City of Hope scientists find a switch that keeps heat-making brown fat cells idle, and blocking it warmed up old mice
The Southern California study may help explain why older people feel cold more easily. It was done in mice, and no human treatment exists.
Scientists at City of Hope, a cancer and research center in Duarte, Calif., have found a chemical switch that keeps many brown fat cells from making heat, and blocking it in old mice restored their ability to warm themselves, according to a study published Nov. 11 in the journal Nature. The authors say it offers a basic explanation for why older people often become sensitive to cold.
Brown fat is a type of body fat that burns energy to make heat, unlike ordinary white fat, which stores energy. It is what keeps the body warm without shivering. Its heat comes from a protein called UCP1. Earlier work by the same lab found two kinds of brown fat cells: ones with a lot of UCP1 that make plenty of heat, and ones with little UCP1 that make less.
What the study found
- Immune cells release a signal called IL-1β that keeps nearby brown fat cells in the low-heat state. It does so by making the cells produce active stress hormones, which turn down UCP1.
- Cold lowers the IL-1β signal, flipping cells into the high-heat state. Warm weather does the opposite.
- In old mice, IL-1β stayed high, leaving their brown fat stuck in low gear and the mice less able to handle cold.
- Blocking the stress-hormone receptor in old mice restored the balance of heat-making cells, restarted heat production and raised the energy, or calories, they burned.
What it could mean if it holds up in people
If the same switch works in humans, it could lead to treatments for the cold sensitivity many older people live with. The authors wrote that the stress-hormone signal inside brown fat “could be targeted to correct age-related cold intolerance and significantly increase basal metabolism,” the calories the body burns at rest.
Burning more calories at rest could matter beyond staying warm. The authors note that the decline of heat-making fat and the weight gain that comes with age contribute to metabolic disorders that come with aging. A drug that reawakens brown fat could, in theory, help with those too, though the study did not test that.
The drug the team used in old mice, RU-486, blocks stress-hormone receptors all over the body, so its effects can’t be pinned on brown fat alone, the authors wrote. The team says its next step is to block the signal only in heat-making fat cells. No human testing has been announced.
Limits
All the experiments were in mice. The paper does not test any drug or treatment in people, and blocking stress-hormone signals throughout the body could have side effects. Whether the same switch controls brown fat in humans still has to be shown. The authors declared no competing interests.