Science News for Students - Spring 2021

This fat’s color comes from a high flow of blood and many tiny power factories, known as mito- chondria. Low temperatures turn on those power factories in brown fat. Mitochondria convert into heat the chemical energy in food and stored white fat. This helps infants staywarm and small mam- mals survive cold winters. In 2009, researchers showed that adult humans have brown fat that responds to cold tempera- tures. Adults also have beige fat scattered within their white fat. Beige fat is not quite white or brown but somewhere in between. When needed, it becomes brown to turn more calories into warmth. It becomes white-ish again when that’s no longer needed. Howmuch brown and beige fat adults host is unknown. However, it’s a lot less than what is in mice. The amount strongly depends on someone’s body composition. Lean people tend to have more active brown and beige fat than do obese people. Scientists had wondered whether they could treat obesity by turning white fat into brown, notes Yu-Hua Tseng. She is a molecular biologist at Harvard Medical School in Boston, Mass. Her team has now done this in mice. The group described how on August 26, 2020 in Science Translational Medicine . HUMBLE is powerful innovation Plastic surgeons on Tseng’s team took cells that will become fat from the necks of patients. In the lab, this tissue grows into white and brown fat. To make the white fat behave like brown fat, the researchers used a technology for modifying DNA known as CRISPR/Cas9. CRISPR often is used to swap out some genetic building blocks with others. Tseng’s team instead used the technology to insert a molecular switch into the DNA of white fat cells. This switch turned on a gene called UCP1. In brown fat, that gene causes mitochondria to churn out heat. The inserted switch boosted almost 20-fold howmuch protein the UCP1 gene made. That extra protein turned the white fat cells into cells the researchers call HUMBLE. It’s an acronym for “human brown-like.” They then transplanted HUMBLE cells into mice. (First, they disabled the immune system. Otherwise, a mouse’s immune cells would have attacked and destroyed the for- eign human cells.) One set of mice were normal weight. They ate fatty food for two weeks before the transplant and for four weeks after. A second set of mice was already obese.

Gene editing can alter body fat and may fight diabetes In animals on a fatty diet, this DNA tweaking left them slimmer and healthier By Silke Schmidt P eople are among mammals that have “bad” fat and “good” fat. The bad, white type stores energy. But too much of it makes us obese. The brown type burns

energy, helping us stay lean. Scientists have now created human brown fat cells in the lab and transferred them into mice. These rodents gained less weight from a fatty diet. They also became healthier. Scientists hope such a strategy might do the same thing in people. It’s been well known that infants and hibernat- ing animals have brown fat. Mice, for example, have deposits of it between their shoulder blades.

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28 SCIENCE NEWS FOR STUDENTS | Invention & Innovation