A longitudinal magnetic resonance imaging (MRI) study of differences in abdominal fat distribution between normal mice, and lean overexpressors of mitochondrial uncoupling protein‐3 (UCP‐3)

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Abstract
Aim: To characterize evolution and distribution of abdominal adipose fat between 6 and 18 weeks of age in an animal model of energy consumption based on mice overexpressing the mitochondrial uncoupler protein 3 (UCP‐3). Methods: T2‐weighted multislice MRI was performed six times during the 12 week study; visceral, subcutaneous and intermuscular fat depots were quantified. Results: The overexpressor (UCP‐3tg) mice consistently have less subcutaneous, visceral, interskeletal muscle and total fat throughout the experiment. Mean (standard error) volumes (ml) of the three distinct depots change between week 6 and week 18 as follows: wild type: subcutaneous 1.93 (0.28) to 6.18 (0.47), visceral 2.15 (0.34) to 6.37 (0.64), intermuscular 0.23 (0.04) to 0.53 (0.03); UCP‐3tg: subcutaneous 1.47 (0.17) to 4.07 (0.57), visceral 1.18 (0.04) to 3.69 (0.59), intermuscular 0.23 (0.01) to 0.32 (0.04). Although they eat more (4.3 g compared with 3.4 g per day) the UCP‐3tg's always weigh less than controls. In wild‐type control animals, increases of all fat pools between week 6 and week 18 is highly significant, as it is for subcutaneous, visceral and total pools in the UCP‐3tg animals. The UCP‐3tg mice, however, show no significant absolute or relative increase in intermuscular fat; UCP‐3 is predominantly overexpressed in skeletal muscle. Conclusion: MRI provides an excellent approach to comparative studies of fat distribution in animal models of energy expenditure such as the UCP‐3tg mouse.