Shabalina 2017 MiP2017
Brown adipose tissue (BAT) dissipates energy as heat through the mitochondrial uncoupling protein 1 (UCP1). UCP1 knock-out (KO) mice hosted under standard animal house condition (22 °C) have preserved mitochondrial oxidative capacity and do not develop alternative uncoupling mechanisms via UCP3 or ATP/ADP-antiporter . In the present study, we characterized the effect of prolonged cold exposure on BAT mitochondrial function, tissue infiltration with immune cells, apoptosis as well as mouse whole body composition.
UCP1 wildtype (WT) and KO female mice (C57Bl/6 background) were single-caged, acclimated for 2 weeks at 18°C and then at 4°C for at least 4 weeks. Oxygen consumption of isolated mitochondria was analyzed with an Oroboros O2k-FluoRespirometer. Apoptosis was analyzed by western blot and DNA fragmentation measurement. Immune cells were analyzed by flow cytometry after collagenase digestion or by RT-qPCR on whole tissue mRNA. Mouse body composition (body fat and lean mass) was measured with in vivo magnetic resonance imaging.
After prolonged cold exposure, the number of mitochondria and their oxidative capacity were significantly reduced in UCP1 KO BAT compared to WT. UCP1 KO BAT presented a 150-fold increase in DNA fragmentation compared to WT, as well as an increased cleaved caspase-3 level. Impaired BAT mitochondria and increased apoptosis in UCP1 KO BAT was associated with high infiltration of immune cells, i.e. T and natural killer lymphocytes, as well as of macrophages. Gene expression of the macrophage markers F4/80, IL10, Mgl1, Mrc1, IL1β and TNFα was also increased in BAT of UCP1 KO. BAT inflammation status was compared to the status of inguinal brite/beige adipose tissue, in which the mitochondrial oxidative capacity was preserved (as we earlier have shown ). Notable, no signs of inflammation were observed in inguinal brite/beige adipose tissue. Total body fat content and specifically visceral fat content increased in the UCP1 KO mice.
Our results show that prolonged cold exposure in the absence of UCP1 leads to an impairment of mitochondrial function, induction of apoptosis and immune cell infiltration in BAT but not in brite/beige adipose tissue. This impairment of BAT was associated with an increase of visceral obesogenic adiposity.
Labels: MiParea: Respiration, Genetic knockout;overexpression, Comparative MiP;environmental MiP
Stress:Cell death, Temperature Organism: Mouse Tissue;cell: Fat Preparation: Isolated mitochondria
- Dept Molecular Bioscience Wenner-Gren Inst, Stockholm Univ, Stockholm, Sweden. - [email protected]
- Shabalina IG, Kramarova TV, Nedergaard J, Cannon B (2006) Carboxyatractyloside effects on brown-fat mitochondria imply that the adenine nucleotide translocator isoforms ANT1 and ANT2 may be responsible for basal and fatty-acid-induced uncoupling respectively. Biochem J 399:405-14.
- Shabalina IG, Petrovic N, de Jong JM, Kalinovich AV, Cannon B, Nedergaard J (2013) UCP1 in brite/beige adipose tissue mitochondria is functionally thermogenic Cell Rep 5: 1196-203.