bims-mimbat 2024-08-04 papers

bims-mimbat

Biomed News

on Mitochondrial metabolism in brown adipose tissue

Issue of 2024–08–04
nine papers selected by
José Carlos de Lima-Júnior, Washington University

Single-nucleus transcriptomics identifies separate classes of UCP1 and futile cycle adipocytes.
Development of a functional beige fat cell line uncovers independent subclasses of cells expressing UCP1 and the futile creatine cycle.
Comparative functional analysis reveals differential nucleotide sensitivity between human and mouse UCP1.
Glucocorticoid modulates oxidative and thermogenic function of rat brown adipose tissue and human brown adipocytes.
Searching for Proton Transfer Channels in Respiratory Complex I.
An efficient AAV vector system of Rec2 serotype for intravenous injection to study metabolism in brown adipocytes in vivo.
Transport and inhibition mechanisms of the human noradrenaline transporter.
Housing mice near vs. below thermoneutrality affects drug-induced weight loss but does not improve prediction of efficacy in humans.
MGA deletion leads to Richter's transformation by modulating mitochondrial OXPHOS.

Cell Metab. 2024 Jul 26. pii: S1550-4131(24)00276-6. [Epub ahead of print]

Single-nucleus transcriptomics identifies separate classes of UCP1 and futile cycle adipocytes.

Tongtong Wang, Anand Kumar Sharma, Chunyan Wu, Claudia Irene Maushart, Adhideb Ghosh, Wu Yang, Patrik Stefanicka, Zuzana Kovanicova, Jozef Ukropec, Jing Zhang, Myrtha Arnold, Manuel Klug, Katrien De Bock, Ulrich Schneider, Cristina Popescu, Bo Zheng, Lianggong Ding, Fen Long, Revati Sumukh Dewal, Caroline Moser, Wenfei Sun, Hua Dong, Martin Takes, Dominique Suelberg, Alexander Mameghani, Antonio Nocito, Christoph Johannes Zech, Alin Chirindel, Damian Wild, Irene A Burger, Michael R Schön, Arne Dietrich, Min Gao, Markus Heine, Yizhi Sun, Ariana Vargas-Castillo, Susanna Søberg, Camilla Scheele, Miroslav Balaz, Matthias Blüher, Matthias Johannes Betz, Bruce M Spiegelman, Christian Wolfrum.

  Adipose tissue can recruit catabolic adipocytes that utilize chemical energy to dissipate heat. This process occurs either by uncoupled respiration through uncoupling protein 1 (UCP1) or by utilizing ATP-dependent futile cycles (FCs). However, it remains unclear how these pathways coexist since both processes rely on the mitochondrial membrane potential. Utilizing single-nucleus RNA sequencing to deconvolute the heterogeneity of subcutaneous adipose tissue in mice and humans, we identify at least 2 distinct subpopulations of beige adipocytes: FC-adipocytes and UCP1-beige adipocytes. Importantly, we demonstrate that the FC-adipocyte subpopulation is highly metabolically active and utilizes FCs to dissipate energy, thus contributing to thermogenesis independent of Ucp1. Furthermore, FC-adipocytes are important drivers of systemic energy homeostasis and linked to glucose metabolism and obesity resistance in humans. Taken together, our findings identify a noncanonical thermogenic adipocyte subpopulation, which could be an important regulator of energy homeostasis in mammals.

Keywords:  energy homeostasis; futile cycling; human metabolism; single-nucleus RNA sequencing; thermogenesis

DOI:  https://doi.org/10.1016/j.cmet.2024.07.005
Cell Metab. 2024 Jul 24. pii: S1550-4131(24)00273-0. [Epub ahead of print]

Development of a functional beige fat cell line uncovers independent subclasses of cells expressing UCP1 and the futile creatine cycle.

Ariana Vargas-Castillo, Yizhi Sun, Amanda L Smythers, Louisa Grauvogel, Phillip A Dumesic, Margo P Emont, Linus T Tsai, Evan D Rosen, Nathan W Zammit, Sydney M Shaffer, Martha Ordonez, Edward T Chouchani, Steven P Gygi, Tongtong Wang, Anand K Sharma, Miroslav Balaz, Christian Wolfrum, Bruce M Spiegelman.

