kim S, Liu XY, Barry DM, Wan L, Liu ZC, Li H, Turkoz A, Ma K, Cornelius LA, Kopan R, Battey JF Jr, Zhong J, Chen ZF. J Clin Invest. 2013 Oct 15. pii: 70528. doi: 10.1172/JCI70528. [Epub ahead of print] PMID: 24216512

Staphylococcus δ-toxin induces allergic skin disease by activating mast cells. Nakamura Y, Oscherwitz J, Cease KB, Chan SM, Muñoz-Planillo R, Hasegawa M, Villaruz AE, Cheung GY, McGavin MJ, Travers JB, Otto M, Inohara N, Núñez G. Nature. 2013 Nov 21;503(7476):397-401. doi: 10.1038/nature12655. Epub 2013 Oct 30. PMID:24172897

The mission of the NIAMS, a part of the U.S. Department of Health and Human Services' National Institutes of Health, is to support research into the causes, treatment and prevention of arthritis and musculoskeletal and skin diseases; the training of basic and clinical scientists to carry out this research; and the dissemination of information on research progress in these diseases. For more information about the NIAMS, call the information clearinghouse at (301) 495-4484 or (877) 22-NIAMS (free call) or visit the NIAMS website at http://www.niams.nih.gov.



Information of the protein Thymic stromal lymphopoietin, mentioned as a source of itching in the NIH article above under the heading “Nerve Cells – First Responders,” is covered by Wikipedia. I’ve never heard the name before, and was prompted to Google it. See below.

https://en.wikipedia.org/wiki/Thymic_stromal_lymphopoietin

Thymic stromal lymphopoietin
From Wikipedia, the free encyclopedia

Thymic stromal lymphopoietin (TSLP) is a protein belonging to the cytokine family. It is known to play an important role in the maturation of T cell populations through activation of antigen presenting cells.

TSLP is produced mainly by non-hematopoietic cells such as fibroblasts, epithelial cells and different types of stromal or stromal-like cells.[citation needed] These cells are located in regions where TSLP activity is required. (NOTE: according to Wikipedia, hematopoietic stem cells or HSCs, located in the “red bone marrow,” are responsible for the creation of blood cells including platelets and lymphoid cells. The last category includes T-cells which are related to immunity.)(Also on the term antigen, Wikipedia defines it as “any substance that causes an immune system to produce anti-bodies against it.”)

. . . . Atopic dermatitis[edit]

TSLP-activated Langerhans cells of the epidermis induce the production of pro-inflammatory cytokines like TNF-alpha by T cells potentially causing atopic dermatitis.[4] It is thought that understanding the mechanism of TSLP production and those potential substances that block the production, one may be able to prevent or treat conditions of asthma and/or eczema.[12]” [NOTE: Per Merriam-Webster, “Definition of Langerhans cell: a cell found in the epidermis that functions as an antigen-presenting cell which binds antigen entering through the skin.”]



A POTENTIAL CURE FOR THE ANNOYING EXCEMA ITCHING PROBLEM:

http://medicalxpress.com/news/2013-10-blocking-nerve-cells-symptoms-eczema.html

Blocking nerve cells could prevent symptoms of eczema
October 3, 2013

Graphics -- The itch and inflammation of eczema may be prevented by itch-receptor blockers, based on new research linking the nervous system and the immune system. Credit: Diana Bautista, UC Berkeley


A new picture of how the nervous system interacts with the immune system to cause the itch and inflammation associated with eczema, a chronic skin disease, could lead to new therapies for the condition, according to University of California, Berkeley, scientists.

Some 10 percent of the population suffers from eczema, or atopic dermatitis, at some point in their lives, but there are no cures or even good treatments for it. Symptoms range from dry, flaky and itchy skin to flaming red rashes, and in severe cases, particularly in children, the disease often progresses to nasal allergies and asthma.

Eczema's cause is unknown, but most research today focuses on the immune system's role in reacting to chemicals that cause itching and inflammation. UC Berkeley neuroscientist Diana M. Bautista and graduate students Sarah R. Wilson and Lydia Thé, however, discovered that sensory nerves in the skin are the first to react to these chemicals, and that blocking the skin's itch receptors not only stops the scratching, but may head off the worst consequences of eczema.

"Most drug development has focused on trying to find a way to inhibit the immune response," said Bautista, assistant professor of molecular and cell biology and a member of the Helen Wills Neuroscience Institute. "Now that we have found that sensory neurons may be the first responders, that changes how we think about the disease."

"By just blocking what is happening in the neurons, you could block the symptoms of chronic itch, including the big immune response leading to asthma and allergy," Wilson added. "And you prevent the patient from scratching, which damages skin cells and makes them release more chemicals that cause inflammation and help maintain chronic itch."

