bims-mimbat Biomed News
on Mitochondrial metabolism in brown adipose tissue
Issue of 2022‒05‒29
nine papers selected by
José Carlos de Lima-Júnior
University of California San Francisco

  1. Nature. 2022 May 25.
      Mitochondria generate heat due to H+ leak (IH) across their inner membrane1. IH results from the action of long-chain fatty acids on uncoupling protein 1 (UCP1) in brown fat2-6 and ADP/ATP carrier (AAC) in other tissues1,7-9, but the underlying mechanism is poorly understood. As evidence of pharmacological activators of IH through UCP1 and AAC is lacking, IH is induced by protonophores such as 2,4-dinitrophenol (DNP) and cyanide-4-(trifluoromethoxy) phenylhydrazone (FCCP)10,11. Although protonophores show potential in combating obesity, diabetes and fatty liver in animal models12-14, their clinical potential for treating human disease is limited due to indiscriminately increasing H+ conductance across all biological membranes10,11 and adverse side effects15. Here we report the direct measurement of IH induced by DNP, FCCP and other common protonophores and find that it is dependent on AAC and UCP1. Using molecular structures of AAC, we perform a computational analysis to determine the binding sites for protonophores and long-chain fatty acids, and find that they overlap with the putative ADP/ATP-binding site. We also develop a mathematical model that proposes a mechanism of uncoupler-dependent IH through AAC. Thus, common protonophoric uncouplers are synthetic activators of IH through AAC and UCP1, paving the way for the development of new and more specific activators of these two central mediators of mitochondrial bioenergetics.
  2. Nature. 2022 May 25.
      Mitochondria are epicentres of eukaryotic metabolism and bioenergetics. Pioneering efforts in recent decades have established the core protein componentry of these organelles1 and have linked their dysfunction to more than 150 distinct disorders2,3. Still, hundreds of mitochondrial proteins lack clear functions4, and the underlying genetic basis for approximately 40% of mitochondrial disorders remains unresolved5. Here, to establish a more complete functional compendium of human mitochondrial proteins, we profiled more than 200 CRISPR-mediated HAP1 cell knockout lines using mass spectrometry-based multiomics analyses. This effort generated approximately 8.3 million distinct biomolecule measurements, providing a deep survey of the cellular responses to mitochondrial perturbations and laying a foundation for mechanistic investigations into protein function. Guided by these data, we discovered that PIGY upstream open reading frame (PYURF) is an S-adenosylmethionine-dependent methyltransferase chaperone that supports both complex I assembly and coenzyme Q biosynthesis and is disrupted in a previously unresolved multisystemic mitochondrial disorder. We further linked the putative zinc transporter SLC30A9 to mitochondrial ribosomes and OxPhos integrity and established RAB5IF as the second gene harbouring pathogenic variants that cause cerebrofaciothoracic dysplasia. Our data, which can be explored through the interactive online resource, suggest biological roles for many other orphan mitochondrial proteins that still lack robust functional characterization and define a rich cell signature of mitochondrial dysfunction that can support the genetic diagnosis of mitochondrial diseases.
  3. J Biol Chem. 2022 May 19. pii: S0021-9258(22)00490-2. [Epub ahead of print] 102050
      The double-stranded RNA-dependent protein kinase (PKR) activating protein (PACT), an RNA-binding protein (RNAbp) that is part of the RNA-induced silencing complex (RISC), plays a key role in microRNA (miR)-mediated translational repression. Previous studies showed that PACT regulates the expression of various miRs, selects the miR strand to be loaded onto RISC, and determines proper miR length. Apart from PACT's role in mediating the anti-viral response in immune cells, what PACT does in other cell types is unknown. Strikingly, it has also been shown that cold exposure leads to marked downregulation of PACT protein in mouse brown adipose tissue (BAT), where mitochondrial biogenesis and metabolism play a central role. Here, we show that PACT establishes a post-transcriptional brake on mitochondrial biogenesis (mitobiogenesis) by promoting the maturation of miR-181c, a key suppressor of mitobiogenesis that has been shown to target mitochondrial Complex IV subunit I (Mtco1) and Sirtuin 1 (Sirt1). Consistently, we found that a partial reduction in PACT expression is sufficient to enhance mitobiogenesis in brown adipocytes in culture as well as during BAT activation in mice. In conclusion, we demonstrate an unexpected role for PACT in the regulation of mitochondrial biogenesis and energetics in cells and BAT.
