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Biology

Visualization and Quantification of Brown and Beige Adipose Tissues in Mice using [18F]FDG Micro-PET/MR Imaging

Published: July 1st, 2021

DOI:

10.3791/62460

1State Key Laboratory of Pharmaceutical Biotechnology, The University of Hong Kong, 2Department of Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, 3Department of Diagnostic Radiology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, 4School of Biomedical Sciences, Institute of Vascular Medicine, Chinese University of Hong Kong
* These authors contributed equally

Functional imaging and quantitation of thermogenic adipose depots in mice using a micro-PET/MR imaging-based approach.

Brown and beige adipocytes are now recognized as potential therapeutic targets for obesity and metabolic syndromes. Non-invasive molecular imaging methods are essential to provide critical insights into these thermogenic adipose depots. Here, the protocol presents a PET/MR imaging-based method to evaluate the activity of brown and beige adipocytes in mouse interscapular brown adipose tissue (iBAT) and inguinal subcutaneous white adipose tissue (iWAT). Visualization and quantification of the thermogenic adipose depots were achieved using [18F]FDG, the non-metabolizable glucose analog, as the radiotracer, when combined with the precise anatomical information provided by MR imaging. The PET/MR imaging was conducted 7 days after cold acclimation and quantitation of [18F]FDG signal in different adipose depots was conducted to assess the relative mobilization of thermogenic adipose tissues. Removal of iBAT substantially increased cold-evoked [18F]FDG uptake in iWAT of the mice.

In response to changing nutritional needs, adipose tissue serves as an energy cache to adopt either lipid storage or mobilization mode to meet the needs of the body1. Moreover, adipose tissue also plays a key function in thermoregulation, via a process called non-shivering thermogenesis, also called facultative thermogenesis. This is typically achieved by the brown adipose tissue (BAT), which expresses abundant level of mitochondria membrane protein uncoupling protein 1 (UCP1). As a proton carrier, UCP1 generates heat by uncoupling the proton transport and ATP production2. Upon cold stimulation, thermogenesis in BAT is s....

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The protocol described below follows the animal care guidelines of The University of Hong Kong. The animals used in the study were 8-week-old C57BL/6J mice.

1. Animal surgical procedures and cold challenge

  1. Perform interscapular BAT (iBAT) dissection.
    1. Anesthetize the mice by intraperitoneal injection of ketamine/xylazine (100 mg/kg bodyweight ketamine and 10 mg/kg bodyweight xylazine). After anesthesia, shave the hair of the mouse from the neck to just below the scapulae.......

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Three groups of mice (n = 3 per group) underwent micro-PET/MR imaging in this study, where they were housed at either thermoneutrality (30 °C) or cold (6 °C) for 7 days. One group of mice (n = 3) had their iBAT removed (iBATx) prior to cold treatment (Figure 1A). This method led to an alteration to the white adipose tissue activity in all three mice. In particular, a remarkable increase in [18F]FDG uptake was observed in iWAT using micro-PET/MR imaging (

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In this study, a PET/MR -based imaging and quantification of functional brown and beige adipose tissue in small animal was described. This method uses the non-metabolizable glucose analog [18F]FDG as an imaging biomarker so as to identify the adipose tissues with high glucose-demand in a non-invasive manner. MR offers good soft tissue contrast and can better differentiate adipose fat tissues from the neighboring soft tissues and muscle. When combined with PET, this enables imaging and quantifying of the activa.......

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We thank the support of National Natural Science Foundation of China (NSFC) - Excellent Young Scientists Fund (Hong Kong and Macau) (81922079), Hong Kong Research Grants Council General Research Fund (GRF 17121520 and 17123419), and Hong Kong Research Grants Council Collaborative Research Fund (CRF C7018-14E) for small animal imaging experiments.

....

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Name Company Catalog Number Comments
0.9% sterile saline BBraun 0.9% sodium chloride intravenous infusion, 500 mL
5 mL syringe Terumo SS05L 5 mL syringe Luer Lock
Dose Calibrator Biodex Atomlab 500
Eye lubricant Alcon Duratears Sterile ocular lubricant ointment, 3.5 g
Insulin syringe Terumo 10ME2913 1 mL insulin syringe with needle
InterView Fusion software Mediso Version 3.03 Post-processing and image analysis software
Isoflurane Chanelle Pharma Iso-Vet, inhalation anesthetic, 250 mL
Ketamine Alfasan International B.V. HK-37715 Ketamine 10% injection solution, 10 mL
Medical oxygen Linde HKO 101-HR compressed gas, 99.5% purity
Metacam Boehringer Ingelheim 5 mg/mL Meloxicam solution for injection for dogs and cats, 10 mL
nanoScan PET/MR Scanner Mediso 3 Tesla MR
Nucline nanoScan software Mediso Version 3.0 Scanner operating software
Wound clips Reflex 7 203-100 7mm Stainless steel wound clips, 20 clips
Xylazine Alfasan International B.V. HK-56179 Xylazine 2% injection solution, 30 mL

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