Why do humans have Alzheimer’s and dogs don’t? – basic research

By Eduardo Zimmer

The answer might lie in our friends’ less developed astrocytes

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In 1820, human life expectancy was around 33 years. Today everyone knows at least one centenarian person (or knows someone who knows …). The advances in health associated with the evolutionary process of the species have enabled us to reach an advanced age. But this development has its price: it brought with it a number of diseases related to aging.

In order for the person to live the so-called third age with quality of life, it is necessary to understand these diseases, which are more and more common in the elderly. Alzheimer’s, for example, is the leading cause of dementia worldwide and affects more than 1 million people in Brazil – an extremely underestimated number, according to experts. In the absence of drugs that can prevent the disease from progressing, one of the global health research priorities is to better understand it.

To understand this pathology, our best friends, dogs who are already helping us walk when we cannot see, travel by plane when we are in a panic to recover from neuropsychiatric disorders can help us again.

The life expectancy of these animals has doubled over the past thirty years. A small dog that used to live about nine years can now reach a spectacular eighteen years. Another notable fact is how they live. While at work I follow the daily life of my dog ​​Baleia (that’s right, a tribute to the book “Vidas Secas” by Graciliano Ramos). Her routine is very similar to mine: she has her hours of eating, walking, sleeping, and being distracted by her toys. At the height of her ten months, she is already responding to orders, afraid of the word “no”, and recently learned to warn me if she wants a cookie.

Can these “humanized” dogs develop Alzheimer’s in old age? Dogs may even show some degree of cognitive decline, but they rarely manifest the severe symptoms of dementia that affect the end-stage disease in humans. What fascinates us, however, is that, like humans, they accumulate insoluble clumps of beta-amyloid protein in the brain – tiny “pebbles” that help characterize Alzheimer’s disease. It is believed that these “pebbles” disrupt communication between neurons, causing the brain to atrophy and cause symptoms. Despite the presence of these lumps, dogs do not develop serious manifestations like us. What makes it resilient? What Makes Us Vulnerable? Understanding the differences between the human brain and the dog can be very useful in understanding and even treating the diseases that affect our brains.

Few people are aware of the existence of the astrocyte, a brain cell that was first described in the mid-19th century and apparently developed much more strongly in humans than in dogs and other mammals. This specialized cell is very common in the human brain in the form of a star: To give you an idea: the cerebral cortex, which is our most developed brain region and makes up 82% of the brain’s mass, seems to have more astrocytes than neurons. In recent years they, who have always been considered the helpers of neurons (the robin of the couple), have won the role of the protagonist.

Several studies have shown that these cells can control our memory and perception – scientists have been able to manipulate our ability to remember something or not by simply turning it on and off. Are they responsible for human susceptibility to Alzheimer’s disease? The differences between the properties of astrocytes in humans and dogs can help, who knows, answer that question. We already have an answer in advance – dogs really are our best friends.

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Eduardo Zimmer is a biochemist and professor at the Institute of Pharmacology at the Federal University of Rio Grande do Sul.

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