Loss of adipocyte FNIP1 leads to increased mitochondrial biogenesis and respiration in iWAT. (A) Representative electron micrographs of the iWAT showing mitochondria in sections from indicated male mice. Scale bar: 1 μm. n = 4 mice per group. (B) Percentage of mitochondrial area and mitochondrial size were quantified from the indicated male mice. n = 4 mice per group. 11–12 electron micrographs from each group were measured. (C) Results of qPCR to determine mitochondrial DNA levels in iWAT of the indicated male mice. n = 6–8 mice per group. (D) Mitochondrial respiration rates were determined from the iWAT of the indicated male mice using pyruvate as substrates. Pyruvate/malate (Pyr/M)-stimulated, ADP-dependent respiration, and oligomycin-induced (Oligo) are shown. n = 8 mice per group. (E) Body weight of indicated chow-fed 16-wk-old male mice. n = 7–10 mice per group. (F and G) Energy expenditure rates (VO₂ and VCO₂) of chow-fed 16-wk-old male mice under basal conditions. n = 7–10 mice per group. (H) Body weight of indicated chow-fed 8-wk-old female mice. n = 4–7 mice per group. (I–K) Energy expenditure rates (VO₂, VCO₂, and heat production) of chow-fed 8-wk-old female mice after CL injection (0.5 mg/kg). n = 4–7 mice per group. (L) Rectal temperature recordings taken hourly during 4 h of cold exposure using a rectal digital probe. Notably, female mice were fasted for 12 h before cold-exposure experiments. n = 7–9 mice per group. Values represent mean ± SEM. *, P < 0.05; **, P < 0.01; ***, P < 0.001. P value was determined using two-tailed unpaired Student’s t-test (B, C, D, E, and H), or two-way ANOVA and Fisher’s LSD post-hoc test (F, G, and I–L). Data are representative of two independent experiments (A and D).