Mitochondrial turnover: A phenotype distinguishing brown adipocytes from interscapular brown adipose tissue and white adipose tissue [Bioenergetics]
February 1st, 2015 by Gospodarska, E., Nowialis, P., Kozak, L. P.
To determine the differences between brown adipocytes from iBAT and those induced in white adipose tissue (WAT) with respect to their thermogenic capacity, we examined two essential characteristics: the dynamics of mitochondrial turnover during reversible transitions from 29° to 4°C, and the quantitative relationship between UCP1 and selected subunits of mitochondrial respiratory complex (RC) in the fully recruited state. To follow the kinetics of induction and involution of mitochondria, we determined the expression pattern of UCP1 and other mitochondrial proteins, as well as analyzed mtDNA content, after cold stimulation and reacclimation to thermoneutrality. We showed that UCP1 turnover is very different in iBAT and ingWAT; the former showed minimal changes in protein content, while the latter major changes. Similarly, in iBAT both mtDNA content and the expression of mitochondrial proteins were stable and expressed at similar levels during reversible transitions from 29° to 4°C, whereas ingWAT revealed dynamic changes. Further analysis showed that in iBAT, the expression patterns for UCP1 and other mitochondrial proteins resembled each other, whereas in ingWAT, UCP1 varied about 100-fold during the transition from cold to warmth, and no other mitochondrial proteins matched UCP1. In turn, quantitative analysis of thermogenic capacity determined by estimating the proportion of UCP1 to RC components, showed no significant differences between brown and brite adipocytes, suggesting similar thermogenic potentiality. Our results indicate that dynamics of brown adipocytes turnover during reversible transition from warm to cold may determine the thermogenic capacity of an individual in a changing temperature environment.