\u201cIt was surprising to see acylcarnitines in the bloodstream,\u201d remarks lead author and postdoctoral fellow Judith Simcox. \u201cThe dogma was that once cells generated them, they used them right away.\u201d<\/p>\n

Scientists had seen circulating acylcarnitines before but it was always considered to be a sign of trouble. In infants, high levels of the lipid indicate they have a metabolic disease. The molecules also mount in the bloodstream during exercise, considered a flag for muscles under stress. The context in which Villanueva and Simcox saw acylcarnitines accumulate hinted that the buildup could also be part of a healthy process.<\/p>\n

To see what the lipids were doing, Simcox traced their migration as originating from the liver, the first time the organ has been implicated in cold adaptation. The lipids traveled through the bloodstream, ending up in a small number of energy-intensive tissues including brown fat. Once there, the fatty tissue broke down the lipids and metabolized them, indicating that they had become fuel for the main function of these specialized cells: to generate heat.<\/p>\n

Cementing the idea, depleting the lipid from circulation caused even young mice to lose their ability to adequately warm up in the cold.<\/p>\n

\u201cThis work is putting a new face on an old character,\u201d says Simcox. \u201cWe\u2019re changing how we think about cold-induced thermogenesis.\u201d<\/p>\n

Energy well spent<\/strong><\/p>\n

One reason it might be so difficult for aging animals to shirk off the cold is that doing so is costly from an energy standpoint. Simcox says that what is considered a disadvantage evolutionarily could be turned into an advantage for people.<\/p>\n

She explains that because of brown fat\u2019s ability to burn calories, jump-starting the cold adaptation process may not just be useful for fixing cold sensitivity but could also become a way to fight obesity. Now, with an activator of brown fat in hand, scientists have a handle on manipulating brown fat\u2019s power.<\/p>\n

\u201cThe idea is to increase fuel utilization to drive the energy demanding process of adapting to the cold,\u201d says Villanueva. \u201cIf we can find a way to tell the body to expend more energy than it is taking in, the calories lost can lead to weight loss.\u201d<\/p>\n

# # #<\/p>\n

Funding was provided by the National Institutes of Health and the Margolis Research Foundation<\/p>\n