The researchers already have identified a potential drug, now in Phase 1 clinical trials for a different inflammatory disease, that stops mice from scratching when it is applied to the skin.

Their new model of eczema is based on findings reported online today (Thursday, Oct. 3) in the journal Cell by Bautista, Wilson, Thé and their UC Berkeley colleagues.

Block that wasabi

"We started out looking at acute itch and asked the question, 'Why do we scratch? Why do we have that urge, and how does it work that scratching gives you some relief, when normally it feels terrible if you don't have an itch and scratch yourself that hard?'" Bautista said. "But the many types of chronic itch that humans experience are all very different. We believe that, through identifying molecular mechanisms, we can find new treatments and therapies for these diseases."

Immunologists several years ago identified a chemical – TSLP (thymic stromal lymphopoietin), a so-called cytokine – that induces itch when expressed in the skin. Because immune cells have receptors for this chemical, TSLP triggers them to release chemicals that attract other immune cells and to create the red, itchy inflammation typical of eczema. These inflammatory chemicals seem to spread through the body and induce inflammation in the lungs, gut and nasal passages that lead to asthma and allergies, Bautista said.

Wilson and Bautista, however, focused on what causes the immediate or acute itch. Probing itch-sensitive neurons in the skin, they found that these neurons also have receptors for TSLP, and that TSLP makes these neurons, like immune cells, release chemical mediators that cause inflammation. Furthermore, by looking at human skin cells (keratinocytes) in culture, they discovered the triggers that make skin cells release TSLP in the first place.

"Our hypothesis is that skin cells release TSLP, which triggers neurons to release mediators that lead to more inflammation and recruitment of immune cells," helping to set up chronic inflammation, Bautista said.

"These itch-sensitive neurons are a small population," she added. "If we could just block the 2 percent of neurons that respond to TSLP, we could have a really selective drug that treats chronic itch, but keeps all of the important functions of skin – normal pain function, normal temperature and tactile sensations – and the many parts of the immune system intact."

Interestingly, the TSLP receptor works through an ion channel, TRPA1, that Bautista discovered when she was a post-doctoral researcher. The channel was named the wasabi ion channel because it is sensitive to "mustard compounds" like those found in Dijon or wasabi. Blockers of the wasabi channel thus would block the action of TSLP and stop itch.

Alternatively, Wilson said, drug developers could look for chemicals that block the release of TSLP from damaged skin cells.

Bautista and her colleagues are continuing to explore the relative contributions of different types of nerve and immune cells to atopic dermatitis and chronic itch and are developing mouse models in which to test their hypotheses.

Explore further: Pain and itch connected down deep



https://www.ucsf.edu/news/2015/04/124956/first-look-wasabi-receptor-brings-insights-pain-drug-development

First Look at ‘Wasabi Receptor’ Brings Insights for Pain Drug Development

Protein’s Structure Will Guide Hunt for New Treatments of Inflammation-Induced Pain
By Pete Farley on April 08, 2015

In a feat that would have been unachievable only a few years ago, researchers at UC San Francisco have pulled aside the curtain on a protein informally known as the “wasabi receptor,” revealing at near-atomic resolution structures that could be targeted with anti-inflammatory pain drugs.

Officially named TRPA1 (pronounced “trip A1”), the newly visualized protein resides in the cellular membrane of sensory nerve cells. It detects certain chemical agents originating outside our bodies—pungent irritants found in substances ranging from wasabi to tear gas—but is also triggered by pain-inducing signals originating within, especially those that arise in response to tissue damage and inflammation.

This detailed 3D model of the "wasabi receptor" was made from thousands of cryo-EM images.

“The pain system is there to warn us when we need to avoid things that can cause injury, but also to enhance protective mechanisms,” said David Julius, PhD, professor and chair of UCSF’s Department of Physiology, and co-senior author of the new study, which appears in the April 8, 2015 online issue of Nature. “We’ve known that TRPA1 is very important in sensing environmental irritants, inflammatory pain, and itch, and so knowing more about how TRPA1 works is important for understanding basic pain mechanisms. Of course, this information may also help guide the design of new analgesic drugs.”

TRPA1 receptor proteins form pores called ion channels in sensory nerve cell membranes. These channels, normally closed, open in response to certain chemical signals, which allows ions to pass into the cell’s interior, triggering a warning impulse. But without knowing enough about the receptor’s overall structure to see where a given compound might connect, designing a drug to alleviate pain by controlling the action of the ion channel is something of a shot in the dark.