  Although uncoupling protein 1 (UCP1) is established as a major contributor to adipose thermogenesis, recent data have illustrated an important role for alternative pathways, particularly the futile creatine cycle (FCC). How these pathways co-exist in cells and tissues has not been explored. Beige cell adipogenesis occurs in vivo but has been difficult to model in vitro; here, we describe the development of a murine beige cell line that executes a robust respiratory response, including uncoupled respiration and the FCC. The key FCC enzyme, tissue-nonspecific alkaline phosphatase (TNAP), is localized almost exclusively to mitochondria in these cells. Surprisingly, single-cell cloning from this cell line shows that cells with the highest levels of UCP1 express little TNAP, and cells with the highest expression of TNAP express little UCP1. Immunofluorescence analysis of subcutaneous fat from cold-exposed mice confirms that the highest levels of these critical thermogenic components are expressed in distinct fat cell populations.

Keywords:  Alpl gene; SV40 large T antigen; TNAP; UCP1; aP2-Prdm16 transgenic mice; functional beige cell line; futile creatine cycle; immortalized beige adipocytes; thermogenesis

DOI:  https://doi.org/10.1016/j.cmet.2024.07.002
Acta Physiol (Oxf). 2024 Jul 29. e14209

Comparative functional analysis reveals differential nucleotide sensitivity between human and mouse UCP1.

Eva Musiol, Tobias Fromme, Julia Hau, Antonella Di Pizio, Martin Klingenspor.

   AIM: Mitochondrial uncoupling protein 1 (UCP1) is a unique protein of brown adipose tissue. Upon activation by free fatty acids, UCP1 facilitates a thermogenic net proton flux across the mitochondrial inner membrane. Non-complexed purine nucleotides inhibit this fatty acid-induced activity of UCP1. The most available data have been generated from rodent model systems. In light of its role as a putative pharmacological target for treating metabolic disease, in-depth analyses of human UCP1 activity, regulation, and structural features are essential.
METHODS: In the present study, we established a doxycycline-regulated cell model with inducible human or murine UCP1 expression and conducted functional studies using respirometry comparing wild-type and mutant variants of human UCP1.
RESULTS: We demonstrate that human and mouse UCP1 exhibit similar specific fatty acid-induced activity but a different inhibitory potential of purine nucleotides. Mutagenesis of non-conserved residues in human UCP1 revealed structural components in α-helix 56 and α-helix 6 crucial for uncoupling function.
CONCLUSION: Comparative studies of human UCP1 with other orthologs can provide new insights into the structure-function relationship for this mitochondrial carrier and will be instrumental in searching for new activators.

Keywords:  brown adipose tissue; fatty acids; mitochondrial carriers; mutagenesis; proton leak; purine nucleotides; thermogenesis; uncoupling proteins

DOI:  https://doi.org/10.1111/apha.14209
J Cell Physiol. 2024 Aug 01. e31397

Glucocorticoid modulates oxidative and thermogenic function of rat brown adipose tissue and human brown adipocytes.

Anaysa Paola Bolin, Flaviane de Fatima Silva, Rafael Barrera Salgueiro, Bruna Araújo Dos Santos, Ayumi Cristina Medeiros Komino, Sandra Andreotti, Érica de Sousa, Érique de Castro, Caroline Cristiano Real, Daniele de Paula Faria, Gerson Profeta Souza, Henrique Camara, Carlos Arterio Sorgi, Yu-Hua Tseng, Fábio Bessa Lima, Alice Cristina Rodrigues.

  Chronic and excessive glucocorticoid (GC) exposure can cause Cushing's syndrome, resulting in fat accumulation in selected body areas. Particularly in the brown adipose tissue (BAT), GC acts negatively, resulting in whitening of the tissue. We hypothesized that dysregulation of microRNAs by GC could be an additional mechanism to explain its negative actions in BAT. Male Wistar rats were divided into two groups: (1) Control sham and (2) GC group that was administered dexamethasone 6.25 mg/200 μL via osmotic pump implantation over 28 days. After this period, the animals were euthanized and BAT tissue was properly stored. Human fat cells treated with dexamethasone were used to translate the experimental results found in animals to human biology. GC-treated rat BAT presented with large lipid droplets, severely impaired thermogenic activation, and reduced glucose uptake measured by 18F-FDG PET/CT. GC exposure induced a reduction in the mitochondrial OXPHOS system and oxygen consumption. MicroRNA profiling of BAT revealed five top-regulated microRNAs and among them miR-21-5p was the most significantly upregulated in GC-treated rats compared to the control group. Although upregulation of miR-21-5p in the tissue, differentiated primary brown adipocytes from GC-treated rats had decreased miR-21-5p levels compared to the control group. To translate these results to the clinic, human brown adipocytes were treated with dexamethasone and miR-21-5p inhibitor. In human brown cells, inhibition of miR-21-5p increased brown adipocyte differentiation and prevented GC-induced glucose uptake, resulting in a lower glycolysis rate. In conclusion, high-dose GC therapy significantly impacts brown adipose tissue function, with a notable association between glucose uptake and miR-21-5p.

