Figure 4. Brown adipose tissue (BAT)-derived fibroblast growth factor 21 (FGF21) is required for increased resting metabolic rates and improved thermoregulation in mice lacking optic atrophy 1 (OPA1) in BAT during isocaloric feeding.

(A–L) Data characterizing 8–12-week-old OPA1/FGF21 DKO mice. (A) mRNA expression of Opa1 and Fgf21 in BAT of DKO mice. (B) FGF21 serum levels collected under ad libitum-fed conditions. (C) Total body mass. (D) Percent fat mass. (E) Percent lean mass. (F) BAT mass. (G) Inguinal white adipose tissue (iWAT) mass. (H) Gonadal white adipose tissue (gWAT) mass. (I) Regression plot comparing oxygen consumption as a function of body mass in mice housed at 30°C. (J) Core body temperature (30°C). (K) Core body temperature (4°C) (data is represented as average core body temperature during the light and dark cycles over 3 days of continuous monitoring). (L) Final core body temperature recorded for each individual mouse (4°C). (M–S) Data of iWAT from 8-week-old DKO mice. (M). Representative immunoblot for OPA1 and uncoupling protein 1 (UCP1) in isolated mitochondria (dashed line separates genotypes). (N) Densitometric analysis of OPA1 and UCP1 protein levels normalized to succinate dehydrogenase (SDH). (O) Representative immunoblot for tyrosine hydroxylase (TH) in iWAT (images were cropped from the same membrane). (P) Densitometric analysis of TH protein levels normalized to tubulin. (Q) mRNA expression of thermogenic genes in iWAT. (R, S) Functional analysis of mitochondria isolated from iWAT. (R) State 2 and state 3 pyruvate-malate-supported mitochondrial OCR. (S) State 2 and state 3 palmitoyl-carnitine-supported mitochondrial oxygen consumption rate (OCR). Data are expressed as means ± SEM. Significant differences were determined by Student's t‐test or two-way ANOVA, using a significance level of p<0.05. *Significantly different vs. wild-type (WT) mice. VO₂ data was analyzed by ANCOVA.

Figure 4—figure supplement 1. Data collected in optic atrophy 1 (OPA1)/fibroblast growth factor 21 (FGF21) brown adipose tissue (BAT) DKO mice and their wild-type littermate controls (WT).

Related to Figure 4. (A) State 2 and state 3 pyruvate-malate-supported oxygen consumption rates (OCRs) in mitochondria isolated from BAT. (B) State 2 and state 3 palmitoyl-carnitine-supported OCR in mitochondria isolated from BAT. (C) mRNA expression of thermogenic genes in BAT tissue collected from mice raised at room temperature (22°C). (D) Locomotor activity in 10-week-old male mice measured at thermoneutrality (30°C). (E) Average food intake in 10-week-old male mice measured at thermoneutrality. (F) Regression plot comparing oxygen consumption as a function of body mass in 10-week-old male mice housed at 4°C for 3 days. (G) Locomotor activity measured in 10-week-old male mice housed at 4°C for 3 days. (H) Average food intake measured in 10-week-old male mice housed at 4°C for 3 days. Data are expressed as means ± SEM. Significant differences were determined by Student's t‐test, using a significance level of p<0.05. *Significantly different vs. WT mice. VO₂ data was analyzed by ANCOVA.