Sjogren’s syndrome

Why self-defense turns self-attack

By Jinghong Chen | Bond Life Sciences Center

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Mahmoud Khalafalla, a Ph.D. student at Weisman’s lab, is isolating RNA from salivary glands of Sjögren’s syndrome mouse model to look for the expression of pro-inflammatory genes. | photo by Jinghong Chen, Bond LSC

Our immune system is often the key to our health. Everyday, it works to protect us from foreign invaders such as bacteria and virus, but what happens when it attacks our own tissues?

Gary Weisman, a Curator’s Distinguished Professor of Biochemistry at the Bond Life Sciences Center, is working to advance our understanding of the mechanisms behind immune system function and autoimmune diseases such as Sjögren’s syndrome.

In our immune system, B cells are responsible for producing antibodies to recognize foreign invaders. However, in many autoimmune diseases, B cells produce autoantibodies that recognize our own proteins, causing inflammation and tissue damage. In Sjögren’s syndrome (SS), they attack the glands that produce saliva and tears.

Patients with SS often suffer chronic dry eyes and dry mouth, which might lead to bacterial infection, difficulties in swallowing and speech.

“The symptoms decrease the quality of life rather than the length of life,” said Lucas Woods, research lab manager in Weisman’s lab.

Although SS patients are at higher risk of developing lymphoma cancers and other concurrent autoimmune diseases that may increase mortality, Woods further explained.

According to the Sjögren’s Syndrome Foundation, there are an estimated four million people living with the disease in the U.S. For unknown reasons, 90 percent of them are female.

Yet, current clinical treatments only reduce symptoms by using artificial saliva and tears or cholinergic agents to promote fluid secretion, but there is no approved treatment to reduce the inflammation of the glands themselves. This is the focus of Weisman’s lab.

Sensor of danger

There are 15 different types of nucleotide receptors in humans that regulate numerous cell processes from inflammatory responses to tissue regeneration. Those receptors are stimulated by nucleotides such as ATP. In the past three and a half years, Mahmoud Khalafalla, a Ph.D. student in Weisman’s lab, has focused on one of them in particular – the P2X7 receptor.

Previous studies show increased P2X7 expression in salivary glands from SS patients, as compared to healthy individuals. To understand the reasons behind this, Weisman’s lab used genetically modified mice that develop disease traits similar to SS patients.

In this mouse model, Sjögren’s-like disease occurs when the immune cells invade salivary glands and damage the tissue, leading to decreased saliva production. The invasion of immune cells is triggered by proinflammatory cytokines, a type of signaling molecule that promotes the recruitment of immune cells to the inflamed areas.

But what induces those cytokines?

Weisman’s lab tries to piece together the answer. For the first time, they found that the P2X7 receptor is responsible for the release of these proinflammatory molecules from salivary gland epithelial cells.

To function, most cell-surface receptors require ligands that bind to the receptor to induce cellular responses. The ligand for the P2X7 receptor is ATP – the “energy currency inside of cells.” P2X7 receptors are activated when high concentrations of ATP are released to the outside of the cells, which typically occurs when the cells are injured during inflammation.

“P2X7 receptors [act like] the sensor of danger,” Khalafalla said.

After identifying the role of the P2X7 receptor, the lab then asked: if we stop its activation, what would happen?

Using a drug that inhibits P2X7 receptor activation, they blocked the receptor in their SS mouse model to determine its effect on the development of autoimmune disease. Interestingly, saliva secretion was restored when the P2X7 receptor is blocked while the levels of invading immune cells in salivary glands were dramatically reduced.

“This gives us the thought that [blockade of the] P2X7 receptor is really a promising strategy to reduce salivary inflammation. This may not only relate to Sjögren’s syndrome, but to other autoimmune diseases as well,” Khalafalla said.

Our receptor

Another similar receptor that plays a role in autoimmune diseases is the P2Y2 receptor, which has been referred to as “our receptor” by Weisman’s lab.

As one of the researchers who proved the existence of this receptor, Weisman has spent most of his career studying it.

One of his research projects investigating P2Y2 receptors in human disease recently gained a grant extension for another five years from the National Institutes of Health. The lab found that in a mouse model of SS, similar to the P2X7 receptor, the expression of P2Y2 receptors was increased in both the salivary gland epithelial cells and immune cells.

Furthermore, after they knocked out the P2Y2 receptor in the SS mouse model by breeding them with genetically-modified P2Y2 receptor knockout mice, the inflammation of salivary glands was dramatically reduced.

“The very next step is that we are going to isolate these immune cells out of the diseased mouse salivary glands, and characterize what kinds of cells they are. We want to know exactly which ones are controlling the development of autoimmune diseases, and how P2Y2 receptors and nucleotides like ATP in general are contributing to the diseases,” Woods said.