  4. Int J Mol Sci. 2022 May 10. pii: 5321. [Epub ahead of print]23(10):
      A balanced omega (ω)-6/ω-3 polyunsaturated fatty acids (PUFAs) ratio has been linked to metabolic health and the prevention of chronic diseases. Brown adipose tissue (BAT) specializes in energy expenditure and secretes signaling molecules that regulate metabolism via inter-organ crosstalk. Recent studies have uncovered that BAT produces different PUFA species and circulating oxylipin levels are correlated with BAT-mediated energy expenditure in mice and humans. However, the impact of BAT ω-6/ω-3 PUFAs on metabolic phenotype has not been fully elucidated. The Fat-1 transgenic mice can convert ω-6 to ω-3 PUFAs. Here, we demonstrated that mice receiving Fat-1 BAT transplants displayed better glucose tolerance and higher energy expenditure. Expression of genes involved in thermogenesis and nutrient utilization was increased in the endogenous BAT of mice receiving Fat-1 BAT, suggesting that the transplants may activate recipients' BAT. Using targeted lipidomic analysis, we found that the levels of several ω-6 oxylipins were significantly reduced in the circulation of mice receiving Fat-1 BAT transplants than in mice with wild-type BAT transplants. The major altered oxylipins between the WT and Fat-1 BAT transplantation were ω-6 arachidonic acid-derived oxylipins via the lipoxygenase pathway. Taken together, these findings suggest an important role of BAT-derived oxylipins in combating obesity-related metabolic disorders.
    Keywords:  Fat-1; brown adipose tissue; signaling lipidomics; transplantation; ω-6 arachidonic acid-derived oxylipins
  5. Eur J Pharmacol. 2022 May 19. pii: S0014-2999(22)00301-6. [Epub ahead of print] 175040
      Extensive studies have shown that the increasing brown adipose tissue (BAT) mass/activity possesses a strong ability to prevent obesity and its related complications. The Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signal pathway is known to play a role in adipocyte differentiation and development. However, its impact on thermogenic properties of mature brown adipocytes has not yet been clarified. Nifuroxazide (NFX), a potent inhibitor of STAT3, has received widespread attention due to its alternative anti-tumor and anti-inflammatory effects. Herein, we report that NFX induces lipolysis with subsequent downregulation of ACCα and FAS, while ATGL and pHSL levels are elevated in mature brown adipocytes. Furthermore, NFX treatment promotes the mitochondrial respiration of mature brown adipocytes, as evidenced by increased expression of thermogenic transcriptional factors and mitochondrial content. In addition, it also alleviates the IL-6 and TNFα inhibition on brown thermogenic programming via suppressing the STAT3/NF-κB/IL-6 signaling pathway. In general, these findings suggest that the blockade of the JAK/STAT3 pathway by NFX has a pro-thermogenic effect on mature brown adipocytes which opens new perspectives for NFX repurposing and potential therapeutic route to counteract obesity and related metabolic disorders.
    Keywords:  Adipocytes differentiation; JAK/STAT3 pathway; Mature brown adipocytes; Nifuroxazide
  6. Nat Commun. 2022 May 26. 13(1): 2958
      The pleiotropic function of long noncoding RNAs is well recognized, but their direct role in governing metabolic homeostasis is less understood. Here, we describe a human adipocyte-specific lncRNA, ADIPINT, that regulates pyruvate carboxylase, a pivotal enzyme in energy metabolism. We developed an approach, Targeted RNA-protein identification using Orthogonal Organic Phase Separation, which identifies that ADIPINT binds to pyruvate carboxylase and validated the interaction with electron microscopy. ADIPINT knockdown alters the interactome and decreases the abundance and enzymatic activity of pyruvate carboxylase in the mitochondria. Reduced ADIPINT or pyruvate carboxylase expression lowers adipocyte lipid synthesis, breakdown, and lipid content. In human white adipose tissue, ADIPINT expression is increased in obesity and linked to fat cell size, adipose insulin resistance, and pyruvate carboxylase activity. Thus, we identify ADIPINT as a regulator of lipid metabolism in human white adipocytes, which at least in part is mediated through its interaction with pyruvate carboxylase.
