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Published August 22, 2010, 12:00 AM

Scientist links mice and good health

North Dakota professor studying the qualities in mice that make them live longer and applying those findings to people
GRAND FORKS – In her hands, University of North Dakota professor Holly Brown-Borg holds up two mice born on the same day in separate litters.

By: Tu-Uyen Tran, Forum Communications Co., INFORUM

GRAND FORKS – In her hands, University of North Dakota professor Holly Brown-Borg holds up two mice born on the same day in separate litters. One is a squirming handful, about as big as any mouse you might find in the kitchen. The other is the size of a man’s thumb, a mouse of a mouse.

The larger mouse likely will stay spry and active until age 18 months before dying at 2 years. That’s about as long as a normal mouse can expect to live in ideal lab conditions, without the threat of predators or the ravages of cold and hunger.

The dwarf mouse, on the other hand, likely will stay active until at least 30 months and die at 3 years. In human terms, this is the equivalent of living to 120 and not showing signs of aging until 100.

There is some biological relationship between size and aging, Brown-Borg said, and it has some bearing on how people age as well.

There is some evidence, based purely on observations of natural human populations, that very short people do live longer, healthier lives than people of average height while very tall people, the sort who break world records, have much shorter life spans than average.

Why that should be is the subject of two major studies the professor is working on. She has a $1.3 million grant from the National Institutes of Health and $800,000 from the Ellison Medical Foundation, enough to hire workers for several years and expand her lab at UND’s medical school.

Early in her academic career, Brown-Borg and her husband, Kurt Borg, were research assistants at Southern Illinois University studying the immune systems of mice. One day, they went down to the animal facility to find older mice to experiment with and noticed that there were an awful lot of these dwarf mice and very few normal mice of suitable age.

Her adviser, Andrzej Bartke, said the dwarf mice, a mutant strain called the Ames Dwarf, which lack growth hormones, just seemed to live longer.

The next step was to find out why the dwarf mice live longer.

Brown-Borg theorizes that, in simple terms, dwarf mice spend less energy growing big, leaving plenty of energy to fight off the stresses of aging. At the cellular level, their cells don’t replicate as much, and they repair damage to the cells more.

Consider that from the time a person is conceived until to about age 35, the cells that make up a body replicate just about perfectly with all their genetic material reproduced with few if any flaws, and those flaws are easily fixed by the cells.

After this point, for reasons that still aren’t clear to scientists, cells have a harder time replicating until the genetic material is so flawed that the cells don’t survive.

At the same time, cells in older people have a harder time repairing genetic damage caused by everything from excessive free radicals to carcinogens in cigarette smoke to ultraviolet radiation from sunlight.

These two factors are at play in nearly all cells in all animals.

The lack of growth hormone in dwarf mice appears to mean that their cells are not replicating as much – meaning it takes longer for them to reach the point at which they can’t replicate – and can put more effort into repairing damage.

How does that help those of us who have the normal dosage of growth hormones?

To start with, Brown-Borg said, don’t take growth hormones if you’re elderly and want to stay active. This is a treatment that’s growing in popularity for seniors, she said, but while it makes the body leaner, research shows it does nothing to improve strength. And, she said, in the long run, it will only make cells deteriorate faster by suppressing the cells’ ability to repair themselves.

Understanding how growth hormones work, she said, could also help develop ways to reduce the harm they do in old age, reducing instances of age-related diseases such as arthritis, diabetes and maybe Alzheimer’s.

Even if the research doesn’t extend the human life span – and, currently, nobody really knows how to do that – it can at least extend our “health span.” That’s the buzzword in the field of aging.

“ ‘Life span’ was the big word for a long time in my field, and it still is,” she said, “but what we’re truly after is keeping us out of the nursing home. If you can live to 90 or say 100 and you only spent the last year or the last six weeks struggling versus the 10 years or 20 years before, it would be beautiful.”

Tu-Uyen Tran is a writer for the Grand Forks Herald