White Adipose Tissue Undergoes ‘browning’ in Tree Shrews (Tupaia belangeri) During Cold Acclimation

Cold induces a transformation of adipocytes in white adipose tissue (WAT) into ‘beige’ adipocytes with a brown adipose-like phenotype in a process known as ‘browning’. In the present study, cold acclimation was characterized over 49 days of exposure to 5°C (with controls housed at 25°C) in Tupaia belangeri using physiological indices, positron emission tomography-computed tomography (PET/CT) scan, adipose tissue morphology study, and flow cytometry. The results showed that during cold acclimation, body mass and WAT mass and content increased significantly, and there were significant effects of cold exposure on the mean standardized uptake values (SUV) for inguinal, omental, and mesenteric WAT. Adipose tissue morphology showed that the abdominal omental WAT had taken on characteristics of beige adipocytes, including smaller lipid droplets, and expression of uncoupling protein 1 (UCP1). Flow cytometric analysis showed that a new cell population had appeared in WAT by day 49. In the R1 (original) and R2 (new) groups of cells, 69.6% and 95.3% of the cells were positive for UCP1, respectively. All of these results indicate that cold exposure induced WAT browning, which would increase thermogenic properties in T. belangeri under cold acclimation.