bims-mimbat Biomed News
on Mitochondrial metabolism in brown adipose tissue
Issue of 2023–05–07
nine papers selected by
José Carlos de Lima-Júnior, Washington University
  1. Molecular determinants of inhibition of UCP1-mediated respiratory uncoupling.
  2. Oxaloacetate regulates complex II respiration in brown fat: dependence on UCP1 expression.
  3. Optogenetic activation of UCP1-dependent thermogenesis in brown adipocytes.
  4. Reduced hepatic bradykinin degradation accounts for cold-induced BAT thermogenesis and WAT browning in male mice.
  5. The secret life of lactate: A novel cell-cycle regulatory mechanism.
  6. MICU1 occludes the mitochondrial calcium uniporter in divalent-free conditions.
  7. Mitochondrial protein import clogging as a mechanism of disease.
  8. A phosphate-sensing organelle regulates phosphate and tissue homeostasis.
  9. The electron-proton bottleneck of photosynthetic oxygen evolution.
  1. Nat Commun. 2023 May 05. 14(1): 2594
    Molecular determinants of inhibition of UCP1-mediated respiratory uncoupling.
    Antoine Gagelin, Corentin Largeau, Sandrine Masscheleyn, Mathilde S Piel, Daniel Calderón-Mora, Frédéric Bouillaud, Jérôme Hénin, Bruno Miroux.
      Brown adipose tissue expresses uncoupling protein 1 (UCP1), which dissipates energy as heat, making it a target for treating metabolic disorders. Here, we investigate how purine nucleotides inhibit respiration uncoupling by UCP1. Our molecular simulations predict that GDP and GTP bind UCP1 in the common substrate binding site in an upright orientation, where the base moiety interacts with conserved residues R92 and E191. We identify a triplet of uncharged residues, F88/I187/W281, forming hydrophobic contacts with nucleotides. In yeast spheroplast respiration assays, both I187A and W281A mutants increase the fatty acid-induced uncoupling activity of UCP1 and partially suppress the inhibition of UCP1 activity by nucleotides. The F88A/I187A/W281A triple mutant is overactivated by fatty acids even at high concentrations of purine nucleotides. In simulations, E191 and W281 interact with purine but not pyrimidine bases. These results provide a molecular understanding of the selective inhibition of UCP1 by purine nucleotides.
    DOI:  https://doi.org/10.1038/s41467-023-38219-9
  2. Am J Physiol Cell Physiol. 2023 May 01.
    Oxaloacetate regulates complex II respiration in brown fat: dependence on UCP1 expression.
    Ritu Som, Brian D Fink, Liping Yu, William I Sivitz.
      We previously found that skeletal muscle mitochondria incubated at low membrane potential (ΔΨ) or interscapular brown adipose tissue (IBAT) mitochondria, wherein ΔΨ is intrinsically low, accumulate oxaloacetate (OAA) in amounts sufficient to inhibit complex II respiration. We proposed a mechanism wherein low ΔΨ reduces reverse electron transport (RET) to complex I causing a low NADH/NAD+ ratio favoring malate conversion to OAA. To further assess the mechanism and its physiologic relevance we carried out studies of mice with inherently different levels of IBAT mitochondrial inner membrane potential. Isolated complex II (succinate)-energized IBAT mitochondria from obesity resistant 129SVE mice compared to obesity prone C57BL/6J displayed greater UCP1 expression, similar O2 flux despite lower ΔΨ, similar OAA concentrations, and similar NADH/NAD+. When GDP was added to inhibit UCP1, 129SVE IBAT mitochondria, despite their lower ΔΨ, exhibited much lower respiration, 2-fold greater OAA concentrations, much lower RET (as marked by ROS), and much lower NADH and NADH/NAD+ ratios compared to the C57BL/6J IBAT mitochondria. UCP1 knock-out abolished OAA accumulation by succinate-energized mitochondria associated with markedly greater ΔΨ, ROS, and NADH, but equal or greater O2 flux compared to WT mitochondria. GDP addition, compared to no GDP, increased ΔΨ and complex II respiration in wildtype mice associated with much less OAA. Respiration on complex I substrates followed the more classical dynamics of greater respiration at lower ΔΨ. These findings support the above-mentioned mechanism for OAA- and ΔΨ-dependent complex II respiration and support its physiological relevance.
