Figure 4. Prolonged bile acid signaling stimulates BAT uncoupled respiration.

(A and B) 3-week HFD-fed WT (n = 10) and NTCP-KO mice (n = 6) were fasted 4 to 5 hours and subsequently i.v. injected with radiolabeled [¹⁴C]deoxyglucose and [³H]triolein-labeled VLDL-like particles. Plasma clearance and uptake by organs at 15 minutes after injection were determined by assessing ³H and ¹⁴C activity by liquid scintillation counting. Blood volume was estimated as 4.706% of total body weight. iBAT, interscapular brown adipose tissue; sBAT, supraclavicular brown adipose tissue; gWAT, gonadal white adipose tissue. (C and D) Uncoupling protein 1 (Ucp1) mRNA (C) and UCP1 protein (D) expression levels, determined by reverse transcription quantitative PCR (RT-qPCR) and Western blotting, respectively, in BAT of WT and NTCP-KO mice fed an LFD or HFD for 16 weeks (n = 10–13). RT-qPCR samples are relative to the geometric mean of control genes 36b4 and Hprt and were normalized to WT LFD. The Western blot shown in D is representative of all mice, and for each mouse the relative UCP1 (32 kDa) to tubulin (50 kDa) protein expression was determined. (E) Body temperature, measured by temperature transponders, of the mice in C and D. Per animal, average body temperature was calculated from 10 individual observations. Error bars show ± SEM; each dot represents an individual animal. *P < 0.05, calculated by Student’s t test (A and B) or 1-way ANOVA (C–E).