3,5 Diiodo-l-Thyronine (T2) Promotes the Browning of White Adipose Tissue in High-Fat Diet-Induced Overweight Male Rats Housed at Thermoneutrality

Figure 1. Insulin Tolerance test (ITT). Glycemia after insulin administration at different time points in N, HFD, and HFD + T2 rats. Area under the curve (AUC). Values are means ± SEM of five independent experiments (N = 5) $ p < 0.05 vs. N and HFD-T2. After 10 min from insulin injection, both N and HFD showed a small but not significant increase in glucose level, but this is not surprising and can happen frequently [49].

Figure 2. Effects of T2 administration on BAT morphology and on BAT UCP1 content. (a) Representative images (at low magnification-20×) showing different cellular organization within BAT parenchyma (haematoxylin and eosin staining). Insets: cellular shapes in the central part of the lobule in BAT parenchyma (40×), and (b) western blot analysis and quantification of the signals of UCP1 protein levels detected in the whole lysate. For total lysate, each lane contained 15 µg of protein from a single rat. Values are means ± SEM of five independent experiments (N = 5), * p < 0.05 vs. N.

Figure 3. Effects of T2 administration on sWAT morphology. (a) Histological analysis, (b) morphometrical analysis, and (c) UCP1 immunohistochemistry of anterior sWAT of N, HFD, and HFD+T2 rats. Adipocytes from HFD rats are significantly larger than those from N rats. After T2 administration, the mean area and frequency distribution of the adipocytes were normalized to control values. A number of UCP1-stained paucilocular adipocytes are shown (arrows and panel (c)). More than 720 adipocytes were quantified from N = 3 rats from each group. Data are presented as Means ± SEM. ** p < 0.01 vs. N; *** p < 0.001 vs. HFD.

Figure 4. Effects of T2 administration on expression of the main browning genes in sWAT. Western blot images and densitometry showing relative expression of the main browning genes in sWAT of rats. (a) UCP1, Voltage-dependent Anion Channel (VDAC) in mitochondrial of sWAT, and (b) PRDM16, (c) and C/EBPβ and β-actin in sWAT lysates. Values are means ± SEM of five independent experiments (N = 5), * p < 0.05 vs. N-HFD.

Figure 5. qPCR analysis of PGC1α and CIDEA in sWAT of N, HFD, and HFD-T2 rats. Values are means ± SEM of five independent experiments (N = 5), # p < 0.05 vs. N; * p < 0.05 vs. N-HFD.

Figure 6. qPCR analysis of miR-133a in sWAT of N, HFD, and HFD-T2 rats. Values are means ± SEM of five independent experiments (N = 5), ** p < 0.05 vs. N-HFD.

Figure 7. qPCR analysis of miR-196a in sWAT of N, HFD, and HFD-T2 rats. (a) qPCR analysis of miR-196a in sWAT of N, HFD, and HFD-T2 rats; (b) Immunoblots and densitometry showing relative expression of HOXC8 and β-actin in sWAT lysates. Values are means ± SEM of five independent experiments (N = 5), * p < 0.05 vs. N-HFD; ** p < 0.05 vs. HFD # p < 0.05 vs. N.

Figure 8. Effects of T2 administration on MKK6 and P-p38 in sWAT. (a,b) Immunoblot and densitometry showing relative expression of MKK6, P-p38, and total p-38 in sWAT lysates. Values are means ± SEM of five independent experiments. N = 5, # p < 0.05 vs. N; ** p < 0.05 vs. HFD.

Figure 9. Effects of T2 administration on Irisin and P-AMPK in sWAT. (a) Irisin serum levels detected by a competitive Enzyme Linked-Immunosorbent Assay (ELISA) and (b) immunoblot and densitometry showing relative expression of P-AMPK and total AMPK in sWAT lysates. Values are means ± SEM of five independent experiments. N = 5, * p < 0.05 vs. N and HFD.