Genetic Markers of Brown Adipose Tissue Identity and In Vitro Brown Adipose Tissue Activity in Humans

Objective Human brown adipose tissue (BAT) activity decreases with age and obesity. In addition to uncoupling protein 1 (UCP1), several genetic markers of BAT in humans have been published. However, the link between human BAT activity and genetic markers has been inadequately explored. Methods White adipose tissue (WAT) and BAT biopsies were obtained from 16 patients undergoing deep neck surgery. In vitro differentiated adipocytes were used to measure norepinephrine‐stimulated mitochondrial uncoupling as a measure of in vitro BAT activity. Gene expression was determined in adipose tissue biopsies. Results Norepinephrine increased in vitro BAT activity in adipocytes derived from human BAT, and this increase was abolished by propranolol. Furthermore, in vitro BAT activity showed a negative correlation to age and BMI. UCP1 messenger RNA (mRNA) expression showed a positive correlation to in vitro BAT activity, while zinc finger protein of cerebellum 1 (ZIC1) mRNA showed a negative correlation to in vitro BAT activity. In human BAT biopsies, UCP1 mRNA showed negative correlations to age and BMI, while ZIC1 mRNA showed positive correlations to age and BMI. Conclusions Differentiated adipocytes derived from human BAT maintain intrinsic characteristics of the donor. High ZIC1 mRNA does not necessarily reflect high BAT activity.