fed extremely high-fat diets. The mice lack a gene that makes an enzyme called FIH, which affects the body's physiological response to low oxygen levels. At first, the researchers thought the lack of the gene might kill them in utero.
"In fact the mouse was quite happy and didn't seem to notice it all," says Randall Johnson, a professor of biology at the University of California, San Diego, who directed the research. But when scientists studied it, they realized it was significantly leaner than normal mice.
Not only that. The mouse was constantly hyperventilating, taking in 20-40% more air than normal, with a faster heart rate. It also drank 30-40% more than regular mice.
When researchers analyzed it, they found that the mouse was reacting as if it had been taken up to the top of Mount Rainier, about 14,000 feet.
Air at sea level contains about 22% oxygen. At the top of Washington State's Mount Rainier, it's about 15% and at the top of Mount Everest, at the far edge of what humans can survive, it goes down to 11 to 12%.
These mice react much as humans would at a 15% oxygen level. Except in humans, the body quickly reacts to altitude, increasing respiration and adding more red blood cells to compensate until it has adapted.
The mice never adapt. Instead, they expend a huge amount of energy breathing.
It might be socially a little problematic to go around hyperventilating all the time, but Johnson says it's possible a similar state might be induced by drugs.
"It's intriguing that the least diabetic state is Colorado. So there's a possibility that there's a link between higher altitude and improved insulin sensitivity," he says.
Cell Metabolism April 14, 2010