bims-mimbat 2023-07-16 papers

bims-mimbat

Biomed News

on Mitochondrial metabolism in brown adipose tissue

Issue of 2023–07–16
nine papers selected by
José Carlos de Lima-Júnior, Washington University

Nipsnap1-A regulatory factor required for long-term maintenance of non-shivering thermogenesis.
Inhibition of AXL receptor tyrosine kinase enhances brown adipose tissue functionality in mice.
Mitochondrial respiratory complex I deficiency inhibits brown adipogenesis by limiting heme regulation of histone demethylation.
Adipocyte NMNAT1 expression is essential for nuclear NAD+ biosynthesis but dispensable for regulating thermogenesis and whole-body energy metabolism.
Ribonucleotide synthesis by NME6 fuels mitochondrial gene expression.
Adenine nucleotide carrier protein dysfunction in human disease.
Increased mitochondrial free Ca2+ during ischemia is suppressed, but not eliminated by, germline deletion of the mitochondrial Ca2+ uniporter.
Mechanism of ATP hydrolysis dependent rotation of bacterial ATP synthase.
Crosstalk between regulatory elements in disordered TRPV4 N-terminus modulates lipid-dependent channel activity.

Mol Metab. 2023 Jul 07. pii: S2212-8778(23)00104-7. [Epub ahead of print] 101770

Nipsnap1-A regulatory factor required for long-term maintenance of non-shivering thermogenesis.

Yang Liu, Yue Qu, Chloe Cheng, Pei-Yin Tsai, Kaydine Edwards, Siwen Xue, Supriya Pandit, Sakura Eguchi, Navneet Sanghera, Joeva J Barrow.

   OBJECTIVE: The activation of non-shivering thermogenesis (NST) has strong potential to combat obesity and metabolic disease. The activation of NST however is extremely temporal and the mechanisms surrounding how the benefits of NST are sustained once fully activated, remain unexplored. The objective of this study is to investigate the role of 4-Nitrophenylphosphatase Domain and Non-Neuronal SNAP25-Like 1 (Nipsnap1) in NST maintenance, which is a critical regulator identified in this study.
METHODS: The expression of Nipsnap1 was profiled by immunoblotting and RT-qPCR. We generated Nipsnap1 knockout mice (N1-KO) and investigated the function of Nipsnap1 in NST maintenance and whole-body metabolism using whole body respirometry analyses. We evaluate the metabolic regulatory role of Nipsnap1 using cellular and mitochondrial respiration assay.
RESULTS: Here, we show Nipsnap1 as a critical regulator of long-term thermogenic maintenance in brown adipose tissue (BAT). Nipsnap1 localizes to the mitochondrial matrix and increases its transcript and protein levels in response to both chronic cold and β3 adrenergic signaling. We demonstrated that these mice are unable to sustain activated energy expenditure and have significantly lower body temperature in the face of an extended cold challenge. Furthermore, when mice are exposed to the pharmacological β3 agonist CL 316, 243, the N1-KO mice exhibit significant hyperphagia and altered energy balance. Mechanistically, we demonstrate that Nipsnap1 integrates with lipid metabolism and BAT-specific ablation of Nipsnap1 leads to severe defects in beta-oxidation capacity when exposed to a cold environmental challenge.
CONCLUSION: Our findings identify Nipsnap1 as a potent regulator of long-term NST maintenance in BAT.

Keywords:  Brown adipose tissue; Energy expenditure; Lipid metabolism; Nipsnap1; Thermogenesis maintenance

DOI:  https://doi.org/10.1016/j.molmet.2023.101770
Nat Commun. 2023 Jul 13. 14(1): 4162

Inhibition of AXL receptor tyrosine kinase enhances brown adipose tissue functionality in mice.

Vissarion Efthymiou, Lianggong Ding, Miroslav Balaz, Wenfei Sun, Lucia Balazova, Leon G Straub, Hua Dong, Eric Simon, Adhideb Ghosh, Aliki Perdikari, Svenja Keller, Umesh Ghoshdastider, Carla Horvath, Caroline Moser, Bradford Hamilton, Heike Neubauer, Christian Wolfrum.

