Some stem cells have the ability to build fat, according to a study in the Oct. 17 issue of the journal Cell.
Researchers have yet to show whether the cells can renew themselves, but transplants of the progenitor cells isolated from the fat tissue of normal mice can generate normal fat tissue in animals without it.
The study results could provide clues to the causes of obesity, which sees an increase in the number and size of fat cells.
"The question is: What are the events that lead to that increase?" said researcher Matthew Rodeheffer of The Rockefeller University. "You need to know how fat cell number is normally regulated to know what goes wrong in obesity. Identifying fat cell precursors is a first step toward understanding this process."
Previous research had identified cells with the capacity to differentiate into fat - but only in lab dishes. The cells couldn't replicate the feat in living animals.
In the new study, the research team, led by Jeffrey Friedman, took fat tissue from mice and treated it with an enzyme to break it down into individual cells. The mature fat cells were then separated out, while the remaining cells were sorted based on which proteins were expressed on their surfaces. After isolating those cells with proteins that are known to identify other types of stem cells, the researchers found that two of the cell populations could produce fat in lab dishes.
Only one of the two populations was able to re-grow normal fat in mice, which had diabetes and a condition called lipodystrophy, in which animals can't produce fat normally. (Antiretroviral drugs can result in lipodystrophy in humans.) Injection with the newly discovered fat cell progenitors reversed the animals' diabetes and restored their fat levels within two weeks, the researchers report.
There are likely to be analogous cells in humans, Rodeheffer said, and the cells could be used to treat people with lipodystrophy. Leftover fat cells from operations are also under consideration for use in regenerating heart and other tissues, he noted.
"Fat is an attractive source for adult stem cells because it is readily available and easy to obtain via liposuction," Rodeheffer said. "You can imagine plenty of people would be willing donors."
The cell might also prove useful for other tissue-regenerating applications: The researchers discovered that the cells isolated in the new study can also form bone, muscle, and cartilage, when used in the right conditions.