Abstract
Uncoupling protein 1 (UCP1) is a mitochondrial protein that is expressed in both brown and beige adipocytes. UCP1 uncouples the mitochondrial electron transport chain from ATP synthesis to produce heat via non-shivering thermogenesis. Due to their ability to dissipate energy as heat and ameliorate metabolic disorders, UCP1-expressing adipocytes are considered as a potential target for anti-obesity treatment. To monitor the expression of UCP1 in live mice in a non-invasive manner, we generated the Ucp1-iRFP720 knock-in (Ucp1-iRFP720 KI) mice, in which the gene encoding a near-infrared fluorescent protein iRFP720 is inserted into the Ucp1 gene locus. Using the heterozygous Ucp1-iRFP720 KI mice, we observed robust iRFP fluorescence in the interscapular region where brown adipose tissue is located. Moreover, the iRFP fluorescence was clearly observable in inguinal white adipose tissues in live mice administered with β3-adrenergic receptor agonist CL316,243. We also found that the homozygous Ucp1-iRFP720 KI mice, which are deficient in UCP1, displayed prominent iRFP fluorescence in the inguinal regions at the standard housing temperature. Consistent with this, the mice exhibited expanded populations of beige-like adipocytes in inguinal white adipose tissue, in which the Ucp1 promoter was dramatically activated. Thus, the Ucp1-iRFP720 KI mice provide a convenient model for non-invasive in vivo imaging of UCP1 expression in both brown and beige adipocytes in live mice.
Highlights
Uncoupling protein 1 (UCP1) is a mitochondrial protein that uncouples respiration from ATP synthesis to produce heat [1]
In this study we generated the Ucp1-iRFP720 KI mice that allow in vivo imaging of UCP1 expression via iRFP720 fluorescence. iRFPs are near-infrared fluorescent proteins recently engineered from bacterial phytochrome photoreceptors [33]. iRFPs bind to chromophore biliverdin, which is naturally present in mammalian tissues, and exhibit bright fluorescence without an exogenous supply of the chromophore [33]
We show here that iRFP720 expressed from the Ucp1 locus is visualized in brown adipose tissue (BAT) of live mice
Summary
Uncoupling protein 1 (UCP1) is a mitochondrial protein that uncouples respiration from ATP synthesis to produce heat [1]. UCP1 is expressed in brown adipose tissue (BAT) as well as in some white adipose tissues (WATs), in which beige adipocytes are induced upon various stimuli [2]. Recent studies revealed that human adults possess active BAT [3][4][5], which appears to comprise both classical brown adipocytes and beige adipocytes [6][7][8][9]. Human BAT is associated with leanness [3][4][10], and its reduction during aging may accelerate accumulation of body fat [11]. Human BAT may play a protective role against hyperglycemia and related.
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