Abstract: Objective To observe the effects and mechanisms of Y-box protein 3(YBX3)deletion in brown adipose tissue(BAT)on thermogenesis and energy consumption in mice. Methods The mice were placed in a 4 ℃ environment as a cold stimulation method. Lentiviral infection assay was used to construct a human stromal vascular fraction cell line that overexpresses YBX3 or inhibits YBX3 expression. Oxygen consumption rate was used to assess mitochondrial function. Mouse BAT was injected with YBX3 siRNA(si-Ybx3)to inhibit YBX3 expression in BAT. The oxygen consumption rate, CO₂ release rate and energy consumption rate of mice were detected to evaluate the energy metabolism of mice. qRT-PCR, Western blotting, and immunofluorescence staining assays were used to detect peroxisome proliferator-activated receptor gamma coactivator 1α(PGC-1α), uncoupling protein 1(UCP1)and YBX3 expression. HE staining was used to detect the size of lipid droplets of adipocytes in BAT. RNA-binding protein immunoprecipitation was used to extract the mRNA bindsing specifically to YBX3. Next-generation sequencing assay was used to identify mRNA. Dual-luciferase reporter gene systems were used to detect the binding of YBX3 to the target sequence. Results YBX3 expression in BAT of wild-type mice was induced by cold stimulation(P<0.05). Overexpressing YBX3 promoted the expression of the thermogenic gene PGC-1α and UCP1 after human stromal vascular fraction cell line cells being induced into mature brown adipocytes(P<0.05). Silencing YBX3 in human stromal vascular fraction cell line cells inhibited the expression of PGC-1α and UCP1(P<0.05)and mitochondrial oxidative phosphorylation after being induced into mature brown adipocytes(P<0.05). Compared with the control group, mice injected with si-Ybx3 had significantly lower energy consumption(P<0.05), lower body temperature in a cold environment(P<0.05), and lower expression levels of thermogenic genes(P<0.05). The size of lipid droplets in adipocytes increased significantly(P<0.05). Compared with at 25 ℃, the expression of YBX3 in the nucleus of brown adipocytes significantly increased from mice kept at 4 ℃(P<0.05). YBX3 specifically bound to the target sequence in the 3' untranslated region of PGC-1α mRNA(P<0.05). YBX3 specifically bound to PGC-1α and UCP1 promoter regions(P<0.05). Conclusion YBX3 in BAT can affect thermogenesis and energy metabolism by regulating the expressions of PGC-1α and UCP1.

Key words: Y-box binding protein 3, Thermogenesis, Energy expenditure, Brown adipose tissue, Uncoupling protein 1