Adipocytes possess remarkable adaptive capacity to respond to nutrient excess, fasting or cold exposure, and they are thus an important cell type for the maintenance of proper metabolic health. Although the endoplasmic reticulum (ER) is a critical organelle for cellular homeostasis, the mechanisms that mediate adaptation of the ER to metabolic challenges in adipocytes are unclear. Here we show that brown adipose tissue (BAT) thermogenic function requires an adaptive increase in proteasomal activity to secure cellular protein quality control, and we identify the ER-localized transcription factor nuclear factor erythroid 2–like 1 (Nfe2l1, also known as Nrf1) as a critical driver of this process. We show that cold adaptation induces Nrf1 in BAT to increase proteasomal activity and that this is crucial for maintaining ER homeostasis and cellular integrity, specifically when the cells are in a state of high thermogenic activity. In mice, under thermogenic conditions, brown-adipocyte-specific deletion of Nfe2l1 (Nrf1) resulted in ER stress, tissue inflammation, markedly diminished mitochondrial function and whitening of the BAT. In mouse models of both genetic and dietary obesity, stimulation of proteasomal activity by exogenously expressing Nrf1 or by treatment with the proteasome activator PA28α in BAT resulted in improved insulin sensitivity. In conclusion, Nrf1 emerges as a novel guardian of brown adipocyte function, providing increased proteometabolic quality control for adapting to cold or to obesity.
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We are grateful to K. Claiborn for her expert editorial input, M. McGrath for his support of the project, M. Yilmaz, Y. Lee and V. Byles for assistance with experiments, K. Seedorf, P. Delerive and Servier for their continuous support of the project, R. Bronson and the Harvard Medical School Rodent Histopathology Core, M. Ericson and the Harvard Medical School Electron Microscopy Facility, N. Lupoli and the Harvard T.H. Chan School of Public Health Trace Metals Laboratory, and R. Kunz and the Thermo Fisher Scientific Center for Multiplexed Proteomics at Harvard Medical School and the Harvard T.H. Chan School of Public Health Animal Facility team for their support of the project. We acknowledge the prosperous scientific environment in the Hotamisligil lab and thank all lab members for their critical input and discussions. We are grateful to X. Wang (University of South Dakota) for generously sharing the PA28α-expressing adenovirus, E. Rosen (Beth Israel Deaconess Medical Center) for providing us with the Ucp1–Cre and the Adipoq–Cre mouse models and T. Iwawaki (Gunma University) for the conditional Ern1-deletion mouse model. A.B. was supported by a Deutsche Forschungsgemeinschaft Research Fellowship (BA 4925/1-1). S.B.W. was supported by a Canadian Institutes of Health Research fellowship. C.S. was supported by a University Medical Center Hamburg–Eppendorf MD/PhD program fellowship. R.L.S.G. was supported by the Barth Syndrome Foundation. This work has received support in part from the US National Institutes of Health (NIH) through the Laser Biomedical Research Center grants P41-EB015871 (M.G.B.) and 5-U54-CA151884 (M.G.B.), by the National Science Foundation grant ECCS-1449291 (D.F. and M.G.B.) and by the Massachusetts Institute of Technology through the Institute for Soldier Nanotechnologies grant W911NF-13-D-0001 (M.G.B.). D.F. was supported by a fellowship of the Boehringer Ingelheim Fonds. O.T.B. was supported by a European Molecular Biology Organization Long-term Fellowship. Y.-H.T. and L.O.L. were supported in part by NIH grants R01DK077097, R01DK102898 and P30DK036836. M.D.L. was supported by NIH grants T32DK007260, F32DK102320 and K01DK111714. A.P.A. was supported by the Pew Foundation. We apologize to colleagues whose work we could not cite due to space limitations. The study was supported by an industry-sponsored research agreement between Harvard University and Servier.
The authors declare no competing financial interests.
Supplementary Figures 1–13 and Supplementary Methods (PDF 5513 kb)
The brown fat ubiquitome (XLSX 3031 kb)
The Differential brown fat ubiquitome (XLSX 1589 kb)
Pathway analysis of hyperubiquitinated proteins (XLSX 67 kb)
Plasma parameters in high-fat diet-fed wild-type and Nfe2l1ΔBAT mice (XLSX 40 kb)
Additional information on adenoviral experiments (XLSX 41 kb)
Primers and antibodies information (XLSX 43 kb)
SWIR-QD-lipoprotein uptake imaging of a cold-exposed wild-type mouse: A representative SWIR movie of a cold-exposed control wild-type mouse. After tail vein injection, lipoproteins labeled with short-wave infrared (SWIR) quantum dots (QD) are taken up into liver, spleen and brown adipose tissue. (AVI 14278 kb)
SWIR-QD-lipoprotein uptake imaging of a cold-exposed Nfe2lΔBAT mouse: A representative SWIR movie of a cold-exposed control Nfe2lΔBAT mouse. After tail vein injection, lipoproteins labeled with short-wave infrared (SWIR) quantum dots (QD) are taken up into liver, spleen but not into brown adipose tissue. (AVI 13941 kb)
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Bartelt, A., Widenmaier, S., Schlein, C. et al. Brown adipose tissue thermogenic adaptation requires Nrf1-mediated proteasomal activity. Nat Med 24, 292–303 (2018). https://doi.org/10.1038/nm.4481
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