The current obesity epidemic and high prevalence of metabolic diseases necessitate efficacious and safe treatments. Brown adipose tissue in this context is a promising target with the potential to increase energy expenditure, however no pharmacological treatments activating brown adipose tissue are currently available. Here, we identify AXL receptor tyrosine kinase as a regulator of adipose function. Pharmacological and genetic inhibition of AXL enhance thermogenic capacity of brown and white adipocytes, in vitro and in vivo. Mechanistically, these effects are mediated through inhibition of PI3K/AKT/PDE signaling pathway, resulting in induction of nuclear FOXO1 localization and increased intracellular cAMP levels via PDE3/4 inhibition and subsequent stimulation of the PKA-ATF2 pathway. In line with this, both constitutive Axl deletion as well as inducible adipocyte-specific Axl deletion protect animals from diet-induced obesity concomitant with increases in energy expenditure. Based on these data, we propose AXL receptor as a target for the treatment of obesity.

DOI: https://doi.org/10.1038/s41467-023-39715-8
Mitochondrion. 2023 Jul 12. pii: S1567-7249(23)00067-3. [Epub ahead of print]

Mitochondrial respiratory complex I deficiency inhibits brown adipogenesis by limiting heme regulation of histone demethylation.

Jingjing Liu, Wen Lu, Dongyue Yan, Junyuan Guo, Li Zhou, Bimin Shi, Xiong Su.

  Mitochondrial functions play a crucial role in determining the metabolic and thermogenic status of brown adipocytes. Increasing evidence reveals that the mitochondrial oxidative phosphorylation (OXPHOS) system plays an important role in brown adipogenesis, but the mechanistic insights are limited. Herein, we explored the potential metabolic mechanisms leading to OXPHOS regulation of brown adipogenesis in pharmacological and genetic models of mitochondrial respiratory complex I deficiency. OXPHOS deficiency inhibits brown adipogenesis through disruption of the brown adipogenic transcription circuit without affecting ATP levels. Neither blockage of calcium signaling nor antioxidant treatment can rescue the suppressed brown adipogenesis. Metabolomics analysis revealed a decrease in levels of tricarboxylic acid cycle intermediates and heme. Heme supplementation specifically enhances respiratory complex I activity without affecting complex II and partially reverses the inhibited brown adipogenesis by OXPHOS deficiency. Moreover, the regulation of brown adipogenesis by the OXPHOS-heme axis may be due to the suppressed histone methylation status by increasing histone demethylation. In summary, our findings identified a heme-sensing retrograde signaling pathway that connects mitochondrial OXPHOS to the regulation of brown adipocyte differentiation and metabolic functions.

Keywords:  brown adipocytes; differentiation; heme; histone methylation; oxidative phosphorylation

DOI:  https://doi.org/10.1016/j.mito.2023.07.004
Biochem Biophys Res Commun. 2023 Jul 04. pii: S0006-291X(23)00855-0. [Epub ahead of print]674 162-169

Adipocyte NMNAT1 expression is essential for nuclear NAD+ biosynthesis but dispensable for regulating thermogenesis and whole-body energy metabolism.

Shintaro Yamaguchi, Daiki Kojima, Tooba Iqbal, Shotaro Kosugi, Michael P Franczyk, Nathan Qi, Yo Sasaki, Keisuke Yaku, Kenji Kaneko, Kenichiro Kinouchi, Hiroshi Itoh, Kaori Hayashi, Takashi Nakagawa, Jun Yoshino.

  Nicotinamide adenine dinucleotide (NAD+) functions as an essential cofactor regulating a variety of biological processes. The purpose of the present study was to determine the role of nuclear NAD+ biosynthesis, mediated by nicotinamide mononucleotide adenylyltransferase 1 (NMNAT1), in thermogenesis and whole-body energy metabolism. We first evaluated the relationship between NMNAT1 expression and thermogenic activity in brown adipose tissue (BAT), a key organ for non-shivering thermogenesis. We found that reduced BAT NMNAT1expression was associated with inactivation of thermogenic gene program induced by obesity and thermoneutrality. Next, we generated and characterized adiponectin-Cre-driven adipocyte-specific Nmnat1 knockout (ANMT1KO) mice. Loss of NMNAT1 markedly reduced nuclear NAD+ concentration by approximately 70% in BAT. Nonetheless, adipocyte-specific Nmnat1 deletion had no impact on thermogenic (rectal temperature, BAT temperature and whole-body oxygen consumption) responses to β-adrenergic ligand norepinephrine administration and acute cold exposure, adrenergic-mediated lipolytic activity, and metabolic responses to obesogenic high-fat diet feeding. In addition, loss of NMNAT1 did not affect nuclear lysine acetylation or thermogenic gene program in BAT. These results demonstrate that adipocyte NMNAT1 expression is required for maintaining nuclear NAD+ concentration, but not for regulating BAT thermogenesis or whole-body energy homeostasis.

