Pinealectomy increases thermogenesis and decreases lipogenesis

Abstract

The present study was designed to determine the effects of pineal gland‑derived melatonin on obesity by employing a rat pinealectomy (Pnx) model. After 10 weeks of a high‑fat diet, rats received sham or Pnx surgery followed by a normal chow diet for 10 weeks. Reverse transcription‑quantitative PCR, western blotting analysis, immunohistochemistry and ELISA were used to determine the effects of Pnx. Pnx decreased the expression of melatonin receptor (MTNR)1A and MTNR1B, in brown adipose tissues (BAT) and white adipose tissues (WAT). Pnx rats showed increased insulin sensitivity compared with those that received sham surgery. Leptin levels were significantly decreased in the serum of the Pnx group. In addition, Pnx stimulated thermogenic genes in BAT and attenuated lipogenic genes in both WAT and the liver. Histological analyses revealed a marked decrease in the size of lipid droplets and increased expression of uncoupling protein 1 in BAT. In the liver of the Pnx group, the size and number of lipid droplets had also decreased. In conclusion, the results presented in the current study suggested that Pnx increases thermogenesis in BAT and decreases lipogenesis in WAT and the liver.

Figure 1.

Pnx increases insulin sensitivity. (A) Changes in body weight, (B) PGTT, (C) food intake, (D) water intake and (E) plasma leptin levels. Values are presented as the mean ± SD. **P<0.01, ***P<0.001 vs. the sham group. Pnx, pinealectomy; PGTT, peritoneal glucose tolerance test; OP, operation.

Figure 2.

Expression of MTNR1A and MTNR1B in WAT and BAT. mRNA expression levels of MTNR1A and MTNR1B in (A) WAT and (B) BAT were examined by reverse transcription-quantitative PCR and normalized to β-actin. Protein expression levels of MTNR1A and MTNR1B in (C) WAT and (D) BAT were examined by western blotting. Values are presented as the mean ± SD. *P<0.05, ***P<0.001 vs. the sham group. Pnx, pinealectomy; WAT, white adipose tissue; BAT, brown adipose tissue; MTNR, melatonin receptor.

Figure 3.

Thermogenic genes and PRDM16 in BAT. (A) Protein expression of SIRT1, PGC1α, UCP1 and DIO2 were examined by western blot analysis (upper panel), and relative band density was semi-quantified (lower panel). (B) mRNA expression levels of PGC1α, UCP1, and DIO2 (C) PRDM16 was examined by reverse transcription-quantitative PCR and normalized to β-actin. (D) Changes in size of lipid droplets and UCP1 expression in BAT. Representative images of BAT from the sham group and Pnx group stained with H&E (upper panel) and immune-histochemical images stained with UCP1 antibody (lower panel). Magnification, ×200. Values are presented as the mean ± SD. **P<0.01, ***P<0.001 vs. the sham group. Pnx, pinealectomy; BAT, brown adipose tissue; PGC1α, peroxisome proliferator-activated receptor γ coactivator 1-α; UCP1, uncoupling protein 1; PPARγ, peroxisome proliferator-activated receptor γ; DIO2, deiodinase 2; PRDM16, PR domain 16; H&E, hematoxylin and eosin; SIRT1, sirtuin 1.

Figure 4.

Lipogenesis genes in WAT. mRNA expression levels of (A) the lipogenic genes, SREBP1c, SCD1, DGAT1 and FASN, (B) the mitochondrial biogenesis genes, PGC1α and Cyt C, and (C) fatty acid oxidation genes, CPT1a, CPT1b and MCAD, in WAT were examined by reverse transcription-quantitative PCR and normalized to β-actin. Values are presented as the mean ± SD. *P<0.05, **P<0.01, ***P<0.001 vs. the sham group. Pnx, pinealectomy; WAT, white adipose tissue; SREBP1c, sterol regulatory element-binding protein 1; SCD1, stearoyl-CoA desaturase 1; DGAT1, diacylglycerol O-acyltransferase 1; FASN, fatty acid synthase; CPT, carnitine palmitoyltransferase; MCAD, medium-chain acyl-CoA dehydrogenase; PGC1α, peroxisome proliferator-activated receptor γ coactivator 1-α; Cyt C, cytochrome c.

Figure 5.

Changes in hepatic histology and lipogenesis genes in the liver. (A) Liver sections were stained with H&E. Magnification at ×100 in the upper panel and ×200 in the lower panel. mRNA expression levels of the (B) lipogenic genes, SREBP1c, SCD1, DGAT1 and FASN, (C) mitochondrial biogenesis genes, PGC1α and Cyt C, and (D) fatty acid oxidation genes, CPT1a, CPT1b and MCAD, in the liver were examined by reverse transcription-quantitative PCR and normalized to β-actin. (E) Protein expression levels of p-AKT, AKT and GAPDH were examined by western blotting. Values are presented as the mean ± SD. *P<0.05, **P<0.01 vs. the sham group. Pnx, pinealectomy; SREBP1c, sterol regulatory element-binding protein 1; SCD1, stearoyl-CoA desaturase 1; DGAT1, diacylglycerol O-acyltransferase 1; FASN, fatty acid synthase; CPT, carnitine palmitoyltransferase; MCAD, medium-chain acyl-CoA dehydrogenase; PGC1α, peroxisome proliferator-activated receptor γ coactivator 1-α; Cyt C, cytochrome c; H&E, hematoxylin and eosin; p-, phosphorylated.