High-fat diet feeding disrupts the coupling of thermoregulation to energy homeostasis

Abstract

Objective: Preserving core body temperature across a wide range of ambient temperatures requires adaptive changes of thermogenesis that must be offset by corresponding changes of energy intake if body fat stores are also to be preserved. Among neurons implicated in the integration of thermoregulation with energy homeostasis are those that express both neuropeptide Y (NPY) and agouti-related protein (AgRP) (referred to herein as AgRP neurons). Specifically, cold-induced activation of AgRP neurons was recently shown to be required for cold exposure to increase food intake in mice. Here, we investigated how consuming a high-fat diet (HFD) impacts various adaptive responses to cold exposure as well as the responsiveness of AgRP neurons to cold.

Methods: To test this, we used immunohistochemistry, in vivo fiber photometry and indirect calorimetry for continuous measures of core temperature, energy expenditure, and energy intake in both chow- and HFD-fed mice housed at different ambient temperatures.

Results: We show that while both core temperature and the thermogenic response to cold are maintained normally in HFD-fed mice, the increase of energy intake needed to preserve body fat stores is blunted, resulting in weight loss. Using both immunohistochemistry and in vivo fiber photometry, we show that although cold-induced AgRP neuron activation is detected regardless of diet, the number of cold-responsive neurons appears to be blunted in HFD-fed mice.

Conclusions: We conclude that HFD-feeding disrupts the integration of systems governing thermoregulation and energy homeostasis that protect body fat mass during cold exposure.

Keywords: AgRP neurons; Core temperature; Energy expenditure; Energy intake; High-fat diet; Thermoregulation.

Figure 1

Effect of ambient temperature on energy homeostasis in DIO mice. Photoperiod-averaged 24-h profiles and mean measures of (A–C) core temperature, (D–F) heat production and (G–I) energy intake, the relationship between (J) heat production and (K) energy intake and ambient temperature, and (L) change in body weight in adult male wild-type mice fed either standard laboratory chow or high-fat diet for 12 weeks that were housed at either 14 °C, 22 °C and 30 °C for five days. n = 8 per group. Mean ± SEM. ∗p < 0.05 vs. 22 °C, #p < 0.05 vs. chow.

Figure 2

Effect of acute mild cold exposure to rapidly increase energy intake is blunted in DIO mice. Time-course and mean (A and B) heat production and (C and D) energy intake measured over (A and C) 4 h or (B and D) 24 h in adult male wild-type mice fed either standard laboratory chow or high-fat fed for 12 weeks and acutely housed at either 14 °C or 22 °C. n = 11 per group. Mean ± SEM. ∗∗∗∗p < 0.0001.

Figure 3

Effect of short-term. HFD feeding on the adaptive response to cold exposure (A) Body weight in adult male wild-type mice at the onset and 12 days following exposure to standard laboratory chow or high-fat diet. (B) Mean heat production, (C) percent change in energy intake, (D) change in body weight, (E) change in body fat and (F) change in lean body mass in adult male wild-type mice fed either standard laboratory chow or high-fat fed for 12 days that were then studied for five consecutive days using indirect calorimetry at 22 °C, followed by an additional five consecutive days at 14 °C. n = 8 per group. Mean ± SEM. ∗p < 0.05 vs. 22 °C, #p < 0.05 vs. chow.

Figure 4

Time-course effect of HFD feeding on cold-induced thermogenesis and hyperphagia. Time-course and mean (A, C, E, G, I and K) heat production and (B, D, F, H, J and L) energy intake following exposure to either 14 °C or 22 °C for 4 h at baseline in (A and B) chow-fed mice and (C and D) 1 wk, (E and F) 2 wk, (G and H) 5 wk, (I and J) 8 wk and (K and L) 10 wk following exposure to a high-fat diet. n = 10–16 per group. Mean ± SEM. ∗∗∗∗p < 0.0001, ∗∗p < 0.01.

Figure 5

Effect of DIO on AgRP mRNA levels in response to chronic cold exposure. Hypothalamic mRNA levels of agouti-related protein (AgRP), Neuropeptide Y (Npy), pro-opiomelanocortin (Pomc) and melanin concentrating hormone (Mch) in adult male wild-type mice maintained on either (A) standard chow or (B) high-fat diet for 12 wk and exposed to either 22 °C or 14 °C for 5 days. To control for differences in energy intake during cold exposure, chow-fed mice were pair-fed to the intake of high-fat diet fed mice. n = 8–10 per group. Mean ± SEM. ∗p < 0.05 vs. 22 °C.

Figure 6

Effect of DIO on cold-induced activation of Fos in AgRP neurons. (A) Representative sagittal and coronal images and AgRP hybridization in situ from Allen Brain Institute of the arcuate nucleus (ARC). (B) Immunohistochemical detection of AgRP-locus driven green fluorescent protein (GFP) (green), Fos (red), and colocalization of GFP and Fos (two right panels) in the ARC of either chow-fed or 12-wk high-fat diet fed AgRP-Cre:GFP mice 90 min after housing at either 14 °C, 22 °C, or 30 °C. Quantitation of (C) total ARC Fos + cells, and the (D) total number and (E) percentage of AgRP neurons that co-express Fos in the ARC. n = 3–6 per group. Mean ± SEM. ∗p < 0.05; #p < 0.05 vs. Chow.

Figure 7

Time-course effect of high-fat diet feeding on cold-induced increases in AgRP neuronal activity. (A) Trace of averaged dF/F (%) GCaMP6s signal and (B) quantification of mean dF/F (%) differences between 30 °C and 10 °C GCaMP6s activity during 10 min exposure at baseline in chow-fed animals and at weeks 1, 2, 5, 8, and 10 in either chow-fed or high-fat diet fed mice. Transition ramps between temperatures were all set to 60 s. Gray bar signifies 10-min at 10 °C. n = 6 per group. Mean ± SEM. ∗p < 0.05 vs. EYFP.

Supplemental Figure 1. Effect of ambient temperature on respiratory quotient and ambulatory activity in DIO mice. Photoperiod-averaged 24-h profiles and mean measures of (A–C) respiratory quotient (RQ) and (D–F) ambulatory activity in adult male wild-type mice fed either standard laboratory chow or high-fat fed for 12 weeks and that were housed at either 14 °C, 22 °C and 30 °C for five days. n = 8 per group. Mean ± SEM. ∗p < 0.05 vs. 22 °C, #p < 0.05. vs. chow.