Confetti in the head: Why the smell decreases with age

Confetti in the head: Why the smell decreases with age

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Stem cell research: Why people can smell worse in old age

In mammals such as humans, the ability to smell decreases with age. Researchers have now investigated why this is so. For the analysis, the scientists followed the stem cell development in the brain of mice with so-called confetti reporters.

Disorders of the sense of smell affect the quality of life

A few years ago, researchers from the USA reported on their study, according to which the nose not only perceives 10,000 different smells, but also about a trillion (1,000,000,000,000) smells. If the olfactory cells do not work properly, the quality of life is considerably reduced. Because disorders of the sense of smell mean a massive restriction in the everyday life of those affected. But with increasing age, the smell in humans - as in other mammals - decreases. An interdisciplinary research team from the Helmholtz Zentrum München and the Mainz University Medical Center examined why this is the case in the journal Cell Reports.

Olfactory nerves originating from stem cells

In mammals, the formation of nerve cells (neurogenesis) is largely limited to early childhood and only occurs in a few regions of the forebrain in adulthood.

One such exception are olfactory nerves, which arise from stem cells over several intermediate stages.

"The production of these nerve cells runs out with age," explains the head of the research group at the Institute of Computational Biology (ICB) at the Helmholtz Zentrum München, Dr. Carsten Marr, in a message.

"We wanted to clarify in the current work how this comes about and what contribution the stem cells have to it," said the scientist.

Confetti reporter

To answer this question, Dr. Marr with mathematician Lisa Bast and stem cell researchers Dr. Filippo Calzolari (today at the Institute of Physiological Chemistry at the University Medical Center Mainz) and Prof. Dr. Jovica Ninkovic an interdisciplinary team of experts.

"Our approach to the current work works via so-called confetti reporters in mice: We make individual stem cells and all of their progeny - so-called clones - shine in a specific color," explains Dr. Calzolari.

In this way, the researchers were able to follow the development of individual clones and distinguish them as different colored dots, which gives the process its name.

"In the next step, by comparing young and older mice, we wanted to find out what contribution individual stem cells and intermediates make to the neurogenesis of the finished olfactory cells," continues Calzolari.

Fewer cells develop into olfactory cells in old age

However, the systematic evaluation of the images is difficult for humans: the available data were extremely heterogeneous and a comparison of young and old brains was difficult.

Here came the expertise of Dr. Marr and his team to bear. You are specialists in the quantification of single cell dynamics, so the question: Which and how many cells of a large cluster develop and how?

To do this, the scientists use artificial intelligence, design mathematical models and program algorithms that can evaluate the image data for them.

"We compared the confetti measurements with several mathematical models of neurogenesis," explains Lisa Bast.

"In this way, we were able to determine that, especially in certain intermediate stages - the so-called transit amplifying progenitors - the ability for self-renewal decreases in old age."

The analysis also shows that so-called asymmetric cell division in stem cells and their resting phases increased in older mice.

“This means that fewer cells develop into olfactory cells in old age and remain inactive in the stem cell pool, causing production to stop,” says Jovica Ninkovic.

According to the information, the work is the first in which scientists were able to use a mathematical model to quantitatively investigate the behavior of nerve stem cells in the living mammalian brain. (ad)

Author and source information

Video: ILSI NA: Defining Healthy Aging - Nutrition and age-related changes Beverly Cowart (July 2022).


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