Abstract: BACKGROUND: In mammals, white adipose tissue stores energy, whereas brown adipose tissue dissipates energy. Conversion from White to brown/beige adipocytes is a potential therapeutic strategy to fight obesity, but the molecular mechanisms that drive this process is unclear.  
OBJECTIVE: To reveal the potential relationship between Hr mutation and adipocyte browning.
METHODS: Ten 10-week-old male Yuyi hairless mice and 10 littermate wild-type controls were selected and changes in food intake, body mass and inguinal white adipose tissue mass were recorded. Serum levels of leptin and adiponectin were estimated by ELISA. Glucose tolerance test was used to assess glucose metabolic function and insulin tolerance test was performed to analyze insulin sensitivity. Hematoxylin-eosin staining was performed to observe pathological changes of inguinal white adipose tissue in mice. Real-time fluorescence quantitative PCR and immunofluorescent staining were performed to analyze the expression of genes and proteins associated with browning of white adipose tissue in the groin.
RESULTS AND CONCLUSION: (1) Compared with wild-type mice, Yuyi hairless mice had increased brown fat content and ultimately increased glucose tolerance and insulin sensitivity. Hr mutation reduced body mass and inguinal adipose mass in mice, but food intake did not change significantly compared with wild-type mice, suggesting that there was a reduction in body mass and adipose mass but not in food intake. (2) Hematoxylin-eosin staining results showed browning of adipocytes in the inguinal white adipose tissue of Yuyi hairless mice, which became smaller, rounder and accompanied by the appearance of multilocular cells. (3) There was increased level of peroxisome proliferator-activated receptor γ coactivator 1α and activation of thyroid hormone receptor α, uncoupling protein 1, and the mitochondria-shaping genes (nuclear respiratory factor 1 and mitochondrial transcription factor A), thereby promoting browning of adipocytes. Thus, Hr mutation activates the peroxisome proliferator-activated receptor γ coactivator 1α/thyroid hormone receptorα/uncoupling protein 1 signaling pathway and increases brown adipose content in mice, thereby promoting energy expenditure and thermogenesis and inhibiting obesity.

Key words: hairless gene, white adipocyte browning, peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α)/thyroid hormone receptor α (TRα)/uncoupling protein 1 signaling pathway (UCP1) signaling pathway, uncoupling protein 1, obesity, Yuyi hairless mouse