    Keywords:  brown adipose tissue; mitochondria; mitochondrial complex II; oxaloacetate; succinate dehydrogenase
    DOI:  https://doi.org/10.1152/ajpcell.00565.2022
  3. iScience. 2023 Apr 21. 26(4): 106560
    Optogenetic activation of UCP1-dependent thermogenesis in brown adipocytes.
    Chad C Doucette, Daniel C Nguyen, Davide Barteselli, Sophia Blanchard, Mason Pelletier, Devesh Kesharwani, Ed Jachimowicz, Su Su, Michele Karolak, Aaron C Brown.
      Brown adipocytes are unique in that they expend energy and produce heat to maintain euthermia through expression of uncoupling protein-1 (UCP1). Given their propensity to stimulate weight loss and promote resistance to obesity, they are a compelling interventional target for obesity-related disorders. Here, we tested whether an optogenetic approach could be used to activate UCP1-dependent thermogenesis in brown adipocytes. We generated brown adipocytes expressing a bacterial-derived photoactivatable adenylyl cyclase (bPAC) that, upon blue light stimulation, increases UCP1 expression, fuel uptake and thermogenesis. This unique system allows for precise, chemical free, temporal control of UCP1-dependent thermogenesis, which can aid in our understanding of brown adipocyte biology and development of therapies that target obesity-related disorders.
    Keywords:  Metabolic engineering; Molecular biology experimental approach; Specialized functions of cells
    DOI:  https://doi.org/10.1016/j.isci.2023.106560
  4. Nat Commun. 2023 May 02. 14(1): 2523
    Reduced hepatic bradykinin degradation accounts for cold-induced BAT thermogenesis and WAT browning in male mice.
    Fei Xiao, Haizhou Jiang, Zi Li, Xiaoxue Jiang, Shanghai Chen, Yuguo Niu, Hanrui Yin, Yousheng Shu, Bo Peng, Wei Lu, Xiaoying Li, Zhigang Li, Shujue Lan, Xiaoyan Xu, Feifan Guo.
      An important role for liver in the regulation of adipose tissue thermogenesis upon cold exposure has been suggested; however, the underlying mechanisms remain incompletely defined. Here, we identify elevated serum bradykinin levels in response to acute cold exposure in male mice. A bolus of anti-bradykinin antibodies reduces body temperature during acute cold exposure, whereas bradykinin has the opposite effect. We demonstrate that bradykinin induces brown adipose tissue thermogenesis and white adipose tissue browning, and bradykinin increases uncoupling protein 1 (UCP1) expression in adipose tissue. The bradykinin B2 receptor (B2R), adrenergic signaling and nitric oxide signaling are involved in regulating bradykinin-increased UCP1 expression. Moreover, acute cold exposure inhibits hepatic prolyl endopeptidase (PREP) activity, causing reduced liver bradykinin degradation and increased serum bradykinin levels. Finally, by blocking the breakdown of bradykinin, angiotensin-converting enzyme inhibitors (ACEIs) increase serum bradykinin levels and induce brown adipose tissue thermogenesis and white adipose tissue browning via B2R. Collectively, our data provide new insights into the mechanisms underlying organ crosstalk in whole-body physiology control during cold exposure and also suggest bradykinin as a possible anti-obesity target.
    DOI:  https://doi.org/10.1038/s41467-023-38141-0
  5. Cell Metab. 2023 May 02. pii: S1550-4131(23)00133-X. [Epub ahead of print]35(5): 730-732
    The secret life of lactate: A novel cell-cycle regulatory mechanism.
