Cold exposure promotes obesity and impairs glucose homeostasis in mice subjected to a high‑fat diet

Abstract

Cold exposure is considered to be a form of stress and has various adverse effects on the body. The present study aimed to investigate the effects of chronic daily cold exposure on food intake, body weight, serum glucose levels and the central energy balance regulatory pathway in mice fed with a high‑fat diet (HFD). C57BL/6 mice were divided into two groups, which were fed with a standard chow or with a HFD. Half of the mice in each group were exposed to ice‑cold water for 1 h/day for 7 weeks, while the controls were exposed to room temperature. Chronic daily cold exposure significantly increased energy intake, body weight and serum glucose levels in HFD‑fed mice compared with the control group. In addition, 1 h after the final cold exposure, c‑fos immunoreactivity was significantly increased in the central amygdala of HFD‑fed mice compared with HFD‑fed mice without cold exposure, indicating neuronal activation in this brain region. Notably, 61% of these c‑fos neurons co‑expressed the neuropeptide Y (NPY), and the orexigenic peptide levels were significantly increased in the central amygdala of cold‑exposed mice compared with control mice. Notably, cold exposure significantly decreased the anorexigenic brain‑derived neurotropic factor (BDNF) messenger RNA (mRNA) levels in the ventromedial hypothalamic nucleus and increased growth hormone releasing hormone (GHRH) mRNA in the paraventricular nucleus. NPY‑ergic neurons in the central amygdala were activated by chronic cold exposure in mice on HFD via neuronal pathways to decrease BDNF and increase GHRH mRNA expression, possibly contributing to the development of obesity and impairment of glucose homeostasis.

Figure 1.

Flowchart of the methodology employed in the present study. (A) Animal groupings. (B) Timeline of the experiments performed. CH, standard chow diet; CS, cold stress; HFD, high-fat diet; c-fos, c-fos immunoreactivity test; ISH, in situ hybridization; PPs: physiological parameters testing; TC, tissue collection; BW, body weight; FI, food intake; GTT, glucose tolerance test; ITT, insulin tolerance test.

Figure 1.

Flowchart of the methodology employed in the present study. (A) Animal groupings. (B) Timeline of the experiments performed. CH, standard chow diet; CS, cold stress; HFD, high-fat diet; c-fos, c-fos immunoreactivity test; ISH, in situ hybridization; PPs: physiological parameters testing; TC, tissue collection; BW, body weight; FI, food intake; GTT, glucose tolerance test; ITT, insulin tolerance test.

Figure 2.

Effect of HFD and cold stress on (A) body weight (n=7 mice per group) and (B) energy intake (n=7 mice per group. Effect of cold stress and HFD on (C) blood glucose (n=7 mice per group) and (D) insulin tolerance (n=5–6 mice per group). *P<0.05, **P<0.01 and ***P<0.001 vs. Chow; ^##P<0.01 vs. cold stress + HFD; ^&P<0.05 vs. HFD. HFD, high-fat diet; i.p., intraperitoneal.

Figure 3.

Effect of cold stress and HFD on (A) WAT and (B) BAT. Data are presented as the mean ± standard error of the mean (n=7 mice per group). *P<0.05, **P<0.01 and ***P<0.001, as indicated. HFD, high-fat diet; BAT, brown adipose tissue; WAT, white adipose tissue; WATi, inguinal WAT; WATe, epididymal WAT; WATm, mesenteric WAT; WATr, retroperitoneal WAT; WASum, total WAT mass.

Figure 4.

Different c-fos immunoreactivity in the CA in response to cold stress with or without HFD. Data are presented as the mean ± standard error of the mean (n=7 mice per group). **P<0.01 and ***P<0.001, as indicated. HFD, high-fat diet; CA, central amygdala.

Figure 5.

Different number of positive NPY-green fluorescent protein neurons in the CA in response to cold stress and/or HFD. (A) Chow, (B) cold stress + chow, (C) HFD, (D) cold stress + HFD and (E) quantification. Data are presented as the mean ± standard error of the mean (n=7 mice per group). Scale bars, 60 µm. ***P<0.001 vs. chow; ^##P<0.01 vs. cold stress + chow. CA, central amygdala; NPY, neuropeptide Y.

Figure 6.

Cold-stress with high-fat diet induces c-fos expression in the central amygdala. Co-localization (61%) in mice exposed to cold stress with high-fat diet for 7 weeks. Scale bars, (A) 25 µm, and (B) 100 µm. NPY, neuropeptide Y; GFP, green fluorescent protein.

Figure 7.

(A) Quantification of BDNF mRNA in the ventromedial hypothalamic nucleus expressed as a percentage of standard chow-fed mice. (B) Quantification of GHRH mRNA in the paraventricular nucleus expressed as a percentage of standard chow-fed mice. Data are presented as the mean ± standard error of the mean (n=7 mice per group). **P<0.01 and ***P<0.001, as indicated. HFD, high-fat diet; BDNF, brain-derived neurotropic factor; GHRH, growth hormone releasing hormone.