Abstract
Proper function of the endoplasmic reticulum (ER) and mitochondria is crucial for cellular homeostasis, and dysfunction at either site has been linked to pathophysiological states, including metabolic diseases. Although the ER and mitochondria play distinct cellular roles, these organelles also form physical interactions with each other at sites defined as mitochondria-associated ER membranes (MAMs), which are essential for calcium, lipid and metabolite exchange. Here we show that in the liver, obesity leads to a marked reorganization of MAMs resulting in mitochondrial calcium overload, compromised mitochondrial oxidative capacity and augmented oxidative stress. Experimental induction of ER-mitochondria interactions results in oxidative stress and impaired metabolic homeostasis, whereas downregulation of PACS-2 or IP3R1, proteins important for ER-mitochondria tethering or calcium transport, respectively, improves mitochondrial oxidative capacity and glucose metabolism in obese animals. These findings establish excessive ER-mitochondrial coupling as an essential component of organelle dysfunction in obesity that may contribute to the development of metabolic pathologies such as insulin resistance and diabetes.
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Acknowledgements
We are indebted to D. Clapham and N. Blair for their help in the Ca2+ imaging experiments and generously allowing the use of their laboratory facilities. We would like to thank M. Ericson, L. Trakimas and E. Benecchi for their assistance in electron microscopy and M. Strauss and L. Cameron for helping with the serial-section EM reconstruction and confocal microscopy, respectively. IP3R1 antibody was a gift from R. Wojcikiewicz. The Ca2+ FRET reporter was a gift from R. Tsien (University of California, San Diego). Linker plasmid was a gift from G. Hajnóczky (Thomas Jefferson University). PACS-2–specific antibody was a gift from G. Thomas (University of Pittsburgh). We thank A. Gimenez-Cassina for helping with some of the Seahorse experiments. We thank the anonymous reviewer of the manuscript for suggesting the experiments with PACS-2. We also want to thank L. Yang, S. Fu and E. Calay for their technical assistance. We extend a special thanks to K. Claiborn for critical reading and editing of the manuscript. This work was supported in part by the US National Institutes of Health (DK52539 and 1RC4-DK090942). A.P.A. is supported by PEW Charitable Trusts. B.M.P. is supported by Alfred Benzon Foundation (Denmark).
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A.P.A. and B.M.P. designed the project, performed experiments, analyzed and interpreted the results, and wrote the manuscript; G.P. and E.G. performed image quantification and in vitro experiments. K.I. performed animal experiments; G.S.H. designed the project, analyzed and interpreted the data, and wrote the manuscript.
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Supplementary Text and Figures
Supplementary Figures 1–10 (PDF 21445 kb)
Serial-section EMs of liver showing ER and mitochondrial morphology in a lean mouse.
Serial sections were 60 nm apart. (MOV 22290 kb)
3D reconstruction of serial-section EM of liver from a lean mouse.
The images in the stack were aligned by the auto alignment tool of the IMOD Etomo software and interpolated in ImageJ. 3D segmentation was generated using IMOD 3dMOD software. (MOV 32289 kb)
Serial section EMs of liver showing ER and mitochondrial morphology in an ob/ob mouse.
Serial sections were 60 nm apart. (MOV 21134 kb)
3D reconstruction of serial-section EM of liver from an ob/ob mouse.
The images in the stack were aligned by the auto alignment tool of the IMOD Etomo software and interpolated in ImageJ. 3D segmentation was generated using IMOD 3dMOD software. (MOV 18044 kb)
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Arruda, A., Pers, B., Parlakgül, G. et al. Chronic enrichment of hepatic endoplasmic reticulum–mitochondria contact leads to mitochondrial dysfunction in obesity. Nat Med 20, 1427–1435 (2014). https://doi.org/10.1038/nm.3735
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DOI: https://doi.org/10.1038/nm.3735
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