bims-mimbat 2024-07-07 papers

bims-mimbat

Biomed News

on Mitochondrial metabolism in brown adipose tissue

Issue of 2024‒07‒07
nine papers selected by
José Carlos de Lima-Júnior, Washington University

PAQR4 regulates adipocyte function and systemic metabolic health by mediating ceramide levels.
SLC25A19 is required for NADH homeostasis and mitochondrial respiration.
NCLX controls hepatic mitochondrial Ca2+ extrusion and couples hormone-mediated mitochondrial Ca2+ oscillations with gluconeogenesis.
Lipid-associated macrophages reshape BAT cell identity in obesity.
Mitochondrial Thermogenesis Can Trigger Heat Shock Response in the Nucleus.
The mitochondrial aspartate/glutamate carrier does not transport GABA.
Structural robustness of the NADH binding site in NADH:ubiquinone oxidoreductase (complex I).
Proton-pumping photoreceptor controls expression of ABC transporter by regulating transcription factor through light.
Proton diffusion on the surface of mixed lipid membranes highlights the role of membrane composition.

Nat Metab. 2024 Jul 03.

PAQR4 regulates adipocyte function and systemic metabolic health by mediating ceramide levels.

Qingzhang Zhu, Shiuhwei Chen, Jan-Bernd Funcke, Leon G Straub, Qian Lin, Shangang Zhao, Chanmin Joung, Zhuzhen Zhang, Dae-Seok Kim, Na Li, Christy M Gliniak, Charlotte Lee, Alberto Cebrian-Serrano, Line Pedersen, Nils Halberg, Ruth Gordillo, Christine M Kusminski, Philipp E Scherer.

PAQR4 is an orphan receptor in the PAQR family with an unknown function in metabolism. Here, we identify a critical role of PAQR4 in maintaining adipose tissue function and whole-body metabolic health. We demonstrate that expression of Paqr4 specifically in adipocytes, in an inducible and reversible fashion, leads to partial lipodystrophy, hyperglycaemia and hyperinsulinaemia, which is ameliorated by wild-type adipose tissue transplants or leptin treatment. By contrast, deletion of Paqr4 in adipocytes improves healthy adipose remodelling and glucose homoeostasis in diet-induced obesity. Mechanistically, PAQR4 regulates ceramide levels by mediating the stability of ceramide synthases (CERS2 and CERS5) and, thus, their activities. Overactivation of the PQAR4-CERS axis causes ceramide accumulation and impairs adipose tissue function through suppressing adipogenesis and triggering adipocyte de-differentiation. Blocking de novo ceramide biosynthesis rescues PAQR4-induced metabolic defects. Collectively, our findings suggest a critical function of PAQR4 in regulating cellular ceramide homoeostasis and targeting PAQR4 offers an approach for the treatment of metabolic disorders.

DOI: https://doi.org/10.1038/s42255-024-01078-9
Free Radic Biol Med. 2024 Jun 27. pii: S0891-5849(24)00536-7. [Epub ahead of print]222 317-330

SLC25A19 is required for NADH homeostasis and mitochondrial respiration.

Zongsheng Jiang.

  Mitochondrial transporters facilitate the translocation of metabolites between the cytoplasm and mitochondria and are critical for mitochondrial functional integrity. Although many mitochondrial transporters are associated with metabolic diseases, how they regulate mitochondrial function and their metabolic contributions at the cellular level are largely unknown. Here, we show that mitochondrial thiamine pyrophosphate (TPP) transporter SLC25A19 is required for mitochondrial respiration. SLC25A19 deficiency leads to reduced cell viability, increased integrated stress response (ISR), enhanced glycolysis and elevated cell sensitivity to 2-deoxyglucose (2-DG) treatment. Through a series of biochemical assays, we found that the depletion of mitochondrial NADH is the primary cause of the impaired mitochondrial respiration in SLC25A19 deficient cells. We also showed involvement of SLC25A19 in regulating the enzymatic activities of complexes I and III, the tricarboxylic acid (TCA) cycle, malate-aspartate shuttle and amino acid metabolism. Consistently, addition of idebenone, an analog of coenzyme Q10, restores mitochondrial respiration and cell viability in SLC25A19 deficient cells. Together, our findings provide new insight into the functions of SLC25A19 in mitochondrial and cellular physiology, and suggest that restoring mitochondrial respiration could be a novel strategy for treating SLC25A19-associated disorders.

