Unexpected evidence for active brown adipose tissue in adult humans

Abstract

The contention that brown adipose tissue is absent in adult man has meant that processes attributed to active brown adipose tissue in experimental animals (mainly rodents), i.e., classical nonshivering thermogenesis, adaptive adrenergic thermogenesis, diet-induced thermogenesis, and antiobesity, should be either absent or attributed to alternative (unknown) mechanisms in man. However, serendipidously, as a consequence of the use of fluorodeoxyglucose positron emission tomography (FDG PET) to trace tumor metastasis, observations that may change that notion have recently been made. These tomography scans have visualized symmetrical areas of increased tracer uptake in the upper parts of the human body; these areas of uptake correspond to brown adipose tissue. We examine here the published observations from a viewpoint of human physiology. The human depots are somewhat differently located from those in rodents, the main depots being found in the supraclavicular and the neck regions with some additional paravertebral, mediastinal, para-aortic, and suprarenal localizations (but no interscapular). Brown adipose tissue activity in man is acutely cold induced and is stimulated via the sympathetic nervous system. The prevalence of active brown adipose tissue in normal adult man can be only indirectly estimated, but it would seem that the prevalence of active brown adipose tissue in the population may be at least in the range of some tens of percent. We conclude that a substantial fraction of adult humans possess active brown adipose tissue that thus has the potential to be of metabolic significance for normal human physiology as well as to become pharmaceutically activated in efforts to combat obesity.

Lipodystrophy in HIV 1-infected patients: lessons for obesity research

“…25,[57][58][59] Until recently, the re-appearance of substantial amounts of brown adipocytes in adult humans had been reported only in adipose tissue surrounding pheochromocytomas 54 but recent data obtained from positron emission tomography analysis has led to the unexpected finding of substantial amounts of active brown fat in some anatomical sites of adult humans including the neck region. 60 Thus, regardless of the precise mechanisms eliciting the appearance of 'buffalo humps' in HALS patients, this phenomenon confirms that in adult humans there is a pool of cells in adipose depots capable of proliferation and differentiation into an adipocyte phenotype that includes brown fat-like features.…”

Mfn2 is critical for brown adipose tissue thermogenic function

“…Both white adipose tissue (WAT) and BAT are characterized by a high lipid storage capacity in intracellular lipid droplets (LDs), but they differ in their physiological functions. While WAT is the primary site for lipid storage, BAT is specialized for non‐shivering thermogenic functions by increasing energy expenditure through uncoupled respiration (Nedergaard et al , 2007). Activation of the BAT has been shown to enhance energy expenditure and glucose tolerance in mice and humans (Peirce et al , 2014).…”

Uncoupling protein 1 expression in adipocytes derived from skeletal muscle fibro/adipogenic progenitors is under genetic and hormonal control

“…It has been proposed that beige adipocytes can derive from a distinct precursor and display a gene expression pattern different from that of brown adipocytes 9. Recent studies also reported the presence of BAT and the formation of UCP1‐expressing adipocytes within WAT depots in adult humans 10, 11. In humans, UCP1‐positive adipocytes exhibiting both brown12, 13, 14 and beige13, 14, 15, 16 molecular signatures have been described.…”