a, Diagram of the following animal study. Created with BioRender.com. b, Administration of AAV-shRNA-Errα into BAT significantly suppressed ERRα expression compared to scramble group in JunB FKO mice (n = 7, control; n = 8, FKO). c, JunB deficiency-induced cold-induced oxygen consumption was compromised when ERRα was suppressed under cold stress conditions (n = 8 per group). d, Data analysis of oxygen consumption from c using CaIR software64 (n = 8 per group). e, The upregulated expression levels of UCP1 and TFAM were attenuated by Errα suppression in JunB KO BAT under cold stress conditions (n = 8 per group). f, The increased ratio of mtDNA/nDNA was diminished by Errα suppression in JunB KO BAT after cold stimulation (n = 8 per group). g, Suppressing ERRα partially reversed the increase in mitochondrial copy number in JunB-deficient BAT. h, Quantification of mitochondrial copy number in g (n = 5 per group). Data were analysed using an unpaired one-sided t-test.