Hunger-Spiking Neurons and Salt Overload are linked to Autoimmune Diseases

29 March 2013 & 11 July 2013 -- Over the last few years, there has been a steady increase in the number of Americans with autoimmune diseases. Membranous Nephropathy and Multiple Sclerosis (MS) are believed to be mediated by immune mechanisms. These illnesses occur when the person's own immune system attacks healthy tissue and cells if they were harmful pathogens. How different types of T-cells interact are at the heart of fighting off infections as well as the development of autoimmune disorders.

In research published in the Proceedings of the National Academy of Sciences (PNAS), a peer-reviewed journal, scientists studies AgRP neurons, which are normally appetite-promoting. They found that chronic suppression of AgRP neurons appear to result in less appetite and a lighter body weight. As a result, T-cells tend to promote inflammation-like processes resulting in certain autoimmune responses. Scientists at Yale School of Medicine discovered a correlation between these autoimmune responses and autoimmune diseases, including MS.

The authors explained that neurons that regulate hunger in the central nervous system also control the functions of immune cells, suggesting that eating behavior is a defense mechanism against infections and the development of autoimmune disease.

Lead author Tamas Horvath, the Jean and David W. Wallace Professor of Biomedical Research and chair of comparative medicine at Yale School of Medicine, said: "If we can control this mechanism by adjusting eating behavior and the kinds of food consumed, it could lead to new avenues for treating autoimmune diseases."

Horvath and team carried out an animal experiment in which mice had Sirt1 - a signaling molecule that controls the hunger-promoting neuron AgRP in the hypothalamus - knocked out. These mice, referred to as 'Sirt1-deficient mice,' had reduced regulatory T-cell function and greater effector T-cell activity, making them more vulnerable to developing an animal-equivalent of multiple sclerosis.

"This study highlights the important regulatory role of the neurons that control appetite in peripheral immune functions," Horvath said. He continued "AgRP neurons represent an important site of action for the body's immune responses."

The authors believe that losing weight after using medications that give the patient a sensation of fullness may have unexpected effects on the spread of autoimmune disorders.

Can high salt diets increase autoimmune risk?

There is a fine balance between to little and too much activity in our immune system. Too little and we become susceptible to infections and cancer, too much and our risk of developing autoimmune diseases and allergies increase.

The journal Nature published three studies online in March 2013 focused on T-cells. The results suggest that how much salt we consume may influence this balance by indirectly encouraging the overproduction of immune cells.

In related research, by scientists at University College London Hospitals, it appears that salt 'overload' in the brain is one of the major factors to blame for the disabling symptoms of MS. The researchers found that high sodium levels are a major trigger for nerve cell damage. This damage is a key factor in devastating long-term effects of MS, such as walking difficulties and vision problems.

Healthy people have normal levels of sodium in their nerve cells. However, the researchers discovered MS patients had above-average levels. This is because the cells are too weak to pump it out quickly enough, leading to a build-up of sodium which then causes long-term damage.

"We urgently need treatments for people with progressive forms of multiple sclerosis and the results of this study, and others funded by the MS Society, open up more options for researchers to investigate potential medicines that could slow or even stop the accumulation of disability," said Dr. Susan Kohlhaas.

MS is a condition of the central nervous system, in which the coating around nerve fibers is damaged, causing a range of symptoms. There is no cure. It is normally diagnosed in people between the ages of 20 and 40 and affects almost three times as many women as men.

The researchers used an MRI scanner to assess salt levels in the brains of patients. Ninety-seven people with MS took part in the study.

Dr. David Paling, lead author of the study, said scientists would investigate ways of blocking the sodium build-up. "The study is important because it proves sodium accumulation in the nerves affects the progressive nature of the disease," he said. "We can now move forward to plan trials with medications that prevent sodium from getting into cells and causing damage."

"In addition, we now have an effective test to check if these treatments are working for MS patients, instead of waiting five to 10 years."

One MS sufferer who took part in the research was Dominic Weaver, 46, from west London. The sound engineer and dubbing mixer for television and film was diagnosed in 2011 and now walks using a stick. He said: "I can still walk but I don’t know if tomorrow I may not be able to get out of bed again. Any treatment which could halt the progression of the disease is a step forward."

Researchers said further studies need to be carried out to determine what the link is between high salt intake and autoimmune diseases.

Sources: Sophie Goodchild and Christian Nordqvist
Special thanks to Medical News Today