Keywords:  Electron transport chain; Idebenone; Mitochondrial respiration; Mitochondrial transporter; NADH; SLC25A19; TPP

DOI:  https://doi.org/10.1016/j.freeradbiomed.2024.06.019
Mol Metab. 2024 Jul 01. pii: S2212-8778(24)00113-3. [Epub ahead of print] 101982

NCLX controls hepatic mitochondrial Ca2+ extrusion and couples hormone-mediated mitochondrial Ca2+ oscillations with gluconeogenesis.

Mahmoud Taha, Essam A Assali, Tsipi Ben-Kasus, Grace E Stuzmann, Orian S Shirihai, Michal Hershfinkel, Israel Sekler.

  OBJECTIVE: Hepatic Ca2+ signaling has been identified as a crucial key factor in driving gluconeogenesis. The involvement of mitochondria in hormone-induced Ca2+ signaling and their contribution to metabolic activity remain, however, poorly understood. Moreover, the molecular mechanism governing the mitochondrial Ca2+ efflux signaling remains unresolved. This study investigates the role of the Na+ /Ca2+ exchanger, NCLX, in modulating hepatic mitochondrial Ca2+ efflux, and examines its physiological significance in hormonal hepatic Ca2+ signaling, gluconeogenesis, and mitochondrial bioenergetics.METHODS: Primary mouse hepatocytes from both an AAV-mediated conditional hepatic-specific and a total mitochondrial Na+/Ca2+ exchanger, NCLX, knock-out (KO) mouse models were employed for fluorescent monitoring of purinergic and glucagon/vasopressin-dependent mitochondrial and cytosolic hepatic Ca2+ responses in cultured hepatocytes. Isolated liver mitochondria and permeabilized primary hepatocytes were utilized to analyze the ion-dependence of Ca2+ efflux. Utilizing the conditional hepatic-specific NCLX KO model, the rate of gluconeogenesis was assessed first through the monitoring of glucose levels in fasted mice in vivo and by subjecting the fasted mice to a pyruvate tolerance test while monitoring blood glucose. Additionally, cultured primary hepatocytes from both genotypes were assessed in vitro for glucagon-dependent glucose production and cellular bioenergetics through glucose oxidase assay and Seahorse respirometry, respectively.
RESULTS: Analysis of Ca2+ responses in isolated liver mitochondria and cultured primary hepatocytes from NCLX KO versus WT mice showed that NCLX serves as the principal mechanism for mitochondrial calcium extrusion in hepatocytes. We then determined the role of NCLX in glucagon and vasopressin-induced Ca2+ oscillations. Consistent with previous studies, glucagon and vasopressin triggered Ca2+ oscillations in WT hepatocytes, however, the deletion of NCLX resulted in selective elimination of mitochondrial, but not cytosolic, Ca2+ oscillations or level of IP3R1 expression, underscoring NCLX's pivotal role in mitochondrial Ca2+ regulation. Subsequent in vivo investigation for hepatic NCLX role in gluconeogenesis revealed that, as opposed to WT mice which maintained normoglycemic blood glucose levels when fasted, conditional hepatic-specific NCLX KO mice exhibited a faster drop in glucose levels, becoming hypoglycemic, and with a compromised conversion of pyruvate to glucose when provided challenged under fasting conditions. Concurrent in vitro assessments showed impaired glucagon-dependent glucose production and compromised bioenergetics in KO hepatocytes, thereby underscoring NCLX's significant contribution to hepatic glucose metabolism.
CONCLUSIONS: The study findings demonstrate that NCLX acts as the primary Ca2+ efflux mechanism in hepatocytes. NCLX is indispensable for the regulation of hormone-induced mitochondrial Ca2+ oscillations, mitochondrial metabolism and sustenance of hepatic gluconeogenesis.

Keywords:  Calcium signaling; Mitocondrial calcium; NCLX; gluconeogenesis; hepatic calcium signaling

DOI:  https://doi.org/10.1016/j.molmet.2024.101982
Cell Rep. 2024 Jul 03. pii: S2211-1247(24)00776-9. [Epub ahead of print]43(7): 114447

Lipid-associated macrophages reshape BAT cell identity in obesity.

Francesca Sciarretta, Andrea Ninni, Fabio Zaccaria, Valerio Chiurchiù, Adeline Bertola, Keaton Karlinsey, Wentong Jia, Veronica Ceci, Claudia Di Biagio, Ziyan Xu, Francesco Gaudioso, Flavia Tortolici, Marta Tiberi, Jiabi Zhang, Simone Carotti, Sihem Boudina, Paolo Grumati, Beiyan Zhou, Jonathan R Brestoff, Stoyan Ivanov, Katia Aquilano, Daniele Lettieri-Barbato.

