HSL Null Mice Figure 2. Subcutaneous and visceral adipose tissue stores are decreased in HSL mice. Representative CT scan images displaying body fat distribution in 10–11 months old female wildtype and HSL mice fed either a control diet or a HFD for 6 months (n = 7). The filled black arrow and the dotted black arrow indicate the location of the subcutaneous and visceral WAT, respectively. The red arrow indicates the location of the muscle layer separating the two adipose tissue depots. doi:10.1371/journal.pone.0001793.g002 Periovarial WAT from female HFD-fed mice was collected and analyzed by transmission electron microscopy (TEM) (Figure 7A). An increase in the size of the mitochondria from HSL mice compared to wildtype littermates was observed (Figure 7B), and estimated to 50% (p,0.001) using morphometric analysis (Figure 7C). Cristae, however, appeared less dense in mitochon- dria from HSL mice (Figure 7B). The change in color of WAT towards a more brownish appearance together with the increase in size of mitochondria from HFD-fed HSL mice, led us to hypothesize that WAT of HSL mice had attained BAT characteristics. To investigate this, we first analyzed the protein expression of UCP-1, the highly specific marker of BAT, in WAT using western blot analysis. UCP-1 protein expression was found to be more than 7-fold increased in HFD-fed HSL mice compared to wildtype littermates (Figure 8). Next we analyzed the mRNA expression of UCP-1 and other proteins known to be differentially expressed between white and brown adipocytes using real-time quantitative Figure 3. Plasma levels of adipokines are altered in HSL mice. (A) Plasma leptin protein levels in the fed state after 2 and 24 weeks of HFD feeding in female wildtype and HSL mice, fed the HFD from 16 weeks of age (n = 6). (B) Plasma adiponectin protein levels in the fed state after 3 and 22 weeks of HFD feeding in female wildtype and HSL mice, fed the HFD from 16 weeks of age (n = 6). Values given are mean6SEM, ** p,0.01, analyzed with Mann-Whitney U tests. doi:10.1371/journal.pone.0001793.g003 PLoS ONE | www.plosone.org 4 2008 | Volume 3 | Issue 3 | e1793