PMC

Model. YY1 recruits PGC-1α and induces classical thermogenesis by activating mitochondrial and canonical thermogenic genes in brown fat. However, YY1 plays a direct suppressor role in the control of alternative thermogenic genes, including Bmp8b and Gdf15, and has indirect control of the genes Fgf21, Angptl6, Neuromedin B, and Nesfatin linked to energy expenditure. With excessive caloric intake and loss of YY1, these factors are secreted from BAT, increase thermogenesis in beige and white fat cells, and protect against diet-induced obesity.

YY1 deficiency in adipose tissue leads to increased energy expenditure without changes in food intake or physical activity. (A and B) Accumulated food intake measured by CLAMS analysis (A) and by weighing food pellets (B) for individually caged mice at the indicated time points. (C) Total spatial mouse movement in 3 dimensions analyzed by CLAMS. (D and E) Total O₂ consumption and CO₂ production in (D) YY1aKO and (E) YY1bKO mice versus control mice fed a high-fat diet for 2 weeks. Data are represented as means ± SEM. *, P < 0.05, and **, P < 0.01, by t test (n = 8).

Browning of subcutaneous white adipose tissue in YY1 KO mice fed a high-fat diet. (A) Gene expression of IWAT from YY1bKO versus control mice fed a high-fat diet. (B) Gene Set Expression Analysis (GSEA) of IWAT from YY1bKO versus control mice indicating increased catabolic pathways. (C) Western blot analysis of mitochondrial proteins in IWAT from YY1bKO versus control mice on a high-fat diet. (D) H&E staining of IWAT cross sections from YY1bKO versus control mice fed a high-fat diet. (E) Ex vivo oxygen consumption of IWAT homogenates from YY1bKO versus control mice measured by Clark electrode. (F) Fatty acid oxidation rates measured by released ¹⁴CO₂ from IWAT homogenates incubated with ¹⁴C-radiolabeled oleic acid in YY1bKO and control mice. Data are represented as means ± SEM. *, P < 0.05, and **, P < 0.01, by t test (n = 6 to 10).

Increased nutrient uptake and energy consumption pathways in visceral white adipose tissue of YY1aKO mice. (A) Images of dissected visceral white adipose tissue from control and YY1aKO mice. (B) Gene expression array heat map showing the identification of genes of the Slc25 family increased in EWAT of YY1aKO mice versus control mice. (C and D) Gene expression of EWAT from YY1aKO mice versus control mice fed a high-fat diet for 3 months (C) or exposed to cold for 4 days (D). (E and F) Oleic acid oxidation (E) and glutamine oxidation (F) rates measured by released ¹⁴CO₂ of EWAT tissue homogenates from YY1aKO mice versus control mice fed a high-fat diet for 2 weeks. (G) Ex vivo oxygen consumption of EWAT homogenates from YY1aKO versus control mice measured by Clark electrode. Data are represented as means ± SEM. *, P < 0.05, and **, P < 0.01, by t test (n = 5 to 8).

YY1 deficiency in adipose tissue protects against diet-induced obesity through increased energy expenditure. (A and B) Total body weight curves of (A) YY1aKO and (B) YY1bKO mice versus littermate controls when chronically fed a high-fat diet. (C and D) Decreased fat content measured by adipose tissue depot weights from (C) YY1aKO and (D) YY1bKO mice. (E and F) Total body weight (BW), adiposity, or lean mass measured by MRI citi-scan in (E) male and (F) female mice chronically fed a high-fat diet. (G and H) Increased energy expenditure of (G) YY1aKO and (H) YY1bKO mice versus control mice as indicated by O₂ consumption (VO2) and CO₂ production (VCO2) analyzed by CLAMS. Data show representative results from two independent experiments for body weight measurements (n = 8 to 10). Data are represented as means ± standard errors of the means (SEM). *, P < 0.05, and **, P < 0.01, by t test.

Loss of YY1 in brown adipose tissue leads to a mitochondrial and thermogenic defect. (A to C) Expression of mitochondrial and thermogenic genes (A) and transcriptional regulator and lipid metabolism genes (B) of BAT from YY1bKO and YY1aKO (C) mice versus control mice fed a high-fat diet. (D and E) Western blot analysis (D) of mitochondrial proteins and CREB signaling (E) of BAT from control and YY1bKO mice. (F) Plasmatic norepinephrine levels measured by ELISA in YY1bKO versus control mice fed a high-fat diet for 2 weeks (n = 10). (G and H) Endogenous coimmunoprecipitation of YY1 or the IgG control with specific antibodies followed by pulldown with protein G magnetic beads from brown adipose tissue of mice housed at thermoneutrality (30°C) or cold (4°C) for 3 h (G) and from brown adipose cells of the De2.3 line (H) treated with DMSO or 10 μM forskolin (FSK) and detection of PGC-1α by Western blot analysis. (I) Histological analysis of BAT cross sections stained with hematoxylin and eosin (H&E). (J) Fatty acid oxidation rates by [¹⁴C]oleic acid oxidation from BAT extracts of YY1aKO versus control mice. (K) Oxygen consumption of isolated mitochondria of BAT from YY1aKO versus control mice measured by Seahorse Bioscience technology. FCCP, carbonyl cyanide p-trifluoromethoxyphenylhydrazone. Data are represented as means ± SEM. *, P < 0.05, and **, P < 0.01, by t test (n = 8 to 10).

Identification of brown fat-secreted factors, including the products of the Gdf15 and Bmp8b genes, elevated in brown adipose tissue of YY1 mutant mice. (A) Gene expression validation of identified secreted proteins by qPCR (n = 8). (B) Detection of plasma GDF15 by Western blotting and quantification of band intensities from YY1bKO versus control mice fed a high-fat diet (2 weeks). (C and D) Gene expression of IWAT from YY1bKO (C) and YY1aKO (D) mice fed a high-fat diet for 2 weeks (n = 6 to 8). (E) Gene expression of primary BAT cells from YY1aKO mice showing differentiation markers. (F) Gene expression of primary BAT adipocytes from control and YY1aKO mice treated with DMSO or 10 μM forskolin (n = 3). (G) YY1 ChIP in BAT from wild-type mice showing the relative binding versus IgG in Gdf15 and Bmp8b promoters. Cytochrome c (Cycs) was used as a positive control. The genomic position of YY1 binding is indicated as relative distance from the transcription start site (TSS) in base pairs. (H) ChIP of the repressive H3K27me3 mark in BAT from YY1bKO versus control mice (n = 3) in Gdf15 and Bmp8b promoters indicating the relative position of the TSS. Cytochrome c was used as the negative control. (I) BAT gene expression of wild-type mice exposed to cold or thermoneutrality for 4 days (n = 5). (J) BAT gene expression of wild-type mice fed on chow or a high-fat diet (HFD) (n = 6). Data are represented as means ± SEM. In panels A to E and G to H, * indicates P < 0.05 and ** indicates P < 0.01 (t test). Analysis of variance (ANOVA) with Bonferroni multiple comparisons was used in panel F (*, P < 0.05; +, P < 0.05).