Keywords:  Cushing's syndrome; adipose tissue; dexamethasone; miR; miR‐21‐5p

DOI:  https://doi.org/10.1002/jcp.31397
Biophys J. 2024 Aug 01. pii: S0006-3495(24)00518-6. [Epub ahead of print]

Searching for Proton Transfer Channels in Respiratory Complex I.

Panyue Wang, Jackson Demaray, Stanislav Moroz, Alexei A Stuchebrukhov.

  We have explored a strategy to identify potential proton transfer channels using computational analysis of a protein structure based on Voronoi partitioning, and applied it for the analysis of proton transfer pathways in redox-driven proton pumping respiratory complex I. The analysis results in a network of connected voids/channels which represent the dual structure of the protein; we then hydrated the identified channels using our water placement program Dowser++. Many theoretical water molecules found in the channels perfectly match the observed experimental water molecules in the structure; some other predicted water molecules have not been resolved in the experiments. The channels are of varying cross-section. Some channels are big enough to accommodate water molecules that are suitable to conduct protons; others are too narrow to hold water but require only minor conformational changes to accommodate proton transfer. We provide a preliminary analysis of proton conductivity of the network channels, classifying the proton transfer channels as open, closed, and partially open, and discuss possible conformational changes that can modulate, i.e. open and close, the channels.

Keywords:  Complex I; Dowser++; Electron Transport Chain; proton channels; proton pumping; proton transfer; water in proteins

DOI:  https://doi.org/10.1016/j.bpj.2024.07.041
Mol Metab. 2024 Jul 31. pii: S2212-8778(24)00130-3. [Epub ahead of print] 101999

An efficient AAV vector system of Rec2 serotype for intravenous injection to study metabolism in brown adipocytes in vivo.

Janina Behrens, Ingke Braren, Michelle Y Jaeckstein, Luka Lilie, Markus Heine, Finnja Sass, Judith Sommer, Dagmar Silbert-Wagner, Marceline M Fuh, Anna Worthmann, Leon Straub, Tarek Moustafa, Joerg Heeren, Ludger Scheja.

  Recombinant adeno-associated virus (rAAV) vectors are powerful tools for the sustained expression of proteins in vivo and have been successfully used for mechanistic studies in mice. A major challenge associated with this method is to obtain tissue specificity and high expression levels without need of local virus administration. To achieve this goal for brown adipose tissue (BAT), we developed a rAAV vector for intravenous bolus injection, which includes an expression cassette comprising an uncoupling protein-1 enhancer-promoter for transcription in brown adipocytes and miR122 target sequences for suppression of expression in the liver, combined with packaging in serotype Rec2 capsid protein. To test tissue specificity, we used a version of this vector expressing Cre recombinase to transduce mice with floxed alleles to knock out MLXIPL (ChREBP) or tdTomato-Cre reporter mice. We demonstrated efficient Cre-dependent recombination in interscapular BAT and variable effects in minor BAT depots, but little or no efficacy in white adipose tissues, liver and other organs. Direct overexpression of glucose transporter SLC2A1 (GLUT1) using the rAAV vector in wild type mice resulted in increased glucose uptake and glucose-dependent gene expression in BAT, indicating usefulness of this vector to increase the function even of abundant proteins. Taken together, we describe a novel brown adipocyte-specific rAAV method to express proteins for loss-of-function and gain-of-function metabolic studies. The approach will enable researchers to access brown fat swiftly, reduce animal breeding time and costs, as well as enable the creation of new transgenic mouse models combining multiple transgenes.

Keywords:  Cre recombinase; Rec2; adeno-associated virus vector; brown adipose tissue; de novo lipogenesis; glucose transport

DOI:  https://doi.org/10.1016/j.molmet.2024.101999
Nature. 2024 Jul 31.

Transport and inhibition mechanisms of the human noradrenaline transporter.

Tuo Hu, Zhuoya Yu, Jun Zhao, Yufei Meng, Kristine Salomon, Qinru Bai, Yiqing Wei, Jinghui Zhang, Shujing Xu, Qiuyun Dai, Rilei Yu, Bei Yang, Claus J Loland, Yan Zhao.