  Obesity and type 2 diabetes cause a loss in brown adipose tissue (BAT) activity, but the molecular mechanisms that drive BAT cell remodeling remain largely unexplored. Using a multilayered approach, we comprehensively mapped a reorganization in BAT cells. We uncovered a subset of macrophages as lipid-associated macrophages (LAMs), which were massively increased in genetic and dietary model of BAT expansion. LAMs participate in this scenario by capturing extracellular vesicles carrying damaged lipids and mitochondria released from metabolically stressed brown adipocytes. CD36 scavenger receptor drove LAM phenotype, and CD36-deficient LAMs were able to increase brown fat genes in adipocytes. LAMs released transforming growth factor β1 (TGF-β1), which promoted the loss of brown adipocyte identity through aldehyde dehydrogenase 1 family member A1 (Aldh1a1) induction. These findings unfold cell dynamic changes in BAT during obesity and identify LAMs as key responders to tissue metabolic stress and drivers of loss of brown adipocyte identity.

Keywords:  CP: Metabolism; adipocytes; extracellular mitochondria; immunometabolism; metabolism; mitochondria; single-cell RNA sequencing; thermogenesis; type 2 diabetes

DOI:  https://doi.org/10.1016/j.celrep.2024.114447
ACS Cent Sci. 2024 Jun 26. 10(6): 1231-1241

Mitochondrial Thermogenesis Can Trigger Heat Shock Response in the Nucleus.

Myeong-Gyun Kang, Hwa-Ryeon Kim, Hee Yong Lee, Chulhwan Kwak, Hyewon Koh, Byoung Heon Kang, Jae-Seok Roe, Hyun-Woo Rhee.

Mitochondrial thermogenesis is a process in which heat is generated by mitochondrial respiration. In living organisms, the thermogenic mechanisms that maintain body temperature have been studied extensively in fat cells with little knowledge on how mitochondrial heat may act beyond energy expenditure. Here, we highlight that the exothermic oxygen reduction reaction (ΔH f° = -286 kJ/mol) is the main source of the protonophore-induced mitochondrial thermogenesis, and this heat is conducted to other cellular organelles, including the nucleus. As a result, mitochondrial heat that reached the nucleus initiated the classical heat shock response, including the formation of nuclear stress granules and the localization of heat shock factor 1 (HSF1) to chromatin. Consequently, activated HSF1 increases the level of gene expression associated with the response to thermal stress in mammalian cells. Our results illustrate heat generated within the cells as a potential source of mitochondria-nucleus communication and expand our understanding of the biological functions of mitochondria in cell physiology.

DOI: https://doi.org/10.1021/acscentsci.3c01589
Biochim Biophys Acta Bioenerg. 2024 Jun 28. pii: S0005-2728(24)00457-2. [Epub ahead of print]1865(4): 149487

The mitochondrial aspartate/glutamate carrier does not transport GABA.

Vito Porcelli, Serena Barile, Loredana Capobianco, Simona Nicole Barile, Ruggiero Gorgoglione, Giuseppe Fiermonte, Barbara Monti, Francesco Massimo Lasorsa, Luigi Palmieri.

  ɣ-aminobutyric acid (GABA) is a four‑carbon amino acid acting as the main inhibitory transmitter in the invertebrate and vertebrate nervous systems. The metabolism of GABA is well compartmentalized in the cell and the uptake of cytosolic GABA into the mitochondrial matrix is required for its degradation. A previous study carried out in the fruit fly Drosophila melanogaster indicated that the mitochondrial aspartate/glutamate carrier (AGC) is responsible for mitochondrial GABA accumulation. Here, we investigated the transport of GABA catalysed by the human and D. melanogaster AGC proteins through a well-established method for the study of the substrate specificity and the kinetic parameters of the mitochondrial carriers. In this experimental system, the D. melanogaster spliced AGC isoforms (Aralar1-PA and Aralar1-PE) and the human AGC isoforms (AGC1/aralar1 and AGC2/citrin) are unable to transport GABA both in homo- and in hetero-exchange with either glutamate or aspartate, i.e. the canonical substrates of AGC. Moreover, GABA has no inhibitory effect on the exchange activities catalysed by the investigated AGCs. Our data demonstrate that AGC does not transport GABA and the molecular identity of the GABA transporter in human and D. melanogaster mitochondria remains unknown.

Keywords:  AGC; Aralar; Citrin; GABA; Mitochondrial carriers

DOI:  https://doi.org/10.1016/j.bbabio.2024.149487
Biochim Biophys Acta Bioenerg. 2024 Jul 01. pii: S0005-2728(24)00461-4. [Epub ahead of print]1865(4): 149491

Structural robustness of the NADH binding site in NADH:ubiquinone oxidoreductase (complex I).