 

Gary Weisman is a Curator’s Distinguished Professor of Biochemistry at the Bond Life Sciences Center. His research focuses on the relationship between inflammatory diseases and nucleotide receptors. He currently works on a collaborative research project with Dr. Carisa Petris, an eye surgeon at the MU Hospital, to understand the mechanism of how Sjögren’s syndrome damages the tear-secreting lacrimal glands in mice.

 

Standing out through saliva

Bond LSC scientist internationally recognized for work on salivary glands and autoimmune disorders
By Phillip Sitter | Bond LSC

You might not think too highly of spit, but you would quickly regret not having any.

People with Sjögren’s syndrome suffer chronic dry mouth and eyes from an overzealous immune system that attacks salivary and tear ducts, causing serious health issues.

Gary Weisman’s research might hold the key to understanding and managing this immune response, leading to effective treatment or even prevention of this ailment.

For this, the International Association of Dental Research, or IADR, awarded him the 2016 Distinguished Scientist Award for Salivary Research. Weisman accepted the award in June at the opening ceremonies of the IADR conference in Seoul, Republic of Korea.

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Gary Weisman stands in his lab in Bond LSC where he studies the cellular mechanisms of auto-immune disease, specifically how the release of ATP from damaged cells signals receptors that trigger an immune response. | Phillip Sitter, Bond LSC

“We want the good, but not the bad,” said Weisman, a Bond Life Sciences Center investigator, of what we ideally want from our immune system’s functions.

Mice with un-checked autoimmune disease of their salivary glands have their glands destroyed. The disease can spread to other secretory organs next. An over-reactive immune system on a civil war-path can extend its damage to cause pancreatic failure and death.

The destruction wrought by Sjögren’s syndrome is self-inflicted, caused by an overreaction of our bodies’ defenses against infection and injury. This is what an autoimmune disease is.

But, our bodies’ immune cellular response team is complicated. Weisman said dozens of different cell types have been isolated and identified as part of the immune system, and he likens the immune system to fire, police and construction services in human society all working together.

While firefighters are meant to prevent further damage from an inferno, sometimes our bodies’ first responders start doing the equivalent of using dynamite to stop the spread of a fire.

In chronic inflammation, that autoimmune response can mean a burning, throbbing, constant pain. The key to a healthy immune response is balance. The balance has to be between containment and repair of damage caused by infection or injury and damage caused by chronic inflammation if that emergency response continues unabated.

Weisman has spent almost 30 years studying how to prevent our bodies’ immune system from over-reacting to threats and causing further harm.

Earlier in his career, Weisman studied how extracellular ATP plays a critical role in immune responses, and how too much of it can cause the over-reaction that leads to tissue destruction in autoimmune diseases. ATP, or adenosine 5’-triphosphate, is the main molecule used for energy in cellular activities inside cells. Weisman was one of the first scientists to study how damaged cells release ATP as a distress signal.

The released ATP signals receptors that “send out the alarm to the fire station” — the body’s immune cells, he said.

Once he understood this, Weisman began to manipulate the actions of released ATP to see how that would affect an immune response.

Mice with salivary gland autoimmune disease got healthy when the released ATP was prevented from activating their receptors on the surface of cells. Preventing the ATP receptors from being activated slowed down and even stopped the advance of autimmune disease.

Conversely, if you prevent the activation of the ATP receptors in lab mice with Alzheimer’s disease they die much more rapidly from the disease, Weisman said, suggesting that activation of immune cells by ATP is beneficial in slowing the progression of this disease.

Alzheimer’s disease and autoimmune diseases such as Sjögren’s syndrome are only some of the inflammatory diseases that Weisman has studied. With each of these diseases, the role of ATP receptors has to be investigated individually, suggesting that Weisman’s work may extend beyond salivary glands and the brain to other parts of the body.

“Our [ATP] receptor is also involved in heart disease,” Weisman said, and he added that other diseases like cystic fibrosis, cancer, lupus and arthritis have inflammatory components, too.

For now, we all fight a losing battle when it comes to our bodies’ management of the immune system. As we and our immune system age, it has the potential to destroy more than it protects and “eventually you could slip over to the dark side and die,” Weisman said.

In the meantime, Weisman said that a better understanding of the immune system could lead to more effective, targeted treatments of chronic inflammation and other autoimmune disorders. This could provide a new approach to control undesirable activation of the immune system beyond the use of with anti-histamines, anti-cytokines and ibuprofen.

Weisman is a Curator’s Distinguished Professor of Biochemistry. He began his salivary gland research at MU 27 years ago with Professor John Turner, before Turner’s retirement. Since then, his research has been continuously funded by the National Institutes of Health, where one of his recent grants was well scored and will likely be extended for another five years.