The noradrenaline transporter (also known as norepinephrine transporter) (NET) has a critical role in terminating noradrenergic transmission by utilizing sodium and chloride gradients to drive the reuptake of noradrenaline (also known as norepinephrine) into presynaptic neurons1-3. It is a pharmacological target for various antidepressants and analgesic drugs4,5. Despite decades of research, its structure and the molecular mechanisms underpinning noradrenaline transport, coupling to ion gradients and non-competitive inhibition remain unknown. Here we present high-resolution complex structures of NET in two fundamental conformations: in the apo state, and bound to the substrate noradrenaline, an analogue of the χ-conotoxin MrlA (χ-MrlAEM), bupropion or ziprasidone. The noradrenaline-bound structure clearly demonstrates the binding modes of noradrenaline. The coordination of Na+ and Cl- undergoes notable alterations during conformational changes. Analysis of the structure of NET bound to χ-MrlAEM provides insight into how conotoxin binds allosterically and inhibits NET. Additionally, bupropion and ziprasidone stabilize NET in its inward-facing state, but they have distinct binding pockets. These structures define the mechanisms governing neurotransmitter transport and non-competitive inhibition in NET, providing a blueprint for future drug design.

DOI: https://doi.org/10.1038/s41586-024-07638-z
Cell Rep. 2024 Jul 25. pii: S2211-1247(24)00830-1. [Epub ahead of print]43(8): 114501

Housing mice near vs. below thermoneutrality affects drug-induced weight loss but does not improve prediction of efficacy in humans.

Julie M Jacobsen, Natalia Petersen, Lola Torz, Marina K Gerstenberg, Kent Pedersen, Søren Østergaard, Birgitte S Wulff, Birgitte Andersen, Kirsten Raun, Berit Ø Christoffersen, Linu M John, Marc L Reitman, Rune E Kuhre.

  Evaluation of weight loss drugs is usually performed in diet-induced obese mice housed at ∼22°C. This is a cold stress that increases energy expenditure by ∼35% compared to thermoneutrality (∼30°C), which may overestimate drug-induced weight loss. We investigated five anti-obesity mechanisms that have been in clinical development, comparing weight loss in mice housed at 22°C vs. 30°C. Glucagon-like peptide-1 (GLP-1), human fibroblast growth factor 21 (hFGF21), and melanocortin-4 receptor (MC4R) agonist induced similar weight losses. Peptide YY elicited greater vehicle-subtracted weight loss at 30°C (7.2% vs. 1.4%), whereas growth differentiation factor 15 (GDF15) was more effective at 22°C (13% vs. 6%). Independent of ambient temperature, GLP-1 and hFGF21 prevented the reduction in metabolic rate caused by weight loss. There was no simple rule for a better prediction of human drug efficacy based on ambient temperature, but since humans live at thermoneutrality, drug testing using mice should include experiments near thermoneutrality.

Keywords:  CP: Metabolism; FGF21; GDF15; GLP-1; MC4R; PYY; diet-induced obese mice; energy expenditure; glucose tolerance; housing temperature; human translatability; pharmaco-mediated weight loss; thermoneutrality

DOI:  https://doi.org/10.1016/j.celrep.2024.114501
Sci Transl Med. 2024 Jul 31. 16(758): eadg7915

MGA deletion leads to Richter's transformation by modulating mitochondrial OXPHOS.

Prajish Iyer, Bo Zhang, Tingting Liu, Meiling Jin, Kevyn Hart, Jibin Zhang, Viola Siegert, Marianne Remke, Xuesong Wang, Lei Yu, Joo Song, Girish Venkataraman, Wing C Chan, Zhenyu Jia, Maike Buchner, Tanya Siddiqi, Steven T Rosen, Alexey Danilov, Lili Wang.

Richter's transformation (RT) is a progression of chronic lymphocytic leukemia (CLL) to aggressive lymphoma. MGA (Max gene associated), a functional MYC suppressor, is mutated at 3% in CLL and 36% in RT. However, genetic models and molecular mechanisms of MGA deletion that drive CLL to RT remain elusive. We established an RT mouse model by knockout of Mga in the Sf3b1/Mdr CLL model using CRISPR-Cas9 to determine the role of Mga in RT. Murine RT cells exhibited mitochondrial aberrations with elevated oxidative phosphorylation (OXPHOS). Through RNA sequencing and functional characterization, we identified Nme1 (nucleoside diphosphate kinase) as an Mga target, which drives RT by modulating OXPHOS. Given that NME1 is also a known MYC target without targetable compounds, we found that concurrent inhibition of MYC and electron transport chain complex II substantially prolongs the survival of RT mice in vivo. Our results suggest that the Mga-Nme1 axis drives murine CLL-to-RT transition via modulating OXPHOS, highlighting a potential therapeutic avenue for RT.

DOI: https://doi.org/10.1126/scitranslmed.adg7915