  7. J Exp Med. 2022 Jul 04. pii: e20211894. [Epub ahead of print]219(7):
      Given the clinical, economic, and societal impact of obesity, unraveling the mechanisms of adipose tissue expansion remains of fundamental significance. We previously showed that white adipose tissue (WAT) levels of 3-mercaptopyruvate sulfurtransferase (MPST), a mitochondrial cysteine-catabolizing enzyme that yields pyruvate and sulfide species, are downregulated in obesity. Here, we report that Mpst deletion results in fat accumulation in mice fed a high-fat diet (HFD) through transcriptional and metabolic maladaptation. Mpst-deficient mice on HFD exhibit increased body weight and inguinal WAT mass, reduced metabolic rate, and impaired glucose/insulin tolerance. At the molecular level, Mpst ablation activates HIF1α, downregulates subunits of the translocase of outer/inner membrane (TIM/TOM) complex, and impairs mitochondrial protein import. MPST deficiency suppresses the TCA cycle, oxidative phosphorylation, and fatty acid oxidation, enhancing lipid accumulation. Sulfide donor administration to obese mice reverses the HFD-induced changes. These findings reveal the significance of MPST for white adipose tissue biology and metabolic health and identify a potential new therapeutic target for obesity.
  8. Free Radic Biol Med. 2022 May 21. pii: S0891-5849(22)00194-0. [Epub ahead of print]
      MitoNEET is the first iron-sulfur protein found in mitochondrial outer membrane. Abnormal expression of mitoNEET in cells has been linked to several types of cancer, type II diabetes, and neurodegenerative diseases. Structurally, mitoNEET is anchored to mitochondrial outer membrane via its N-terminal single transmembrane alpha helix. The C-terminal cytosolic domain of mitoNEET binds a [2Fe-2S] cluster via three cysteine and one histidine residues. It has been shown that mitoNEET has a crucial role in energy metabolism, iron homeostasis, and free radical production in cells. However, the exact function of mitoNEET remains elusive. Previously, we reported that the C-terminal soluble domain of mitoNEET has a specific binding site for flavin mononucleotide (FMN) and can transfer electrons from FMNH2 to oxygen or ubiquinone-2 via its [2Fe-2S] cluster. Here we have constructed a hybrid protein using the N-terminal transmembrane domain of Escherichia coli YneM and the C-terminal soluble domain of human mitoNEET and assembled the hybrid protein YneM-mitoNEET into phospholipid nanodiscs. The results show that the [2Fe-S] clusters in the nanodisc-bound YneM-mitoNEET can be rapidly reduced by FMNH2 which is reduced by flavin reductase using NADH as the electron donor. Addition of lumichrome, a FMN analog, effectively inhibits the FMNH2-mediated reduction of the [2Fe-2S] clusters in the nanodisc-bound YneM-mitoNEET. The reduced [2Fe-2S] clusters in the nanodisc-bound YneM-mitoNEET are quickly oxidized by oxygen under aerobic conditions or by ubiquinone-10 in the nanodiscs under anaerobic conditions. Because NADH oxidation is required for cellular glycolytic activity, we propose that the mitochondrial outer membrane protein mitoNEET may promote glycolysis by transferring electrons from FMNH2 to oxygen or ubiquinone-10 in mitochondria.
    Keywords:  Electron transfer activity; FMN; Mitochondria; NADH; Nanodisc; mitoNEET
  9. Biophys J. 2022 May 24. pii: S0006-3495(22)00422-2. [Epub ahead of print]
      Proton coupled peptide transporters (POTs) are crucial for the uptake of di- and tri-peptides as well as drug and pro-drug molecules in prokaryotes and eukaryotic cells. We illustrate from multiscale modeling how transmembrane proton flux couples within a POT protein to drive essential steps of the full functional cycle: 1) protonation of a glutamate on transmembrane helix (TM) 7 opens the extracellular gate, allowing ligand entry; 2) inward proton flow induces the cytosolic release of ligand by varying the protonation state of a second conserved glutamate on TM10; 3) proton movement between TM7 and TM10 is thermodynamically driven and kinetically permissible via water proton shuttling without the participation of ligand. Our results, for the first time, give direct computational confirmation for the alternating access model of POTs, and point to a quantitative multiscale kinetic picture of the functioning protein mechanism.