Sanaz Göppert-Asadollahpour, Daniel Wohlwend, Thorsten Friedrich.

  Energy converting NADH:ubiquinone oxidoreductase, complex I, is the first enzyme of respiratory chains in most eukaryotes and many bacteria. Mutations in genes encoding subunits of human complex I may lead to its dysfunction resulting in a diverse clinical pattern. The effect of mutations on the protein structure is not known. Here, we focus on mutations R88G, E246K, P252R and E377K that are found in subunit NDUFV1 comprising the NADH binding site of complex I. Homologous mutations were introduced into subunit NuoF of Aquifex aeolicus complex I and it was attempted to crystallize variants of the electron input module, NuoEF, with bound substrates in the oxidized and reduced state. The E377K variant did not form crystals most likely due to an improper protein assembly. The architecture of the NADH binding site is hardly affected by the other mutations indicating its unexpected structural robustness. The R88G, E246K and P252R mutations led to small local structural rearrangements that might be related to their pathogenicity. These minor structural changes involve substrate binding, product release and the putative formation of reactive oxygen species. The structural consequences of the mutations as obtained with the bacterial enzyme might thus help to contribute to the understanding of disease causing mutations.

Keywords:  Complex I; Crystallography; Leigh syndrome mutations; NADH binding; NADH dehydrogenase; NuoEF

DOI:  https://doi.org/10.1016/j.bbabio.2024.149491
Commun Biol. 2024 Jun 29. 7(1): 789

Proton-pumping photoreceptor controls expression of ABC transporter by regulating transcription factor through light.

Jin-Gon Shim, Kimleng Chuon, Ji-Hyun Kim, Sang-Ji Lee, Myung-Chul Song, Shin-Gyu Cho, Chenda Hour, Kwang-Hwan Jung.

Light is a significant factor for living organisms with photosystems, like microbial rhodopsin-a retinal protein that functions as an ion pump, channel, and sensory transduction. Gloeobacter violaceus PCC7421, has a proton-pumping rhodopsin gene, the Gloeobacter rhodopsin (GR). The helix-turn-helix family of transcriptional regulators has various motifs, and they regulate gene expression in the presence of various metal ions. Here, we report that active proton outward pumping rhodopsin interacted with the helix-turn-helix transcription regulator and regulated gene expression. This interaction is confirmed using ITC analysis (KD of 8 μM) and determined the charged residues required. During in vitro experiments using fluorescent and luciferase reporter systems, ATP-binding cassette (ABC) transporters and the self-regulation of G. violaceus transcriptional regulator (GvTcR) are regulated by light, and gene regulation is observed in G. violaceus using the real-time polymerase chain reaction. These results expand our understanding of the natural potential and limitations of microbial rhodopsin function.

DOI: https://doi.org/10.1038/s42003-024-06471-4
Biophys J. 2024 Jul 02. pii: S0006-3495(24)00441-7. [Epub ahead of print]

Proton diffusion on the surface of mixed lipid membranes highlights the role of membrane composition.

Ambili Ramanthrikkovil Variyam, Mateusz Rzycki, Anna Yucknovsky, Alexei A Stuchebrukhov, Dominik Drabik, Nadav Amdursky.

  Proton circuits within biological membranes, the foundation of natural bioenergetic systems, are significantly influenced by the lipid compositions of different biological membranes. In this study, we investigate the influence of mixed lipid membrane composition on the proton transfer (PT) properties on the surface of the membrane. We track the excited-state PT (ESPT) process from a tethered probe to the membrane with time-scales and length-scales of PT relevant to bioenergetic systems. Two processes can happen during ESPT: the initial PT from the probe to the membrane at short timescales, followed by diffusion of dissociated protons around the probe on the membrane, and the possible geminate recombination with the probe at longer timescales. Here, we use membranes composed of mixtures of phosphatidylcholine (PC) and phosphatidic acid (PA). We show that the changes in the ESPT properties are not monotonous with the concentration of the lipid mixture; at low concentration of PA in PC, we find that the membrane is a poor proton acceptor. Molecular dynamics simulations indicate that the membrane is more structured at this specific lipid mixture with the least defects. Accordingly, we suggest that the structure of the membrane is an important factor in facilitating PT. We further show that the composition of the membrane affects the geminate proton diffusion around the probe, whereas, on a time-scale of tens of nanoseconds, the dissociated proton is mostly lateral restricted to the membrane plane in PA membranes, while in PC, the diffusion is less restricted by the membrane.

Keywords:  Lateral diffusion; Membrane biophysics; Membranes; Photoacids; Proton transport

DOI:  https://doi.org/10.1016/j.bpj.2024.07.002