Paracrine & Endocrine Role of BAT
It is now well recognized that WAT is an active endocrine organ that secretes numerous signaling molecules, such as adipokines, which have both endocrine and paracrine effects. The role of BAT as a secretory organ is controversial, although it is being recognized that BAT may have some role as a producer of some hormones. Similar to WAT, BAT secretes retinol binding protein 4 which modulates insulin resistance and glucose metabolism and has a role in diabetes. Brown adipocytes are also a major site for synthesis of triiodothyronine, which may be released for systemic purposes in conditions of high BAT thermogenesis. Other adipokines, such as interleukins and IGF-1, may also be synthesized and secreted by brown adipocytes and it was reported at the meeting that, during active thermogenesis, BAT is a site for the NE-mediated synthesis and release of FGF-21.
The role of BAT in lipoprotein metabolism and brown adipocytes demonstrate a high uptake of triglyceride-rich lipoproteins. Findings presented at the meeting demonstrate the presence of BAT in vital locations such as the epicardial adipose tissue in humans where brown adipocytes may act as lipid clearing mechanisms to protect the myocardium and coronary vessels from hyperlipidemia.
It was proposed that although its exact role remains unclear, BAT may have some endocrine and paracrine influences that could explain the association between BAT activity and systemic metabolism even when amounts of BAT are scarce, as in adult humans. Further studies demonstrating the role of BAT in aging, shown by the increased life span of transgenic mice expressing UCP1 in skeletal muscles particularly when on a high-fat diet, revealed new insights into the role of BAT in mammalian physiology.
BAT research is entering a new phase and the meeting highlighted the latest advances in understanding of BAT physiology, thermogenesis, molecular and genetic mechanisms underlying BAT development and activity as well as the application of various techniques to study the presence and activation of BAT in humans. Such studies have boundless potential to produce translational research for the prevention and treatment of obesity and the metabolic conditions with which it is associated.
Financial & competing interests disclosure
The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.
No writing assistance was utilized in the production of this manuscript.
Expert Rev Endocrinol Metab. 2013;8(2):123-125. © 2013 Expert Reviews Ltd.