Thursday, November 02, 2006

An Engine that Runs Cool Lasts Longer?

It's a truism among mechanics that an engine that overheats is gonna break sooner. All engines (and computers) are made with a fan to help vent the heat.

Now, Conti et al. in Science Magazine has discovered the same may hold true Picture of cartoon grey mouse with sunglasses playing a yellow sax with purple background, with pink words saying live cool 4-everfor animals. The mice in this study had body temperatures 0.3 to 0.5 degree C lower than normal, due to a mutation that caused "overheating" of the hypothalmus, the body's thermostat located in the brain, hence making it misread the body temperature slightly and work harder to keep the body cool.

This recent discovery of long-lived sangfroid mice will add fuel to the continuing debate over what exactly determines aging. One debate centers on energy expenditure rate vs body size vs lifespan for a while-- an idea called"rate of living", which has been disproved by analyzing metabolic rate and lifespan in various animals. Warmblooded mammals have much higher metabolism than reptiles and fish to maintain a constant body temperature, and they also live much shorter lives. Yet, birds have higher metabolism AND live longer than mammals. Very confusing.

The mice's body temperature decrease is mild enough that in humans, it would not cause hypothermia . Indeed, humans only start shivering after their body temperature drops by around 1 degree C.

As Northerners would say, "Hoff Da! Of course we live longer because we're too frozen to wrinkle!" Not quite. the longevity effect observed in the "longevity belt" only holds true for people who grew up there, not those who move there as adults, indicating the influence may be congenital or start in childhood, long before wrinkles ever form.

Also, they're not the only ones that get cold. We all have our body temperature drop when we sleep. During a phase of sleep, we are in effect cold-blooded again as our metabolism drops. Circadian rhythm studies how this most commonly occurs around 3 AM in the morning, shortly before when our lungs are least effective. 3 AM is the cold hour when people will most commonly have their worst nightmares.

Whenever I wake up from a nightmare, it will be 3 AM and my spine will be so COLD it takes some warming up, or my heart will be pounding away. Other people may vary in their nightmare patterns, though.

This brings us back to food. If you have read the longevity belt link, you'll have noticed that Sardinia and Okinawa are both considered to be long-lived due to lower caloric intake. Caloric restriction diets in worms, mice and men seem to prolong life slightly. Now, obviously carrying around lots of lard isn't good, but why would eating very little, being hungry all the time, and being as skinny as a scarecrow make you live longer?

Researcher wondered if a changed metabolic rate, one of the effects of the caloric restriction diet, might be the key. This idea is supported by Yoda the Snell dwarf mouse, who needed a regular companion mouse to keep him warm at nights. Like all of his tribe, he had a mutation that disrupted the Pit-1 gene which is key to proper pituitary development. The pituitary controls growth and metabolism, hence Yoda's small size. A simple deficiency in growth hormone in the little mouse increases life expectancy by 25%.

Researchers already compared the gene expression of Snell dwarf mice and caloric-restricted mice, and they found 29 genes that are expressed similarly in both groups. Snell dwarf mice on a caloric restricted diet will live longer than normal mice on a caloric-restricted diet, so diet alone doesn't work. It looks like dwarves live longer in all conditions so far. Good news for gnomes!

I gotta hold my horses. Snell dwarf mice used to live really short lives. It does bring to mind the chinese saying "One disease, long life. No disease, short life." Sometimes being built to last isn't the same as being built tough. And that's where the luck of life comes in. We have tamed many diseases, nearly eradicated smallpox from the world, removed rubella from the United States thanks to the MMR vaccine, and so on. But there remains hundred of thousands of potential pathogens in the environment, and we have added thousands of new, unknown compounds to the environment since 1950.

It might be that if we all found the magic formula and germ-free rooms and hygenic chow, we would live much longer than we do right now. But, really, who wants to live in a bubble for over 100 years, even if that little wheel sure is good exercise? I'll take the cupboard any day.