Keywords:  Adipose tissue; Energy metabolism; NAD(+); NMNAT1; Nucleus; Thermogenesis

DOI:  https://doi.org/10.1016/j.bbrc.2023.07.007
EMBO J. 2023 Jul 13. e113256

Ribonucleotide synthesis by NME6 fuels mitochondrial gene expression.

Nils Grotehans, Lynn McGarry, Hendrik Nolte, Vanessa Xavier, Moritz Kroker, Álvaro Jesús Narbona-Pérez, Soni Deshwal, Patrick Giavalisco, Thomas Langer, Thomas MacVicar.

  Replication of the mitochondrial genome and expression of the genes it encodes both depend on a sufficient supply of nucleotides to mitochondria. Accordingly, dysregulated nucleotide metabolism not only destabilises the mitochondrial genome, but also affects its transcription. Here, we report that a mitochondrial nucleoside diphosphate kinase, NME6, supplies mitochondria with pyrimidine ribonucleotides that are necessary for the transcription of mitochondrial genes. Loss of NME6 function leads to the depletion of mitochondrial transcripts, as well as destabilisation of the electron transport chain and impaired oxidative phosphorylation. These deficiencies are rescued by an exogenous supply of pyrimidine ribonucleosides. Moreover, NME6 is required for the maintenance of mitochondrial DNA when the access to cytosolic pyrimidine deoxyribonucleotides is limited. Our results therefore reveal an important role for ribonucleotide salvage in mitochondrial gene expression.

Keywords:  NME6; mitochondria; mitochondrial DNA; mitochondrial transcription; nucleotide metabolism

DOI:  https://doi.org/10.15252/embj.2022113256
IUBMB Life. 2023 Jul 14.

Adenine nucleotide carrier protein dysfunction in human disease.

Gargi Mishra, Liam P Coyne, Xin Jie Chen.

Adenine nucleotide translocase (ANT) is the prototypical member of the mitochondrial carrier protein family, primarily involved in ADP/ATP exchange across the inner mitochondrial membrane. Several carrier proteins evolutionarily related to ANT, including SLC25A24 and SLC25A25, are believed to promote the exchange of cytosolic ATP-Mg2+ with phosphate in the mitochondrial matrix. They allow a net accumulation of adenine nucleotides inside mitochondria, which is essential for mitochondrial biogenesis and cell growth. In the last two decades, mutations in the heart/muscle isoform 1 of ANT (ANT1) and the ATP-Mg2+ transporters have been found to cause a wide spectrum of human diseases by a recessive or dominant mechanism. Although loss-of-function recessive mutations cause a defect in oxidative phosphorylation and an increase in oxidative stress which drives the pathology, it is unclear how the dominant missense mutations in these proteins cause human diseases. In this review, we focus on how yeast was productively used as a model system for the understanding of these dominant diseases. We also describe the relationship between the structure and function of ANT and how this may relate to various pathologies. Particularly, mutations in Aac2, the yeast homolog of ANT, were recently found to clog the mitochondrial protein import pathway. This leads to mitochondrial precursor overaccumulation stress (mPOS), characterized by the toxic accumulation of unimported mitochondrial proteins in the cytosol. We anticipate that in coming years, yeast will continue to serve as a useful model system for the mechanistic understanding of mitochondrial protein import clogging and related pathologies in humans.

DOI: https://doi.org/10.1002/iub.2767
Cell Rep. 2023 Jul 07. pii: S2211-1247(23)00746-5. [Epub ahead of print]42(7): 112735

Increased mitochondrial free Ca2+ during ischemia is suppressed, but not eliminated by, germline deletion of the mitochondrial Ca2+ uniporter.

Courtney E Petersen, Junhui Sun, Kavisha Silva, Anna Kosmach, Robert S Balaban, Elizabeth Murphy.

