Astrocytes – Dr. Jekyll and Mr. Hyde

Aggressive subtype of nervous system cells detected

Anna Stavina, XX2 century, according to Medical News Today: 'Helper cells' can turn toxic in brain injury and diseases

For many years, the study of neurodegenerative diseases and spinal cord and brain injuries has focused on the harm that these diseases cause to nerve cells or neurons. However, as part of a new study, scientists decided to study the work of astrocytes. Normally, astrocytes should surround and protect neurons, contributing to the normal functioning of the latter. But, as it turned out, sometimes a subspecies of astrocytes can arise in the body, engaged in the destruction of neurons, and not their recovery after illness or injury.

The international study involved specialists from the Stanford University School of Medicine and the University of Melbourne. The results of the work are published in the publication Nature (Liddelow et al., Neurotoxic reactive astrocytes are induced by activated microglia).

The authors believe that their discovery may lead to the emergence of new approaches to the treatment of traumatic brain injuries and such serious neurological diseases as Parkinson's disease and Alzheimer's disease.

Lead author of the study, Dr. Shane Liddelow, who works in the Department of Pharmacology and Therapy at the University of Melbourne and in the Department of Neuroscience at Stanford, says that astrocytes are usually described as "helper cells." However, in some cases – and this has already been described in the scientific literature – astrocytes begin to destroy other brain cells. Thus, former "assistants" aggravate the damage caused by illness or injury.

"So different functions characteristic of astrocytes have puzzled scientists. But the distribution of astrocytes into two subspecies, performed in our work, can help solve this mystery," says Dr. Liddelow.

For a long time it was believed that astrocytes – star–shaped cells located in the nervous system - are something like "packaging material". The number of astrocytes in the brain is approximately five times the number of neurons. It was assumed that these auxiliary cells simply form the structure in which the "main" cells of the nervous system, neurons, are located.

However, it has recently become clear that the functions of astrocytes are not at all reduced to the mechanical support of neurons. On the contrary, stellate cells play many complex and important roles, participating in the work of the nervous system as a whole. It has already been established, for example, that astrocytes contribute to the survival of neurons and participate in the formation of neural networks.

It is also known that as a result of traumatic brain injury or illness, astrocytes at rest can turn into "reactive astrocytes". The properties of cells change at the same time, but it is not yet clear to scientists whether this transformation refers to useful or harmful.

The authors of the new study were able to detect a subtype of reactive astrocytes, called A1.

A1 astrocytes lose their ability to help neurons survive and create new connections. Instead, they induce the death of neurons and oligodendrocytes, cells involved in the production of myelin. The latter is a kind of "isolation" that covers nerve fibers and accelerates the transmission of a signal through them.

The researchers also found that A1 astrocytes are present in large quantities in the nervous system of patients suffering from neurodegenerative diseases, including multiple sclerosis, Parkinson's disease, Alzheimer's disease, Huntington's disease and amyotrophic lateral sclerosis.

For example, in tissue samples of the prefrontal cortex of a patient suffering from Alzheimer's disease, about 60% of astrocytes belonged to subtype A1. On the other hand, it is known that this disease causes the most serious damage in the prefrontal cortex.

Senior author Ben Barres, professor of neurobiology, developmental biology, neurology and neuroscience at Stanford University, noted that astrocytes are not always the "good guys" and concluded: "Abnormal astrocytes in suspiciously large quantities are present in brain tissue samples of patients who have suffered trauma or severe neurological diseases. From the point of view of practical medicine, this discovery has a very good potential."

Portal "Eternal youth" http://vechnayamolodost.ru  08.02.2017