A standardized infrared imaging technique that specifically detects UCP1-mediated thermogenesis in vivo

Abstract

The activation and expansion of brown adipose tissue (BAT) has emerged as a promising strategy to counter obesity and the metabolic syndrome by increasing energy expenditure. The subsequent testing and validation of novel agents that augment BAT necessitates accurate pre-clinical measurements in rodents regarding the capacity for BAT-derived thermogenesis. We present a novel method to measure BAT thermogenesis using infrared imaging following β3-adrenoreceptor stimulation in mice. We show that the increased body surface temperature observed using this method is due solely to uncoupling protein-1 (UCP1)-mediated thermogenesis and that this technique is able to discern differences in BAT activity in mice acclimated to 23 °C or thermoneutrality (30 °C). These findings represent the first standardized method utilizing infrared imaging to specifically detect UCP1 activity in vivo.

Keywords: BAT; Beige fat; Brite fat; Brown adipose tissue; Brown fat; CT, computed tomography; Diabetes; FDG-PET, fluorodeoxyglucose positron emission tomography; MRS, magnetic resonance spectroscopy; Metabolism; Obesity; Thermography; Uncoupling protein-1; fMRI, functional magnetic resonance imaging.

Figure 1

Infrared thermography specifically detects UCP1-mediated thermogenesis in vivo. (A) Time course of the indirect calorimetry and infrared thermography measurements. (B) A representative image of the region of interest (ROI) boxes overlaid on a mouse infrared image during Amide image analysis. (C) Oxygen uptake (VO₂) and dorsal surface temperature within a region of interest (ROI) surrounding, (D) the interscapular BAT area, and (E) the entire body of Ucp1^+/+ and Ucp1^−/− mice following i.p. injection of saline or CL-316,243. N = 8–9 per group. Surface temperature is calculated as the average of the highest 10% area of the ROI. (F) Representative infrared images of Ucp1^+/+ and Ucp1^−/− mice following the two separate treatments. Images are displayed using the rainbow high contrast color palette in the FLiR Research IR program using a temperature linear display between 28 and 32 °C. Scale bar is 1 cm. *Indicates a significant difference (P < 0.05) from the indicated group as determined using a 2-way repeated measures ANOVA. Data are mean ± SEM.

Figure 2

Surface temperature changes in response to a β₃-adrenergic agonist reflect brown adipose tissue activity differences due to the ambient housing temperature. (A) Oxygen uptake (VO₂) and dorsal surface temperature within a region of interest (ROI) surrounding, (B) the interscapular BAT area, and (C) the entire body of C57Bl6 mice housed at 30 °C or 23 °C following i.p. injection of saline or CL-316,243. Surface temperature is calculated as the average of the highest 10% area of the ROI. (D) Representative infrared images of each ambient temperature group after saline or CL-316,243 injection. Images are displayed using the rainbow high contrast color palette in the FLiR Research IR program using a temperature linear display between 30 and 34 °C. Scale bar is 1 cm. Significant (P < 0.05) correlations between changes in metabolic rate (VO₂) and changes in dorsal surface temperature using the (E) interscapular or (F) the whole body ROIs. N = 8–9 per group. Oxygen uptake and temperature data were compared using a 2-way repeated measures ANOVA with injection condition and housing temperature as factors. Correlations were performed using Pearson's Regression. Significance was considered as P < 0.05. *Indicates a significant difference due to a 2-way interaction. †Indicates an overall effect of ambient housing temperature. ‡Indicates an overall effect of CL-316,243 treatment. Data are mean ± SEM.