  Mitochondrial Ca2+ overload is proposed to regulate cell death via opening of the mitochondrial permeability transition pore. It is hypothesized that inhibition of the mitochondrial Ca2+ uniporter (MCU) will prevent Ca2+ accumulation during ischemia/reperfusion and thereby reduce cell death. To address this, we evaluate mitochondrial Ca2+ in ex-vivo-perfused hearts from germline MCU-knockout (KO) and wild-type (WT) mice using transmural spectroscopy. Matrix Ca2+ levels are measured with a genetically encoded, red fluorescent Ca2+ indicator (R-GECO1) using an adeno-associated viral vector (AAV9) for delivery. Due to the pH sensitivity of R-GECO1 and the known fall in pH during ischemia, hearts are glycogen depleted to decrease the ischemic fall in pH. At 20 min of ischemia, there is significantly less mitochondrial Ca2+ in MCU-KO hearts compared with MCU-WT controls. However, an increase in mitochondrial Ca2+ is present in MCU-KO hearts, suggesting that mitochondrial Ca2+ overload during ischemia is not solely dependent on MCU.

Keywords:  CP: Developmental biology; MCU; calcium; cardioprotection; ischemia-reperfusion; mitochondria

DOI:  https://doi.org/10.1016/j.celrep.2023.112735
Nat Commun. 2023 07 10. 14(1): 4090

Mechanism of ATP hydrolysis dependent rotation of bacterial ATP synthase.

Atsuki Nakano, Jun-Ichi Kishikawa, Kaoru Mitsuoka, Ken Yokoyama.

F1 domain of ATP synthase is a rotary ATPase complex in which rotation of central γ-subunit proceeds in 120° steps against a surrounding α3β3 fueled by ATP hydrolysis. How the ATP hydrolysis reactions occurring in three catalytic αβ dimers are coupled to mechanical rotation is a key outstanding question. Here we describe catalytic intermediates of the F1 domain in FoF1 synthase from Bacillus PS3 sp. during ATP mediated rotation captured using cryo-EM. The structures reveal that three catalytic events and the first 80° rotation occur simultaneously in F1 domain when nucleotides are bound at all the three catalytic αβ dimers. The remaining 40° rotation of the complete 120° step is driven by completion of ATP hydrolysis at αDβD, and proceeds through three sub-steps (83°, 91°, 101°, and 120°) with three associated conformational intermediates. All sub-steps except for one between 91° and 101° associated with phosphate release, occur independently of the chemical cycle, suggesting that the 40° rotation is largely driven by release of intramolecular strain accumulated by the 80° rotation. Together with our previous results, these findings provide the molecular basis of ATP driven rotation of ATP synthases.

DOI: https://doi.org/10.1038/s41467-023-39742-5
Nat Commun. 2023 Jul 13. 14(1): 4165

Crosstalk between regulatory elements in disordered TRPV4 N-terminus modulates lipid-dependent channel activity.

Benedikt Goretzki, Christoph Wiedemann, Brett A McCray, Stefan L Schäfer, Jasmin Jansen, Frederike Tebbe, Sarah-Ana Mitrovic, Julia Nöth, Ainara Claveras Cabezudo, Jack K Donohue, Cy M Jeffries, Wieland Steinchen, Florian Stengel, Charlotte J Sumner, Gerhard Hummer, Ute A Hellmich.

Intrinsically disordered regions (IDRs) are essential for membrane receptor regulation but often remain unresolved in structural studies. TRPV4, a member of the TRP vanilloid channel family involved in thermo- and osmosensation, has a large N-terminal IDR of approximately 150 amino acids. With an integrated structural biology approach, we analyze the structural ensemble of the TRPV4 IDR and the network of antagonistic regulatory elements it encodes. These modulate channel activity in a hierarchical lipid-dependent manner through transient long-range interactions. A highly conserved autoinhibitory patch acts as a master regulator by competing with PIP2 binding to attenuate channel activity. Molecular dynamics simulations show that loss of the interaction between the PIP2-binding site and the membrane reduces the force exerted by the IDR on the structured core of TRPV4. This work demonstrates that IDR structural dynamics are coupled to TRPV4 activity and highlights the importance of IDRs for TRP channel function and regulation.

DOI: https://doi.org/10.1038/s41467-023-39808-4