The Journal of endocrinology
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The discovery of irisin as an exercise-regulated myokine inducing browning of WAT has gained interest as a potential new strategy to combat obesity and its associated disorders, such as type 2 diabetes. However, there are inconsistencies regarding the relevance of irisin in humans. The regulation of FNDC5 mRNA expression by exercise and contraction could not be reproduced by a number of human studies using several exercise protocols and in vitro approaches. ⋯ Independent of the presence and regulation of FNDC5/irisin in humans, the application of recombinant irisin could still represent a therapeutic strategy to fight obesity. However, the current data obtained from human cell models reveal that FNDC5/irisin has no effect on browning of the major WAT depots in humans and is likely to selectively target a small subpopulation of adipocytes, which are located in classical BAT regions, such as the supraclavicular adipose tissue. Thus, other candidates, such as BMP7 or CNPs, seem to be more prominent candidates as inducers of browning in humans.