Figure 7. Activating transcription factor 4 (ATF4) is required for fibroblast growth factor 21 (FGF21) induction in optic atrophy 1 (OPA1) brown adipose tissue (BAT) knockout (KO) mice.

(A, B) Analysis of endoplasmic reticulum (ER) stress in BAT tissue from wild-type (WT) and OPA1 BAT KO mice (KO). (A) Representative immunoblot for phosphorylated eukaryotic translation initiation factor 2A (eIF2α) over total eIF2α and respective densitometric quantification (images were cropped from the same membrane). (B) mRNA expression of ER stress markers. (C–R) Data collected in 8–10-week-old OPA1/ATF4 BAT DKO mice. (C) mRNA expression of Atf4 in BAT. (D) mRNA expression of Opa1 in BAT. (E) Fgf21 mRNA expression in BAT. (F) FGF21 serum levels at ambient temperature and ad libitum-fed conditions. (G) Body mass. (H) BAT mass normalized to body mass. (I) Gonadal white adipose tissue (gWAT) mass normalized to body mass. (J) Inguinal white adipose tissue (iWAT) mass normalized to body mass. (K) Regression plot comparing oxygen consumption as a function of body mass in mice housed at 30°C. (L) Core body temperature measured at 30°C. (M) mRNA expression of thermogenic genes in iWAT samples collected at ambient temperature. (N) Core body temperature in DKO mice exposed to 4°C (data is represented as average core body temperature during the light and dark cycles over 3 days of continuous monitoring). (O) Final core body temperature recorded for each individual mouse (4°C). (P) mRNA expression of thermogenic genes in BAT samples. (Q) mRNA expression of thermogenic genes in iWAT samples. (R) Representative immunoblot for uncoupling protein 1 (UCP1) normalized to GAPDH (images were cropped from the same membrane) in iWAT and respective densitometric quantification (P–R collected after 3 days at 4°C). 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. VO₂ data was analyzed by ANCOVA.