Julius and co-senior author Yifan Cheng, PhD, associate professor of biochemistry and biophysics, were able to capture images of TRPA1 that reveal its structure in three dimensions, including a cleft in which an experimental drug molecule sits when it binds to the channel. “A few drugs have been developed that target TRPA1, and in our 3-D structure we can see where one such drug binds,” said Julius. “This provides important insight into how this one major class of drugs interacts with TRPA1 and thus how it may work to block channel function.”

UCSF postdoctoral fellows and co-first authors Candice Paulsen, PhD, and Jean-Paul Armache, PhD, spearheaded the TRPA1 project. Yuan Gao, a graduate student in Cheng’s lab, also took part in the work. The team used an approach called electron cryo-microscopy (cryo-EM), an imaging technique in which proteins are bombarded with electrons at very low temperatures.

Thanks to a number of innovative hardware and software advances—some developed at UCSF by Cheng and David Agard, PhD, professor of biophysics and biochemistry and a Howard Hughes Medical Institute investigator—cryo-EM has undergone a revolution in image quality over the past several years. Using these tools, the group imaged TRPA1 at a resolution of about 4 angstroms. By way of comparison, the thickness of a credit card is about 8 million angstroms.

Julius and Cheng began their cryo-EM collaborations about six years ago when they were in pursuit of the structure of a related channel called TRPV1. Sometimes called the capsaicin receptor, TRPV1 can be triggered by the chemical that lends “heat” to chili peppers, but it also responds to actual heat when temperatures reach uncomfortably high levels. TRPV1 was the first protein of such small size to be imaged to near-atomic resolution by cryo-EM, work that was reported in Nature in December 2013.

The determination of TRPV1’s structure by cryo-EM “sent shockwaves through the field of structural biology,” Cheng said, because many researchers had dismissed the method as “blob-ology”: until quite recently cryo-EM’s resolution—about 15 angstroms at best—was far too coarse to discern the subtleties of structure in molecules as small as TRP ion channels.

For decades, X-ray crystallography, which involves first coaxing a protein of interest to crystallize, and then analyzing diffraction patterns created as X-rays pass through the crystal, has been the standard method of determining molecular structures. While crystallography can attain resolutions below 3 angstroms, it requires large quantities of a protein. Moreover, obtaining a usable crystal can take years, and many biologically important proteins—especially membrane proteins, which are crucial to cellular signaling—have never been successfully crystallized.

TRP channels were among these, so “we came at it from a different angle,” said Cheng. “Since crystallization was so difficult, we decided to try cyo-EM, which bypasses this requirement.”

For cryo-EM, the proteins of interest are placed in an aqueous solution, then frozen in a very thin sheet of ice, so quickly that the water doesn’t have time to form crystals. It is critical that the ice remains in a glassy state, because formation of any ice crystals would damage proteins embedded within ice and interfere with determining the structure of the proteins in their native conformation.

With many copies of the proteins suspended in this glassy ice, like insects trapped in amber, the researchers capture as many as 100,000 images, then computationally combine these thousands of two-dimensional views to generate the three-dimensional structure of the protein.

The images Julius and Cheng’s group produced for the TRPA1 ion channel show it in three different states—closed, open, and partially open—a range that offers a lot of insight into the channel’s workings. Though the images of TRPA1 generated in the new study represent only slightly different conformations, the scientists expect to generate additional structures in more distinct conformations in future research.

The research was supported by the National Institutes of Health and the UCSF Program for Breakthrough Biomedical Research. Co-first author Paulsen was supported by a Postdoctoral Training Grant from the UCSF Cardiovascular Research Institute, and is currently a Howard Hughes Medical Institute Fellow of the Helen Hay Whitney Foundation.

“Cryo-EM has undergone a ‘resolution revolution’ that has enabled us to literally see TRP channels in all their glory,” said Julius. “We’ve had some idea what TRPA1 might look like, but there’s something elegant and satisfying about obtaining the structure, because seeing really is believing.”

The "wasabi receptor" is only about a hundred angstroms wide, which means 8 million of them stacked together would be about the thickness of a credit card. Using the earlier method of negative stain imaging, scientists couldn't see the detailed shape and different chemical binding sites on the protein.

UCSF is the nation's leading university exclusively focused on health. Now celebrating the 150th anniversary of its founding as a medical college, UCSF is dedicated to transforming health worldwide through advanced biomedical research, graduate-level education in the life sciences and health professions, and excellence in patient care. It includes top-ranked graduate schools of dentistry, medicine, nursing and pharmacy; a graduate division with world-renowned programs in the biological sciences, a preeminent biomedical research enterprise and top-tier hospitals, UCSF Medical Center and UCSF Benioff Children's Hospitals.

Video credits: Special thanks to David Julius, PhD, for narrating, to Jean-Paul Armache, PhD, for expertly programming the 3D model, and to Candice Paulsen, PhD, for clearly explaining the science.