Figure 7. BAT-Specific Ablation of FGF21 Significantly Reduces the Increased BAT Thermogenic Activity, BAT Mass, and Beige Cell Emergence in iWAT Observed from BAT-Specific miR-32 Overexpression.

(A) FGF21 mRNA expression in BAT but not in liver or iWAT was ablated in miR-32-AAV-BS+Cre mice (n = 6) and control-AAV-BS+Cre mice (n = 6).

(B) FGF21 protein expression in BAT but not in liver or iWAT was ablated in miR-32-AAV-BS+Cre mice (n = 6) and control-AAV-BS+Cre mice (n = 6).

(C) Quantification of relative protein expression using ImageJ showed that protein level of FGF21 in BAT but not in liver or iWAT was ablated in miR-32-AAV-BS+Cre mice (n = 6) and control-AAV-BS+Cre mice (n = 6).

(D) Serum FGF21 levels were decreased in miR-32-AAV-BS+Cre mice (n = 6) and control-AAV-BS+Cre mice (n = 6) compared to wild-type mice (n = 4).

(E) miR-32-AAV-BS+Cre mice (n = 6) showed higher core body temperatures only during first 48 hr of cold exposure when compared to control-AAV-BS+Cre mice (n = 6).

(F) Total energy expenditure was similar after 7 days’ cold stress in miR-32-AAV-BS+Cre mice (n = 6) as compared with control-AAV-BS+Cre mice (n = 6). Energy expenditure was normalized to lean body mass.

(G) Average total energy expenditure was slightly higher in miR-32-AAV-BS+Cre mice (n = 6) than control-AAV-BS+Cre mice (n = 6) but not statistically significant.

(H) Percentage BAT mass was slightly higher in miR-32-AAV-BS+Cre mice (n = 6) compared to control-AAV-BS+Cre mice (n = 6).

(I) In BAT, mRNA levels of Tob1 were lower in miR-32-AAV-BS+Cre mice (n = 6) compared to control-AAV-BS+Cre mice (n = 6), whereas expression of several thermogenic genes including UCP1 was higher in miR-32-AAV-BS+Cre mice.

(J) Protein levels of PGC1α and UCP1 were higher in miR-32-AAV-BS+Cre mice (n = 6) compared to control-AAV-BS+Cre mice (n = 6).

(K) Quantification of relative protein expression using ImageJ showed that protein levels of PGC1 and UCP1 were higher in miR-32-AAV-BS+Cre mice (n = 6) compared to control-AAV-BS+Cre mice (n = 6). Average intensities were normalized to that of Calnexin.

(L) mRNA levels of thermogenic genes in iWAT were similar in both groups of mice (both n = 6). Data were normalized to PPIA.

(M) Immunoblots showed that miR-32-AAV-BS+Cre mice (n = 6) had similar UCP1 and PGC1α protein levels in iWAT compared to control-AAV-BS+Cre mice (n = 6).

(N) Quantification of relative UCP1 and PGC1α protein levels using ImageJ. Average intensities were normalized to that of Calnexin.

(O) Proposed mechanism by which miR-32 promotes BAT thermogenesis by inhibiting Tob1, activating p38/MAPK signaling and driving UCP1, PGC1α, and FGF21 expression in BAT. The BAT secreted FGF21 functions in a paracrine fashion to promote further thermogenic gene expression in BAT as well as in an endocrine fashion to promote iWAT browning.

Data represent mean ± SEM. *p < 0.05, **p < 0.01, and ***p < 0.001. See also Figure S7.