    Ahmad A Cluntun, Jared Rutter.
      Recently, Liu et al. uncovered an unexpected L-lactate-Zn2+ interaction in the active site of the deSUMOylating enzyme SENP1 that triggers a sequence of events that lead to mitotic exit. This study opens the door to new research avenues of metabolite-metal interactions controlling cellular decisions and functions.
    DOI:  https://doi.org/10.1016/j.cmet.2023.04.006
  6. Proc Natl Acad Sci U S A. 2023 May 09. 120(19): e2218999120
    MICU1 occludes the mitochondrial calcium uniporter in divalent-free conditions.
    Macarena Rodríguez-Prados, Elena Berezhnaya, Maria Teresa Castromonte, Sergio L Menezes-Filho, Melanie Paillard, György Hajnóczky.
      Mitochondrial Ca2+ uptake is mediated by the mitochondrial uniporter complex (mtCU) that includes a tetramer of the pore-forming subunit, MCU, a scaffold protein, EMRE, and the EF-hand regulatory subunit, MICU1 either homodimerized or heterodimerized with MICU2/3. MICU1 has been proposed to regulate Ca2+ uptake via the mtCU by physically occluding the pore and preventing Ca2+ flux at resting cytoplasmic [Ca2+] (free calcium concentration) and to increase Ca2+ flux at high [Ca2+] due to cooperative activation of MICUs EF-hands. However, mtCU and MICU1 functioning when its EF-hands are unoccupied by Ca2+ is poorly studied due to technical limitations. To overcome this barrier, we have studied the mtCU in divalent-free conditions by assessing the Ru265-sensitive Na+ influx using fluorescence-based measurement of mitochondrial matrix [Na+] (free sodium concentration) rise and the ensuing depolarization and swelling. We show an increase in all these measures of Na+ uptake in MICU1KO cells as compared to wild-type (WT) and rescued MICU1KO HEK cells. However, mitochondria in WT cells and MICU1 stable-rescued cells still allowed some Ru265-sensitive Na+ influx that was prevented by MICU1 in excess upon acute overexpression. Thus, MICU1 restricts the cation flux across the mtCU in the absence of Ca2+, but even in cells with high endogenous MICU1 expression such as HEK, some mtCU seem to lack MICU1-dependent gating. We also show rearrangement of the mtCU and altered number of functional channels in MICU1KO and different rescues, and loss of MICU1 during mitoplast preparation, that together might have obscured the pore-blocking function of MICU1 in divalent-free conditions in previous studies.
    Keywords:  EMRE; MICU1; Na+; mitochondrial calcium uniporter; mitoplast
    DOI:  https://doi.org/10.1073/pnas.2218999120
  7. Elife. 2023 May 02. pii: e84330. [Epub ahead of print]12
    Mitochondrial protein import clogging as a mechanism of disease.
    Liam P Coyne, Xiaowen Wang, Jiyao Song, Ebbing de Jong, Karin Schneider, Paul T Massa, Frank A Middleton, Thomas Becker, Xin Jie Chen.
      Mitochondrial biogenesis requires the import of >1,000 mitochondrial preproteins from the cytosol. Most studies on mitochondrial protein import are focused on the core import machinery. Whether and how the biophysical properties of substrate preproteins affect overall import efficiency is underexplored. Here, we show that protein traffic into mitochondria can be disrupted by amino acid substitutions in a single substrate preprotein. Pathogenic missense mutations in ADP/ATP translocase 1 (ANT1), and its yeast homolog Aac2, cause the protein to accumulate along the protein import pathway, thereby obstructing general protein translocation into mitochondria. This impairs mitochondrial respiration, cytosolic proteostasis and cell viability independent of ANT1's nucleotide transport activity. The mutations act synergistically, as double mutant Aac2/ANT1 cause severe clogging primarily at the Translocase of the Outer Membrane (TOM) complex. This confers extreme toxicity in yeast. In mice, expression of a super-clogger ANT1 variant led to neurodegeneration and an age-dependent dominant myopathy that phenocopy ANT1-induced human disease, suggesting clogging as a mechanism of disease. More broadly, this work implies the existence of uncharacterized amino acid requirements for mitochondrial carrier proteins to avoid clogging and subsequent disease.
