Maintaining muscle: 'Use it or lose it,' McMaster scientist says

Researchers have discovered a protein key to the aging process - one that, if inactive as it is in older adults, prevents muscle retention and paves the way for muscle loss.

Muscle maintenance could speed recovery time for broken bones and surgeries

New research out of McMaster University has found a protein responsible for clearing the junk out of a muscle to maintain muscle mass -- one that's "dialled down" as your age. (Andres Stapff/Reuters)

Gregory Steinberg wants you to think of your muscles like a car. Every once in a while, parts that wear out need replacing for it to run smoothly. But what happens on Sundays when the repair shop is closed? What if when you age it never opens up?

Your car dies. And your muscles do the same thing.

This is what happens when you age, when a protein called AMP-activated protein kinase (AMPK) gets "dialled down" and muscles stop repairing themselves, ultimately leading to erosion of muscle mass.

It's the use it or lose it phenomena. If you don't switch on the AMPK regularly with intense exercise, it does tend to get switched down or dialled down with aging.- Gregory Steinberg, McMaster University professor of medcine

And with that knowledge, Steinberg, a professor of medicine at the Michael G. DeGroote School of Medicine, says they're one step closer to finding a solution to stop muscle loss with a drug.

"That's really how the AMPK controls the aging process because it clears out the damaged proteins in the muscle," said Steinberg. "Without the AMPK, that doesn't happen."

Use it or lose it

Steinberg said that without strenuous exercise, the body's signal to produce AMPK is "dialled down," allowing the "junk" to build up in the muscle, leaving two options to prevent the muscle loss: vigorous exercise or waiting on industry to produce a drug. In fact, some drugs have already been produced — ones that try to turn a metabolism back on, with some used in Type 2 diabetes.

"It's the use it or lose it phenomena," Steinberg said. "If you don't switch on the AMPK regularly with intense exercise, it does tend to get switched down or dialled down with aging... If you maintain an active lifestyle that might not happen to the same degree."

Steinberg said his team genetically removed AMPK in mice and found the lab rodents aged at an accelerated rate.

"Mice lacking AMPK in their muscle developed much greater muscle weakness than we would have expected to see in a middle-aged mouse," said Steinberg. "Instead these mice, which were the equivalent of being just 50 years old, had muscles like that of an inactive 100-year-old."

Obesity: aging, accelerated

That finding was especially important for one of Steinberg's other pursuits, MAC-Obesity, the metabolism and childhood obesity research program at McMaster University where he is co-director.

"Obesity is really a disease of accelerated aging," Steinberg said, "and what we're seeing is obese kids will start to develop these disorders more and more at a younger age… Inactivity is big component of that."

To activate the production of AMPK and open up the pathway to clear out the junk from muscles, there is a certain threshold of exercise that you need to hit to unlock the protein naturally.

"Maybe just walking is not enough," added Steinberg.

What if you can't exercise?

The maximum aerobic output of a person is measured with a value called VO2 Max. Walking may take up 25 per cent of a person's VO2 Max, not enough to turn on production of AMPK.

Most children and younger adults will not have an excuse not to exercise, but Steinberg said there are plent of reasons why someone can't exercise to a point where AMPK production is turned on, and why a drug could save the healthcare system from a "significant financial burden."

Elderly slips and falls and surgeries are the major uses. If muscle can be maintain around a leg, knee and hip following a fall, an elderly person could have a better chance at full recovery rather than permanent loss. The same thinking goes for weekend warriors undergoing knee surgery, or anyone with a broken bone. 

Any immobile state leads to muscle loss, something, Steinberg hopes, could be reversed with this knowledge, published in the journal Cell Metabolism.


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