Simulated microgravity led to increased brown adipose tissue activity in rats

Long-term spaceflight has been proven to induce metabolic dysfunction. Brown adipose tissue (BAT) plays an important role in whole-body energy metabolism. We speculated that BAT function would change under microgravity. Here, we employed a tail suspension (TS) rat model to simulate the effects of microgravity and found that TS increased BAT activity including 1.79, 2.74, 2.69 folds upregulation of UCP1 mRNA at different TS time and induced a phenotypic switch from white adipose tissue (WAT) to brown fat. Furthermore, serum metabolomics revealed abnormal fatty acid metabolism pathway in TS rats. Additionally, we observed that TS led to higher levels of circulating epinephrine (1.28, 1.2, 1.26 folds), norepinephrine (1.12, 1.08, 1.26 folds), adiponectin (1.52, 1.36, 1.64 folds), and FGF21 (2.2, 1.9, 2.7 folds) in different TS rats groups respectively, which contributed to the metabolic disorder in TS rats. In summary, our results indicated that microgravity increased the activity of BAT which might contribute to metabolic dysfunction during long-term exposure to the space environment.