The Remaining Mysteries about Brown Adipose Tissues

Figures

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  Figure 1. BATs are located alongside of large arteries and in peri-adrenal gland spaces. (a) A 18FDG-PET/CT examination result of a young adult with acute cold exposure at 19 °C for 2 h. Adopted from Figure 7B in Reference [14].; (b) Schematic presentation of body BAT localization in humans. BATs are located in deep neck regions, supraclavicular regions, axillary regions, paravertebral regions, and periaortic regions, which can be summarized as alongside of large arteries, as reported in the case of deep neck BAT [35], and in suprarenal regions, which have been determined as peri-adrenal gland spaces [36]. These regions receive abundant adrenergic signals, which contribute to the maintenance of BAT.

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  Figure 2. The existence of iBAT in adult humans. (a) An anatomical study of humans reported the presence of “a brown colored fat depot” beneath the trapezius muscle (Tr) [38]. It was described that this fat “extends horizontally toward the centre of the interscapular region, where it forms a somewhat T-shaped mass over and between the rhomboidii muscles” and “is entirely covered by the trapezius muscle” [38]. This brown fat depot reportedly possesses morphological and histological characteristics of BATs [38]. Figure was created by referring to Figure 2 in Reference [38]. (b) Schematic presentation of iBAT in adult humans drawn according the descriptions in Reference [38].

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  Figure 3. Development of BAT during embryogenesis. (a) Schematic presentation of the development of BAT. Brown adipocyte progenitors are differentiated from Myf5-positive myotomes, which are dorsal portions of dermatomyotomes. Myf5-positive cells also consist of back muscle progenitors. Dermatomyotomes are differentiated from somites, which are derived from paraxial mesoderm. Figure was created by referring to Figure 2 in Reference [40]. (b) Schematic presentation of the localization and migration of the trapezius muscle progenitors and those of brow adipocytes. Figure was created by referring to Figure 1 in Reference [39]. (c) Schematic presentation of relative positional relationship between the trapezius muscle (Tz) and iBAT in mouse (left) and human (right). Figure was created by referring to Figure 1 in Reference [39].

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  Figure 4. Gene expression profiles of BATokine genes in murine tissues for Fgf21 (a), Il6 (b), Gdf15 (c), Bmp8b (d), Angptl8 (e), Ngr4 (f), Slit2 (g), Epdr1 (h) and Pltp (i). The information regarding gene expressions in each BATokine gene was retrieved by searching the data in BioGPS database [47] using a dataset of GeneAtlas MOE430, gcrma [48]. Although this dataset contains not only the gene expression data of murine tissues but also those of cell lines, only the former were used in creating graphs.

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  Figure 5. BAT activation enhances the formation of lipid droplets in rats and humans. (a) hES-BA [14] was treated with isoproterenol (100 nM) for 4 h and phase contrast micrographs were taken before and after the treatment. (b) Schematic presentation the effects of cold acclimation of rats [64] and those of b-adrenergic stimuli of hES-BA. In both cases, lipid accumulation is augmented as a result of upregulated FFA uptake by activated brown adipocytes.