Newborn babies may not be able to walk or talk but they can do something that makes adults very jealous: burn extra calories without exercising. This feat is accomplished with the help of brown fat which is abundant in infants (and hibernating animals) but barely detectable in adults. However, a new study in Scientific Reports shows that cold temperatures can nudge mesenchymal stem cells – found in the bone marrow – toward a brown fat cell fate, a finding that may uncover new strategies for combating obesity and other metabolic diseases.

Side by side comparision of brown fat, or adipose, cells and white fat cells.
Image: AHAJournals.org

So, what’s so magical about cells that carry brown fat, the so-called “good” fat? Like the more common “bad’ white fat cells, brown fat cells store energy in the form of fat droplets and can burn that energy to meet the demands of the body’s functions like pumping the heart and moving the limbs. But brown fat can also burn calories independent of the body’s energy needs. It’s like stepping on a car’s clutch and gas pedal at the same time: the body burns the fuel but doesn’t do any usable work, so those calories just dissipate as heat. This source of heat is critical for babies because they are not yet able to regulate their own body temperature and lose heat rapidly.

Scientists have known for quite some time that cold temperatures stimulate the production of brown fat but didn’t know exactly why (a CIRM-funded study we blogged about last week identified a protein that also boosts brown fat production). In the current study, a team at the University of Nottingham in the U.K., examined the effect of cold temperature on the fate of bone marrow-derived mesenchymal stem cells which give rise to both white and brown fat tissue as well as bone, cartilage and muscle. Petri dishes containing the cells were placed in incubators at 89°F (32°C) and stimulated to become fat cells. That may not seem cold, but if your core body temperature went that low (instead of the normal 98.6F) you would be beyond shivering, close to collapsing and in need of an emergency room.

With that temperature drop, the researcher observed a “browning” of the stem cells towards a brown fat cell fate. The brown color, in case you’re interested, is cause by the increased number of mitochondria within the cells. These “power factories” of the cell are the source of the heat generation. This result has promising implications for adults struggling with their body weight.

Virginie Sottile

“The good news from these results is that our cells are not pre-programmed to form bad fat and our stem cells can respond if we apply the right change in lifestyle,” explained Dr Virginie Sottile, one of the team leaders on the project, in a press release.

 

Ok, I know what you’re thinking: moving to Antarctica to lose weight is not my idea of a doable lifestyle change! That’s a point well taken. But the ultimate goal for the researchers is to use this cell system to more carefully study the cellular events that occur under reduced temperatures. This type of inquiry could help identify drug targets that mimic the effects of colder temperatures:

“The next step in our research is to find the actual switch in the cell that makes it respond to the change of temperature in its environment,” said Dr Sottile. “That way, we may be able to identify drugs or molecules that people could swallow that may artificially activate the same gene and trick the body into producing more of this good fat.”