The Power of Irisin
"Browning" White Fat
The two main types of human fat tissue are white adipose tissue (WAT) and brown adipose tissue (BAT). WAT exists as visceral (generally around the torso) and subcutaneous (generally present in the lower body and more predominant in women). The main function of WAT is to store excess energy. An overabundance of visceral white adipose tissue is undesirable due to its negative effects on human health, such as in contributing to obesity and type 2 diabetes. On the other hand, brown adipose tissue is preferential because it is thermogenic, having the ability to dissipate energy as heat, and has a positive effect on body mass index. It has been long thought that only infants have BAT and that it could not be produced, however, small amounts have been recently found in adults.1 In a publication out of the University of Florida and led by Yuan Zhang, irisin is examined. Irisin, derived from full-length fibronectin-type III domain-containing 5 (FDNC5) and containing 121 amino acids, has been found to “brown” white adipocytes by converting them into the more favorable BAT. It is a myokine that is produced by WAT after exercise. Once WAT is converted into BAT by irisin, there is increased thermogenesis. Their data also found that irisin may promote osteogenic differentiation and therefore be a possible osteoporosis treatment.2,4 This finding is also shared by Jin Zhang, et al., in a publication in Bone Research. Zhang and his group found lower levels of irisin in type 2 diabetics and noted a resulting increased risk in bone fractures and osteoporosis. On the other hand, increased levels of irisin correlated with increased osteoblasts and bone mineralization.3
- D. C. Berry, D. Stenesen, D. Zeve, & J.M. Graff, Development, 140, 3939 (2013).
- K. N. Frayn et al., International Journal of Obesity, 27, 875 (2003).
- J. Zhang et al., Bone Research, 5, 16056 (2017).
- Y. Zhang et al., Am J Physiol Endocrinol Metab, 311, E530 (2016).