    Keywords:  S. cerevisiae; biochemistry; chemical biology; mouse
    DOI:  https://doi.org/10.7554/eLife.84330
  8. Nature. 2023 May 03.
    A phosphate-sensing organelle regulates phosphate and tissue homeostasis.
    Chiwei Xu, Jun Xu, Hong-Wen Tang, Maria Ericsson, Jui-Hsia Weng, Jonathan DiRusso, Yanhui Hu, Wenzhe Ma, John M Asara, Norbert Perrimon.
      Inorganic phosphate (Pi) is one of the essential molecules for life. However, little is known about intracellular Pi metabolism and signalling in animal tissues1. Following the observation that chronic Pi starvation causes hyperproliferation in the digestive epithelium of Drosophila melanogaster, we determined that Pi starvation triggers the downregulation of the Pi transporter PXo. In line with Pi starvation, PXo deficiency caused midgut hyperproliferation. Interestingly, immunostaining and ultrastructural analyses showed that PXo specifically marks non-canonical multilamellar organelles (PXo bodies). Further, by Pi imaging with a Förster resonance energy transfer (FRET)-based Pi sensor2, we found that PXo restricts cytosolic Pi levels. PXo bodies require PXo for biogenesis and undergo degradation following Pi starvation. Proteomic and lipidomic characterization of PXo bodies unveiled their distinct feature as an intracellular Pi reserve. Therefore, Pi starvation triggers PXo downregulation and PXo body degradation as a compensatory mechanism to increase cytosolic Pi. Finally, we identified connector of kinase to AP-1 (Cka), a component of the STRIPAK complex and JNK signalling3, as the mediator of PXo knockdown- or Pi starvation-induced hyperproliferation. Altogether, our study uncovers PXo bodies as a critical regulator of cytosolic Pi levels and identifies a Pi-dependent PXo-Cka-JNK signalling cascade controlling tissue homeostasis.
    DOI:  https://doi.org/10.1038/s41586-023-06039-y
  9. Nature. 2023 May 03.
    The electron-proton bottleneck of photosynthetic oxygen evolution.
    Paul Greife, Matthias Schönborn, Matteo Capone, Ricardo Assunção, Daniele Narzi, Leonardo Guidoni, Holger Dau.
      Photosynthesis fuels life on Earth by storing solar energy in chemical form. Today's oxygen-rich atmosphere has resulted from the splitting of water at the protein-bound manganese cluster of photosystem II during photosynthesis. Formation of molecular oxygen starts from a state with four accumulated electron holes, the S4 state-which was postulated half a century ago1 and remains largely uncharacterized. Here we resolve this key stage of photosynthetic O2 formation and its crucial mechanistic role. We tracked 230,000 excitation cycles of dark-adapted photosystems with microsecond infrared spectroscopy. Combining these results with computational chemistry reveals that a crucial proton vacancy is initally created through gated sidechain deprotonation. Subsequently, a reactive oxygen radical is formed in a single-electron, multi-proton transfer event. This is the slowest step in photosynthetic O2 formation, with a moderate energetic barrier and marked entropic slowdown. We identify the S4 state as the oxygen-radical state; its formation is followed by fast O-O bonding and O2 release. In conjunction with previous breakthroughs in experimental and computational investigations, a compelling atomistic picture of photosynthetic O2 formation emerges. Our results provide insights into a biological process that is likely to have occurred unchanged for the past three billion years, which we expect to support the knowledge-based design of artificial water-splitting systems.
    DOI:  https://doi.org/10.1038/s41586-023-06008-5
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