14 DAY TRIAL // The couch potato mouse is the new model for studying muscle function, and it is the result of the latest research carried out by Daniel Kelly, MD, and his colleagues at Sanford-Burnham Medical Research Institute (Sanford-Burnham) at Lake Nona.
The couch potato effect comes from a missing protein called PGC-1, that allows the muscles to convert fuel into energy, so these mice keep having a normal activity and body mass, but they are unable to exercise (run on a treadmill).
This is the first time that PGC-1 has been completely removed from muscle tissue, so the researchers were able to analyze the precise role of the protein in muscle development, metabolism and exercise.
Dr Kelly's team report that when PGC-1 is missing, mitochondria is unable to function correctly, so cells must work harder to stay energetic, which leads to early fatigue.
This actually means that PGC-1 is necessary for exercise, but it is not needed for normal muscle development and activity.
There was another thing that amazed the researchers: couch potato mice were not obese and had normal responses to insulin, which means that they are unlikely to develop diabetes even if their do not exercise and have mitochondrial problems.
This contradicts previous scientific beliefs, which linked dysfunctional mitochondria to insulin resistance and diabetes, and launches a new theory that says that maybe malfunctioning mitochondria are not a cause of diabetes, but a result.
“Part of our interest in understanding the factors that allow muscles to exercise is the knowledge that whatever this machinery is, it becomes inactive in obesity, aging, diabetes and other chronic conditions that affect mobility,” explained Dr. Kelly.
In healthy individuals, physical stimulation normally increases PGC-1 activity in muscle cells, triggering fuel storage and resulting in an 'exercised' muscle.
Obese people have very low PGC-1 levels, which reduces their ability to exercise and creates a vicious circle, but couch potato mice without muscle PGC-1 looked normal and walked around without difficulty, but were unable to run on a treadmill.
“Lo and behold, even though these animals couldn't run, they showed no evidence of insulin resistance,” said Dr. Kelly.
“We are now investigating what happens when we boost PGC-1 activity intermittently, as normally occurs when a person exercises.”
This research was published in the December 1 issue of Cell Metabolism.
Watch a video of Dr Kelly explaining the experiment:
The Couch Potato Effect from Sanford-Burnham Institute on Vimeo.